Saimm 202312 dec

VOLUME 123 NO. 12 DECEMBER 2023

Redpath globally provides the following services:

The Southern African Institute of Mining and Metallurgy OFFICE BEARERS AND COUNCIL FOR THE 2023/2024 SESSION

PAST PRESIDENTS

Honorary President

* W. Bettel (1894–1895) * A.F. Crosse (1895–1896) * W.R. Feldtmann (1896–1897) * C. Butters (1897–1898) * J. Loevy (1898–1899) * J.R. Williams (1899–1903) * S.H. Pearce (1903–1904) * W.A. Caldecott (1904–1905) * W. Cullen (1905–1906) * E.H. Johnson (1906–1907) * J. Yates (1907–1908) * R.G. Bevington (1908–1909) * A. McA. Johnston (1909–1910) * J. Moir (1910–1911) * C.B. Saner (1911–1912) * W.R. Dowling (1912–1913) * A. Richardson (1913–1914) * G.H. Stanley (1914–1915) * J.E. Thomas (1915–1916) * J.A. Wilkinson (1916–1917) * G. Hildick-Smith (1917–1918) * H.S. Meyer (1918–1919) * J. Gray (1919–1920) * J. Chilton (1920–1921) * F. Wartenweiler (1921–1922) * G.A. Watermeyer (1922–1923) * F.W. Watson (1923–1924) * C.J. Gray (1924–1925) * H.A. White (1925–1926) * H.R. Adam (1926–1927) * Sir Robert Kotze (1927–1928) * J.A. Woodburn (1928–1929) * H. Pirow (1929–1930) * J. Henderson (1930–1931) * A. King (1931–1932) * V. Nimmo-Dewar (1932–1933) * P.N. Lategan (1933–1934) * E.C. Ranson (1934–1935) * R.A. Flugge-De-Smidt (1935–1936) * T.K. Prentice (1936–1937) * R.S.G. Stokes (1937–1938) * P.E. Hall (1938–1939) * E.H.A. Joseph (1939–1940) * J.H. Dobson (1940–1941) * Theo Meyer (1941–1942) * John V. Muller (1942–1943) * C. Biccard Jeppe (1943–1944) * P.J. Louis Bok (1944–1945) * J.T. McIntyre (1945–1946) * M. Falcon (1946–1947) * A. Clemens (1947–1948) * F.G. Hill (1948–1949) * O.A.E. Jackson (1949–1950) * W.E. Gooday (1950–1951) * C.J. Irving (1951–1952) * D.D. Stitt (1952–1953) * M.C.G. Meyer (1953–1954) * L.A. Bushell (1954–1955) * H. Britten (1955–1956) * Wm. Bleloch (1956–1957) * H. Simon (1957–1958) * M. Barcza (1958–1959) * R.J. Adamson (1959–1960)

Nolitha Fakude President, Minerals Council South Africa

Honorary Vice Presidents

Gwede Mantashe Minister of Mineral Resources and Energy, South Africa Ebrahim Patel Minister of Trade, Industry and Competition, South Africa Blade Nzimande Minister of Higher Education, Science and Technology, South Africa

President

W.C. Joughin

President Elect E. Matinde

Senior Vice President G.R. Lane

Junior Vice President T.M. Mmola

Incoming Junior Vice President M.H. Solomon

Immediate Past President Z. Botha

Honorary Treasurer E. Matinde

Ordinary Members on Council W. Broodryk Z. Fakhraei R.M.S. Falcon (by invitation) B. Genc K.M. Letsoalo S.B. Madolo F.T. Manyanga K. Mosebi

M.C. Munroe S. Naik G. Njowa S.J. Ntsoelengoe S.M. Rupprecht A.T. van Zyl E.J. Walls

Co-opted Council Members M.A. Mello

Past Presidents Serving on Council N.A. Barcza R.D. Beck J.R. Dixon V.G. Duke I.J. Geldenhuys R.T. Jones A.S. Macfarlane

C. Musingwini S. Ndlovu J.L. Porter M.H. Rogers D.A.J. Ross-Watt G.L. Smith W.H. van Niekerk

G.R. Lane – TP Mining Chairperson Z. Botha – TP Metallurgy Chairperson K.W. Banda – YPC Chairperson S. Nyoni – YPC Vice Chairperson

Branch Chairpersons Botswana DRC Johannesburg Limpopo Namibia Northern Cape North West Pretoria Western Cape Zambia Zimbabwe Zululand

Vacant Not active N. Rampersad S. Zulu Vacant I. Tlhapi I. Tshabalala Vacant A.B. Nesbitt J.P.C. Mutambo (Interim Chairperson) Vacant C.W. Mienie

*Deceased

* W.S. Findlay (1960–1961) * D.G. Maxwell (1961–1962) * J. de V. Lambrechts (1962–1963) * J.F. Reid (1963–1964) * D.M. Jamieson (1964–1965) * H.E. Cross (1965–1966) * D. Gordon Jones (1966–1967) * P. Lambooy (1967–1968) * R.C.J. Goode (1968–1969) * J.K.E. Douglas (1969–1970) * V.C. Robinson (1970–1971) * D.D. Howat (1971–1972) * J.P. Hugo (1972–1973) * P.W.J. van Rensburg (1973–1974) * R.P. Plewman (1974–1975) * R.E. Robinson (1975–1976) * M.D.G. Salamon (1976–1977) * P.A. Von Wielligh (1977–1978) * M.G. Atmore (1978–1979) * D.A. Viljoen (1979–1980) * P.R. Jochens (1980–1981) * G.Y. Nisbet (1981–1982) A.N. Brown (1982–1983) * R.P. King (1983–1984) J.D. Austin (1984–1985) * H.E. James (1985–1986) H. Wagner (1986–1987) * B.C. Alberts (1987–1988) * C.E. Fivaz (1988–1989) * O.K.H. Steffen (1989–1990) * H.G. Mosenthal (1990–1991) R.D. Beck (1991–1992) * J.P. Hoffman (1992–1993) * H. Scott-Russell (1993–1994) J.A. Cruise (1994–1995) D.A.J. Ross-Watt (1995–1996) N.A. Barcza (1996–1997) * R.P. Mohring (1997–1998) J.R. Dixon (1998–1999) M.H. Rogers (1999–2000) L.A. Cramer (2000–2001) * A.A.B. Douglas (2001–2002) S.J. Ramokgopa (2002-2003) T.R. Stacey (2003–2004) F.M.G. Egerton (2004–2005) W.H. van Niekerk (2005–2006) R.P.H. Willis (2006–2007) R.G.B. Pickering (2007–2008) A.M. Garbers-Craig (2008–2009) J.C. Ngoma (2009–2010) G.V.R. Landman (2010–2011) J.N. van der Merwe (2011–2012) G.L. Smith (2012–2013) M. Dworzanowski (2013–2014) J.L. Porter (2014–2015) R.T. Jones (2015–2016) C. Musingwini (2016–2017) S. Ndlovu (2017–2018) A.S. Macfarlane (2018–2019) M.I. Mthenjane (2019–2020) V.G. Duke (2020–2021) I.J. Geldenhuys (2021–2022) Z. Botha (2022-2023)

Editorial Board S.O. Bada R.D. Beck P. den Hoed I.M. Dikgwatlhe R. Dimitrakopolous* B. Genc R Hassanalizadeh R.T. Jones W.C. Joughin A.J. Kinghorn D.E.P. Klenam J. Lake H.M. Lodewijks D.F. Malan R. Mitra* H. Möller C. Musingwini S. Ndlovu P.N. Neingo S.S. Nyoni M. Phasha P. Pistorius P. Radcliffe N. Rampersad Q.G. Reynolds I. Robinson S.M. Rupprecht K.C. Sole A.J.S. Spearing* T.R. Stacey E. Topal* D. Tudor* D. Vogt* *International Advisory Board members

Editor /Chairperson of the Editorial Board R.M.S. Falcon

Typeset and Published by The Southern African Institute of Mining and Metallurgy PostNet Suite #212 Private Bag X31 Saxonwold, 2132 E-mail: journal@saimm.co.za

Printed by

Camera Press, Johannesburg

VOLUME 123 NO. 12 DECEMBER 2023

Contents Journal Comment: The Future of mining research in South Africa

by D.F. Malan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

iv

Presidential Address: Reflections on 2023

by W.C. Joughin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

v

NEWS OF INTEREST

SAMCODES Updates – December 2023 . . . . . . . . . . . . . . . . . . . . . . .

vi-viii

THE INSTITUTE, AS A BODY, IS NOT RESPONSIBLE FOR THE STATEMENTS AND OPINIONS ADVANCED IN ANY OF ITS PUBLICATIONS. Copyright© 2023 by The Southern African Institute of Mining and Metallurgy. All rights reserved. Multiple copying of the contents of this publication or parts thereof without permission is in breach of copyright, but permission is hereby given for the copying of titles and abstracts of papers and names of authors.

Permission to copy illustrations and short extracts from the text of individual contributions is usually given upon written application to the Institute, provided that the source (and where appropriate, the copyright) is acknowledged. Apart from any fair dealing for the purposes of review or criticism under The Copyright Act no. 98, 1978, Section 12, of the Republic of South Africa, a single copy of an article may be supplied by a library for the purposes of research or private study. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means without the prior permission of the publishers. Multiple copying of the contents of the publication without permission is always illegal.

U.S. Copyright Law applicable to users In the U.S.A. The appearance of the statement of copyright at the bottom of the first page of an article appearing in this journal indicates that the copyright holder consents to the making of copies of the article for personal or internal use. This consent is given on condition that the copier pays the stated fee for each copy of a paper beyond that permitted by Section 107 or 108 of the U.S. Copyright Law. The fee is to be paid through the Copyright Clearance Center, Inc., Operations Center, P.O. Box 765, Schenectady, New York 12301, U.S.A. This consent does not extend to other kinds of copying, such as copying for general distribution, for advertising or promotional purposes, for creating new collective works, or for resale.

Honorary Legal Advisers M H Attorneys

Auditors

Genesis Chartered Accountants

Secretaries

The Southern African Institute of Mining and Metallurgy 7th Floor, Rosebank Towers, 19 Biermann Avenue, Rosebank, 2196 PostNet Suite #212, Private Bag X31, Saxonwold, 2132 E-mail: journal@saimm.co.za

Advertising Representative Barbara Spence Avenue Advertising Telephone (011) 463-7940 . E-mail: barbara@avenue.co.za ISSN 2225-6253 (print) . ISSN 2411-9717 (online)

Directory of Open Access Journals

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PROFESSIONAL TECHNICAL AND SCIENTIFIC PAPERS Flyrock in surface mining Part II — Causes, sources, and mechanisms of rock projection

by T. Szendrei and S. Tose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The fracturing and movement of rock that occurs in the vicinity of a stemmed borehole explosive charge in open–pit mining operations are described. Three principal modes of momentum transferred to fractured rock are identified. The generation of flyrock can be interpreted and modelled in terms of the principal mechanisms of rock projection described in this study.

Appointment of women to mining boards – Evidence of tokenism

by N.V. Moraka. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The experiences of women board members in mining were investigated by means of in-depth interviews with 20 women and 16 men across six listed companies. Data analysis revealed evidence of tokenism where recruitment to mining boards is informal, compliance-based, and is driven by male dominated nominations committees. This study recommends that a strong Board Chair and nominations committee is critical to ensure sustainable recruitment of competent and suitably qualified women.

Selected trace element concentrations in run-of-mine coal, discard, and coal product, and environmental implications

by R.M. Mashishi, O.J. Okonkwo, and T. Malehase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The concentrations of selected trace elements in run-of-mine coal, discard, and coal product were investigated to assess the efficiency of the beneficiation process in reducing trace element concentrations, and ultimately to ascertain whether there may be environmental implications. The order in which trace elements occurred from the highest to lowest throughout the production chain was Pb>As>Hg>Cd. The study suggests that the current beneficiation process is unable to reduce the level of Pb. This is because Pb exists in the organic fraction of the coal and is not easily removed by beneficiation.

Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption at a coper-cobaltzinc plant

by Y. Jeong and K. Kim. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The effects of reducing the water content in tailings slurry were investigated at a copper-cobalt-zinc mine in Mexico. An environmentally friendly polymer was used as a drag reduction agent to offset the increase in solids percentage, and a model was developed to assess the potential risks to the pipelines. The annual water savings were found to be significant, increasing from about 1.852 Mm3 at 35% solids to 3.915 Mm3 at 45% solids.

Investigation of a conveyor belt fire in an underground coal mine: Experimental studies and CFD analysis

by C.O. Aksoy, G.G.U. Aksoy, A. Fişne, I. Alagoz, E. Kaya . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

In 2014, a conveyor belt fire in an underground coal mine in Turkey caused 301 fatalities. The accident was studied by means of combustion tests in a purpose-built research gallery, comparison of the test results with mine records, and CFD modelling of the mine environment. The results showed that The intensity of the fire was sufficient to redirect the air flow underground, flooding almost the entire mine with toxic gases in approximately 15 minutes. It is recommended that CFD analysis be used in planning emergency action strategies in underground mines.

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The Future of mining research in South Africa

ent

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here is currently a flurry of bad news emanating from the mining industry.

The electricity shortages, logistical problems, and low commodity prices have resulted in the proverbial perfect storm, and this is testing the resilience of our industry. As an encouragement to the readers affected, this is not the first time the industry had to survive exceptionally difficult periods. With ingenuity and a bit of luck, we always seem to pull through. For example, the gold price was artificially low in the 1960s owing to the London Gold Pool’s actions to defend the dollar price of $35 an ounce. Many of the marginal gold mining operations in South Africa had to close. The strong mining units survived, however, and they did exceptionally well in the 1970s during the gold boom that followed. Commodity prices will always be subjected to cyclic volatility, and we need to build our mining houses on solid rock to weather the occasional storm.

Part of building this resilience involves ensuring that we conduct the necessary research to improve our productivity and lower production costs. The Leon Commission of Inquiry into safety in the mining industry wrote in their 1995 report: ‘ Furthermore, as no other region of economic significance has similar geometry, no mining industry outside South Africa pursues the solution to this problem. The platinum mines have essentially the same difficulty.

The solution must therefore be found in South Africa.’

The key aspect is highlighted in bold, and we therefore need to foster mining research in South Africa.

In terms of geometry, the Commission was referring to our tabular orebodies at a very flat dip with a small mining height. This makes mechanization extremely difficult, and it results in very high stress levels ahead of the mining faces in deep excavations. Furthermore, the decreasing extraction ratio of the shallow bord and pillar mines with increasing depth needs to be studied in detail and good solutions found. Multi-reef mining with a small middling between the reefs also requires further study. Unfortunately, the mining research capacity in our country has shrunk drastically over the last two decades. In his 2006 paper in this journal – Beyond Coalbrook: what did we really learn? – van der Merwe described the transfer of COMRO to the CSIR and the subsequent collapse of CSIR Miningtek. ‘ Due to disillusionment and internal problems in the CSIR, there was an exodus of qualified and experienced researchers from 2003 onwards. It is estimated that in the period 2003 to 2005, an aggregate of over 1 000 years of research experience was lost. In retrospect, the collapse of Miningtek could well in future be seen as having a more severe impact than the collapse of Coalbrook.’

The situation has only become worse in the years following the publication of van der Merwe‘s paper.

An innovative solution to this research challenge must be found and may in part lie with the small mining research groups that still survive at the tertiary institutions. Postgraduate students from industry are keen to do research and further their qualifications. A new ‘distributed research organization’, involving both industry and the universities, may therefore make a huge contribution to generating new knowledge. The mining industry and government must support and grow these mining departments. The current limited funding initiatives, unfortunately, seem to become increasingly complex, and simple ‘no-strings-attached’ support is required to enable the few surviving good researchers to focus on research only and to train the next generation of academics.

This edition of the Journal features several papers focusing on environmental and safety aspects in mining, and these are valuable studies for the South African industry. I congratulate the authors on their contributions to research.

D.F. Malan

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Reflections on 2023

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he mining industry in South Africa faced significant challenges in 2023. The robust economic recovery post-COVID that had led to impressive returns for mining companies in 2022 did not continue. In 2023 there was a general decline in revenue and profits across the industry, with the notable exception of gold miners. Volatility in commodity prices emerged as a major disruptive force, impacting the sector as a whole.

Platinum companies, the main contributors to industry revenue, bore the brunt of the challenges, grappling with a substantial reduction in platinum group metal (PGM) basket prices. While the depreciation of the South African rand offered some relief, this advantage was offset by escalating import costs. The industry contended with additional hurdles, including persistent electricity supply challenges (load shedding), logistical constraints, a shortage of essential skills, and the ongoing issue of illegal mining activities. These factors played a significant role in driving down overall returns for the South African mining industry.

Despite these challenges, our mining industry continued to embrace technological advancements and digitalization efforts. This focus on innovation could lead to increased efficiency, reduced operational costs, and enhanced sustainability, positioning the industry for long-term success. The industry also demonstrated an increased commitment to Environmental, Social, and Governance (ESG) practices, acknowledging the importance of responsible and sustainable mining.

The SAIMM was engaged in a diverse array of events during 2023, showcasing its commitment to knowledge-sharing and professional development. The Institute successfully hosted a total of 14 conferences, 15 webinars, four short courses, two branch events, and two book launches. Furthermore, the SAIMM expanded its communication channels by introducing a podcast platform known as ‘The Crucible’.

Over the course of the year, the Institute used this platform to present six podcasts.

The events and activities organized by the SAIMM spanned a broad spectrum of subjects, including the crucial technical aspects of mining and metallurgy and wider themes pertinent to the industry. The topics covered incorporated discussions on ESG, mine closure strategies, and the ongoing process of digitalization. The Institute also highlighted its dedication to promoting diversity and inclusion within the sector. This comprehensive approach demonstrates the SAIMM’s recognition of the multifaceted challenges and opportunities in the field and contributes significantly to the enrichment of industry knowledge and practices.

I would like to personally thank our members who organized and participated in these events. The success of these activities is a testament to their commitment to the needs and demands of the minerals industry. The establishment of these platforms for people to engage and discuss important issues is essential for the future of our industry.

I trust that our members have had the opportunity to enjoy a well-deserved break over the festive season. As we embark on the challenges of 2024, I hope you feel recharged and ready to face the opportunities and endeavours that lie ahead.

Wishing you all a prosperous and fulfilling year ahead.

W.C. Joughin President, SAIMM

The Journal of the Southern African Institute of Mining and Metallurgy

VOLUME 123

DECEMBER 2023

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SAMCODESUpdates Snaps –- December SAMCODES December 2023 2023 What’s hAPPening with the monthly Quiz?

• • •

One SAMREC and one SAMVAL quiz was sent out on the SAMCODES App. Users got immediate feedback (scores) on how they did on the +-10 questions.

Apple app development is still ongoing and CPD points being investigated.

The SAMCODES App is available for download on the Play store and instructions for downloading iOS version is available here: https://www.samcode.co.za/codes/category/31general?download=287:samcodes-app-user-guide-v4-2022072

Training programmes 1. The S-K 1300 follow-up workshop in October 2023 was a knowledge update based on feedback from listed entities and consultants concerning the SEC’s views and recommendations ensuing from round 1 of S-K1300 reporting. This provided feedback for further lobbying with the SEC to streamline reporting for QPs/CPs.

Feedback is also available on the SSC S-K 1300 forum site, which you can register for here: https://www.samcode.co.za/forum/s-k-1300-forum

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2.

2.

2.

2.

3.

3.

3.

3.

An introduction to SAMCODES course was also held successfully in October 2023 for An introduction to SAMCODES course was also held successfully in October 2023 for students.

An introduction to SAMCODES course was also held successfully in October 2023 for students.

An introduction to SAMCODES course was also held successfully in October 2023 for UNFC Workshop 20 February 2024, to be hosted by GSSA, will focus on what the UNFC is, students. students.

UNFC Workshop 20 February to be hosted

by GSSA, will focusAct, on what the UNFC is, including case studies of how it2024, is applied, the Critical Raw Minerals AMREC, and brief UNFC Workshop 20 February 2024, to be hosted by GSSA, will focus on what the UNFC is, including case studies of how it what is applied, the Critical Raw Minerals Act, AMREC, and brief UNFC Workshop 20 February to hosted by GSSA, will focus on what UNFC is, introduction to PARC, and then2024, thebesituation is in South Africa, as well as the an update on including case studies of how it is applied, the Critical Raw Minerals Act, AMREC, and brief introduction to PARC, and then what the situation is in South Africa, as well as an update on including how it isdocument: applied, the Critical Raw Minerals Act, AMREC, and brief the UNFCcase and studies CRISCOofbridging introduction to PARC, and then what the situation is in South Africa, as well as an update on the UNFC and CRISCO bridging document: introduction to PARC, and then what the situation is in South Africa, as well as an update on https://www.gssa.org.za/uploads/newsletters/Events/UNFC_Workshop.pdf the UNFC and CRISCO bridging document: the UNFC and CRISCO bridging document: https://www.gssa.org.za/uploads/newsletters/Events/UNFC_Workshop.pdf Committee updates https://www.gssa.org.za/uploads/newsletters/Events/UNFC_Workshop.pdf https://www.gssa.org.za/uploads/newsletters/Events/UNFC_Workshop.pdf Committee updates

Committee updates Committee updates

The committee has been driving the use of the SAMCODES App and The committee running quizzeshas been driving the use of the SAMCODES App and The committee been driving the use of the SAMCODES App and running quizzeshas The committee has and beennon-solid driving the use of the App and Reporting of brines minerals, S-KSAMCODES 1300 disclosure running quizzes running quizzes Reporting of brines and non-solid minerals, S-K 1300 disclosure requirements and discount rates were discussed Reporting of brines and non-solid minerals, S-K 1300 disclosure requirements and discount rates were discussed Reporting of brines and non-solid minerals, S-K 1300 disclosure SAMOG updates commence the new year requirements and to discount ratesinwere discussed requirements and discount rates were discussed SAMOG updates to commence in the new year SAMOG updates to commence in the new year SAMOG updates to commence in the new year

SAMCODES ESG Working Group Activities SAMCODES ESG Working Group Activities The ESG Working continued work for incorporating ESG recommendations into the SAMCODES ESGGroup Working Groupwith Activities SAMCODES ESGGroup Working Groupwith Activities The ESG Working continued work for incorporating ESG recommendations into the SAMCODES through the following activities, since the follow-up ESG workshop held in July 2023: The ESG Working Group continued with work forthe incorporating ESG recommendations the SAMCODES through the following activities, since follow-up ESG workshop held in Julyinto 2023: The ESG Working Group continued with work for incorporating ESG recommendations into the • The front end of is essentially SAMCODES through theSAMREC followingCode activities, since thecomplete. follow-up ESG workshop held in July 2023: SAMCODES through theSAMREC followingCode activities, since thecomplete. follow-up ESG workshop held in July 2023: •• The front end of essentially SAMREC Table 1 completed, withisESG Section (5.5) is in progress.

• The front end of SAMREC Code is essentially complete.

SAMREC Table 1SAMREC completed, withis ESG Section (5.5) is in progress.

•• The end ofsection Code essentially complete.

ESGfront summary for addition in SAMREC in progress.

• SAMREC Table 1 completed, with ESG Section (5.5) is in progress.

•• SAMREC ESG summary for addition in progress.

Tablesection 1 completed, with ESG Section in (5.5) is in progress.

SAMVAL Code and SAMVAL Table 1 SAMREC is complete.

• ESG summary section for addition in SAMREC in progress.

•• ESG SAMVAL Code and SAMVAL Table 1 is complete. summary section for addition in SAMREC in progress.

SAMESG Guideline update is in progress.

• SAMVAL Code and SAMVAL Table 1 is complete.

SAMESGCode Guideline update isTable in progress.

• SAMVAL and SAMVAL 1 is complete.

• SAMESG Guideline update is in progress.

• SAMESG Guideline update is in progress.

International Liaison

International Liaison CRIRSCO – ESG definitions have been issued during the recent CRIRSCO AGM in Brazil, including International Liaison International Liaison CRIRSCO – ESG definitions have been issued during the recent CRIRSCO AGM in Brazil, including

reference to ESG factors which will be used as guidance for SAMCODES. Philippines became a CRIRSCO – ESG havewill been issued during the recent CRIRSCO AGM in Brazil,became including reference ESG definitions factors which be members. used as guidance for SAMCODES. Philippines a CRIRSCO –CRIRSCO, ESG definitions have been issued during the recent CRIRSCO AGM in Brazil, including member ofto so now up to 15 reference to ESG factors which will be used as guidance for SAMCODES. Philippines became a member oftoCRIRSCO, so now to 15 reference ESG factors whichupwill be members. used as guidance for SAMCODES. Philippines became a member of CRIRSCO, so now up to 15 members. member of CRIRSCO, so now up to 15 members.

Guideline for Reporting of Industrial Minerals Guideline for Reporting of Industrial Minerals The need tofor compile a Guideline for the estimation Guideline Reporting of Industrial Mineralsand reporting of mineral resources and mineral Guideline Reporting of Industrial Mineralsand reporting of mineral resources and mineral The need tofor compile a Guideline for the estimation reserves for industrial minerals is being considered by the SSC and SAMREC. The needfor to compile aminerals Guideline theconsidered estimation andthe reporting of SAMREC. mineral resources and mineral reserves is for being SSC and The need to industrial compile a Guideline for the estimation by and reporting of mineral resources and mineral reserves for industrial minerals is being considered by the SSC and SAMREC. reserves for industrial minerals is being considered by the SSC and SAMREC.

JSE Reader’s Panel JSE Reader’s Panel SinceReader’s inception Panel of the JSE Reader’s Panel, a total of 282 reports have been reviewed by the JSE JSE SinceReader’s inception Panel of the JSE Reader’s Panel, a total of 282 reports have been reviewed by the

Reader’s Panel. During the past five years, 25% of CPRs were accepted on first submission, 58% Since inception of the JSE Reader’s Panel, a total of 282 reports haveonbeen reviewed by58% the Reader’s Panel.

During theremainder past five years, 25% of CPRs were accepted first submission, Since inception of the and JSE Reader’s Panel, a total of 282 reports haveimprovement been reviewed by the on second submission on third submission, a considerable in quality of Reader’s Panel.

Duringand theremainder past five years, 25% of CPRs were accepted improvement on first submission, 58% on second submission on third submission, a considerable in quality of Reader’s Panel.

During the of past five years, 25%by ofthe CPRs were accepted on pie firstchart submission, CPRs since 2016.

The split minerals covered CPRs is shown in the below. 58% on second submission and remainder on third submission, a considerable improvement in quality of CPRs sincesubmission 2016. The and splitremainder of mineralsoncovered by the CPRs is shown in the pie chart below. on second third submission, a considerable improvement in quality of CPRs since 2016. The split of minerals covered by the CPRs is shown in the pie chart below.

CPRs since 2016.

The split of minerals covered by the CPRs shown in theDECEMBER pie chart below. vii ◀ The Journal of the Southern African Institute of Mining and Metallurgy VOLUMEis123 2023

*Industrial minerals include all non-metallic minerals SSC Changes for 2024 SSC Chair:

Sifiso Siwela (GSSA)

SSC Vice-Chair:

Joseph Mainama (SAIMM)

SSC Immediate Past Chair:

Andy McDonald (SAIMM)

SAMREC Committee Chair/CRIRSCO representative:

Nicole Wansbury

GSSA representative on SSC:

Jacques Nel

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The Journal of the Southern African Institute of Mining and Metallurgy

Flyrock in surface mining Part II — Causes, sources, and mechanisms of rock projection

by T. Szendrei1 and S. Tose2

Affiliation:

1 Dynamic Physics Consultants,

Johannesburg, South Africa.

2 AECI Mining Explosives, Johannesburg,

South Africa.

Correspondence to: T. Szendrei

Email:

szendrei@icon.co.za

Dates:

Synopsis

The fracturing and movement of rock that occurs in the vicinity of a stemmed borehole charge in open pit mining operations are described by examining the effects of the emitted stress waves – shock and elastic – and the expansion of high-pressure detonation product gases. Three principal modes of momentum transfer to fractured rock are identified, all linked to gas expansion work. This work can be delivered radially (burden), axially (stemming), and in the collar zone (cratering). Flyrock is generated under unusual combinations of blast parameters and rock properties. Although infrequent and seldom predictable, the generation of flyrock can nonetheless be interpreted and modelled in terms of the principal mechanisms of rock projection described in this study. The physical processes underlying these principal mechanisms are identified and will permit the development of predictive models for flyrock velocities.

Keywords

flyrock momentum, stress waves, gas action, cratering, face-burst, stemming.

Received: 19 Jan. 2023 Revised: 28 Apr. 2023 Accepted: 13 Sep. 2023 Published: December 2023

How to cite:

T. Szendrei and Tose, S. 2023 Flyrock in surface mining Part II — Causes, sources, and mechanisms of rock projection.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 123, no. 12. pp. 557–564 DOI ID: http://dx.doi.org/10.17159/24119717/2583/2023 ORCID: T. Szendrei http://orcid.org/0000-0002-5693-7850 S. Tose http://orcid.org/0000-0002-2514-5308

Background Flyrock can be defined as the throw of rock fragments from a surface or open pit blast that travel distances beyond the expected range or a pre-set safety zone, and which pose a serious threat of damage to property and infrastructure, and injury to people in and around the mine property. In a previous paper (Szendrei and Tose, 2022) it was pointed out that empirical approaches to the prediction of flyrock throw distances are necessarily limited for the reason that such models are unable to predict the two primary determinants of throw distance – flyrock mass and initial velocity.

Conventional models of flyrock do not consider the physical mechanisms of rock projection nor their motion through air, and are based on statistical correlations that are derived from measured throw distances at specific sites. It was further pointed out that two well–known models of flyrock velocity (Lundborg et al., 1975; McKenzie, 2009 that are based on more comprehensive ballistic trajectory calculations, are flawed.

The Lundborg model for maximum throw distance is based on a model of momentum transfer to rocks that is not supported by present-day knowledge of the properties of blast waves and overestimates the throw distance by factors of 2 or more. McKenzie (2009) calibrated his scaled–depth–of–burial model against Lundborg’s velocity values and therefore his predictions of flyrock velocities and throw distances are also questionable.

It is evident that progress in the analysis and prediction of flyrock would require a deeper understanding of the mechanisms by which rocks acquire momentum in a blast and are propelled from the bench. We further pointed out that on a fundamental level, and irrespective of any details of blast design or rock mass properties, the range of a flyrock of a given mass and shape depends only on the launch velocity, and its prediction would require calculation by a realistic trajectory model that includes air drag.

Figure 1 is a schematic illustration of the general layout of a bench blasting operation and the terminology used to describe the elements of the blast pattern, many of which are relevant to discussions of flyrock.

The ‘burden’ that is of direct relevance to flyrocks is the separation of the first row of blast-holes from the free face, which is generally vertical. As noted later in this study, the as–drilled burden may vary significantly about its nominal planned value.

The aim of this study is to identify the physical processes by which fragmented rocks acquire velocities that propel them to distances of some hundreds of metres from the muckpile in the short period of time (tens of milliseconds) between the detonation of a column charge and the throw of rock fragments from the bench.

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Flyrock in surface mining Part II — Causes, sources, and mechanisms of rock projection

Figure 1—General layout of a blast pattern for a bench blast

Figure 2—Sources of flyrock in surface mining

Causes and sources of flyrock Many workers have attempted to identify the reasons for the occurrence of flyrock, and based on some of these perceived causes various equations have been proposed to predict flyrock throw distances. These equations are normally based on various parameters of the blast design and charge load, and less often on the properties of the rock mass. Raina, Murthy, and Soni (2015), for example, listed 13 parameters from published studies on the causes of flyrock, and 16 parameters used in various models of flyrock range. It has been noted (e.g. Raina and Murthy, 2016) that there is often a disparity between the perceived causes of flyrock and the measurable empirical parameters that are used for the prediction of range. This may be due to the difficulty of defining appropriate parameter values that would link, for instance, the influence of rock geotechnical quality or delay timing errors to flyrock throw distances.

Ghasemi, Sari, and Altaei (2012) used seven parameters to develop a prediction equation for throw distance by multiple regression analysis of linear and nonlinear combinations of blast parameters. In contrast, Raina and Murthy (2016) conducted an artificial neural network (ANN) study that included 21 parameters of blast design, explosive, and rock properties. Despite their 558

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complexity, studies of this nature have not yet yielded a globally applicable model that is capable of ab initio predictions of flyrock throw distances.

The cited causes of flyrock may be grouped in five categories: ➤ Basic geometrical details of the blast pattern and stemming design ➤ Charge and loading details ➤ Errors in blast plan implementation, especially those associated with drilling and charge loading ➤ Delay timing and forward relief ➤ Rock mechanical properties and geotechnical quality.

The most influential parameters for flyrock generation are generally recognized as being: ➤ Insufficient confinement of the charge in general, and the burden in particular ➤ Insufficient or inadequate stemming ➤ Specific charge (kg/m3) and loading deviations ➤ Delay timing ➤ Rock defects and geological anomalies.

Three general sources of flyrock projection from the bench have been recognized, as illustrated in Figure 2.

The Journal of the Southern African Institute of Mining and Metallurgy

Flyrock in surface mining Part II — Causes, sources, and mechanisms of rock projection The velocity values and the indicative angular spread of rock expulsion are based on field measurements and data collected

by AECI Mining Explosives over many of its operations across Africa. Swelling of the ground surface is included in Figure 2 as it is relevant to the interpretation of the so-called scaled-depth-of-burial model of flyrock. A schematic illustration of an incorrect burden resulting in a face-burst is shown in Figure 3.

A face-burst occurs when a jet of high-pressure gas follows a path of least resistance through the burden and projects rocks at velocities that may be multiples of expected burden throw velocity.

Gun-barrelling (rifling) occurs when the stemming is inefficient (too short or absent or of an inadequate material), and is ejected from the borehole at high velocity and gas pressure. This can also occur when unusually high pressure develops in the borehole. Gunbarrelling is usually accompanied by extensive damage to the hole collar.

Cratering occurs on top of the bench as a consequence of the action of the charge load that is present in the collar zone, the type and length of the stemming material, and is considered to be the major source of excessive flyrock as well as wild flyrock. This effect may be pronounced when the collar rock is weak and/or damaged due to poor drilling practises, in particular the collaring of the hole and over-drilling of the previous block (excessive sub-drill), resulting in overbreak in the floor and/or prefractured due to the blast design. Control of the loading of broken rock material from the previous blast and over-digging can also contribute. Insufficient stemming length, and the use of drill cuttings instead of a suitable crushed angular stone may exacerbate the situation.

The above sources of flyrock generate three distinct types of thrown rock (Figure 4): Throw is the planned forward casting of blasted, fragmented rock from the burden to form the muckpile within the blast zone.

Flyrock is the undesired projection of broken rock beyond the blast zone. While undesirable, flyrock is not a safety hazard if it falls within the blast exclusion (or clearance) zone.

Wild flyrock is the unexpected projection of flyrock beyond the exclusion zone, often when there is an abnormality in the blast or rock mass. It is a serious safety hazard for workers and the general public.

The question of the mechanisms by which flyrock is projected from the above sources and at what velocities requires the examination in some detail of the processes that result in the fracturing and throw of rock.

Figure 3—Insufficient burden in a rugged portion of the face resulting in a face-burst

Rock fracture and movement – a historical perspective Stress wave action Historically, a number of theories concerning rock fragmentation and cratering by blasting have been proposed. The most well– known (often mistakenly termed the ‘shock wave’ theory) relied heavily upon tensile scabbing and spalling as the fracture mechanism (Card, 1962). In brief, the explosion pressure in the borehole drives a short-duration, high-amplitude stress wave into the surrounding rock mass as a shock wave. This creates a crush zone and a dense radial pattern of cracks around the blast-hole before propagating outward as an elastic wave at the speed of sound in the rock. Because of the relatively high compressive strength of rocks, the advancing stress wave produces no further damage until it is reflected at a free face as a tensile wave. Fracturing will then occur where the intensity of the inward moving tensile wave exceeds the fracture strength of the rock, this being much less than its compressive strength (1/10 to 1/40). If the original stress pulse is strong enough, several such fractures will form in planes normal to the returning tensile wavefront. The ‘shock wave’ theory states that the cracked rock is displaced outward by spalling and slabbing.

Later modifications of the theory admitted a greater role for radial fractures (e.g. Hustrilid, 1999) but left the essential element of the theory unchanged – tensile fracturing is the primary cause of cratering (and hence of rock throw).

Figure 4—Basic types of flyrock in bench blasting operations (after Little, 2007) The Journal of the Southern African Institute of Mining and Metallurgy

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Flyrock in surface mining Part II — Causes, sources, and mechanisms of rock projection While it cannot be denied that tensile stress projection of fragments from the free face can create shallow craters, it is observed that a crater which extends back to the borehole will involve a much greater volume of rock than can be attributed to spalling. Post-mortem observational evidence has shown that the final fracture surface for the crater is created by fractures that start at the blast-hole and extend to the free surface. This directly contradicts the tensile/spalling model, in which fractures propagate from the free surface inward.

Sellers et al. (2013) noted two other major and demonstrable shortcomings of the tensile fracture model. Its predictions of burden break-out angle as a function of the burden cannot be reconciled with field observations. The model is also unable to account for the energy deficit noted by Ouchterlony et al. (2004). Up to 50% of the chemical energy released in the explosion of a borehole charge cannot be accounted for in terms of processes that underlie the elastic theory of rock breaking.

It is now generally accepted that the tensile stress fracturing model should be replaced by a broader model that includes the influence of longer duration pressure of gaseous products of detonation. Over the years there has been much debate over the relative contributions of these two very different types of loading to the fracturing, fragmentation, and displacement of rock.

Gas pressure action Based on laboratory–scale experiments, Kutter and Fairhurst (1971) demonstrated that the role of reflected stress waves in single hole cratering is not only to cause scabbing, but also to extend the radial fractures in the vicinity of the borehole towards the free face. They also pointed out that the relatively small amount of energy carried away from the borehole by stress waves (5–10%) indicates that the major part of the energy of explosion must be associated with the internal energy of gases remaining in the borehole after the explosion. They argued that this high-pressure gas penetrates into the radially cracked zone surrounding the borehole and creates a pressurized ‘equivalent cavity’ equal in size to the volume defined by the tips of the radial cracks. The stress-induced static stress field set up in the rock around the equivalent cavity would be sufficient for extensive crack propagation and thereby complete the fragmentation of the rock mass. The Kutter and Fairhurst (1971) model of fragmentation does not predict the velocity of the thrown rock.

Fourney et al. (1993), on the other hand, based the mechanisms of cratering on the expansion of gases from the borehole. The displacement of rock is made possible by its prior ‘preconditioning’ through the formation of a network of radial and hoop fractures in the dynamic stress wave phase of a blast. Following this phase, high-ressure gas the acts on the greatly weakened rock mass around a borehole and begins to move the inertial mass in the direction of least resistance – towards the free face. This movement opens and extends the radial cracks to the free face and the fractured material is thrown from the crater.

Other than clearly being associated with gas expansion work, the mechanism by which the thrown material acquires velocity is vague. Sellers et al. (2013) noted that if significant flow of gas into fractured rock mass does occur, it would decrease the energy of explosion product gases and, contrary to conventional thinking, would not enhance heave. Nonetheless, it is evident that gas pressure plays an important role in displacing fractured rock. The details of this action and the sequence of events following the to-and-fro passage of stress waves through the rock mass remain vague.

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Rock fracture and movement − A new perspective Stress wave action The early theories of tensile cracking and cratering were somewhat limited in that they did not consider some specific characteristics of shock wave action and stress wave propagation that ultimately determine the nature and extent of fracturing of the rock mass. A description is given below of these aspects of stress wave action in sufficient detail to identify the physical principles underlying the mechanics of rock projection.

Borehole expansion In recent years it has been recognized that immediately following the detonation of the charge, the borehole undergoes rapid radial expansion under the influence of a shock wave that is transmitted by the detonation product gases into the rock through the skin of the borehole. This typically results in a 2- to 5-fold volumetric expansion(in fully coupled holes (Cunningham and Szendrei, 2004; Cunningham, Sellers, and Szendrei, 2007).This expansion is central to the properties of the stress wave that subsequently propagates away from the borehole.

The crush zone and the ring of dense radial cracks around the expanded borehole mark the radial extent of inelastic rock response to the passage of the shock wave as it propagates away from the blast-hole. The periphery of this zone of inelastic rock response marks the point where the intensity of the shock wave has decreased from its initial value of some gigapascals (GPa) to a value equal to the strength of the rock, commonly taken to be its unconfined compressive strength (UCS). Thereafter a compressive elastic stress wave (σc) propagates outward with this initial amplitude at the speed of sound in the rock, typically 3000–6000 m/s. The duration and length of the stress pulse are directly related to the time of expansion of the borehole to its final size.

Radial fractures After propagating away from the expanded borehole, the compressive stress pulse soon develops a tensile component in its trailing portion as a consequence of the divergent movement of rock particles behind the wave front in cylindrical symmetry. Tensile forces (σt) acting normal to the direction of propagation induce radial splitting of the rock. The strength of these tensile forces at first increases with radial distance, then decreases as the wave amplitude attenuates with increasing distance from the borehole. The net effect is that radial fractures extend only part of the way to the free face.

Once the stress pulse has passed by, the rock is stress free and radial fracture growth ceases.

Figure 5 illustrates the effects of close-range stress wave action on rock surrounding a blast-hole.

In addition to the delineation of various rock response zones, three particular features are notable in Figure 5, namely (i) an enlarge borehole is clearly seen (56% radial and 2.4 volumetric expansion); (ii) the crush zone is of limited extent – 2½ hole diameters in this instance; (iii) tangential (tensile) cracks are seen only outside the intense fracture zone.

Of course, radial fractures are not limited to the rock mass between the boreholes and the bench face. Radial fractures would be generated in the full 360o circle around each borehole. The growth of these fractures would cease as the compressive pulse propagates away in the bench behind the face as an ever-decreasing ground vibration. When multiple boreholes are detonated the rock between two adjacent holes would largely be traversed by radial fractures extending from each hole.

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Flyrock in surface mining Part II — Causes, sources, and mechanisms of rock projection

Figure 5—Example of the fracture pattern surrounding a socket in an underground gold mine (based on work by AECI Mining Explosives)

Attenuation of elastic waves At distances from the borehole that are of interest in bench blasting (some metres) viscous damping of elastic stress waves may be neglected and peak intensity of the elastic pulse will decay, mainly with geometrical attenuation. In the cylindrical symmetry that exists between the column charge and the bench face, wave amplitude will decay as the inverse of the square root of the radial distance. Vertically, between the base of the stemming and the bench top, wave propagation has a three-dimensional character and amplitude will decrease with the inverse of the propagation distance.

These attenuation laws permit the calculation of the relative amplitudes of stress waves arriving at various locations on the bench from the borehole.

Reflection at free faces Reflection of a compressive pulse at a free face results in an inwardmoving tensile pulse of the same amplitude and duration, but only in the event that the angle of incidence (θ) on the free face is zero (i.e. along the surface normal). At larger angles of obliquity both tensile and shear stresses are generated on reflection. Importantly, the amplitude of the reflected tensile wave diminishes with obliquity and generally becomes vanishingly small quite rapidly when θ is 40–60o. This critical angle is specific to the rock and is a function of its Poisson’s ratio, which is a measure of its rigidity.

As the reflected tensile wave runs back towards the borehole, fractures parallel to the wavefront are generated at distances from the free face where the net tension, σt + σc, exceeds the fracture strength of the rock. If the incident pulse is strong enough, several such fractures can form parallel to the wave front in a process called slabbing. This process does not necessarily result in outward projection of scabbed material. This would require a sufficient level of trapped momentum between the two faces of the scabbed material, a condition that is seldom met except in the case of small fragments spalled from the surface.

Because of the obliquity effect in reflection, the rock mass is mostly fractured in tension only within certain limiting angles. The well-fractured mass is wedge-shaped in the burden (cylindrical The Journal of the Southern African Institute of Mining and Metallurgy

symmetry) and cone-shaped in the collar zone (spherical symmetry). In both cases, the apex is at the borehole, the opening angle is about 100o, and the base is located at the free face.

Tangential (hoop) fractures The state of stress in the reflected tensile wave is biaxial – both radial and lateral stress components are tensile so that fractures may form both parallel and normal to the wave front. The effects of biaxial tensile forces are particularly notable when the returning wave runs over the radial cracks in the vicinity of the borehole and connects them together with circumferential (hoop) fractures.

Additionally, the radial cracks, particularly those that are within the wedge of strong tensile action, may undergo extension towards the free face when exposed to renewed tensile forces. Crack extension is a less energy-demanding process than the formation of new cracks.

Fracturing is not limited to an outgoing and an incoming stress wave only. In regions of the rock mass where more than one free face exists, fracturing becomes more complex. The amplitudes of multiple elastic waves – compressive and tensile – can be summed vectorially at any location. This superposition of waves that may be travelling in different directions and with different amplitudes can yield a resultant amplitude that is strong enough to cause localized fracturing. This effect will be especially important in regions of the rock mass that may be traversed by various reflected and rereflected waves, such as the collar zone.

Collar zone fracturing The collar zone may be defined as the rock mass between the top of the charge column and the bench top. Rock in this zone would not experience the same levels of stress wave fracturing as detailed above, for a number of reasons. The specific charge (kg/m3) in the collar zone is less than in the rest of the blasted volume. Also, travel distances for the compressive pulse to free faces on the top and sides of the bench can be longer than radially through the burden in front of the charge columns, and the angles of incidence on the free face would generally be higher. These factors would reduce the strength of the compressive pulse arriving at free faces and weaken the VOLUME 123

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Flyrock in surface mining Part II — Causes, sources, and mechanisms of rock projection subsequent action of the reflected tensile wave. Some contribution to fracturing from the superposition of stress waves can be expected, but this effect would be localized and confined to specific directions and planes that are defined by the geometrical disposition of free faces and the loci of intersection of stress waves.

All in all, it is unlikely that the collar zone would be as well fractures as the rest of the burden rock. This expectation is borne out by Chiapetta’s observation (2009) that the bulk of oversize derives from the collar zone and may constitute up to 40% of the muckpile.

Movement of fractured rock Although the burden from grade to bench top is fractured with a network of radial and tangential cracks, it remains in place at the completion of stress wave action. Except for some possible spalling from free faces and the throw of loose rocks from the top of the bench as momentum missiles, there would be no large-scale displacement and dispersion of broken material. It is the central tenet of our analysis of the causes of flyrock that the movement of rock and its projection at various velocities is the consequence of gas action. Gas action is not mediated by rapid infiltration and pressurization of fractured rock or by extension of existing cracks, but by the mass movement of rock in the burden and collar zone.

At the completion of borehole expansion, detonation product gases are still retained in the expanded holes. Momentum is transferred to fractured rock only when the internal energy of the confined gas is converted by expansion work to kinetic energy of the rock mass. The way this energy is delivered is determined by the various paths of expansion followed in the burden, stemming, and collar zone. These paths of expansion are described in the following section. In addition, two other possible modes of momentum transfer to rocks (as historically postulated) are briefly considered – stress wave action and air blast.

Mechanisms of rock projection The accumulation of explosion product gases in the (initially) closed volume of an expanded borehole possesses considerable internal energy due to its high pressure. Although generated under detonation shock conditions, the released gas quickly equilibrates in the borehole behind the detonation shock front. This pressure acting on the enclosing rock surfaces – borehole walls and the base of the stemming column – accelerates the rock in proportion to the pressure (force per unit area). This fundamental motive force manifests itself in various ways by which momentum is transferred to rock. The following modes of transfer can be identified as direct consequences of the action of gas pressure: (i) Burden movement and face-burst (ii) Stemming ejection and collar damage (iii) Bench top cratering.

Stress wave action and blast wave impulse have been cited in the literature as causes of flyrock, and are briefly considered as possible modes of momentum transfer.

Burden movement Observational evidence (e.g. high-speed videos) indicates that the forward displacement of burden rock may be conceptualized as the opening of a gap between a row of boreholes and the bench face, at least on the scale of metres. For modelling the throw of burden in general and the throw of flyrock from relatively small, localized areas of the face in particular, a physically insightful definition 562

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of the burden is the inertial mass per unit area (MB). This area is taken normal to the radial direction and is large enough to include deviations and imperfections in the face and in the geology of the burden rock.

In related explosives technology areas of military science and engineering, it is common practice to apply the Gurney approach to the prediction of projection velocities of inert materials in contact with explosive charges (Walter and Zukas, 1989). The key concept of the Gurney technique is that the energy liberated by detonation resides as the internal energy of an equi-volume quantity of highly compressed detonation product gases and only a certain fraction of this energy, EG (MJ/kg), can be converted to mechanical work by gas expansion. This fraction is about 70% for high explosives such as TNT, RDX, and HMX (Cooper and Kurowski, 1996), and somewhat less, 55−65%, for various formulations of ANFO and emulsions (Essen et al., 2005). The Gurney energy is an intrinsic property of explosives and is considered to be an accurate estimate of the work capacity of an explosive as applied to its surroundings.

The Gurney velocities of projection (VB) have been calculated for many geometrical arrangements of explosives and inert materials. The particular combination that may be of direct relevance to bench blasting is the so-called asymmetric sandwich arrangement, where the explosive (C) is sandwiched between two ‘plates’. One plate of mass MB is free to move forward and may be associated with the burden. The second plate is a heavy ‘tamper’ of mass N which prevents any significant backward movement and may be associated with the essentially rigid rock mass of the bench behind the row of blast-holes.

Gurney velocity predictions (VB) are generally of the following functional form:

where the shape of the function f is case-specific and can be defined in planar, cylindrical, or spherical symmetry. It is intuitively obvious that high values of the ratio C:MB would yield high values of burden velocity.

Many geometrical details contained in the blast plan will contribute to the variation of MB, e.g. B, S, H, height of stemming, and hole diameter as defined in Figure 1, together with drilling deviations and rugged face profile as well as geological anomalies (cavities, fissures, weak strata, mud etc.). It is more insightful to consider the inertial mass per unit area (MB) as ρBLB where ρB is the effective density of the inertial mass along an expansion path of length LB through the burden to the face.

Clearly, both ρB and LB may show considerable variation over the face. The upper limit is set by competent rock of (say) density 2500 kg/m3 and a burden of 4 m, yielding ρBLB = 10 000 kg/m2. A lower limit would be an open fissure with ρBLB approximately zero.

Similarly, the effective charge mass per unit area of face may vary from the value defined by the nominal charge per linear metre to multiples of this value when the borehole intersects a cavity and other possible reservoirs of excess explosive. It is evident that both the specific charge (kg/m3) and linear charge density (kg/m) as defined in the blast plan are coarse estimates of the actual chargeto-mass ratio in the field ratio, which is the major determinant of burden movement.

The effective burden mass defined as ρBLB may vary between wide limits from place to place on the face as would be shown, for instance, by diamond core drilling. Given this wide range of possible values and its influence on rock velocity, the Gurney model suggests that flyrock is generated when gas action drives fractured rock to The Journal of the Southern African Institute of Mining and Metallurgy

Flyrock in surface mining Part II — Causes, sources, and mechanisms of rock projection unusually high velocities along pathways through the burden where the inertial resistance (ρBLB) is exceptionally low. We suggest this is the root cause of face bursts.

be dispersed at high angles, favouring maximum range of throw.

This view requires further study in order to derive a quantitative physical mechanism for estimating the momentum of thrown rock.

Stemming ejection (gun-barrelling)

Pressure pulses in air and rock

A second – and probably principal source of excessive and wild flyrock – is the stemming and hole collar, where two basic modes of rock projection may be operative. The first is ‘gun-barrelling’, whereby the stemming column is propelled upward by gas pressure acting on its base in a manner closely resembling the acceleration of a projectile in a gun barrel. The second mode is energetic rock projection by cratering in the collar zone.

As in a gun barrel, the expansion of gas behind the stemming converts its internal energy to work done in overcoming the inertial and frictional resistance of the stemming column. The response of the stemming to gas action would depend on its column length, type of material, bulk density, size and angularity of particulates, and frictional resistance at the blast-hole wall. Ejection of the stemming is usually accompanied by the throw of rock from the collar zone. The severity of collar damage would depend upon the ‘muzzle blast’ – the pressure and velocity of the plume of gas emerging from the collar. Normally the expanded blast-hole volume will determine the driving pressure at the start of stemming motion, usually the equivolume pressure in a fully coupled hole as described

by Cunningham (2006). The ‘muzzle’ effect would be enhanced when the venting pressure is unusually high due to lack of forward relief, excessive charge load, and all factors that may influence delay timing and sequencing.

The influence of borehole pressure and many details of the stemming design on the violence of stemming ejection provides an explanation for why stemming has long been considered to be a critical element of blast design. Modelling stemming ejection along the lines of gun internal ballistics would enable calculations of the gas pressure and its streaming velocity at the ‘gun muzzle’, the bench top, as functions of various design details. Gas pressure and velocity at exit are seen as necessary initial conditions for the understanding of rock projection from the collar zone and as necessary inputs for the construction of models for the prediction of flyrock velocities from this zone.

Szendrei and Tose (2022) demonstrated through calculations that air blast is a weak transmitter of momentum and unless implausibly large explosive charges are considered, it cannot propel sizeable rock fragments to far distances. Similarly, stress waves can fracture rock but the impulse transmitted by these waves is far too low to create dangerous flyrock.

Bench top cratering

Mechanisms of rock projection

This is easiest conceptualized in terms of the scaled-depth-of-burial (SDOB) model proposed by Chiapetta (1983) and Mackenzie (2009) and described in detail in the ISEE Blasters’ Handbook (2018). In its original formulation the model predicted the depth of placement of a charge for maximum crater volume and made no predictions of the velocity of the ejected debris. The McKenzie (2009) version presented an equation to calculate the throw velocity. Szendrei and Tose (2022) pointed out that this equation is based on questionable assumptions and overestimates measured throw distances by factors of 2 to 10, as may be inferred from field observations presented by McKenzie (2018).

No model is known for the prediction of rock debris throw distances from crater blasting other than simple correlation equations based on cube root scaling of explosive mass (DDSB, 2009). Observational evidence indicates that rocks thrown from the bench top often possess the highest velocities. The cause of such high velocities remains unclear. Clearly, it must in some way relate to gas pressure generated by the buried charge and venting through the collar zone, together with the doming and eventual bursting of ground around the hole collar. Rocks ejected in such events would The Journal of the Southern African Institute of Mining and Metallurgy

Discussion Shock phase The importance of elastic stress wave action in fracturing rock has generally been acknowledged; the role of the shock wave emanating from the borehole immediately after the detonation of the charge has been less well recognized. While the details of detonation physics resulting in its formation have no direct influence on flyrock generation, the importance of the shock wave lies in two consequences that it leaves behind. One is the creation of an enlarged borehole containing detonation product gases; the other is its conversion to an elastic stress wave that propagates away into the rock mass. The former is the source of energy for the subsequent rock movement; the latter leads to pre–fracturing of the rock prior to gas action.

Gas action The expanded borehole serves as a reservoir of pressurized gas, which will be of the order of 100 MPa for commercial blasting agents. The internal energy of this gas is the source of gas action on fractured rock that ultimately displaces and throws the rock from the bench. Many groups in the explosives and mining industries have presented numerical models of considerable complexity to track detonation and isentropic expansion of detonation product gases. An example of such work, based on AEL’s i–Vixen code, was presented by Cunningham, Sellers, and Szendrei (2007) for pumped emulsion. Adiabatic expansion of high-pressure gas can be adequately modelled as a polytropic process.

Five possible mechanisms for the transfer of momentum to rock are considered in this study. Of these, two – blast wave impulse propagated through air and spalling and momentum fragments generated by stress waves in the rock – make no significant contribution to the throw of flyrock. The other three mechanisms derive from the action of detonation product gases and the work delivered along various paths of gas expansion. All recognized causes of flyrock can be interpreted as contributing in some way to gas expansion work, and hence to the transfer of momentum and kinetic energy to fractured rock. Although some flyrocks acquire exceptionally high velocities, their generation can nonetheless be interpreted within the parameters of the various modes of momentum transfer. Pre–fracturing of rock by stress wave action is seen as a necessary precursor to rock movement.

Flyrock velocity Flyrock is seen as a by-product of the mass movement of rock by gas action due to unusual but plausible combinations of blast design, its implementation, and rock geotechnical details that enhance momentum transfer along certain pathways through the rock.

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Flyrock in surface mining Part II — Causes, sources, and mechanisms of rock projection Conclusions We have presented detailed arguments that the projection of flyrock from the sources, as illustrated in Figures 2 and 3, can be modelled in terms of concepts that are well established in related technological areas of military ballistics and engineering. These concepts are: Gurney energy and charge/inert mass geometry and interaction; internal ballistics of guns and the importance of projectile mass and wall friction; buried explosions and crater formation between the limits that yield the maximum volume or a camouflet. Through suitable adaptations of these concepts to the specifics of bench blasting and the introduction of appropriate initial conditions, it would be possible to establish the scientific underpinnings of flyrock projection and derive quantitative predictive models. This work is currently in progress.

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Appointment of women to mining boards – Evidence of tokenism

by N.V. Moraka1

Affiliation:

1Unisa, South Africa.

Correspondence to: N.V. Moraka

Email:

moraknv@unisa.ac.za

Dates:

Received: 12- Jun. 2023 Revised: 14 Sep. 2023 Accepted: 6 Oct. 2023 Published: December 2023

How to cite:

N.V. Moraka. 2023 Appointment of women to mining boards – Evidence of tokenism.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 123, no. 12. pp. 565–572 DOI ID: http://dx.doi.org/10.17159/24119717/2848/2023 ORCID: N.V. Moraka http://orcid.org/0000-0002-1490-089X

Synopsis

Mining companies are required by law to improve representation of women on their boards.

However, progress in this regard has been slow. Boards of directors play an important role in formulating corporate strategy, risk assessment, and effective governance for sustained financial performance. Although some women have successfully maintained board seats, others have been unable to do so. It is difficult to ascertain whether women are being appointed as tokens to satisfy social pressures, as little is known about the experiences of women board members in mining, which may inform or refute tokenism. In-depth interviews were conducted with 20 women and 16 men across six listed mining companies. Thematic data analysis revealed evidence of tokenism where recruitment to mining boards is compliance-based and is informally driven by influential directors. Adverse boardroom experiences that further confirmed tokenism were reported by women, such as disregarding their contributions, condescending behaviour, and limited influence in decision-making, while other women sought to validate their competence and oppose social exclusion. This study recommends that a strong Board Chair and nominations committee is critical to ensure sustainable recruitment of competent and suitably qualified women; and further foster a culture of inclusivity and valuing gender-diverse boards.

Keywords

women in mining, board of directors, recruitment, chairperson, critical mass, tokenism.

Introduction On a global scale, only a few women occupy board seats (Bianco, Ciavarella, and Signoretti, 2015; Catalyst, 2021; Chatergee and Nag, 2023; Deloitte, 2019; Rahman, Zahid, and Saleh Al-Faryan, 2022). To address this problem, initiatives varying from enforced compliance to voluntary targets have been proposed (Botha, 2017), with many companies worldwide stepping to the fore in improving gender diversity (Catalyst, 2021; Szydło, 2015; Terjesen and Singh, 2008; Rahman, Zahid, and Saleh Al-Faryan, 2022). Many companies have argued that there is a limited pool of potential women directors, but research refutes these claims and proves that a lack of suitably skilled and qualified women can no longer serve as a defence (Bosch and van der Linde, 2020; Sweetman, 1996; Moraka, 2013; 2018; Rahman, Zahid, and Saleh Al-Faryan, 2022). In South Africa, it is estimated that women occupy nearly 20% of boards, and the Johannesburg Stock Exchange (JSE) requires listed companies to indicate commitment and plans to increase the representation of women on boards as part of listing requirements (Bosch and van der Linde, 2020; JSE, 2016).

The South African mining industry presents a unique setting due to its historical male-dominated culture (Benya, 2016). As such, the sector faces various expectations of transforming its gender profile, along with race, at board level and across all occupations and management levels to correct the historical imbalances (Botha, 2017). The principal influencer of equal opportunities in the mining industry is the Broad-Based Black Economic Empowerment Act (BBBEEA), which through the Mining Charter legislates women‘s advancement in mining at all levels, including the boardroom, as part of government’s empowerment strategy (Deloitte, 2015; Moraka and Jansen van Rensburg, 2015). A study conducted by Women in Mining (WiM) in the UK and PricewaterhouseCoopers (PWC) showed that at a global scale, the mining industry has fewer women on company boards than any other industry (van Dyke, 2020).

In the top 100 global mining companies, women account for only 8% of board seats and just four executive directors in this group (van Dyke, 2020). Although mining companies listed on the JSE have more women directors compared to their international counterparts, the industry still lags with its inability to identify female talent pools, as well as institute development initiatives and retention strategies to attract and sustain women directors (PWC, 2013; van Dyke, 2020). Despite laws enacted, women in mining are reported to still be subjected to social, physiological, and employment barriers (Botha, 2017). These reports should not be expected, particularly because the literature indicates that women on boards makes business sense and provides proven benefits such as higher profit margins, higher return on sales, and higher returns

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Appointment of women to mining boards – Evidence of tokenism on invested capital and equity (van Dyke, 2020). Women have also been reported to be sensitive to ethics, social and environmental issues, and important drivers for sustainability of organizations (Moraka, 2018). Despite all these benefits, and the promulgation of legislation, the recruitment and retention of women to mining boards is still a challenge (Botha, 2017). The few women appointed are recycled and there is a high turnover due to the inability to retain women directors (Moraka, 2018).

This article contributes to the understanding of recruitment practices and experiences of female directors in mining boardrooms. It contributes to the theoretical knowledge of recruitment to boards to refute or confirm claims of tokenism by presenting the experiences of women who enter mining boardrooms. A theoretical perspective is presented that offers a framework to evaluate evidence of tokenism, which has rarely been empirically tested (Rahman, Zahid, and Saleh Al-Faryan, 2022).

Then, a discussion is presented on the sampling and interview method with emphasis on the research methodology chosen and interview strategies employed. Lastly, a review and discussion of thematic findings is presented before conclusions are drawn.

Tokenism theory Tokenism refers to a practice where members of minority racial, ethnic, or gender groups are permitted to enter spaces and opportunities previously reserved for the majority group to signify inclusivity (Ruby, 2021), when these groups are not genuinely welcome (Riccucci, 2008). Tokenism theory in the context of boards postulates that when only one woman is appointed on the board, scholars are directed to accept as true that the appointment is solely to satisfy social pressure or the perception of inclusion (Broome, 2008; Kanter, 1977; Rahman, Zahid, and Saleh Al-Faryan, 2022; Rixom, Jackson and Rixom, 2023) or as part of the company’s corporate social responsibility (CSR); thus, a board’s sincere effort to improve board gender composition becomes questionable (Abdullah, 2014). Other indicators of tokenism were established when women were appointed to boards that had only a few or no female representation or when a woman had recently resigned from that board (Farrell & Hersch, 2005; Gregory-Smith, Main, and O’Reilly, 2013). Minorities (in this case women directors) are easily marginalized when their presence in a larger group is diffident (Rahman, Zahid, and Saleh Al-Faryan, 2022; Torchia, Calabró, and Huse, 2011). Bhardwaj (2022) found that women’s behaviour toward token treatment is determined by their own value systems and aspirations rather than their minority status. However, other studies showed that the mere presence of a single female director may not lead to positive outcomes and contribution (Bear, Rahman, and Post, 2010; Rahman, Zahid, and Saleh Al-Faryan, 2022), since token appointees may find it more difficult to voice their opinions and be heard (Nemeth, 1986). In an experiment involving 207 Mturk respondents, Rixom, Jackson, and Rixom (2023) found that women are generally viewed as tokens when their numbers are less than the quota according to legislation. Adverse constraints are expected for women joining male-dominated industries owing to their token status (Holgersson and Romani, 2020).

The theory of tokenism (Kanter, 1977) suggests that women minorities are subject to discriminating behaviour during board meetings, and hence face barriers in influencing board decisions.

Accordingly, the male board members as the dominant group tends to see women chiefly in terms of the social roles they occupy, embodying the sex role stereotype, and only later as board members (Holgersson and Romani, 2020; Nielsen and Madsen, 566

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2019; Terjesen, Sealy, and Singh, 2009). Gender stereotyping make it difficult for women directors to have their opinions and inputs valued, and importantly, listened to on an equal basis with other board members (Holgersson and Romani, 2020; Ruby, 2021). Elstad and Ladegard (2012) argued that these minority problems should, according to the theory, be alleviated when the ratio of women increases beyond the token limit of 15%. Kanter (1977) studied women working within a male-dominated Fortune 500 firm to explore how the ratio of women in a group affects group processes (Elstad and Ladegard, 2012; Torchia, Calabró, and Huse, 2011).

She defined a skewed group as having a ratio of 85:15, where the members of the majority (85% or higher) were labelled ‘dominants’ and the remaining minority members ‘tokens’ (Holgersson and Romani, 2020). Tokens are usually perceived negatively, sometimes with downright mockery (Nemeth, 1986), often doubted and not trusted. Being considered a token engenders feelings of discomfort, isolation, and self-doubt (Kanter, 1977), and is likely to affect performance (Nielsen and Madsen, 2019; Powell, 1993; Rahman, Zahid, and Saleh Al-Faryan, 2022; Rixom, Jackson, and Rixom, 2023). Kanter (1977) established that being a token has three behavioural consequences, namely visibility, polarization, and assimilation.

Visibility implies that the tokens find themselves being watched all the time, resulting in perceptions of performance pressure. In this situation, there are perceptions that even small mistakes can be serious, making tokens feel that they must work harder to receive recognition for any individual achievements (Elstad and Ladegard, 2012; Rixom, Jackson, and Rixom, 2023). The visibility mechanism in tokenism theory predicts that tokens will avoid conflicts and controversies and side with the majority (Li and Wearing, 2004). At the same time, tokens may perceive a pressure not to outperform dominants (Gustafson, 2008), and some will choose to become socially invisible and maintain a low profile (Elstad and Ladegard, 2012), being careful not to argue against the dominants to protect the dominant group’s self-esteem. Empirical evidence shows that tokens exhibit passive and obedient behaviour (Li and Wearing 2004), and feel they are likely to be criticized for their mistakes more than necessary (Gustafson, 2008). For all these reasons, even two women appointed to a board will experience difficulties making a meaningful contribution in the boardroom (Torchia, Calabró, and Huse, 2011).

Polarization suggests the contrasting of the dominants (men) with the tokens. It implies that the men feel threatened or uncomfortable around token women, and consequently they heighten their boundaries by exaggerating their commonality and the differences of the tokens (Kanter, 1977; Westphal and Milton, 2000). Demographic differences lower social cohesion in the boards, causing the women to becone isolated from the rest of the group, and thus perceiving that there are barriers to information as well as social isolation (Rixom, Jackson, and Rixom, 2023; van der Walt and Ingley, 2003). In a corporate board setting, the polarization mechanism may have two behavioural consequences. First, the men may be less inclined to share information with the minority women members, and second, they may exclude the tokens from social interaction outside the boardroom (Elstad and Ladegard, 2012).

For a corporate board, informal discussion and socializing outside formal meetings are important activities (Parker, 2007; Stevenson and Radin, 2009). Women may find it difficult to fully participate in these social interactions with other board members if they are a minority, because they perceive themselves as an out-group (Huse and Solberg, 2006). Accordingly, the polarization mechanism has The Journal of the Southern African Institute of Mining and Metallurgy

Appointment of women to mining boards – Evidence of tokenism the consequence that token women are not aware of or do not participate in informal social interaction outside the boardroom (Elstad and Ladegard, 2012).

Finally, assimilation implies that the tokens are forced into stereotypical categories defined by the dominants (Li and Wearing 2004; Rahman, Zahid, and Saleh Al-Faryan, 2022; Rixom, Jackson, and Rixom, 2023; Ruby, 2021). Tokens are then not seen as they really are. Kanter (1977) labels this role encapsulation, a method that renders tokens into limited and mimicked roles (for example, anticipations as to what is ‘appropriate behaviour’ for a woman).

For the tokens, stereotyping may result in perceptions of barriers to exerting influence on decisions in the boardroom. These three mechanisms – visibility, polarization, and assimilation – are predictions of how the dominants behave towards tokens, as well as the subjective reactions of the tokens in terms of their own status.

Stereotypical prejudices may also have consequences in that the women’s inputs are less considered in board decisions (Rahman, Zahid, and Saleh Al-Faryan, 2022; Westphal and Milton, 2000) demonstrating tokenism.

Sampling and interview method Data in this research is valued, as it is difficult to access board members who are often high-profile persons (Kakabadse et al., 2015). Mining companies were selected for the study due to their male-dominated structure and historical gendered architecture.

For sampling purposes, Patton (2002) suggests that sample size sufficiency should be bound by peer review and that sampling decisions should give grounds for justification. Non-probability purposive sampling allowed for the selection of a sample that would respond to the objectives of the research, without compromising the scientific and ethical rules for research engagement. At the time of data collection JSE-listed mining companies were leading global mining companies and thus were considered sources of accurate cases to identify outliers for best- and worst-performing companies in terms of women‘s representation. This research approach followed a qualitative methodology, using a multiple case study design. To achieve a robust, theoretical in-depth understanding, the focus was on six JSE-listed mining companies. Thirty-six Interviews (20 women and 16 men) were held with board members in these companies, ranging from five to six per company. Creswell (2002) suggests that for each case, an average of four respondents should be adequate, while Guest, Bunce, and Johnson (2006) indicate that saturation may occur anywhere between the 6th and 12th interview.

Given that on average mining boards consist of eight, members, a minimum of three and maximum of six interviews were conducted for each board. Three companies had more than three women on their boards and the other three had fewer than two, which enabled the study to compare the experiences of respondents across cases.

The sample consisted of five Board Chairs (four men and one woman), four CEO’s (all men), 14 independent Non-Executive Directors (11 women and 3 men), one Executive Director (woman), and one Financial Director/Chief Financial Officer (woman).

Interviews ranged from 35 minutes to 90 minute each, on average. Interviews were focused on information related to (1) assessing talent management with respect to recruitment of board members (both males and females); and (2) respondents’ views regarding challenges and opportunities experienced post recruitment. In-depth interviews were advantageous as they allowed board members to share their encounters by narrating their stories and experiences and thus became active participants in the research (Stanley and Wise, 1983). The in-depth interviews enabled The Journal of the Southern African Institute of Mining and Metallurgy

different questions to be asked that placed women‘s development at the centre of the research (Hesse-Biber, 2007). This strategy ensured that research was undertaken for women rather than about women (Letherby, 2014). Interviews were corroborated with field notes which were prepared for analysis. The transcribed data of the interviews and field notes was subjectively interpreted by a process of thematic analysis, whereby coding was used as a way of indexing or categorizing the text to establish a framework of thematic ideas about it (Gibbs, 2002). The methodology and the research process were transparent and ensured that the findings are clearly presented and open to critical analysis (Hesse-Biber, 2007).

Thematic findings Thematic analysis of the interview transcript data revealed evidence of tokenism, which was corroborated with Kanter’s tokenism theory. Six themes emerged to confirm tokenism in mining board recruitment, namely (1) compliance-based recruitment, (2) silence – right to voice diminished, (3) limited influence, (4) condescension, (5) validation seeking, and (6) social exclusion. Table I shows the corroborations of theories, related studies, themes, and supporting quotes.

Discussion Compliance-based recruitment was evident where women were recruited to comply with legislation and boards were compelled to be transparent about measures to increase the membership of women (IoDSA, 2016; JSE, 2016). Scholars believe that when only one woman is appointed on the board, it can be assumed that the appointment was made due to social pressures (Arfken, Bellar, and Helms, 2004; Branson, 2007; Broome, 2008; Burgess and Tharenou, 2002; Holgersson and Romanim, 2020; Kanter, 1977; Kogut, Colomer, and Belinky, 2014; Torchia, Calabró, and Huse, 2011). Respondents in this study believed that mining companies would only act based on enforced compliance. It was therefore determined that quotas play a critical role in addressing the poor representation of women in mining. The respondents, mostly women, disclosed their dislike for quotas due to role categorization, gender stereotypes, and being ignored, signifying polarization, but appreciated the impact of quotas which enabled women appointed to boards to insist on more women being added. The general view was that the mining sector is one industry that needs to be compelled through quotas, otherwise there would not be any improvement. The challenge of compliance-based recruitment happens when a woman is appointed on the board without any board- or mining-related experience, as her apparent contribution will not be realized, confirming tokenism. One woman appointee presented an obvious case of tokensim where she mentioned upfront her lack of any mining-related experience in her interview with the nominations committee, yet she was appointed. It was established that her appointment was a reaction to the recent JSE listing guideline, which stated that listed companies needed to develop gender diversity policies, comply with at least 30% women on boards, or explain why they were not able to meet the target.

Tokenism theory suggest that the appointment of one woman in response to legislation can be referred to as tokenism (Arfken, Bellar, and Helms, 2004; Branson, 2007). The deferment to tokenism increases when one woman remains the only female appointee for some time and the commitment to gender diverse board could be doubted (Broome, 2008; Holgersson and Romanim, 2020; Rahman, Zahid, and Al-Faryan, 2021; Rixom, Jackson, and Rixom, 2023).

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Appointment of women to mining boards – Evidence of tokenism Table I

Tokenism theories, themes, and findings

Theory and rationale Women on Boards research

Women on Boards Studies doctrines

Token theory Kanter, 1977

Arfken, Bellar and Helms, 2004 Branson, 2007 Broome, 2008 Burgess and Tharenou, 2002 Kanter, 1977 Kogut, Colomer and Belinky, 2014 Torchia, Calabro and Huse, 2011

Boards that appoint Compliance - based only one woman on recruitment. lead scholars to believe that the appointment of a woman was due to tokenism to satisfy social pressure or the perception of inclusion.

Initially I think it was tokenism and compliance and now I think increasingly there’s more of an understanding of the actual value that we add to the board. (Female Director) She’s the first woman, so we have one woman on our board now and so the plan is then to also now look to increase it further, but at least we’ve made that. (Male Director) I do think with mining it is one of those where I kind of unapologetically and unashamedly say it is that industry that needs to be beaten over the head and compelled per quota. The industry is perverse as well, you need to compel them. That’s the only time that there will be any room for growth because we’re in a period [where] we can’t keep saying that the skill set is not there. (Female Director) Let’s use the quotas because otherwise we’re not going to have women. Men do not like [working] with women, so we need those quotas. My view, honest view, is some of the things must be imposed, otherwise they are not going to happen. (Female Director) I don’t like (quotas) but I think they are necessary. I don’t like being pigeon-holed I never want to join a board because I am a woman. I never ever would want to be someone like that, you are a woman then we check the box. I think that quotas are important and what I find is that they have created a discipline within boards to search outside of the men’s comfort zone. (Female Director) I think we must make sure that we understand the available pool of women in relation to our objectives. For example, in a Mining Charter 3 draft, the percentages they’ve got in there, what the mining industry is saying, those percentages are not achievable for two reasons. One, there is the demographics and two, the available skills out there.

In terms of just setting our targets or [that] you want to achieve, let’s be sober about the pool that’s available. (Male Director) If you look at it, we have two women only at board level. So, the other one is retiring … I said how can the chairperson of the board be the only queen bee around the table. (Female Director) I was quite upfront [with] them to say I don’t know what made you guys decide to get a candidate of my stature because I’m not going to lie to you and say I understand your business; I don’t. But I will try my level best to do what I can … but they begged me [and said] ‘Please, the chairman and one board member would like you to see them’. I stayed but by the afternoon, that Thursday when I was [at that business trip] I was told that they were quite happy, they didn’t want to see anybody else. (Female Director).

Broome, 2008 Huse and Solberg, 2006 Lansing and Chandra, 2012

Women regarded as tokens may find it more difficult to voice their opinions.

Silence (right to voice diminished).

Patriarchy perpetuates the status quo, the status quo is unequal and in fact it is based on the majority serving to further the ends of a minority. In that process the majority will only be acquiescent if they allow themselves. That is why I think that one must stand up against inequality.

(Female Director) The culture is male and steeped in all traditions. When I came here, I became very confused because to a very large extent I felt like my brain was directed by the environment.

It was not even directed; it was polluted. (Female Director) It’s a real problem, because how people talk, even things like swearing, or you know, where this is just like normal people, oh well we’re very informal. We swear, you know whatever, we could shout at each other across the table. You shut a woman up. You also shut decent men up because most people don’t like to behave like that. (Female Director).

Appointment of one or two women signals tokenism

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Themes (Results)

Findings (Quotations)

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Appointment of women to mining boards – Evidence of tokenism Table I (continues) Theory and rationale Women on Boards Women on Boards research Studies doctrines

Themes (Results)

Findings (Quotations)

Ashfrod, Rothbard, Piderit and Dutton, 1998 Maume, 2011

Women regarded as tokens may find it more difficult to influence decisions.

Limited influence

I got the sense that, when you’re a woman trying to get into an environment like this one, you must go the extra mile in terms of proving yourself that you will be able to do the role. (Female Director) You need your strength; you need to be assertive. It is not going to be enough that you are a competent person and as much as possible you cannot be a quiet Jane or a quiet Susan. Okay, you can’t (Female Director) Expectations are always higher where black women are concerned. As a black woman you must go the extra mile to prove yourself (Female Director) Women don’t have that aggression and therefore how they make their voices heard is something which they must still think about, because we are still a minority in the boardrooms (Female Director) Women who bring their hearts into the workspace and that’s what we do. You come with your heart. I am warm, I am kind, I am collaborative; those traits do not necessarily make you a success in a male-dominated environment (Female Director) Women who are not confident cannot succeed in the boardroom, so confidence is a big thing. If you do not have it, it is a big thing for you as a person because of the nuances and the undertones (Female Director.

Eagly and Karau, 2002 Eagly and Carli, 2007

Women's fitness for boards is often challenged, leading to negative evaluations of women irrespective of their preparation, ability, or performance.

Condescension

Do we have a culture that supports that? No. What happens? They [black people and women] become frustrated, White people say, “They are not competent, they are token appointments”. You know, white people still hold on to their territory; they do not want to transfer skills. They create polarisation in the workplace (Female Director) It’s just people being undermined; that happens a lot.

That is a big problem because there are undertones in the boardroom, some people are more respected than others and some people when they speak, they are not respected.

Some views are more important than others. The bullies win more than the people that are not bullies (Female Director) There are people, directors who are extremely dominant.

All the boards, there are directors who dominate more than others. You’re going to find that in everybody, because [when] you speak, they don’t know what you were going to talk about and then they just chop you down. They do that, they undermine you and they cut you to size. (Female Director) I felt that there was that tendency of condescending, where two members of the board who are the executive board members feel that the board is there to just rubber stamp what they’ve done and what they’re doing. When you then start questioning things, then it becomes an irritation.

(Female Director).

Validation seeking

If you’re interviewing any other black females, you’ll probably be getting the same response irrespective of the industry. That you do feel like you need to be doing a lot more star jumps and jumping through hurdles than even your white counterparts, just to get that recognition, and you almost want a validation to be seen that I’m quite satisfied that the academic background and the underlying qualifications are good enough, but you’re walking into an industry that’s got its own preconditioning and indoctrinated mindset. (Female Director).

Ibarra, 1992 Being labelled tokens, female directors may Mathisen, Ogaard and Marnburg, 2013 feel uncomfortable and isolated, with low selfconfidence.

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Themes (Results)

Findings (Quotations)

I was so frustrated, so frustrated. I had piles and piles of information to go through, and I was grateful that they are an organised company, but I truly was panicking. My kids were like I’ve never seen you like this, you are a confident person, what’s happening and I’m like maybe I’m confident in the space that I’m comfortable in. But this is a space [mining] that I have never thought I would be involved in, and I need to cope with that (Female Director).

You do feel like you need to very slowly and tactfully pull down those barriers to make them see you first as a person before they will recognise you as a professional. Ultimately, your ultimate goal, I think, for any professional is you want that accomplishment and achievement, but to get there you need to … change the mind shift. (Female Director) You’ll work nine times harder than your male counterpart because I think you want to prove a point that I can do this. So, we still have families and you’re trying to balance all of that. I mean I must pick up the kids, put them to sleep, start working and it’s the same cycle, but I think because you don’t want to be seen ‘oh no, but you are just a mother’, I can be professional and it’s not an issue of choosing either or (Female Director).

Elstad and Ladegard, 2012 Gustafson, 2008 Huse and Solberg, 2006 Parker, 2007 Stevenson and Radin, 2009

On a board, men may be less inclined to share information with women, and may exclude the tokens from social interaction outside the boardroom.

Although compliance-based recruitment (through quotas) causes women to face negative experiences, such as being labelled as token appointees, results prove that enforced compliance improves representation and further presents opportunities for women. Nativadad (2012) asserted that without compliance, the recruitment of women would be slow. However, token appointments trap women in distortion of roles and generate discomfort for women who are less experienced than men (De Cabo, Gimeno and Nieto, 2012; Holgersson and Romanim, 2020). It was questionable why nomination committees sought to appoint less experienced women, who had no background in mining. Could this be a deliberate strategy to perpetuate the dominance of men who are more experienced and make women a mockery (Ruby, 2021)?

Assimilation actions became evident in the results as tokens were forced into limited and mimicked roles with no opportunity to make effective contribution. For the tokens, stereotyping may result in perceptions of barriers to exerting influence on decisions in the boardroom. There is evidence to suggest that women less experienced are appointed so that men can retain their power and dominant status, consistent with literature of the tokenism theory (Penner, Toro-Tulla, and Huffman, 2012; Rahman Zahid, and AlFaryan, 2022). The consideration from Dahlerup and Freidenvall (2005) that quotas have the potential to compromise the competitive 570

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Social exclusion

It’s a culture that expects you to fit in. The male board members like golf, I don’t play golf. They’ll go off to play golf together, and over and above that there’s a lot of stuff that goes on there. If you’re not a golf player, then it can lead that you’re left out of certain things that are being talked about on the golf course (Female Director) Often the board members stay in a hotel…. I don’t stay in a hotel; I have a home with a family. I decide to stay at home and that also means that whatever is discussed when everybody is sitting around the hotel room, in the lounge, they drink together, but you can’t allow those things to bother you too much, it’s just the way they are (Female Director).

process of finding suitably qualified candidates is demonstrated by this research. What is ignored is the value of previous research, which also submitted that quotas and merit may complement each other (see Sayce and Özbilgin, 2014) precisely if quotas are not the sole purpose for recruitment, which may be counterproductive.

Silence and a right to voice quickly diminished when only one or few women were appointed on boards. Some observations were that women found it challenging to voice their opinions due to their low numbers and their need to assimilate to the maledominant culture (Broome, 2008; Huse and Solberg, 2006; Lansing and Chandra, 2012). Data shows that patriarchy was the culture that seared through with male dominance, profanity, blasphemous, and obscene language even in the boardroom, which would silence women (also described by Holgersson and Romani, 2020).

Limited influence led women to have little voice on board discussions and decision-making. The literature suggests that women regarded as tokens found it more difficult to influence decisions (Holgersson and Romani, 2020; Maume, 2011). Consistent with the need for visibility and performance pressures, many women felt they had to go an extra mile to prove their contribution, as expectations were higher for women. Women who were not aggressive, but kind and considerate, were considered weak. One woman in the interview reported that despite her 15-year board The Journal of the Southern African Institute of Mining and Metallurgy

Appointment of women to mining boards – Evidence of tokenism experience, often her inputs were not considered, where she was dismissed as a quota candidate and made her feel like she was there to tick a box.

Condescension was one other way women were subjected to being undermined, second-guessed, and sometimes disregarded completely. The literature suggests that women's fitness for boards is often challenged, leading to negative evaluations irrespective of their preparation, ability, or performance (Eagly and Karau, 2002; Eagly and Carli, 2007). These challenges hold in this study as women felt they were regarded as incompetent, and were undermined by the dominant groups.

Validation seeking was a cause for concern as the culture rendered women to seek validation from men by doing more than usual to get more recognition. Women, as a result, became frustrated and felt they had to break down barriers slowly and tactfully by working harder than men for their potential to be recognized. Consistent with the tokenism theory, being labelled as tokens made women feel isolated, uncomfortable, with less confidence (Ibarra, 1992; Mathisen, Ogaard, and Marnburg, 2013; Rahman, Zahid, and Al-Faryan, 2022) which was the case with women in the data-set.

Social exclusion of women from professional and social networks solidified and sustained the network of men in the boardroom. Several scholars showed that the dominant groups were likely to exclude the tokens from social interaction outside the boardroom (Elstad and Ladegard, 2012; Glass and Cook, 2016; Gustafson, 2008; Huse and Solberg, 2006; Parker, 2007; Rahman, Zahid, and Al-Faryan, 2022; Stevenson and Radin, 2009). Yet the social identity theory presents another lens, where men have strong bonds even outside the boardroom, for example playing golf. It was difficult to argue whether this exclusion is intentional as some women may not find golf an enthralling sport, and some social functions would naturally exclude women due to other commitments that women have such as home and child care.

Yet, women were disadvantaged because of exclusions. Whether intended or not, exclusion from informal networks perpetuated the ‘invisible woman syndrome’, which means that women remain ‘outsiders on the inside’, as they are often invisible and not included in social activities outside the boardroom (Moore, 1988).

benefit from female representation by having at least three women on a board (Fitzsimmons, 2012) of average size (9 to 12 members in a mining company). The critical mass theory suggests that having three or more women on boards allows them to positively influence decisions and impact on the innovation and sustainability of companies (Erkut, Kramer, and Konrad, 2008; Lansing and Chandra, 2012). The real change occurs when there are three or more women on the board and women feel more comfortable, less constrained about what the men think, and their interactions become more positive and useful for the organization (Erkut, Kramer, and Konrad, 2008) and any suggestions of tokenism are easily refuted.

Conclusion

Conceptualization – N.V.; Methodology – N.V.; Validation – N.V.; Formal Analysis – N.V.; Investigation – N.V.; Data Curation – N.V.; Writing - Original Draft – N.V.; Writing – Review & Editing –N.V.; Visualization – N.V.; Project Administration – N.V.; Funding Acquisition – UNISA.

Boards need to recognize that gender diversity is not achieved with one or two women directors (Broome, 2008). The appointment of one or two raises further problems as women minorities are often categorized, stereotyped, and ignored by the majority (Broome, 2008; Huse and Solberg, 2006; Lansing and Chandra, 2012). The adverse experiences include aggression, resistance, and negative evaluations by the dominant group – men. Cook and Glass (2015) reported that women board members considered as tokens will be regarded directors of low rank. The labelling of tokens makes them prone to being nonvalue-adding members who are not able to alter organizational practices and influence decisions for better outcomes (Ashfrod et al, 1998; Maume, 2011; Penner et al, 2012 ). Tokens who express contentious or nonconforming viewpoints may risk intensifying group variances, increasing bias, and provoking social disapproval from the majority. Consequently, tokens face pressures to conform tand avoid ‘rocking the boat’ by voicing provocative or innovative ideas (Bradshaw and Wicks, 2000; Kanter, 1977) that may benefit the sustainability of companies.

This article recommends that boards avoid tokenism by appointing competent and suitably qualified women and derive The Journal of the Southern African Institute of Mining and Metallurgy

Limitations of the study and future research By its design, qualitative research has some limitations, stemming from risks of subjectivity, researcher bias, and challenges of time demands for data processing and coding. Commonly, the generalizability of the results, trustworthiness, and quality of findings are usually questioned in qualitative studies. To ensure credibility of the findings, an independent expert individually co-coded the data simultaneously with the researcher, after which the codes and themes were verified by two other experts, one in women‘s studies and another from strategy and corporate governance. The methodological process can be traced and ensures that quotes are openly presented, and subject to critical analysis (Hesse-Biber, 2007).

Future research may be beneficial in assessing the impact of women on mining boards or boards in general on innovation, financial performance, and sustainability of companies. This is based on the premise of the critical mass theory that three or more women board members reduce token experiences and may positively impact board processes, decisions, and ultimately improve company performance.

Acknowledgements The author would like to express appreciation to the University of South Africa for funding this project. The reviewers are also thanked for their feedback that improved the quality of the paper.

CRediT statement

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Selected trace element concentrations in runof-mine coal, discard, and coal product, and environmental implications

by R.M. Mashishi1, O.J. Okonkwo1, and T. Malehase1

Affiliation:

1 Department of Environment, Water,

Earth Sciences, Tshwane University of Technology, South Africa.

Synopsis

Received: 27 Aug. 2023 Accepted: 5 Oct. 2023 Published: December 2023

The concentrations of selected trace elements (As, Cd, Hg, and Pb in run-of-mine (ROM) coal, discard, and coal product were investigated to assess the efficiency of beneficiation in reducing trace element concentrations and ascertain any implications regarding environmental compliance to regulatory frameworks. Samples were collected from a colliery in Mpumalanga Province twice a month for a period of 24 months. The samples were ashed to approximately 0.21 mm, then digested in a mixture of 70% HNO3 and 40% HF and analysed using inductively coupled plasma-mass spectrometry (ICP-MS). Except for Pb, the mean concentration of all elements decreased from the ROM stage to the coal product stage. The order in which trace elements occurred from the highest to lowest throughout the production chain was Pb>As>Hg>Cd. With the exception of Cd, the mean trace element concentrations in the discard were above the total concentration threshold (TCT) set for landfill disposal. The As, Hg, and Cd concentrations in the product were well below the thresholds for all land uses. However, Pb concentrations in the product coal were above legal limits, which is of concern with regard to environmental compliance and the performance and marketability of the product.

How to cite:

Keywords

Correspondence to: O.J Okonkwo

Email:

OkonkwoOJ@tut.ac.za

Dates:

Mashishi, R.M., Okonkwo, O.J., and Malehase, T. 2023 Selected trace element concentrations in run-of-mine coal, discard, and coal product, and environmental implications.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 123, no. 12. pp. 573–578 DOI ID: http://dx.doi.org/10.17159/24119717/3114/2023 ORCID: R.M Mashishi http://orcid.org/0000-0002-5079-481X O.J Okonkwo http://orcid.org/0000-0001-9396-4949 T. Malehase http://orcid.org/0000-0002-5788-3911

trace elements, coal, ROM, discard, product, environmental compliance.

Introduction Coal encompasses a large range of fossil fuels that were derived from the degradation of plant material (Moid, 2008). Coal is one of the world’s most inexpensive, abundant, and most accessible energy sources at present. However, its use creates extensive environmental damage (Ogbonna et al., 2012). Although nuclear and renewable energy are gradually becoming more important for power generation, the combustion of coal is still a major source of power. High-temperature coal combustion for the generation of power results in the emission of pollutants such as NOx, SOx, and particulate matter, among others. Coal also contains trace elements such as As, Hg, Se, Pb, Cr, and Cd, which are highly toxic and have drawn attention from environmental legislators.

Trace elements are nondegradable chemical elements and are emitted during the burning of fossil fuels.

As, Cd, Hg, and Pb exist in trace amounts in coal (Munawer, 2018). The primary anthropogenic sources of trace elements are smelters, mines, foundries, vehicle emissions, and combustion of by-products (Moid, 2008). A study on the bioaccumulation of nutrient and trace elements in plants and soil was conducted near an abandoned coal mine in Nigeria. The study indicated that coal mining is one of the anthropogenic sources of toxic elements in the area (Ogbonna et al., 2012).

Coal mined in South Africa for the competitive international market needs to meet the numerous quality specifications of customers. This is achieved by washing coal in a dense media separation (DMS) plant. As a result, coal wastes such as discard are generated. When coal is combusted, most trace elements collect in the coal ash, which is isolated as much as possible from the environment. Despite this, trace elements are emitted to the receiving environment. These emissions are usually much less compared to the major pollutants; however, the impact of trace elements on ecosystems and human health can be quite significant (Senior et al., 2020).

South African coal is known to have a high ash or mineral content, and therefore a high trace element content. Variations in mineral content cause trace elements to vary in coal from the same seam classification (Mguni, 2015). The term ‘mode of occurrence’ refers to whether an element forms part of a specific mineral or is dispersed within a particular host mineral or in the coal macerals (Finkelman, 1994).

Differences in mode of occurrence are due to geological conditions during coal formation, and knowledge of the geochemistry of trace elements is important in the assessment of the environmental

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Selected trace element concentrations in run-of-mine coal, discard, and coal product impact of coals (Bai, Wang, and Li, 2017). Coal discard is a major waste product from coal mining and coal washing. Coal discard consists of inorganic and organic minerals with high ash content, high pyrite content, and low heating value. Large quantities of coal discard are stockpiled, which can result in serious environmental consequences such as air pollution, and water and soil contamination. Trace elements in coal discards may be released and pose environmental problems in various degrees, depending on the type of trace element (Guo, 2017). Trace elements of concern include, but are not limited to, arsenic, cadmium, mercury, and lead.

According to Burmistrz et al. (2018), the arsenic content in coal can vary between 0.5–80.0 mg kg-1, 0.3–16.6 mg kg-1, and 0.3–11.0 mg kg-1 as reported by Swaine 1990; Saha et al. 2016, and Dai et al.

2005 respectively. Arsenic is a known carcinogen. Arsenic occurs in three dominant forms in coal, namely pyrite, organic materials, and arsenate. Arsenic is considered an environmentally sensitive element and extensive studies have demonstrated that it is strongly associated with pyrite (Moid, 2008). Arsenic is among the top trace elements of concern due to its volatility, toxicity, and its ability to bioaccumulate in the environment. Cadmium is one of the main pollutants emitted from coal mining and coal combustion. It has been reported that even at low concentrations, Cd emitted from coal can cause reproductive system complications, cardiovascular diseases, brain malfunctions, and neurological disease. Cadmium usually occurs at trace amounts in coal, 0.1–3 mg kg-1. The element is moderately volatile during coal combustion (Cui et al., 2019).

The World Health Organization identified Hg as a chemical of concern in the highest category in 2017, because it poses a threat to human health globally. About 2000 metric tons per year according to the US EPA (https://19january2017snapshot.epa.gov/ international-cooperation/mercury-emissions-global-context_. html. Approximately 2000 t of Hg is emitted to the atmosphere globally every year as a result of human activity.

According to the United National Environment Programme (UNEP), Russia, China, South Africa, the USA, Ghana, Colombia, and Indonesia contribute 56% of total anthropogenic emissions to the atmosphere (Singh, Dhyani, and Pujari, 2022). Coal washing and burning are among the major sources of anthropogenic Hg emissions (Pacyna, 1987). According to Pacyna (1987), more than 50% of Hg emissions are from coal-powered power plants. When released through emissions from power plants, Hg, like most

trace elements, circulates in the atmosphere as particulates before it is deposited on vegetation, land, and water (Gade, 2015). The Minamata Convention, which was adopted in 2013, regulates the sources of Hg, trade in Hg, manufacturing methods that use Hg compounds, Hg products, artisanal and small-scale gold mining, emission into air, deposition on land and in water, storage, wastage, polluted sites. and health implications (Singh, Dhyani, and Pujari, 2022).

Lead toxicity and its effects on the human nervous system, immune system, and the environment is well documented (Wang et al., 2021). Lead is rarely found in the environment in its elemental state but occurs as Pb2+, in which form it also occurs naturally in lead minerals. Lead in the environment is very mobile and contaminates the air and water. Mining, burning of coal, and vehicular emissions are among the main sources of Pb in the environment (Munawer, 2018).

It was hypothesized that the concentrations of As, Cd, Hg, and Pb in coal products and discards may be affected by beneficiation processes. The present study was, therefore, aimed at assessing the efficacy of the beneficiation process with respect to the selected trace metals as well as evaluate the different coal fractions in terms of environmental compliance.

Geological setting The project site was a colliery in the Thembisile Hani Local Municipality in Mpumalanga Province, South Africa. The colliery covers an area of about 4 km2 and is situated about 35 km north of Bronkhorstspruit. The site borders Tshwane Metropolitan Municipality of Gauteng Province (Figure 1). The colliery is geologically situated in the Nooitgedacht Outlier, an erosional relict of the Vryheid Formation in the Ecca Group of the Karoo Supergroup. The Karoo Supergroup hosts the largest coal deposit in South Africa, including the Witbank Coalfields (Digby Wells, 2018).

The colliery exploits two coal seams – the main seam and bottom seam. Thick layers of sandstone interbedded with clay and carbonaceous shale mostly overlie the coal seams. The main seam occurs throughout the mining area while the bottom seam is found in the southern section. The mining method employed is opencast truck-and-shovel. Overburden and coal are removed in sequential strips. Excavators and dump trucks are used to load the coal to the ROM stockpiles. The coal is crushed to 40 mm during

Figure 1—Locality of Palesa colliery 574

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Selected trace element concentrations in run-of-mine coal, discard, and coal product Quality assurance and quality control (QA/AC)

the beneficiation process for ease of handling and compliance with marketing specifications. Product and discard are produced, with the discard being returned to the pit.

All glassware was thoroughly washed and rinsed with deionized water and dried between samples. All prepared standard solutions were kept at 4°C in a refrigerator before analysis. Each sample was digested and analysed three times. Blank reagents and reference materials were analysed three times. Blank reagents and reference materials for coal were used in each sample batch to verify the accuracy digestion and analysis.Blank samples and a digested reference material, South African Reference Material (SARM 19) were included to check the accuracy of the digestion and analytical methods.

The recovery rates for the selected trace elements in the reference material (SARM 19) were within the certified ranges of 96%, 97%, 99%, and 99% for As, Cd, Hg, and Pb respectively.

A multi-element standard solution including the elements of interest was used to prepare calibration solutions for trace element concentrations. The calibration curves for the selected trace elements were linear and within the expected ranges.

Materials and method Reagents and materials Trace element standard solutions of analytical grade were used.

Trace metal grade HNO3 (70%) and HF (40%) were purchased from Merck and Sigma Aldrich (Germany).

Samples and sample preparation The ROM coal was the initial step of sample collection. ROM coal is in its natural state before any processing takes place. Therefore, the results of the ROM samples serve as a benchmark to indicate whether trace element concentrations increase or decrease during beneficiation. Two samples at each processing stage ROM, product, and discard were collected per month over a 24-month period.

ROM samples were collected from the ROM conveyor belt using an auto-mechanical sampler and placed in 50 kg containers. An auto-mechanical sampler was also used to collect product samples from the final product conveyor. The discard sample was collected mechanically at the feed end of the conveyor belts. The maximum sample size was 50 kg. All sample details were initially logged into the system and each sample was allocated a unique sample number for internal tracking.

For digestion of the crushed/solid samples, HNO3 (70%) and HCl (40%) were used. A standard operating procedure (SOP) for general microwave digestion of soil and coal samples was employed.

About 10 g of solid sample was initially crushed into a fine powder with a mortar and pestle and passed through a mesh sieve. The solid samples were crushed to 25 mm, later reduced to 6 mm and finally crushed to approximately 0.21 mm. The ashed coal samples were placed in a clean vessel of 7 mL capacity.

The sample was then digested in a mixture of 5 mL 70% HNO3 and 2 mL 40% HF. Ten millilitres of 70% concentrated HNO3 was then added into a 120 mL volumetric container to maintain pressure in the vessel. The loosely closed 7 mL vessel was then placed into the large 120 mL vessel. The vessels were, thereafter, placed into the microwave oven and heated for 1 h at a temperature of 250°C. After the digestion, the samples were transferred into 25 mL calibrated flasks and diluted with HNO3 to give 2–3% solutions. The yellowish solutions were filtered to remove the remaining solids. After dissolution of the samples, the solutions were submitted for analysis using ICP-MS.

Statistical analysis The two sets of data (from the first and second samples taken each month) were combined to produce a monthly average. MS Excel and Pearson‘s correlation coefficient were used to test for relationship and significance.

Results and discussion The results of the study are presented in Table I. Except for Pb, the mean concentration of all elements was lower in the product than in the ROM coal. As, Cd, Hg, and Pb mean concentrations and standard deviation (SD) in the ROM were 8.71 ± 0.479, 0.13 ± 0.017, 0.38 ± 0.098, and 28.35 ± 2.74 mg kg-1, respectively, whereas in discard, As, Cd, Hg, and Pb concentrations were 31.55 ± 3.935, 0.15 ± 0.018, 1.49 ± 0.106, and 31.15 ± 1.597 mg kg-1 respectively.

The mean concentrations of As, Cd, Hg, and Pb in the coal product were 2.93 ± 0.464, 0.12 ± 0.011, 0.20 ± 0.058, and 29.42 ± 2.191 mg kg-1, respectively.

ROM samples The arsenic concentration in ROM coal (8.7 mg kg-1) was found to be lower than the 13.14 mg kg-1 reported by Hlatswayo and Wagner (2005). However, it is higher than the values of 4.96 mg kg-1, 4.6 mg kg-1,4.7 mg kg-1, and 5 mg kg-1 reported by Mohammed (2010), Cairncross, Hart, and Willis (1990), Bergh (2009), and Zhang et al.

(2004) respectively.

Cadmium exhibited a mean concentration of 0.13 mg kg-1 in the ROM, which is marginally higher than the 0.10 mg kg-1 reported by Mohammed (2010) for South African coals. Cadmium concentration in the ROM was, however, much lower than that in Witbank coals (0.3 mg kg-1, Bergh, 2009), Highveld Coalfield no.

4 Seam (0.44 mg kg-1, Hlatshwayo and Wagner, 2005), and global coals (0.6 mg kg-1, Zhang et al., 004).

The mean concentration of Hg in the ROM was 0.38 mg kg-1, a value either below or equal to the South African and global mean

Instrumental analysis A Perkin Elmer Elan 6100 DRC ICP-MS was used for analysis. The percentage recovery of each element was calculated and compared with the values in the certified reference material (CRM). The experimental value is the value calculated from instrumental measurement and the final dilution factor of the extraction. The calibration values gave correlation coefficients that ranged from 0.95 to 0.99.

Table I

Mean concentrations of As, Cd, Hg and Pb in all the samples analyzed Production stage

ROM Discard Product

As

Cd

Hg

Pb

8.71 ± 0.479 31.55± 3.935 2.93 ± 0.464

0.13 ± 0.017 0.15 ± 0.018 0.12 ± 0.011

0.38 ± 0.098 1.49 ± 0.106 0.20 ± 0.058

28.35 ± 2.741 31.15 ± 1.597

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Selected trace element concentrations in run-of-mine coal, discard, and coal product Therefore, it is suggested that Pb in the present study ROM may be in the organic fraction, and hence not easily removed, while in the comparative study by Dalton and Feig (2018) Pb may have existed in the inorganic fraction, hence the low Pb concentrations found in the soil.

Coal product

Figure 2—Comparison of discard trace element levels with total concentration thresholds

values. On the other hand, the Pb concentration was 28.35 mg kg-1, the highest of all the trace elements in the ROM. The order of concentrations of the trace elements in the ROM was Pb>As>Hg>Cd.

Discard samples Arsenic concentration in the discard was 31.55 mg kg-1, which is substantially higher than in the ROM (7.8 mg kg-1). A typical South African washing plant makes use of dense medium separation (DMS) to separate good quality coal from waste material, including ash-forming and sulphur-bearing minerals. As a result, the wastes have a higher ash content and thus a higher elemental concentration than the ROM coal. Moyo (2018) stated that the concentrations of trace elements in coal processing wastes depend on their concentrations and modes of occurrence in the ROM and the nature of the processing operations.

A Department of Minerals and Energy report (DMRE, 2001) indicated that the discards from the DMS plant, which contains most unwanted impurities in the coal, contain more ash-forming minerals and higher sulphur concentrations than the ROM coal (Moyo, 2018). This may explain the elevated trace elements in the discard.

The arsenic concentration in the discard (31. 55 mg kg-1) was higher than the 6.94 mg kg-1 reported for Witbank coal discard.

However, the mean Cd concentration, 0.15 mg kg-1, was lower than the 0.30 mg kg-1 reported in Witbank coal. Lead mean concentration in the Witbank discard (33.24 mg kg-1) was slightly higher than that in the present study discard (31.15 mg kg-1).

Coal product samples Trace element concentrations in the coal product were compared with those in soils around coal-fired power stations. Although coal and soil are two different materials, the combustion emissions ultimately settle in the soil near a coal-fired power station. The As concentration, 2.93 mg kg-1, was either slightly above or in line with the limits for South African soils, but much lower than arsenic concentration (17.5 mg kg-1) in Bangladesh soils (Sahoo, Equeenuddin, and Powell, 2016). The cadmium concentration, 0.12 mg kg-1, was lower than that the 1.22 mg kg-1 in soils near a coal-fired station in Nigeria (Sahoo, Equeenuddin, and Powell, 2016). However, the Pb concentration, 29.42 mg kg-1, was higher than in South African and Nigerian soils (Sahoo et al., 2016), but significantly lower than Pb concentrations in Bangladesh soils (Sahoo, Equeenuddin, and Powell, 2016).

The varying concentrations of trace elements in the final coal product and soils near the coal-fired powered power plants are attributed to geological differences in the coalfields.

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The National Environmental Management Waste Act (2008) and National Environmental Management Act (2008) require land to be investigated if hazardous substances are likely to have been used in or on the land. The use of the soil screening values as an indication of a ‘safe’ or ‘clean’ site is valid in the absence of a specific risk exposure scenario. The soil screening values are used to compare trace element concentrations observed in the present study. As, Hg, and Cd concentrations in the product were well below all the screening values, as indicated in Figure 3.

Therefore, if the coal in the current study were to be combusted, emissions would not result in non-compliance or adversely impact water resource and surrounding soils. The lead concentration in the coal product is higher than the limit set for all land uses (Figure 3) but below all other soil screening values.

Emissions from combustion would result in negative impacts from Pb on the environment.

Conclusion Trace element concentrations in the coal product were lower than in the ROM coal, with the exception of Pb. Therefore, the efficiency of coal beneficiation in reducing impurities, including trace elements, was demonstrated. In terms of legislative guidelines, discard mean concentrations of As, Hg, and Pb were above the TCTs set for landfill disposal; whereas the Cd concentration was below the TCT. The concentrations of As, Cd, and Hg in the coal product were all compliant, but Pb was higher than set thresholds for all land uses. The failure of the beneficiation process to reduce to Pb concentrations to below the legal limits is of concern with regard to the quality and marketability of the coal.

Acknowledgements The authors gratefully acknowledge the financial and technical support from HCI Coal which made this work possible.

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Figure 3—Comparison of soil screening values in the present study with criteria for land use as per the Department of Environmental Affairs (2010) The Journal of the Southern African Institute of Mining and Metallurgy

Selected trace element concentrations in run-of-mine coal, discard, and coal product Bergh, J.P. 2009. The partitioning of trace elements in the No.4 seam of the Witbank coalfield. MSc thesis, University of the Witwatersrand, Johannesburg.

Burmistrz, P., Wierońska, F., Marczak, M., and Makowska, D. The possibilities for reducing mercury, arsenic and thallium emission from coal conversion processes. Earth and Environmental Science, vol. 174. pp.1–9. https://doi :10.1088/1755-1315/174/1/012003 Cairncross, B., Hart, R.J., and Willis, J.P. 1990. Geochemistry and sedimentology of coal seams from the Permian Witbank Coalfield, South Africa, a means of identification. International Journal of Coal Geology, vol. 16, pp. 309–325. https://doi.org/10.1016/0166-5162(90)90056-5 Cui, W., Meng, Q., Feng, Q., Zhou, L., Cui, Y., and Li, W. 2019. Occurrence and release of cadmium, chromium, and lead from stone coal combustion.

International Journal of Coal Science & Technology, vol. 6. pp. 586–595. https:// doi.org/10.1007/s40789-019-00281-4 Dai, S., Ren, D., Tang, Y., Yue, M., and Hao, L. 2005. Concentration and distribution of elements in Late Permian coals from western Guizhou Province, China. International Journal of Coal Geology, vol. 61 pp. 119–137. https://doi. org/10.1016/j.coal.2005.09.001 Dalton, A., Feig, T.G., and Barber, K. 2018. Trace metal enrichment observed in soils around a coal fired powerplant in South Africa. Clean Air Journal, vol. 28, no. 2. pp. 1–9. https://cleanairjournal.org.za/article/view/6945 Department of Minerals and Energy. 2001. National Inventory discard and duff coal 2001 Summary report. Pretoria, South Africa.

Deurbrouck, A.W. and Cavalaro, J.A. 1978. A washability and analytical evaluation of potential pollution from trace elements in coal. https://www.osti. gov/servlets/purl/6811424 [accessed 17 March 2023].

Digby Wells. 2018. Palesa waste characterization geochemistry report.

Johannesburg.

Mohammed, R. 2010. The path of trace elements in a combustion process: from feed coal to ash products. MSc thesis, University of the Witwatersrand, Johannesburg.

Moid, M.C. 2008. The determination of heavy metals in coal ash. BSc (Hons) thesis, University of Malaysia Sarawalk, Malaysia.

Moyo, A. 2018. Characterising the environmental risks of coal preparation wastes: A study of coal slurry waste and discards from South African collieries. MSc thesis. University of Cape Town.

Munawer, M.E. 2018. Human health and environmental impacts of coal combustion and post-combustion wastes. Journal of Sustainable Mining, vol. 17. pp. 87–96. https://doi.org/10.1016/j.jsm.2017.12.007 Ogbonna, P.C., Anigor, T.O., Jamie, A., and Da Silva, T. 2012. Bioaccumulation of nutrients and heavy metals in plants at a coal mine. Terrestrial and Aquatic Environmental Toxicology, vol. 6. pp.127–131.

Pacyna, J.M. 1987. Lead, mercury, cadmium and arsenic in the environment.

Journal of Applied Toxicology, vol. 8. pp. 69–87. https://doi.org/10.1007/978-94010-0403-9_4 Saha, D., Chakravarty, S., Shome, D., Basariya, MR., Kumari, A., and Kundu, AK. 2016. Distribution and affinity of trace elements in Samaleswari coal, Eastern India. Fuel, vol. 181 pp. 376–88. https://doi.org/10.1016/j. fuel.2016.04.134 Sahoo, P.K., Equeenuddin, M.D., and Powell, M.A. 2016. Trace elements in soils around coal mines: Current scenario, impact and available techniques for management. Current Pollution Reports, vol. 2. pp.1–14. https://doi. org/10.1007/s40726-016-0025-5 Senior, C., Granite, E., Linak., W., and Seames, W. 2020. Chemistry of trace inorganic elements in coal combustion systems: A century of discovery. Energy Fuels. pp. 15141–15168. https://doi.org/10.1021/acs.energyfuels.0c02375

Finkelman, R.B. 1994. Modes of occurrence of potentially hazardous elements in coal: Levels of confidence. Fuel Processing Technology, vol. 39. pp. 21–34. https:// doi.org/10.1016/0378-3820(94)90169-4

Singh, S., Dhyani, S., and Pujari, P.R. 2022. Coal‑fired thermal power plants and mercury risks: status and impacts to realize Minamata Convention promises.

Anthropocene Science, vol. 1. pp. 419–427. https://doi.org/10.1007/s44177-02300042-8

Gade, D. 2015. Mercury emissions from power plants. Environmental Management and Risk Assessment (PH 560). Paper 4. Western Kentucky University. https:// digitalcommons.wku.edu/pubh_560/4/

South Africa. 2008. National Environmental Management: Waste Act: National Norms and Standards for Disposal of Waste to Landfill, Act No 59 of 2008.

Government Printer, Pretoria.

Gluskoter, H.J. 1975. Mineral matter and trace elements in coal. Trace Elements in Fuel, vol. 141. pp. 1–22. https://doi 10.1021/ba-1975-0141.ch001

Swaine DJ. 1990. Trace elements in coal. London: Butterworths, pp. 292. https://doi. org/10.1016/0378-3820(94)90176-7

Guo. S. 2017. Trace elements in coal gangue: A review. Contributions to Mineralization. InTech. https://www.intechopen.com/chapters/57250

Wang, Y., Hu, Wang, X, Liu, H., Dong, L., Luo, G., Zhao, Y., and Yao, H. 2021.

A critical review on lead migration, transformation and emission control in Chinese coal‐fired power plants. Journal of Environmental Sciences, vol. 124. pp. 397–413. https://doi.org/10.1016/j.jes.2021.09.039

Hlatshwayo, B. and Wagner, J. 2005. The occurrence of potentially hazardous trace elements in five Highveld coals, South Africa. International Journal of Coal Geology, vol. 63, no. 3-4. pp. 228–246. https://doi.org/10.1016/j.coal.2005.02.014 Mguni, N.G. 2015. Determination of hazardous trace elements in select Hwange, Zimbabwe coal samples with a comparison to select South African coal samples. MSc thesis, University of the Witwatersrand, Johannesburg.

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Zhang, J., Ren, D., Zhu, Y., Chou, C-L., Zeng, R., and Zheng, B. 2004. Mineral matter and potentially hazardous trace elements in coals from Qianxi Fault Depression Area in south-western Guizhou, China. International Journal of Coal Geology, vol. 57, no. 1. pp. 49–61. https://doi.org/10.1016/j. coal.2003.07.001 u

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5TH SCHOOL ON MANGANESE FERROALLOY PRODUCTION THEME: DECARBONIZATION OF THE MANGANESE FERROALLOY INDUSTRY

3-4 JULY 2024 - CONFERENCE 5 JULY 2024 - TECHNICAL VISIT Venue: Boardwalk ICC, Gqeberha, Eastern Cape, South Africa

The energy-intensive industry of manganese (Mn) ferroalloy production is one of the largest producers of direct carbon emissions. The demand for ferromanganese alloy, an additive of steel, follows the demand for steel and continues to increase. This means Mn ore and the production of Mn ferroalloys form an integral part in a future energy sector based on renewable energy technologies. Major structural features of wind turbines, solar panels, and energy storage devices are all made of steel components.

environmental impact of carbon emissions from the production of Mn ferroalloys.

• To provide the opportunity for industrialists and researchers to exchange views on the decarbonization of the Mn ferroalloy industry.

• To further enhance collaborations between parties.

The conversation around the topic will shed light on some of the fundamentals and industrial integration of the various decarbonization strategies.

TARGET AUDIENCE

OBJECTIVE

• To create a platform to discuss the

The current industrial practices and state-of-the-art in Mn ferroalloy production are heavily dependent on the use of fossil-based carbon. The 5th SAIMM school on Mn ferroalloy production thus aims to bring together industry and research in order to support smelters and foster collaborations between researchers towards adopting the transition of decarbonizing the ferroalloy industry.

• Local and international delegates

from the Mn ferroalloy industry or those who support them.

• Existing and potential future industry role players.

• Engineering companies.

• Research/academic institutions.

• Companies providing funding for new Mn projects.

TOPICS

• Commercial production

processes and overview of Mn production in South Africa and Europe, including potential new projects.

• Process fundamentals

on thermodynamics, slag fundamentals, and reaction kinetics based on various decarbonization strategies.

• CO2 reduction programs in the

industry, CO2 capture and energy recovery, Bio-carbon, H2 and, solar energy.

Contact:

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Gugu Charlie, Conference co-ordinator | E-mail: gugu@saimm.co.za Tel: +27 11 538-0238 | Web: www.saimm.co.za

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Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption at a coper-cobalt-zinc plant

by Y. Jeong1 and K. Kim2

Affiliation:

1 Korea Mine Rehabilitation and Mineral

Resources Corporation.

2 SUAVAI Geo LLC, Ada, Oklahoma, USA.

Correspondence to: K. Kim

Email:

kimkm@email.arizona.edu

Dates:

Received: 3 May 2020 Accepted: 9 Oct. 2023 Published: December 2023

How to cite:

Jeong, Y. and Kim, K. 2023 Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption at a copercobalt-zinc plants.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 123, no. 12. pp. 579–588 DOI ID: http://dx.doi.org/10.17159/24119717/1207/2023 ORCID: Y. Jeong http://orcid.org/0000-0003-1898-5576 K. Kim http://orcid.org/0000-0002-3996-7150

Synopsis

Excess water can lead to instability and even failure in tailings storage facilities (TSFs). Simply reducing the amount of water in TSFs could be the best way to ensure the safety of nearby communities. In this case study we investigated the effects of reducing the water content in tailings slurry at a copper-cobalt-zinc mine in Mexico. An environmentally friendly polymer was used as a drag reduction agent (DRA) to offset the increase in solids percentage. The potential effects of the increased solids concentration on the tailings transportation system were also assessed. A series of ‘what if ’ studies was conducted to assess whether adding the polymer would allow the solids concentration to be increased without changing the pressure loss in the tailings pipeline.

The studies entailed conducting pipe loop tests to investigate these changes under various solids/ polymer concentrations and then constructing a computational fluid dynamics (CFD) simulation model using the test results. The validated model was used to determine the optimal polymer percentages needed to maintain the same pressure loss under baseline (30% solids) conditions, and to assess the potential risks (clogging, increased erosion rates) to the pipelines. The potential water savings were found to be significant, varying from about 1.852 Mm3/a at 35% solids to 3.915 Mm3/a at 45% solids.

Keywords

pipe loop tests. computational fluid dynamics (CFD) simulation, TSF stability, tailings transportation, drag reduction agent.

Introduction Tailings are the mixture of crushed rock and processing fluid from a mill plant that remains after economic minerals have been extracted (Lottermoser, 2007). Tailings storage facilities (TSFs) are the structures that are used to dispose of tailings, and raised embankments (surface impoundments) are the most common type. For economic reasons, the most popular method for moving tailings from a mill plant to a TSF is hydraulic transportation through pipelines in the form of slurry (Wilson, 2006). Key to the slurry’s flowability is the solids concentration of the tailings, calculated as the weight of solids divided by the total weight of slurry. The required range (usually 30–50%) can be obtained by adjusting the water content or by the use of chemical additives – drag reduction agents (DRAs) – that work on the pipeline wall by decreasing the Reynolds shear stresses and velocity fluctuations. This reduces the friction between the slurry and the pipeline wall, resulting in a decrease of pressure loss (Warholic,, Massah, and Hanratty, 1999).

Managing TSF water is challenging for several reasons. TSFs are large in scale and may feature internal fractures; in addition, tailings properties vary. These challenges make it difficult to identify and control the phreatic surface, a key factor in TSF stability (Zandarín et al., 2009). Research has demonstrated the importance of controlling this surface. Rico et al. (2008) identified poor water management as the main cause of TSF failures based on an evaluation of 147 cases around the world. Numerical analyses by other researchers have shown that, in general, increasing the water level decreases the TSF factor of safety (Zadari, 2011; Coulibaly, Belem, and Cheng, 2017; Jeong and Kim, 2019). Moreover, the recent failure of Samarco’s tailings embankment in Brazil emphasized the importance of water management to ensure TSF stability (Burritt and Christ, 2018).

One strategy for improving TSF water management is minimizing the water content in the tailings slurry. However, this also poses some challenges. In a conventional mine, modifying the water content requires modifying the tailings transportation system, which features a positive displacement pumping system for paste tailings and a conveyer belt system for filtered tailings. Consequently, various issues must be considered carefully before reducing the water content of tailings. One is the increased pressure loss in the transportation pipeline (Wilson, 2006). Note that this study defines pressure loss as the pressure drop per unit length of pipeline that is caused by energy dissipation, generally due to indiscriminate fluid

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Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption motions (swirling) or friction between the tailings and pipe wall (Warholic, Massah, and Hanratty, 1999). In addition, pressure loss is a key parameter in determining the rheological behaviour of tailings slurry. It is used for selecting the type of pipeline, designing the pumping system, and determining the optimal range of water content in the slurry (Cooke, 2007). This study assumes that, if the pressure loss is kept constant, the rheological behaviour of the slurry remains the same regardless of changes in the solids concentration (Wilson, 2006; Cooke, 2007). Another issue is that reducing the water content increases the solids concentration, which in turn decreases the flow velocity of the slurry in pipelines. When the flow velocity is slower than the deposition velocity, clogging may occur (Abulnaga, 2002; Gillies et al., 2000). Finally, reducing the water content may cause pipelines to erode faster. Factors that contribute to erosion include, inter alia, flow velocity, particle size distribution, and solids concentration (Truscott, 1975). In general, erosion rates tend to increase with higher solids concentrations (Rong et al., 2011).

In this study, a new DRA was applied to enable the water content in tailings to be reduced with minimal changes of pressure loss. This DRA – a nonionic, tri-block amphiphilic polymer – is generally considered to be ‘environmentally friendly’ since it consists of two hydrophilic chains that exhibit relatively low toxicity to animals and humans (Webster et al., 2009). The potential beneficial and adverse effects of the DRA on the tailings transportation system were investigated at the request of the testing mine. Note that a patent application is currently in process for the use of the polymer as a new DRA (Provisional Patent US Application no. 62/571,115).

Testing site A case study was conducted at a copper-cobalt-zinc mine in northern Baja California Sur, Mexico, near the shores of the Gulf of California. The facility currently operates both open pits and underground mines and exploits manto-type ores.

The plant generates an average of 12 000 dry metric tons of tailings per day. Before slurry is pumped to TSFs, the solids concentration (Cw) is adjusted to about 30% by adding water at the neutralization tank. Three diaphragm piston pumps are currently used to pump the tailings at a capacity of 650 m3/h under a pumping pressure of 4.0 MPa. Figure 1 shows the routing of the pipelines. The plant lies at an elevation of 17 m above mean sea level (AMSL). Tailings are pumped to a peak elevation of 260 m AMSL over a distance of 5.7 km.

Table I summarizes the current tailings transportation system, which is constructed using 20-inch HDPE-lined carbon steel pipes.

The pipes’ outside diameter, 508 mm, includes the steel wall (15.09 mm) and the HDPE liner (12.7 mm). The designed capacity is 1720 m3/h, and the target solids concentration and density are 30% and 1238 kg/m3 respectively. The viscosity of slurry is 4 mPa.s, and the yield stress is 24 Pa. A Bingham-Plastic model was applied to design the pipeline facility (McKibben and Sun, 2006).

The particle size distribution of the tailings is shown in Figure 2. The mean particle size is 83 µm, and the D80 (80% passing size) is 102 µm.

Given the climate conditions and the risk of seismic events, the TSF was designed as a downstream-type TSF, which is less vulnerable to earthquakes (Vick, 1990). One common feature of this type of TSF, the typical large amount of water in the decant pond,

Figure 1—Layout of the tailings pipeline facility

Table I

Summary of tailings pipeline operations Pipeline configuration

Material specification Pipe Outside diameter(mm) Steel Wall Thickness (mm) HDPE Liner Thickness (mm) Average Pipe Inner Dia. (mm) Pipeline linear roughness (μm) Maximum Pump Pressure (MPa) 580

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ASTM Grade B Sch 40 508 15.09 12.7 452.42 13 4.0 VOLUME 123

Rheological conditions of tailings

Target of Flow Rate (m3/hr) Weight Concentration (%) Liquid Density (kg/m3) Solids Density (kg/m3) Slurry Density (kg/m3) Slurry Viscosity (mPa.s) Slurry Yield stress (Pa)

1,720 30 1,060 2,040 1,238 4 24

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Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption Pipe loop tests

Figure 2—Particle size distribution of the tailings

can pose a risk for inducing instability. Therefore, minimizing the amount of water in the pond can be beneficial for improving the stability of the TSF.

Experiments: DRA effects analysis The use of the environmentally friendly polymer as a new DRA to reduce inflow to a TSF was investigated. Figure 3 outlines the studies that were conducted for this investigation. First, pipe loop tests were conducted to assess the change in pressure loss for a range of solids concentrations and polymer percentages in the tailings slurry. Then, computational fluid dynamics (CFD) simulations were conducted to determine the optimal polymer percentages that would be required to maintain a constant pressure loss at different solids contents. Real-scale CFD simulations mimicking the tailings transportation system were conducted to determine the deposition velocities that would induce settlement and clogging in the pipelines. Finally, pipeline erosion rates were predicted using CFD-based simulations.

Pipe loop tests were conducted to investigate the effects of the DRA on tailings flow behaviour by measuring pressure losses at varied solids/polymer concentrations. Figure 4 shows the schematic layout of the pipe loop test system.

This testing system was a closed circuit consisting of polyvinyl chloride (PVC) pipe that totalled 10 m in length with an inner diameter of 38 mm. The slurry tank had a 190 l capacity, and a centrifugal pump could supply 36 m3 of slurry with a pumping pressure of 486 kPa. An agitator and digital flow meter were installed to mix the slurry and measure volumetric flow rates, respectively. The testing duration was limited to 10 minutes to minimize changes in the tailings’ rheological properties that could result from the temperature increase.

Twelve test cases were investigated, with two solids percentages (30% and 35%) and six DRA percentages (from 0% to 10% in 2% increments). Pressure changes were monitored using gauges (no.

2–8, see Figure 4); however, only values from gauges 6 and 7 were recorded because they were unaffected by factors such as flow direction and pressure changes near pipe elbows and they provided relatively consistent results in each case. The testing site’s flow velocity of 3 m/s was applied to the loop system.

Before investigating the effects of the DRA, the rheological behaviour of the testing site’s tailings slurry, which usually exhibits non-Newtonian flow behaviour (Boger, Scales, and Sofra, 2006), was investigated. Pre-DRA pressure loss changes were monitored under various solids concentrations. The results indicated a proportional relationship, as shown in Figure 5a; therefore, the slurry can be assumed to follow the principles of non-Newtonian flow, where an increase in solids percentage induces an increase of pressure loss in the pipeline (Wilson, 2006).

Figure 3. Study flow diagram The Journal of the Southern African Institute of Mining and Metallurgy

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Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption Case IV: Effect of increasing the polymer concentration on pressure loss at 35% solids In cases I and II, the pressure loss values at each gauge were simulated and compared to values from the pipe loop tests. In cases III and IV, the effects of increasing the polymer concentration on pressure loss were investigated at 30% and 35% solids concentrations, respectively, while increasing the DRA concentration from 0% to 10% in 2% increments. For these cases, pressure loss was recorded at points E and F (gauges 6 and 7 in Figure 4). As shown in Figure 7, all cases corresponded to the simulated results and showed similar trends, validating the model for use in further studies.

Figure 4—Schematic diagram of the pipe loop test system

The effect of the new DRA on pressure loss are shown in Figure 5b. Pressure loss decreased as the polymer content was increased from 0% to 4%, and then increased as the polymer content was increased from 4% to 10%. This indicates that the optimal polymer concentration for minimizing the pressure loss is about 4%. Further studies are required to determine the reason for the increased pressure loss in the 4–10% range; however, the authors believe this could be related to the DRA’s solubility in that percentage range.

CFD simulations to determine the optimal polymer concentrations ANSYS FLUENT (V. 18.2) software was used to analyse the rheological behaviour of the tailings slurry with realizable k-ε turbulence (ANSYS, 2011). This is one of most popular turbulence models for investigating practical engineering flow issues (Wilcox, 1998; Rolander et al., 2006).

Figure 6 shows the 3D computational mesh used in this study.

The geometry was discretized using 107 136 nodes, 375 950 elements, and triangular grids. The main parameters used for the CFD simulations are listed in Table II. To validate the model, four case studies using CFD simulations were conducted and the simulated pressure loss values compared to data from pipe loop tests. These cases are shown below, and the results of the pressure loss comparisons are depicted in Figure 7.

The cases were designed to investigate the following: Case I: Pressure loss value at each gauge under baseline conditions (30% solids, 0% polymer) Case II: Effect of increasing the solids concentration on pressure loss Case III: Effect of increasing the polymer concentration on pressure loss at 30% solids

Figure 6—3D computational mesh used in the simulation

Table II

Main parameters used for CFD analyses Boundary Condition

Velocity Inlet 3.0 m/sec Turbulence Intensity 5% Hydraulic Diameter 0.381 mm Atmospheric Pressure 101,325 Pa Wall Condition Stationary (non-slip) Model Standard roughness Roughness Height 13 μm Roughness Constant 0.5 Solving Condition Slover SIMPLEX algorithm Convergent Criteria The residuals ≤ 10-6

Number of Iterations ≤ 5,000

Figure 5—Pressure loss changes at (a) various solids concentrations and (b) various polymer concentrations 582

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Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption

Figure 7—Pressure loss comparison results

The model was then used to investigate 35 cases with various percentages of solids (five cases, from 30% to 50% in 5% increments) and polymer (seven cases, from 0% to 6%,in 1% increments). The flow velocity was set at 3.0 m/s to mimic field conditions and the pressure loss was measured at points E and F (see Figure 6). A tailings slurry consisting of 30% solids and 0% polymer was defined as the baseline to mimic the current operational conditions. It was assumed that the rheological flow behaviour of the slurry before and after adding the DRA would remain the same if the pressure loss remained constant; therefore, an increase in pressure loss would indicate a decrease in flow efficiency and vice versa. The simulation results are shown in Figure 8.

Pressure loss decreased when the polymer concentration increased from 0 to 4%, and then increased when polymer concentrations were in the range of 4–6%. In the 50% solids case, the pressure level of 3.0 kPa/m for the baseline condition could not be achieved even though the polymer percentage was enhanced; pressure loss values at 50% solids were higher than the baseline for all polymer concentrations. Therefore, 45% solids was determined to be the maximum possible level, and the 50% solids case was not considered in subsequent tests.

Based on the results shown in Figure 8, the optimal polymer percentages required to maintain the baseline pressure loss were determined for solids percentages of 35%, 40%, and 45%. The corresponding amount of water savings at each percentage was calculated and is shown in Table III. For example, increasing the solids content from 30% to 40% results in a 10.58% water savings, equivalent to 0.09 m3 (91.69 kg in weight) per 1 m3 of tailings slurry.

The pressure loss at 40% solids could be maintained by adding 1.53% polymer (the polymer percentage is obtained by dividing the polymer weight by the weight of water in the tailings slurry). The results demonstrate the potential for using the DRA to reduce the water content in the slurry at the testing site. To calculate the water saving percentages in Table III, the solids concentration was defined as the weight of solids divided by the total weight of slurry (solids + water + polymer); therefore, 35% solids corresponds to 445.99 kg of The Journal of the Southern African Institute of Mining and Metallurgy

Figure 8—Effect of increasing polymer concentration on pressure loss with various solids concentrations

solids, 821.39 kg of water, and 6.87 kg of polymer. Since the amount of water at 30% solids slurry (the baseline) was 866.94 kg, the water savings at 35% solids was calculated to be 5.25% as follows: (866.94 – 821.39)/866.94*100.

CFD simulations to evaluate settling velocity Flow velocities were investigated when solids concentration percentages were changed from the 30% baseline case to 35%, 40%, and 45%. To evaluate the potential for solids particles to settle in the slurry, the field-scale CFD model shown in Figure 9 was used and flow velocities were compared with deposition velocities. Note that solids particles start to settle and form a moving bed (inducing clogging in pipelines) when the deposition velocity exceeds the flow velocity (Abulnaga, 2002). The deposition velocity equation proposed by Durand and Condolios (1952) was employed in this study and is shown in Equation [1].

[1] where VD is the deposition velocity (m/s), FL is the Durand factor based on grain size and volume concentration (unitless), Di is the VOLUME 123

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Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption Table III

Optimal polymer amounts with given solids percentages and corresponding water savings Solid Concentration (%)

30

35

40

45

Solids (kg)

371.55

445.99

524.85

608.56

Water (kg)

866.94

821.39

775.25

727.55

Polymer

(kg)

0.00

6.87

12.03

16.24

(%)

0.0

0.83

1.53

2.18

Water Savings

Weight (kg)

−

45.55

91.69

139.40

Percentage (%)

−

5.25

10.58

16.08

Mass Balance (/1m3 of Slurry)

Table IV

Summary of settling potential studies (deposition and flow velocities) Cw (%) Polymer Addition (%) Cv FL Deposition Velocity (VD, m/sec)

30 35 40

45

0 0.83 1.53 2.18

0.18 0.22 0.26 0.30

0.453 0.479 0.488

1.34 1.37 1.40 1.42

0.498

Study Results (m/sec) Peak Flow velocity Average Flow Velocity

8.44 8.39 8.29 8.22

6.33 6.29 6.23 6.19

a Mean Particle Size (D50): 0.083 mm b Pipe Inner Diameter (Di): 0.452 m c Gravity Acceleration (g): 9.81 m/sec2 d Solid Density (ρs): 2,040 kg/m3 e Liquid Density (ρL): 1,060 kg/m3

Figure 9—3D computational mesh for field-scale simulations

inner pipe diameter (m), g is the gravity acceleration constant (9.81 m/s), ρs is the density of solids in a mixture (kg/m3), and ρL is the density of the liquid carrier (kg/m3). For the Durand velocity factor, Equation [2] proposed by Schiller and Herbich (1991) was used.

Deposition velocities calculated using Equations [1] and [2] are shown in Table IV. [2] where Cv is the solids volume concentration of slurry (fraction) and d50 is mean particle size (mm).

Figure 9 shows the 3D computational mesh used for field-scale simulations. It features the same geometry used for the testing 584

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mine’s pipeline profile. The mesh consists of 2 075 865 nodes and 1 596 691 elements. A hexahedral structured mesh was adapted to mesh the entire volume. The modelling distance ranged from 0+000 to 4+762 km, which corresponds to the location of the peak elevation. Since the flow velocity is controlled mainly by gravity once the slurry reaches the peak elevation, the simulations were designed to examine velocity changes under turbulent flow that originate mainly under high pressure from a pumping system.

The same parameters listed in Table II were used for the simulations. In addition, a pressure inlet condition of 4.0 MPa and an inner (hydraulic) pipeline diameter of 452.42 mm were used as model inputs. Figure 10 shows flow velocities for four solids percentages – 30%, 35%, 40%, and 45% – before and after adding The Journal of the Southern African Institute of Mining and Metallurgy

Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption

Figure 10—Flow velocities at (a) 30% solids, (b) 35% solids, (c) 40% solids, and (d) 45% solids in the pipeline

the polymer. Simulations for flow velocities were conducted for 35%, 40%, and 45% solids before and after adding the polymer (six cases) plus the baseline case (30% solids, with no polymer) as shown in Figure 10. To maintain the same pressure loss as the baseline, polymer was added at concentrations of 0.83%, 1.53%, and 2.18% for 35%, 40%. and 45% solids, and peak flow velocities were changed from 7.99, 7.61, and 7.29 m/s to 8.39, 8.29, and 8.22 m/s, respectively. The peak flow velocity for the baseline condition was 8.44 m/s.

The simulation results showed that peak flow velocities decreased as solids percentages increased and that adding polymer increased these velocities by 5.0% (35% solids), 9.0% (40% solids), and 12.7% (45% solids). This demonstrates that the polymer effectively mitigates the decrease in flow velocity that occurs when solids concentrations are increased, which would otherwise increase the friction between the flow media and pipeline wall. Therefore, the DRA has the potential to reduce the amount of water in tailings slurry and improve TSF stability.

The potential for settling (and associated pipeline clogging) as the solids percentage increases was investigated by comparing deposition and flow velocities. The results of the studies are summarized in Table IV. For all solids percentage cases, the deposition velocities were definitively slower than the flow velocities; therefore, the potential for settling is minimal.

The studies discussed above indicate that the polymer has the ability to mitigate concerns related to pipeline clogging and friction-induced wear when the solids concentration is increased.

To further investigate the effects of increased friction, simulations were conducted to quantify the erosion rate of pipelines.

model for investigating slurry flows in the pipeline. Flow behavior of the tailings slurry was investigated for 30%, 35%, 40%, and 45% solids concentrations enhanced with the optimal polymer concentrations (0%, 0.83%, 1.53%, and 2.18%, respectively). Solids particles were injected uniformly at the inlet area with the same fluid flow velocity. Note that the mean particle size was used rather than the actual particle size distribution shown in Figure 2 in order to simplify the simulation for the purpose of examining the effect of the DRA. The wall boundaries were set with a scaleable function as ‘reflect’ and the outlet boundary was set as ‘escape’. The SIMPLEX algorithm was used to investigate pressures and velocities in the pipelines. Detailed simulation conditions are listed in Table V. Figure 12 shows the results of the erosion rate simulations.

The contours show erosion rates increasing proportionally with increased solids concentrations, regardless of whether polymer was added. The simulation results are detailed in Table VI. Consequently, it was concluded that the polymer did not significantly affect the erosion rate and that this rate was instead driven by the solids concentration. Further studies to investigate pipeline erosion rates with the given tailings slurry were conducted based on the daily throughput at the testing site.

Flow velocity varies in response to the automated operating system at the testing site. This system automatically manipulates the pump stroke and number of operating pumps based on the amount of tailings slurry in the tank. This study assumed that the tailings transportation system had a consistent flow velocity and that the operating time to transport the slurry could represent the efficiency of transportation with the given daily throughput.

Table VII summarizes the results. The daily throughput at the site

CFD simulations to calculate erosion rates of pipelines ANSYS FLUENT was used to model the erosion rates of pipelines when optimal polymer enhancement is applied to the slurry. A 0+500 km area was selected since it is the most curved and would therefore undergo the highest erosion rate (Wood and Jones, 2003).

Figure 11 shows the 3D computational mesh for the area used in the simulations. A hexahedral structured mesh was built with 128 763 nodes and 120 320 elements.

The simulations use a discrete phase model (DPM) for investigating particle movements and the realizable k-ε turbulence The Journal of the Southern African Institute of Mining and Metallurgy

Figure 11—3D computational mesh at 0+500 km area for erosion rate studies VOLUME 123

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Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption Table V

Simulation conditions for erosion rate studies Numerical Model

Slurry flow Particle movement Wall functions Fluid Solids concentration(%) Density(kg/m3) Solids Density(kg/m3) Diameter (mm) Material Density(kg/m3) Velocity Inlet (m/sec) Wall boundary Erosion model Solver divergence term convergent criteria

Fluid

Solids Particle

Wall Boundary Conditions

Solving Condition

Realizable k- ε Turbulence Model Discrete Phase Model (DPM) Scalable Slurry 30, 35, 40, 45 1,238; 1,274; 1,312; 1,352 Tailings 2,040 0.08278 (Dmean) HDPE 970 3 Scalable Generic SIMPLEX algorithm the second-order upwind discretization schemes the residual ≤ 10-5

Figure 12—Erosion rate contours in the pipeline: (a) 30% solids, 0% polymer, (b) 35% solids, 0.83% polymer, (c) 40% solids, 1.53% polymer, (d) 45% solids, 2.18% polymer

Table VI

Erosion rates with various solids percentages and optimal polymer concentrations Cw (%) Polymer (%) D50 (mm) Flow velocity (m/sec) Erosion Rate(generic) (kg/sec. m2) (mm/year) 30 35 40 45

0 0.83 0.08278 3 1.53 2.18

1.02E-08 1.19E-08 1.77E-08 2.37E-08

0.33 0.39 0.58 0.77

Table VII

Erosion rates per day to transport daily slurry amounts with various solids concentrations Daily throughputs (dry tonnes)

Solids concentration (%)

Slurry volume (m3)

Average flow velocity (m/sec)

Equivalent operating time (hour/day)

Total erosion (μm/day.m2)

30 35 40 45

32,297 26,907 22,863 19,719

6.33 6.29 6.23 6.19

8.83 7.41 6.36 5.52

0.334 0.327 0.418

12,000

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The Journal of the Southern African Institute of Mining and Metallurgy

Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption was around 12 000 dry metric tons, and daily volumes of tailings that required transport were 32 297 m3, 26 907 m3, 22 863 m3, and 19.719 m3 when solids percentages were 30%, 35%, 40%, and 45% respectively. Average flow velocities were obtained from the data in Table IV. Equivalent operating times were determined based on the average flow velocities and daily slurry volumes. Since the slurry volume decreased as the solids concentration increased for the given daily throughput, the operating times (hours/day) were decreased accordingly – from 8.83 hours to 7.41 hours (35% solids), 6.36 hours (40% solids), and 5.52 hours (45% solids).

These daily erosion rates were calculated, as shown in Table VII: 0.334 µm for 30% solids and 0% polymer (baseline), 0.327 µm for 35% solids and 0.83% polymer, 0.418 µm for 40% solids and 1.53% polymer, and 0.485 µm for 45% solids and 2.18% polymer. In the case of 35% solids, the erosion rate per year (Table VI) increased from 0.33 mm (baseline) to 0.39 mm but, due to the reduced operating time, the daily erosion rate with the given slurry volume decreased from 0.334 µm to 0.327 µm.

Field application – Potential water saving at the test mine About 9 Mm3 of tailings slurry was discharged at the testing mine in 2018, with about 7.7 Mm3 of water being used for transportation.

Figure 13 shows the monthly volumes of tailings slurry and water discharged at the site. Because of various circumstances, such as periodic maintenance and emergency shutdowns, these volumes varied. The average monthly slurry discharge was 0.91 Mm3, which includes 0.773 Mm3 of water.

The potential water savings that could be achieved by adding polymer was estimated based on the simulations and the discharge record. The total discharge of tailings at the testing site was about 3.384 Mt (dry) in 2018. Note that the solids concentration at that time was 30%.

As shown in Table VIII, the amount of water required to transport 3.384 Mt (dry) of tailings at each solids percentage was calculated as 5.879 Mm3 (35% solids), 4.715 Mm3 (40% solids), and

3.816 Mm3 (45% solids). To maintain the same pressure loss, the required polymer amounts were 50 151 m3 (35% solids); 74 669 m3 (40% solids); and 86 689 m3 (45% solids). These increases in solids result in 1.852 Mm3, 3.016 Mm3, and 3.915 Mm3 of water savings per year, respectively.

Conclusions and future work This study investigated two major aspects of reducing the amount of water in the tailings slurry at the test mine: the effect on the tailings transportation system and the use of a polymer as a new DRA to offset the effects of increasing the percentage solids in the slurry. ➤ The optimal polymer percentages were 0.83%, 1.53%, and 2.18% for 35%, 40%, and 45% solids, respectively. Note that these percentages are designed to maintain the same pressure loss as the baseline condition. ➤ The average flow velocity in the pipeline was 6.33 m/s under the baseline condition (30% solids, 0% polymer). When optimal polymer percentages were applied (0.83% for 35% solids, 1.53% for 40% solids, and 2.18% for 45% solids), the expected flow velocities were 6.29 m/s, 6.23 m/s, and 6.19 m/s, respectively. As the solids percentage increased, flow velocities decreased slightly, regardless of the addition of polymer. The deposition velocity ranges of 1.34–1.42 m/s were definitively lower than the flow velocities, indicating a minimal chance of pipeline clogging. ➤ Erosion rates increased as solids concentration increased, with one major exception – the 35% solids case. For a daily tailings throughput of 12 000 t (dry), the erosion rate decreased from 0.334 μm/d (30% solids, baseline case) to 0.327 μm/d. For the cases simulated with 40% and 45% solids, erosion rates exceeded those of the baseline condition. ➤ The potential water savings was calculated based on the mine’s daily throughput of 12 000 t (dry) and a solids percentage of 35%, which could likely be achieved without modifying the tailings transportation system. Increasing the solids to 35% would require applying polymer at the rate of 50 151 m3/a.

This would not only result in water savings of 1.852 Mm3/a but would also reduce the erosion rate of the pipeline walls, thereby reducing maintenance costs, and could improve TSF stability, thereby reducing the risk of failure. ➤ Currently in the international patenting process, the polymer used in this study also has another key benefit: controlling dust on dried tailings beach areas in upstream-type TSFs. If there are resident communities near a TSF, then these benefits could justify the cost of the polymer.

Future work

Figure 13—Monthly tailings slurry and water volumes discharged at the testing mine in 2018

The results of this investigation suggest that applying the polymer in the field is still premature. Further studies are needed to assess its potential negative effects on the stability of TSFs and mill processing. Additional studies are required to check that the

Table VIII

Potential water savings as solids percentage is increased Solids Concentration (%) 35 Polymer Addition (%) 0.83 Tailings (dry tonnes/year) Water usage (m3/year) 5,879,065 Polymer addition (m3/year) 50,151 Water savings (m3/year) 1,852,374 The Journal of the Southern African Institute of Mining and Metallurgy

40 1.53 3,383,674 4,714,958 74,669 3,016,481 VOLUME 123

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Use of a biocompatible polymer to enhance tailings transportation and reduce water consumption polymer does not affect the geotechnical properties of the deposited tailings, especially the friction angle which is a key factor for the stability of upstream TSFs. Water from discharged tailings in TSFs is collected in a decant pond and recycled to the mill. The authors tested the polymer’s effect on flotation at several copper mines, with varying results; some showed no effects but in others the recovery decreased, indicating that this negative effect may be site-specific. In addition, this study investigated various solids concentrations from 30% to 50%, in 5% increments. However, this increment should be reduced (for example, to 1%) in future studies to determine the optimal solids and polymer concentrations for maximizing water savings and minimizing total costs. Finally, detailed economic feasibility studies are required before the polymer can be used as a new DRA. These studies should consider both the polymer’s benefits (water savings, possible increased TSF stability, less pipeline erosion, and dust control) as well as its potential negative effects (clogging issues, cost, and impacts on mill processing).

Gillies, R.G., Schaan, J., Sumner, R.J., McKibben, M.J., and Shook, C.A. 2000.

Deposition velocities for Newtonian slurries in turbulent flow. Canadian Journal of Chemical Engineering, vol. 78, no. 4. pp. 704–708.

Conflict of interest statement

Schiller, R.E. and Herbich, P.E. 1991. Sediment transport in pipes. Handbook of Dredging. Herbich, P.E. (ed.). McGraw-Hill, New York.

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Jeong, Y. and Kim, K. 2019. A case study: Determination of the optimal tailings beach distance as a guideline for safe water management in an upstream TSF. Mining, Metallurgy & Exploration, vol. 37. pp. 141–151.

McKibben, M. and Sun, R. 2006. Rheology testing of Boleo oxide ore tailings using SRC’s 75mm flow loop. Saskatchewan Research Council, Pipeflow Technology Centre Energy Division, Saskatoon, Canada.

Rico, M., Benito, G., Salgueiro, A.R., Díez-Herrero, A., and Pereira, H.G. 2008. Reported tailings dam failures: A review of the European incidents in the worldwide context. Journal of Hazardous Materials, vol. 152, no. 2. pp. 846–852.

Rolander, N., Rambo, J., Joshi, Y., Allen, J.K., and Mistree, F. 2006. An approach to robust design of turbulent convective systems. Journal of Mechanical Design, vol. 128, no. 4. pp. 844–855.

Rong, H., Peng, Z., Hu, Y., Wang, C., Yue, W., Fu, Z., and Lin, X. 2011.

Dependence of wear behaviors of hard metal YG8B on coarse abrasive types and their slurry concentrations. Wear, vol. 271, no. 7–8. pp. 1156–1165.

Truscott, G.F. 1972. A literature survey on abrasive wear in hydraulic machinery.

Wear, vol. 20, no. 1. pp. 29–50.

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Wood, R.J.K. and Jones, T.F. 2003. Investigations of sand–water induced erosive wear of AISI 304L stainless steel pipes by pilot-scale and laboratory-scale testing. Wear, vol. 255, no. 1–6. pp. 206–218.

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The Journal of the Southern African Institute of Mining and Metallurgy

Investigation of a conveyor belt fire in an underground coal mine: Experimental studies and CFD analysis

by C.O. Aksoy1, G.G.U. Aksoy2, A. Fişne3, I. Alagoz4, E. Kaya1

Affiliation:

1 Dokuz Eylul University, Department of

.

Mining Engineering, Izmir-Turkey.

2 Hacettepe University, Department of

Mining Engineering, Ankara-Turkey.

3 Istanbul Technical University, Department of Mining Engineering, Istanbul, Turkey.

4Electric Production Co. Ankara-Turkey.

Correspondence to: C.O. Aksoy

Email:

okay.aksoy@deu.edu.tr

Dates:

Synopsis

Coal produced in underground mines is transported to the surface by means of conveyor belts throughout long roadways. The combustion of belts puts a large number of employees at great risk. Underground collieries differ from other underground mines -due to the combustible nature of the product. The most prevalent cause of belt fires in underground coal mine is spontaneous combustion due to oxidation of the coal, which also enables the conveyor belt to burn over time.

In 2014, a belt fire in an underground coal mine in Manisa-Soma, Turkey caused 301 fatalities. A study has been conducted on this accident for approximately 3 years, consisting of combustion tests in a purpose-built research gallery, comparison of the test results with mine records of the accident, and CFD modelling of the mine environment. The intensity of the fire was sufficient to redirect the air flow underground, causin large amounts of toxic gases to fill almost the entire mine in approximately 15 minutes. It is recommended that CFD analysis be used in planning emergency action strategies in underground mines.

Keywords

Conveyor belt fire, CFD analysis, emergency plan, toxic gas, underground mine.

Received: 10 Sept. 2021 Accepted: 13 Sept. 2023 Published: December 2023

How to cite:

Aksoy, C.O., Aksoy, G.G.U., Fişne, A., Alagoz, I., Kaya, E. 2023 Investigation of a conveyor belt fire in an underground coal mine: Experimental studies and CFD analysis.

Journal of the Southern African Institute of Mining and Metallurgy, vol. 123, no. 12. pp. 589–598 DOI ID: http://dx.doi.org/10.17159/24119717/1613/2023 ORCID: C.O. Aksoy http://orcid.org/0000-0002-4328-4862 G.G.U. Aksoy http://orcid.org/0000-0002-9328-9899 A. Fişne http://orcid.org/0000-0001-7449-0573 I. Alagoz http://orcid.org/0000-0002-7167-8340 E. Kaya http://orcid.org/0000-0002-8268-2484

Introduction In underground mining, there are many factors that can cause problems ranging from minor accidents to catastrophes. One of the most important of them is the quailty of air in underground airways, because low levels of oxygen or increased concentrations of dangerous gases endanger the health and safety of mineworkers. On the other hand, it is obvious that a healthy workplace results in greater productivity.

Since mining operations began, natural air flow has been used to provide ventilation by exploiting the air pressure differences between different parts of the mine. Altough this is an efficent method of ventilation, in some cases it does not suffice, such as dead end volumes, crosscuts, and blind spaces where the air cannot enter naturally. In order to provide fresh air entry for workers and the efficient operation of machinery, and to dilute contaminant to below the regulatory limits, high air flows are providee via fans.

The air flow that is needed for adequate ventilation has to be calculated in order to guarantee sufficent fresh air is present in both standard operational circumstances and exceptional circumstances or accidents.

For example, during routine excavation and transportation work, the required amount of air to dilute the exhaust gases from machines should be calculated, as well as the flows needed in the case of an accident followed by a mine fire. However, there is another risk that is particularly associated with underground coal mining operations – that of conveyor belt combustion. The combustion process starts with coal oxidation, and if unchecked can ignite the conveyor belt, producing substantial volumes of toxic gases. Barros-Daza et. al. (2021) classified belt fires according to the type (stage) of the fire and method of firefighting. The main hazards include reduced visibility, toxic effects of carbon monoxide (CO), and elevated air temperatures downstream of the fire (Perzak et. al., 1995). Five gaseous products of belt fires have been -identified, i.e., carbon monoxide, carbon dioxide, hydrogen cyanide, hydrogen bromide, and sulphur dioxide (SO2) (NIOSH, 1988; Krawiec, 2021; MSHA, 2008).

In underground ventilation studies the complex air volumes, comprising multiple galleries or branches, are divided into sections with the same aerodynamic characteristics. Each section is assigned an air resistance and the obtained circuits are solved through network techniques such as the Hardy Cross method (Diego, Torno, and Toraño, 2011). In the past 10 years significant improvements have been made in software for ventilation plannoing purposes. There are different tols for calculating and rapidly testing the network, such as VENTSIM, VNET-PC, or VENPRI. In all cases, each software type employs a database of air resistances taken from specialized bibliographies or field measurements.

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Investigation of a conveyor belt fire in an underground coal mine Ventilation studies are a type of fluid mechanics problem, and the most sophisticated method in this field is computational fluid dynamics (CFD). CFD allows for the calculation of the variables that define fluid movement in three-dimensional spaces, after a laborious procedure of model creation, meshing, and adjustment of the equations.

CFD is widely employed and validated in industry for solving fluid problems , with immediate applications in the calculation of ventilation flows in all kinds of systems, as shown by BallesterosTajadura et al. (2006) and Hargreaves and Lowndes (2007), with particular relevance in multiphase studies of fire situations (Galdo Vega et al. 2008; Yuan and You, 2007). Chen et al. (2019) used CFD to simulate fire and smoke movement in a serious fire incident in a road tunnel.

In 2014, an accident occurred at an underground coal mine in Soma-Manisa, Turkey, in which 301 workers died. More than 250 of these workers were employed on a production panel (the S panel) located on the return airway. In this article, the events that developed after fire occured will be discussed more than the cause of the accident. Immediately after the accident, the entire mine was filled with highly concentrated gas emitted by a belt burning in an area where the air flow was almost 0.3 m/s ., which is not sufficient to clean the air in a gallery under normal conditions. The conveyor involved was not a flameproof belt (legislation at the time did not require this).

The esperimental part of the investigation was conducted in a research gallery in which more than 100 conveyor belt fires have been simulated. Reliable data could not be obtained from all experiments, since belt burn-in did not occur in every case.

Furthermore, due to the high gas concentration, it is extremely risky to enter the gallery to obtain data while an experiment is under way The data at the time of the accident was taken from the sensors in the mine and used as input for the CFD analysis. The results of the CFD analysis are comparable with the data from the sensors.

The CFD analysis showed that the thermodynamics of the mine completely changed due to the fire.

was adjusted to ambient. In some trials, experiments were carried out by placing the coal over the belt drum and the belt.

Combustion and post-combustion images obtained in the first experiments are given in Figure 2. As can be seen, the experiments were recorded both from the front of the gallery and from the back (inside). The front of the gallery was kept open in the first experiments, but it was sealed with steel in the later stages of the belt burning experiments and the camera was enclosed in the gallery.

In the combustion experiments, an opening was provided behind the gallery to simulate the air flow in the mine, allowing the intake of air from the fan (Figure 1). Air velocity measurements in this opening and inside the gallery are given in Figure 3.

Approximately 100 experiments were carried out. One of the datasets from the CO sensor during the first experiment is given in Figure 4. The gas sensors were calibrated after each experiment.

Gas measurements were taken in all tests. The most important information gained from these measurements is that the amounts of gas released after belt fire are very similar. As shown in Figure 5, the amount of oxygen in the ambient air is 8.12% (frequently below 3%), the CO level is higher than 10 000 ppm (the sensor's CO measurement limit), the carbon dioxide level is above the measurement limit of the sensor, and the concentration of methane is 3.86%. Although there was no methane in the environment before combustion, the sensors detected methane once combustion

The research gallery IA research gallery was built with the aim of creating an environment similar to that in which the accident occurred, in order to investigate the combustion mechanism of the conveyor belt, to characterize the combustion products, and to determine the sequence of appearance and concentrations of these products. The section of the gallery where the tests were carried out was 16 m2 in cross-section, the same as the site of the fire, and the support and auxiliary equipment were the same. Figure 1 shows a photograph of the gallery. Two gas sensors were used to determine the types and time-dependent concentrations of gases released by the combustion of the belt in the gallery. One sensor was used to measure the amounts of carbon dioxide (max. 500 ppm), carbon monoxide (max.10 000 ppm), methane (max. 4%) and oxygen, and the other measuring hydrogen cyanide (max. 50 ppm), hydrogen sulphide (max. 100 ppm), chlorine (max.50 ppm), and oxygen.

Figure 1—Photograph of the research gallery, showing support elements and auxiliary equipment

Conveyor belt combustion experiments and results Various methods were attempted to burn conveyor belts, including using synthetic thinner, gasoline, coal, wood reinforcement material, coal-wood mixtures, and igniting them with an oxygen source. However, combustion only occurred in conveyor belts where coal and wood materials were used together. During these trials, the belt was not subjected to any force, also its temperature 590

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Figure 2—Burning conveyor belt during the experiments, and burnt wood support materials and burnt belt after experiments The Journal of the Southern African Institute of Mining and Metallurgy

Investigation of a conveyor belt fire in an underground coal mine had started. It was found that the combustion gases that contain hydrocarbons can be detected as methane by the sensors. When the belt started to burn, a very strong flame appeared and it was very difficult to extinguish this fire. The main reason for this is that the hydrocarbons produced by combustion of the petroleum-

Figure 3—Air velocity measurements, (a) air inlet clearance (5.39 m/s); (b) air velocity inside the gallery (0.67 m/s)

derived belt material act as a fuel and feed the fire. Data on the gases measured with the other sensor is given in Figure 6.

As seen in Figure 6, in addition to CO, CH4, O2, and CO2, hydrogen cyanide, hydrogen sulphide, and chlorine were also emitted. These gases can be quickly fatal if inhaled at high concentrations. In the conveyor belt burning experiment depicted in Fıgure 6, the hydrogen cyanide concentration in the ambient air was measured at 50 ppm (the upper limit of detection by this sensor). The chlorine concentration was 17.6 ppm, hydrogen sulfphde concentration 78.9 ppm, and CO concentration 500 ppm (also the upper limit of detection for this sensor, measured above 10 000 ppm with the other sensor). Legislation does not permit work in atmospheres containing less than 19% oxygen, and more than 2% methane, 0.5% carbon dioxide, 50 ppm (0.005%) carbon monoxide and other dangerous gases. The maximum hydrogen sulphide concentration permitted for 8 hours of operation is 20 ppm (0.002%). The upper measurement limits of the sensors used in these experiments wre exceeded for some gases – according to the law, the limit of the sensors in the mine cannot be less than twice the allowable values. Sınce no information was available on the actual gas concentrations, a best-fitting approach was used to estimate concentrations. The simulated CO concentration in the environment is depicted in Figure 7. In this approach, both the sensor data in the mine during the accident (the sensor data in the mine was cut off about 3 minutes after the start of the fire) and the time-dependent gas concentration data from the experiments conducted in the research gallery were used.

Gas data obtained from sensors in the mine

Figure 4—Change in CO concentration with time during the first experiment

Belt fires pose a great risk not only for underground coal mines, but also in other enclosed environments. It is thus very important to examine the events that occurred during the fire in the mine and the behaviour of the toxic gases that were evolved.

In an underground coal mine, a fire on a belt transporting coal may becomr so intense that it affects the thermodynamic conditions across almost the entire mine.

Ventilation in underground mines is provided using pressure differentials. The air moves from high pressure regions to the low pressure regions. However, as the temperature in the gallery increases with the burning process, the air pressure also increases.

Figure 5—Variation in gases in the ambient air as a result of conveyor belt burning (experiment carried out on 3 July2015) The Journal of the Southern African Institute of Mining and Metallurgy

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Time (minute)

Figure 6—Gas concentrations in the gallery air (experiment carried out on 15 September 2016)

The data, from the CO sensors numbers 431, 501 and 545 and CH4 sensor 404 is listed in Table I (extracted from the Committee Report).

30 25 20 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

CFD analysis

0

1

2 m3/dk

3

CO (%)

4

5

6

CO (ppm)*10^5

Concentrations Figure 7—Estimated CO concentration in ambient air 30 minutes after the start of the fire

Therefore, the heated air will move from the fire zone to the other parts of the mine. This movement can be very rapid, substantially altering the ventilation conditions underground.

A CFD analysis was carried out in order to accurately determine how the air flow in the mine was affected by the fire. For this purpose, the structural layout of the mine, and the features of the equipment used (secondery fans, ducts etc.) were modelled. The CFD model view of this mine is shown in Fıgure 8. The gallery walls In the area where the belt fire occurred are composed of rock, not coal. However, there was coal on the belt, the wood support elements, as well as the supporting steel sets . For this reason, an effort was made to create a srealistic an environment as possible in the experimental gallery. In CFD study, the data obtained as a result of the experiments carried out in the research gallery was used.

The mining model for the CFD analysis was prepared on a 1:1 scale.

In this model, the air gates employed in the mine, secondary and main fans, ducts and in-mine settlement were operated exactly as was done in the mine Using the ANSYS FLUENT CFD solver, the mass and momentum conservation equations (Navier-Stokes equations) were solved in order to calculate the air flow (given in Equations [1] and [2]).

Mass conservation equation: [1] Here Sm is the user-defined source term added to the continuous phase.

Momentum conservation equation: [2] Here p is static pressure τ= stress tensor ρg→ gravity effect → F external effects (contains user-defined source terms)

Figure 8—Simplified model of the underground mine and data used for CFD analysis 592

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Investigation of a conveyor belt fire in an underground coal mine Table I

Gas concentrations measured in the mine during the belt fire Time

Sensor 431, CO (ppm)

Sensor 501, CO (ppm)

Sensor 545, CO (ppm)

14:54:00 0 4.973 14:56:00 0 4.973 14:57:00 0 6.969 14:58:00 0 12.957 14:59:00 0 56.871 15:00:00 0 128.729 15:01:00 0 282.427 15:02:00 1.961 0 454.090 15:03:00 1.961 50.980 500* 15:04:00 25.867 135.294 500* 15:05:00 73.678 249.020 500* 15:06:00 169.302 378.431 15:07:00 312.737 500* 15:08:00 500* 500* 15:09:00 500* 500* 15:10:00 500* 15:11:00 N/A 15:12:00 N/A 15:13:00 15:14:00 15:15:00 15:16:00 15:17:00

Sensor 401, CH4 (%)

N/A N/A 3.904 N/A N/A

*Higher values could not be read because 500 ppm is the upper limit of the sensors used in the mine . According to the law, work is not permitted in places where there is less than 19% oxygen, more than 2% methane, more than 0.5% carbon dioxide, more than 50 ppm (0.005%) carbon monoxide and other dangerous gases. The highest concentration of hydrogen sulphide allowed for 8 hours of operation is 20 ppm (0.002%)

The stress tensor is defined as in Equation [3].

[3] Here, μ is the molecular viscosity and I a tensor.

Heat transfer and mass transfer are important in this problem as well as the Navier-Stokes equations, The conservation of energy and transport equation for species are solved as follows (Equations [4] and [5] respectively).

high concentration. There are several methods for integrating this situation into the numerical model. In these methods, the k-e turbulence model is used in CFD analysis to ensure that the air flow in the model is under turbulent flow conditions. The k-e turbulence model has been used in addition to previous models to consider the effect of turbulence in numerical modelling. Accordingly, the turbulent kinetic energy equation and corresponding diffusion rate equation are solved (Equations [6] and [7]).

[6] [4] [7]

Here, keff: effective transmission coefficient (when k+kt, kt is given as a turbulent thermal conduction coefficient) → J j: diffusion of species j: diffusion of flow.

[5] Here, Yi: local mass fraction for each species Ri: the production of net species formed by the chemical reaction Si: user-defined sources.

In gaseous underground coal mines, turbulence ventilation is used in order to dilute the gases in the gallery walls and evacuate them from the mine air. The main purpose is to allow the air to flow in a swirling manner and to remove the dangerous gases that settle in the spaces on the gallery walls before they reach a The Journal of the Southern African Institute of Mining and Metallurgy

In these equations; Gk: turbulent kinetic energy production from velocity gradients Gb: rising turbulent kinetic energy production YM: unstable expansion allowance for compressible turbulence C1ε, C2ε, and C3ε are constants, the Prandtl numbers of turbulence for k and ε are specified as σk and σε. Finally, Sk and S are userdefined source terms.

More detailed information about the equations given above can be found in the ANSYS FLUENT Theory Guide (2013).

The data required for the fire scenario simulation was determined from a literature survey (Wang et al., 2009; Galdo Vega, 2008) and our research results. The model in the literature for such a fire is termed the ‘pool fire’ (Guan et al., 2013) A 7.5 MW fire was simulated for the fire model. In order to establish similarity in CFD analysis, a fire model should be selected. When the fire models were VOLUME 123

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Investigation of a conveyor belt fire in an underground coal mine examined, it was understood that the perfect combustion model for diesel was similar to this study. According to Wang et al. (2009) and Galdo Vega et al. (2008), the pool fire for diesel is considered as complete combustion. The perfect combustion equation for diesel is [8] The atomic mass units of elements and combustion equation variables used in the analysis are given in Tables II and III, respectively.

CFD results The movement of the CO gas with time is depicted in Figure 9, and that of CH4 gas in Figure 10.

From the distribution of CO and CH4 depicted in Figure 11, it is evident that the air flow undergoes a significant change within the gallery. The pre-fire air flow is represented by the green colour, while the post-fire air flow is shown in red. Notably, the return air that should exit the mine is redirected back into the mine after the fire. This phenomenon is primarily attributed to the increased temperature and pressure in the fire zone, causing the heated air to move towards cooler regions of lower pressure. While a portion of the CO and CH4 gases escapes the mine, some gases are redirected back inside due to the intensive emission of CO gas and the limited gallery space. The altered thermodynamic conditions of the mine also contribute to this phenomenon.

In order to analyse the flow direction change the velocity, flow, gas distribution, and temperature were calculated in different regions of the flow volume. Figure 12 shows the locations of six of these measurement points.

The mass flow versus time graphs for four of these measurement points are shown in Figure 13. It can be seen that the mass flow value at points 3 and 4 is initially positive,becoming negative after about 1000 seconds.

With the change of direction of the air flow, it is seen that the mass flow rates increase rapidly in the main galleries, especially at measurement points 1 and 2, after 800 seconds. Velocity-time plots at the same points are shown in Figure 14. Flow lines of one of the fans in the mine are shown in Figure 15.

Table II

Atomic mass units of elements Element

H

C

N

O

Ma

1

12

14

16

The mass ratio-time graph for CO at measurement point 3 is shown in Figure 16. CO reaches this area in about 8 minutes from the start of the fire. Fluctuations between 1220 and 1800 seconds are due to the change in direction of the air flow. This measuring point is the region where the CO gas has the lowest dissemination in the surrounding galleries.

The mass ratio-time graph for CO at measurement point 5 is shown in Figure 17. CO gas reached this region in about 900 seconds from the start of the fire. The sudden changes observed at 1260 seconds are attributed to the change in direction of flow in this region.

The temperature-time graph at measurement point 4, where the flow changes direction, is plotted in Figure 18.

Finally, the mass ratio-time graph for CO gas at measurement point 6 on the main roadway, where the flow moves by changing direction, is shown in Figure 19. It can be seen that the CO gas reaches this region in approximately 1440 seconds.

According to the data obtained, the flow accelerated due to the energy input in the fire zone and combined with the diffusion of gases in the air, caused the air flow to change direction at measurement point 4. The air flow in this main roadway, which is responsible for transporting polluted air to the atmosphere, underwent a reversal some time after the start of the fire.

Conclusıons

In 2014 Soma-Manisa, one of the most important underground coal mines in Turkey, experienced a major accident. The cause of this accident, which had significant consequences, was a belt fire.

In this study, it was found that in addition to combustion products such as CO and CO2, gases such as HCN, Cl2, and H2S, which are quickly fatal at low concentrations, are also released during a belt fire.

Another important finding is that the thermodynamic conditions in an underground mine can change completely in a very short time, depending on the magnitude of the fire.

The belts are made of petroleum derivatives, and hydrocarbon products are among the gases formed during combustion. These products are registered as CH4 by the gas sensors. Furthermore, the fact that these by- product gases are themselves flammable makes it very difficult to extinguish a conveyor fire, because the hydrocarbon combustion by- products in the environment continue to burn.

Also, these products can accumulate in a part of the mine that is not at risk of fire, with the potential to cause an explosion.

The last important result from this study is that the air circulation in the mine can change unexpectedly due to a fire.

For this reason, it is recommended that CFD analysis be used in planning emergency action strategies in underground mines.

Table III

Combustion equation variables Element and Element and compound compound formula weight (Ma)

Reactants

Products

594

C10H12 O2 N2 CO2 H2O N2 DECEMBER 2023

142 32 28 44 18 28

Stoichiometric Element and compound Reaction Total mole number total weight (M) total (Ma) flow rate [kg/s)

1 15,5 58,.8 10 11 58.28 VOLUME 123

142

496 2269.84 1631.84 0,781 25 440 198 2269.4 1631;84

Flow rate (kg/s)

0.048 874 59 0.170 716 879 0.561 658 531 0. 151 442 392 0.068 149 077 0.561 658 531

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Investigation of a conveyor belt fire in an underground coal mine

Figure 9—Path of CO gas during belt fire. A: 180 s, B: 360 s, C: 540 s, D: 1080 s, E: 1440 s, F: 1800 s

References

ANSYS. 2012. Fluent Theory Guide. https://www.afs.enea.it/project/neptunius/docs/ fluent/html/th/main_pre.htm Ballesteros-Tajadura, R., Velarde-Suárez, S., Hurtado-Cruz, J.P., and Santolaria-Morros C. 2006. Numerical calculation of pressure fluctuations in the volute of a centrifugal fan. Journal of Fluids Engineering, vol. 128, no. 2. pp. 359–369.

Diego, I., Torno, S., and Toraño, J. 2008. CFD simulation of aerodynamic resistance in underground spaces ventilation. WIT Transactions on the Built Environment, vol. 102. pp. 12–23.

Galdo Vega, M.G., Argüelles Díaz, K.T., Fernández Oro, J.M., Ballesteros Tajadura, R., and Santolaria Morros, C. 2008. Numerıcal 3d simulation of a longitudinal ventilation system: Memorial Tunnel case. Tunnelling and Underground Space Technology, vol. 23, no. 5. pp. 539–551

Barros-Daza, M.J., Luxbacher, K.D., Lattimer, B.Y., and Hodjes, J.L. Mine conveyor belt fire classification. Journal of Fire Sciences, vol. 40, no. 1. pp. 44–69.

Guan J., Fang, J., Zhang, D., Wang, J., and Zhang, Y. 2013. Experiment study of oil tank fire characteristics dependent on the openıng of tank top. Procedia Engineering, vol. 62. pp. 932–939. https://doi.org/10.1016/J.Proeng.2013.08.145

Chen, Y-J., Shu, C-M., Ho, S-P., Kung, H-C., Chien, S-W., Ho, H-H., and Hsu, W-S. 2019. Analysis of smoke movement in the Hsuehshan tunnel fire.

Tunnelling and Underground Space Technology, vol. 84, pp. 142–150.

Hargreaves, D.M. and Lowndes, I.S. 2007. The computational modeling of the ventilation flows within a rapid development drivage. Tunnelling and Underground Space Technology, vol. 22. pp. 150–160.

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Figure 10—Schematic of change in air flow direction due to fire

Figure 11—Locations of control points for measuring air velocity and flow rate 596

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Figure 12— Locations of control points for measuring air velocity and flow rate The Journal of the Southern African Institute of Mining and Metallurgy

Investigation of a conveyor belt fire in an underground coal mine 5 4.5

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4

40 Measuring Pont 1

20

Measuring Pont 2 Measuring Pont 3

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Measuring Pont 4

-20 -40

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3.5

Mass Ratio [%]

Mass Flow [kg/s]

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3 2.5 2 1

1200 1400 1600 1800 2000

0.5

Time [s]

0

Mass Flow [kg/s]

Figure 13—Mass flow vs time graphs for four different measuring points 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0

CO

1.5

0

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360

540

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1080

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Time [s] Figure 17—Change in mass fraction of CO gas at measurement point 5 340

Measuring Pont 1 Measuring Pont 2

335 330

0

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800

1000 1200

1400 1600

1800 2000

Temperature [K]

Time [s] Figure 14—Velocity-time graphs for measurement points 1 and 2

325 320 315 310 305 300

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1080

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Time [s] Figure 18—Temperature-time graph at measurement point 4

8 7

Figure 15—Flow streamlines of a fan

6 4.5

Temperature [K]

CO

Mass Ratio [%]

4 3.5 3 2.5

5 4 CO

3 2

2

CO

1.5 1

1 0

0.5 0

0 0

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720

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Time [s] Figure 16—Change in mass fraction of CO gas at measuring point 3 Krawiec, P., Warguła, T., Dorota, C K., Paweł, J., Dziechciarz, A., and Kaczmarzyk, P. Chemical compounds released by combustion of polymer composites fat belts. Scientifc Reports, vol. 11. pp. 8269–1-8269–10.

MSHA. 2008. Conveyor belt combustion toxicity and smoke density. Mine Safety and Health Administration, Arlington, VA. NIOSH. 1988, Emission products from combustion of conveyor belts. Report no.

NIOSH/00185370.

Perzak, F.J., Litton, C.D., Mura, K.E., and Lazzara, C.P.1995. Hazards of conveyor belt fires. Report of Investigations 9570. US Bureau of Mines.

Prosser, B.S., Stinnette, J.D., and Paredes, J. 2002. Ventilation optimization at the La Camorra mine. Proceedings of 9th US Mine Ventilation Symposium, The Journal of the Southern African Institute of Mining and Metallurgy

720

900

1080

1260

1440

1620

1800

Time [s]

900 1080 1260 1440 1620 1800

Figure 19—Change in mass ratio of CO gas at measurement point 6

Queens University, Kingston, Ontario. Taylor & Francis. pp. 150–154.

Teacoach, K.A., Rowland, J.H., and Smith, A.C. 2010. Improvments in conveyor belt fire suppression systems for U.S. coal mines. Preprint: SME Annual Meeting, Phoenix, AZ, 28 February–3 March. https://stacks.cdc.gov/view/cdc/9660 Wang Y, Jiang J., and Zhu D. 2009. Diesel oil pool fire characteristic under natural ventılatıon condıtıons in tunnels with roof openıngs. Journal of Hazardous Materials, vol. 166, no. 1. pp. 469–477. https://doi.org/10.1016/J. Jhazmat.2008.11.056 Wang, D.Y., Liu, X.Q., Wang, J.S. Wang, Y.Z., Stec, A.A., and Hull, T.R. 2009.

Preparation and characterisation of a novel fire retardant PET/α-zirconium phosphate nanocomposite. Polymer Degradation and Stability, vol. 94, no. 4. pp. 544–549. u VOLUME 123

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Redpath Thonket breaking world records at Obuasi Mine in Ghana

In 2019, Redpath Africa Limited and Thonket Mining Services joined forces to form Redpath Thonket – a joint venture serving underground mining clients in West Africa. Since its establishment, the JV has secured raiseboring contracts at Chirano, Ahafo, Wassa and Obuasi mines in Ghana.

Phase 3 of AngloGold Ashanti’s Obuasi Mine redevelopment project has commenced and aims to provide robust and efficient infrastructure to support AngloGold Ashanti’s objective of producing 400 koz per annum from the underground mine by progressively delivering 6000 tonnes per day in a cost-efficient manner for the life of the mine.

The new Kwesi Mensah Ventilation Shaft (KMVS), which Redpath Thonket is currently working on, will be used to ventilate the extension of the Obuasi underground gold mine. Redpath Thonket’s scope of work involves the drilling of a 941m deep ventilation shaft with a diameter of 6.5m.

Once completed, the KMVS will be the biggest raiseboring hole drilled to date, worldwide.

The Redbore 90 raise drill machine in operation at Obuasi

Redpath Thonket has achieved several noteworthy milestones on the KMVS project including the completion of the pilot hole on 11 December 2022, with an exceptional accuracy of 0.03%. The halfway reaming mark was reached on 12 November 2023, and the project has maintained an accident-free record since inception. Reaming is expected to be complete by March 2024.

The pilot hole was drilled using a Rotary Vertical Drilling System (RVDS) - a specialised directional drilling technology that corrects pilot hole deviation. The RVDS is used in conjunction with Redpath’s Redbore 90 raise drill and provides the additional accuracy required to maintain verticality of pilot holes.

The Redpath Thonket team at Obuasi is made up of 15 crew members from Ghana and South Africa

In November 2022, Redpath Thonket set the world record for the longest run (691 hours) on one RVDS. The exceptional reliability of the RVDS system, along with skilled personnel and ideal conditions, were key contributors to Redpath Thonket’s achievement of this record. In 2009, Redpath set the previous world record for the longest run (641,6 hours) on one RVDS at the Doyon Gold Mine in Québec, Canada.

Redpath Thonket’s commitment to sustainability and ESG commitments, which are structured around its values and four key areas of care for its people, safety, the natural environment and the social environment, is evident at the KMVS project. The Redbore 90 has been equipped with variable frequency drives to limit power consumption and water used during piloting operations is recycled through specially designed mobile settling dams to minimise water consumption.

Furthermore, Redpath Thonket has prioritised skills transfer by combining unskilled individuals from the local community with skilled and experienced team members, fostering growth and development. Plans are in place to introduce smaller raiseboring machines in 2024 to expedite operator training, further contributing to skills development in Ghana.

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https://www.redpathmining.com/en/regions/africa

NATIONAL & INTERNATIONAL ACTIVITIES 2024 8-9 February 2024 — SANCOT Symposium Cape Town, South Africa Contact: Gugu Charlie Tel: 011 538-0238 E-mail: gugu@saimm.co.za Website: http://www.saimm.co.za 12-13 March 2024 — GMG Kiruna Forum | Tomorrow’s Mining: Innovating to Improve the Way We Mine Contact: Camielah Jardine Website: https://gmggroup.org/gmg-kiruna-forumtomorrows-mining-innovating-to-improve-the-way-wemine/ 12-14 March 2024 — Southern African Pyrometallurgy 2024 International Conference Sustainable Pyrometallurgy - Surviving Today and Thriving Tomorrow Misty Hills Conference Centre, Johannesburg, South Africa Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 19-25 April 2024 — World Tunnel Congress 2024 Shenzhen, China Website: https://www.wtc2024.cn/ 21-23 May 2024 — The 11TH World Conference of Sampling and Blending 2024 Hybrid Conference Misty Hills Conference Centre, Johannesburg, South Africa Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 27-31 May 2024 — Nickel-Cobalt-Copper LithiumBattery Technology-REE 2024 Conference and Exhibition Perth, Australia Website: https://www.altamet.com.au/conferences/alta2024/

18-20 June 2024 — Southern African Rare Earths 2ND International Conference 2024 Swakopmund Hotel and Entertainment Centre, Swakopmund, Namibia Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 3-5 July 2024 — 5TH School on Manganese Ferroalloy Production Decarbonization of the Manganese Ferroalloy Industry Boardwalk ICC, Gqeberha, Eastern Cape, South Africa Contact: Gugu Charlie Tel: 011 538-0238 E-mail: gugu@saimm.co.za Website: http://www.saimm.co.za 5-8 August 2024 — 2nd Battery Materials Conference 2024 The Arena, Emnotweni Casino, Mbombela, Mpumalanga Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 21-22 August 2024 — Mine Closure Conference 2024 Johannesburg, South Africa Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 1-3 September 2024 — Hydrometallurgy Conference 2024 Hydrometallurgy for the Future Hazendal Wine Estate, Stellenbosch, Western Cape, South Africa Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za

11-13 June 2024 — 15TH International Conference on Industrial Applications of Computational Fluid Dynamics Trondhedim, Norway E-mail: Jan.E.Olsen@sintef.no Website: https://www.sintef.no/projectweb/cfd2024/

The Journal of the Southern African Institute of Mining and Metallurgy

VOLUME 123

DECEMBER 2023

ix ◀

Company affiliates The following organizations have been admitted to the Institute as Company Affiliates 3M South Africa (Pty) Limited A and B Global Mining (Pty) Ltd acQuire Technology Solutions AECOM SA (Pty) Ltd AEL Mining Services Limited African Pegmatite (Pty) Ltd Air Liquide (Pty) Ltd Alexander Proudfoot Africa (Pty) Ltd Allied Furnace Consultants AMEC Foster Wheeler AMIRA International Africa (Pty) Ltd ANDRITZ Delkor(pty) Ltd Anglo Operations Proprietary Limited Anglogold Ashanti Ltd Anton Paar Southern Africa (Pty) Ltd Arcus Gibb (Pty) Ltd ASPASA Aurecon South Africa (Pty) Ltd Aveng Engineering Aveng Mining Shafts and Underground Axiom Chemlab Supplies (Pty) Ltd Axis House Pty Ltd Bafokeng Rasimone Platinum Mine Barloworld Equipment -Mining BASF Holdings SA (Pty) Ltd BCL Limited Becker Mining (Pty) Ltd BedRock Mining Support Pty Ltd BHP Billiton Energy Coal SA Ltd Blue Cube Systems (Pty) Ltd Bluhm Burton Engineering Pty Ltd Bond Equipment (Pty) Ltd Bouygues Travaux Publics Caledonia Mining South Africa Plc Castle Lead Works CDM Group CGG Services SA Coalmin Process Technologies CC Concor Opencast Mining Concor Technicrete Council for Geoscience Library CRONIMET Mining Processing SA Pty Ltd CSIR Natural Resources and the Environment (NRE) Data Mine SA DDP Specialty Products South Africa (Pty) Ltd Digby Wells and Associates DRA Mineral Projects (Pty) Ltd DTP Mining - Bouygues Construction Duraset ▶ x

DECEMBER 2023

EHL Consulting Engineers (Pty) Ltd Elbroc Mining Products (Pty) Ltd eThekwini Municipality Ex Mente Technologies (Pty) Ltd Expectra 2004 (Pty) Ltd Exxaro Coal (Pty) Ltd Exxaro Resources Limited Filtaquip (Pty) Ltd FLSmidth Minerals (Pty) Ltd Fluor Daniel SA ( Pty) Ltd Franki Africa (Pty) Ltd-JHB Fraser Alexander (Pty) Ltd G H H Mining Machines (Pty) Ltd Geobrugg Southern Africa (Pty) Ltd Glencore Gravitas Minerals (Pty) Ltd Hall Core Drilling (Pty) Ltd Hatch (Pty) Ltd Herrenknecht AG HPE Hydro Power Equipment (Pty) Ltd Huawei Technologies Africa (Pty) Ltd Immersive Technologies IMS Engineering (Pty) Ltd Ingwenya Mineral Processing (Pty) Ltd Ivanhoe Mines SA Kudumane Manganese Resources Leica Geosystems (Pty) Ltd Loesche South Africa (Pty) Ltd Longyear South Africa (Pty) Ltd Lull Storm Trading (Pty) Ltd Maccaferri SA (Pty) Ltd Magnetech (Pty) Ltd Magotteaux (Pty) Ltd Malvern Panalytical (Pty) Ltd Maptek (Pty) Ltd Maxam Dantex (Pty) Ltd MCC Contracts (Pty) Ltd MD Mineral Technologies SA (Pty) Ltd MDM Technical Africa (Pty) Ltd Metalock Engineering RSA (Pty)Ltd Metorex Limited Metso Minerals (South Africa) Pty Ltd Micromine Africa (Pty) Ltd MineARC South Africa (Pty) Ltd Minerals Council of South Africa Minerals Operations Executive (Pty) Ltd MineRP Holding (Pty) Ltd Mining Projections Concepts Mintek MIP Process Technologies (Pty) Limited MLB Investment CC VOLUME 123

Modular Mining Systems Africa (Pty) Ltd MSA Group (Pty) Ltd Multotec (Pty) Ltd Murray and Roberts Cementation Nalco Africa (Pty) Ltd Namakwa Sands(Pty) Ltd Ncamiso Trading (Pty) Ltd Northam Platinum Ltd - Zondereinde Opermin Operational Excellence OPTRON (Pty) Ltd Paterson & Cooke Consulting Engineers (Pty) Ltd Perkinelmer Polysius A Division of Thyssenkrupp Industrial Sol Precious Metals Refiners Rams Mining Technologies Rand Refinery Limited Redpath Mining (South Africa) (Pty) Ltd Rocbolt Technologies Rosond (Pty) Ltd Royal Bafokeng Platinum Roytec Global (Pty) Ltd RungePincockMinarco Limited Rustenburg Platinum Mines Limited Salene Mining (Pty) Ltd Sandvik Mining and Construction Delmas (Pty) Ltd Sandvik Mining and Construction RSA(Pty) Ltd SANIRE Schauenburg (Pty) Ltd Sebilo Resources (Pty) Ltd SENET (Pty) Ltd Senmin International (Pty) Ltd SISA Inspection (Pty) Ltd Smec South Africa Sound Mining Solution (Pty) Ltd SRK Consulting SA (Pty) Ltd Time Mining and Processing (Pty) Ltd Timrite Pty Ltd Tomra (Pty) Ltd Trace Element Analysis Laboratory Traka Africa (Pty) Ltd Trans-Caledon Tunnel Authority Administarator Ukwazi Mining Solutions (Pty) Ltd Umgeni Water Webber Wentzel Weir Minerals Africa Welding Alloys South Africa Worley

The Journal of the Southern African Institute of Mining and Metallurgy

WCSB11 THE 11TH WORLD CONFERENCE OF SAMPLING AND BLENDING

21-23 MAY 2024 HYBRID CONFERENCE

MISTY HILLS CONFERENCE CENTRE MULDERSDRIFT, JOHANNESBURG

SOUTH AFRICA

The World Conference on Sampling and Blending (WCSB), to be held in South Africa, 21-23 May 2024, is the eleventh such conference to promote the Theory of Sampling (TOS). The WCSB conference provide a meeting place for professionals interested in sampling theory, practice, experience, applications, and standards.

The Conference will provide understanding and insights for academics, manufacturers, engineering firms and practitioners aiming to achieve representative sampling.

TOS effectively identifies the source of sampling variability and provides valuable solutions for minimising each source of sampling uncertainty.

The aim of WCSB11 is to invite and encourage the diverse international sampling community to adopt and disseminate the concepts and ideas for a standardized approach to sampling embodied in the TOS. The Conference will also offer a forum for fruitful discussions between statisticians committed to ‘Measurement of Uncertainty’ (MU) and proponents of the TOS by offering a unifying foundation for development of better and more general standards. While the Theory of Sampling had its historical origins in the mining industry, today it also applies to sampling of a broad range of bulk materials, minerals, agricultural raw materials and products, the food, feed, and pharmaceutical industries, as well as sampling for environmental applications. WCSB11 is an event of global significance that aims to improve sampling practices in all sectors of science, technology, and industry, for consultants, managers, sampling and quality control staff, researchers, engineers, and manufacturers operating in many industries, The opportunity to meet,

exchange ideas, and share practical experiences will be a significant benefit for attendees.

The proceedings of the Conference will be published in electronic format with a strict adherence to an editorial and peer review policy that will allow academics to attract the publication subsidy for published academic research. Adherence to these standards will enable the wider dissemination of the TOS in international scientific, technological, and industrial sectors. WCSBs have helped to promote the teaching of TOS at universities, with postgraduate courses in TOS being taught in some countries. The Pierre Gy Gold Medal is awarded at each WCSB conference to individuals who have been most effective and successful around the world in disseminating and promoting TOS. This achievement will again be celebrated at WCSB11. The medallists are a unified body of champions capable of teaching, promoting, and researching aspects of sampling theory and practice, supporting the efforts of original equipment manufacturers to uphold TOS rules of sample representativeness. WCSB conferences aim to develop a unified vision for specific quality control protocols for sampling and blending activities, with participation and collaboration of industry professionals.

The theme of sustainable science, technology, and industry introduced at WCSB10 is upheld, with emphasis on the UN World Development Goals number 9 and 12, addressing sustainable industry, innovation, and infrastructure, and responsible production and consumption. Topics around societal, industrial, and environmental aspects of particulate sampling in mining,

FOR FURTHER INFORMATION, CONTACT: Camielah Jardine, Head of Conferencing

E-mail: camielah@saimm.co.za Tel: +27 11 538-0237, Web: www.saimm.co.za

SOUTHERN AFRICAN

RARE EARTHS

2ND INTERNATIONAL CONFERENCE 2024

18 JUNE 2024 - WORKSHOP 19-20 JUNE 2024 - CONFERENCE

SWAKOPMUND HOTEL AND ENTERTAINMENT CENTRE, SWAKOPMUND, NAMIBIA

Global Impact and Sustainable Supply ABOUT THE CONFERENCE Due to their unique chemical, catalytic, electrical, magnetic, and optical properties, rare earth metals are critical materials in hightechnology applications with irreplaceable application in areas such as medical devices, electric vehicles, energy-efficient lighting, etc. Recent geopolitical instability/challenges, the supply security of REEs is of global concern. Since the global supply chain is currently concentrated in limited jurisdictions such as China and Australia, the need to diversify the supply of these critical materials creates significant opportunities for African countries. The African

continent is endowed with some of the world’s largest REE deposits, and as such, it can play a vital role in meeting the growing demand for these critical materials.

However, in order to maximize value, there is need to establish and develop capabilities along the value chain. The conference provides a platform for indepth discussions on the global role of African REE deposits and is designed to stimulate debate on opportunities to grow the African rare earths industry.

Overall, the conference seeks to explore the continent’s role in shaping the future of the REEs industry.

ES AND SPONSORSHIP OPPORTUNITILE. AB EXHIBITION SPACE AVAIL FOR FURTHER INFORMATION, CONTACT: Camielah Jardine, Head of Conferencing

E-mail: camielah@saimm.co.za Tel: +27 11 834-1273/7 Web: www.saimm.co.za

OBJECTIVES

The second International Conference on Southern African Rare Earths 2024 will focus on the global impact of African REE deposits and their role in the sustainable supply of these critical materials. The conference will discuss in detail the latest developments in the industry, and explores the opportunities and challenges to the optimization of the African REEs value chain. The conference focuses on the production of rare earth metals, with specific emphasis on geology, exploration, beneficiation, separation and refining, applications, policies, environmental issues including health and safety aspects, new technological developments, market opportunities, and future outlook for the REEs industry.