VOLUME 116 NO. 4 APRIL 2016

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For more information contact us Tel no. +27 (0)10 210 4000 • flsm-za@flsmidth.com • www.flsmidth.com    D.G. Maxwell (1961–1962) J.P. Hugo (1972–1973) (1973–1974) J.R. Dixon (1998–1999) M.H. Rogers (1999–2000) L.A. Cramer (2000–2001) 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.A. Cruise (1994–1995) D.A.J. Ross-Watt (1995–1996) N.A. Barcza (1996–1997) R.D. Beck (1991–1992) J.P. Hoffman (1992–1993) C.E. Fivaz (1988–1989) O.K.H. Steffen (1989–1990) J.D. Austin (1984–1985) H.E. James (1985–1986) H. Wagner (1986–1987) G.Y. Nisbet (1981–1982) A.N. Brown (1982–1983) J.N. van der Merwe (2011–2012) G.L. Smith (2012–2013) M. Dworzanowski (2013–2014) J.L. Porter (2014–2015) * Mohring (1997–1998) R.P. * H. Scott-Russell (1993–1994) * H.G. Mosenthal (1990–1991) * (1987–1988) Alberts B.C. * King (1983–1984) R.P. * Simon (1957–1958) H. * M. Barcza (1958–1959) * R.J. Adamson (1959–1960) * W.S. Findlay (1960–1961) * J. de V. Lambrechts (1962–1963) * J.F. Reid (1963–1964) * Jamieson (1964–1965) D.M. * H.E. Cross (1965–1966) * Gordon Jones (1966–1967) D. * 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) * P.W.J. van Rensburg * R.P. Plewman (1974–1975) * R.E.(1975–1976) Robinson * Salamon (1976–1977) M.D.G. * P.A. Von Wielligh (1977–1978) *Atmore (1978–1979) M.G. * D.A. Viljoen (1979–1980) * P.R. Jochens (1980–1981) * Douglas (2001–2002) A.A.B.        ! !($() ' $)#&"'(" Van Hulsteyns Attorneys #&%!(" Messrs R.H. Kitching '('%$(&'" The Southern African Institute of Mining and Metallurgy Fifth Floor, Chamber of Mines Building 5 Hollard Street, Johannesburg 2001 • P.O. Box 61127, Marshalltown 2107 Telephone (011) 834-1273/7 • Fax (011) 838-5923 or (011) 833-8156 E-mail: [email protected] (1935–1936) )   *Deceased * Bettel (1894–1895) W. * Crosse (1895–1896) A.F. * W.R. Feldtmann (1896–1897) * Butters (1897–1898) C. * J. Loevy (1898–1899) * Williams (1899–1903) J.R. * 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) * (1912–1913) Dowling W.R. * A.(1913–1914) Richardson * Stanley (1914–1915) G.H. * J.E. Thomas (1915–1916) * J.A. Wilkinson (1916–1917) * Hildick-Smith (1917–1918) G. * H.S. Meyer (1918–1919) * J. Gray (1919–1920) * J. Chilton (1920–1921) * (1921–1922) F. Wartenweiler * G.A. (1922–1923) Watermeyer * Watson (1923–1924) F.W. * (1924–1925) C.J. Gray * H.A. White (1925–1926) * Adam (1926–1927) H.R. * Kotze (1927–1928) Sir Robert * J.A.(1928–1929) Woodburn * T.K. Prentice (1936–1937) * R.S.G. Stokes (1937–1938) * P.E. Hall (1938–1939) * E.H.A. Joseph (1939–1940) * H. Pirow (1929–1930) * J. Henderson (1930–1931) * King (1931–1932) A. * (1932–1933) Nimmo-Dewar V. * Lategan (1933–1934) P.N. * (1934–1935) E.C. Ranson * R.A. Flugge-De-Smidt * J.H. Dobson (1940–1941) * Theo Meyer (1941–1942) *V. Muller (1942–1943) John * C. Biccard Jeppe (1943–1944) * P.J. Louis Bok (1944–1945) * J.T. McIntyre (1945–1946) * M. Falcon (1946–1947) * Clemens (1947–1948) A. * F.G. Hill (1948–1949) * Jackson (1949–1950) O.A.E. * 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)    L.E. Dimbungu S. Maleba I. Ashmole N.M. Namate C.A. van Wyk P. Bredell A. Mainza D. Muma S. Ndiyamba C.W. Mienie H. Wagner S.D. Williams I.J. Corrans, R.J. Dippenaar, A. Croll, C. Workman-Davies J.J.L. Cilliers, N.A. Barcza J-M.M. Rendu, P.C. Pistorius ii  !   !!       !     !!    Z. Botha V.G. Duke I.J. GeldenhuysM.F. Handley W.C. Joughin M. Motuku D.D. Munro M.H. Solomon G. Njowa A.G. Smith J.D. Steenkamp M.R. Tlala D. Tudor D.J. van Niekerk J.L. Porter     ! ! !! !!   !! ! ! !!   !!      ! !!  Mosebenzi Zwane Minister of Mineral Resources, Rob Davies South Africa Minister of Trade and Industry, South Africa Minister of Science and Technology,     !!  Mike Teke of South Africa President, Chamber of Mines  )  ) ) ))  )  Northern Cape Western Cape Zambia Zimbabwe Zululand Australia: Austria: Botswana: United Kingdom: USA: DRC Johannesburg Namibia Botswana  !! !     N.A. BarczaR.D. BeckJ.R. DixonM. DworzanowskiF.M.G. Egerton H.E. James G.V.R. Landman M.H. Rogers J.C. Ngoma G.L. Smith S.J. Ramokgopa W.H. van Niekerk C. Musingwini S. Ndlovu A.S. Macfarlane C. Musingwini R.T. Jones

The Southern African Institute of Mining and Metallurgy Institute of Mining African The Southern #&%!(&$)!$(# R.D. Beck J. Beukes P. den Hoed M. Dworzanowski B. Genc M.F. Handley VOLUME 116 NO. 4 APRIL 2016 R.T. Jones W.C. Joughin J.A. Luckmann C. Musingwini J.H. Potgieter T.R. Stacey D.R. Vogt Contents #&%!(&$)! "%$ % Journal Comment—A Council for our Youth D. Tudor by V. Duke...... iv–v '"'%)$ #)&"'#) Obituary—Richard Peter Mohring The Southern African Institute of by J.A. Cruise ...... vi Mining and Metallurgy P.O. Box 61127 President’s Corner %THICS Marshalltown 2107 by R.T. Jones ...... vii Telephone (011) 834-1273/7 Fax (011) 838-5923 E-mail: [email protected] STUDENT EDITION — MINING (& %'#)) Camera Press, Johannesburg Improving the ventilation system at Rosh Pinah zinc mine by E. Develo, M. Pillalamarry, and E. Garab ...... 301 #'(%&"& )'('"' %$%&' Barbara Spence Sub-standard practices: effects on safety performance in South African gold mines Avenue Advertising by G. Kleyn and J.J.L. du Plessis ...... 307 Telephone (011) 463-7940 E-mail: [email protected] A critical investigation into tyre life on an iron ore haulage system The Secretariat by G.C. Lindeque ...... 317 The Southern African Institute of Mining and Metallurgy Review of support systems used in poor ground conditions in platinum room and pillar ISSN 2225-6253 (print) mining: a Zimbabwean case study ISSN 2411-9717 (online) by T. Chikande and T. Zvarivadza ...... 323

STUDENT EDITION — METALLURGY

THE INSTITUTE, AS A BODY, IS NOT RESPONSIBLE FOR THE Slurry abrasion of WC-4wt%Ni cold-sprayed coatings in synthetic minewater STATEMENTS AND OPINIONS by N.B.S. Magagula, N. Sacks, and I. Botef ...... 333 ADVANCED IN ANY OF ITS PUBLICATIONS. Matte – tap-hole clay – refractory brick interaction in a PGM smelter Copyright© 1978 by The Southern African Institute of Mining and Metallurgy. All rights by J. Du Toit, R.D. Cromarty, and A.M. Garbers-Craig ...... 339 reserved. Multiple copying of the contents of this publication or parts thereof without permission is in breach of copyright, but Separation of kimberlite from waste rocks using sensor-based sorting at permission is hereby given for the copying of titles and abstracts of papers and names of Cullinan Diamond Mine authors. Permission to copy illustrations and short extracts from the text of individual by T. Mahlangu, N. Moemise, M.M. Ramakokovhu, P.A. Olubambi, and M.B. Shongwe...... 343 contributions is usually given upon written application to the Institute, provided that the source (and where appropriate, the copyright) An evaluation of the thermal fatigue performance of three alloys for casting is acknowledged. Apart from any fair dealing for the purposes of review or criticism under mould applications The Copyright Act no. 98, 1978, Section 12, of the Republic of South Africa, a single copy of by V. van der Merwe and C.W. Siyasiya...... 349 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 The effect of particle size on the rate and depth of moisture evaporation a retrieval system, or transmitted in any form or by any means without the prior permission of from coal stockpiles the publishers. Multiple copying of the contents of the publication without by *DE'OEDE "-ULLER Q.P. Campbell, M. le Roux, ANDC.B. Espag de Klerk...... 353 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 VOLU ME 11 6 NO. 4 APRIL 2016 paid through the Copyright Clearance Center, R. Dimitrakopoulos, McGill University, Canada Inc., Operations Center, P.O. Box 765, Schenectady, New York 12301, U.S.A. This D. Dreisinger, University of British Columbia, Canada consent does not extend to other kinds of E. Esterhuizen, NIOSH Research Organization, USA copying, such as copying for general H. Mitri, McGill University, Canada distribution, for advertising or promotional purposes, for creating new collective works, or M.J. Nicol, Murdoch University, Australia for resale. E. Topal, Curtin University, Australia

            iii    Career ’ event to remind In August 2013, our students used a ‘ In August 2013, our The students complained about uncertainty This forced Council to go back and question was A Career Guidance and Education Committee Subsequent engagements with undergraduates and Development in the Minerals Industry Development in the Minerals the main objective of the us of their plight. Ironically, a career path’, advising event was on ‘mapping in their first five years of students on what to expect them that they would employment, and reassuring training in their chosen careers. receive the necessary the regarding career prospects in the mining industry, with need for on-the-job training for undergraduates the lack effective mentoring by suitable mentors, and mine for of experiential training opportunities on a new graduates. actually whether the Institute, as a technical society, recently meets the needs of all members, even those graduated or still at university. It was acknowledged that our younger members represent a different success or demographic – one on which the long-term This failure of the Institute will eventually depend. focus resulted in agreement on a need for a renewed on the ‘youth’ amongst our current and potential and that by future mining and metallurgical engineers, all of our developing them from within the SAIMM, youth within the industry would benefit. formed some time ago by the SAIMM. It successfully industry encouraged new students to enter the mining by focusing on the building of a mining and metallurgy exhibition at the Sci-Bono Exhibition Centre and by attendance at various school science festivals in South Africa. It seemed logical to widen the focus of this committee to include the needs of our undergraduates. This plan did not succeed. There was very little support from industry, and it also became clear that our youth have a very different viewpoint to that of the majority of the members of the committee, and even Council, when it comes to debating the opportunities or threats to their future careers. We were trying to make decisions for younger people without knowing what their ‘real’ requirements were. At a meeting in July 2014 the question was raised whether we should rather be looking at how to enable our youth to help themselves. young postgraduates at various academic institutions        A Council for our Youth A Council for our Journal Comment Journal , and the quality of Journal   

embership of the Southern African Institute embership of the Southern (SAIMM) includes of Mining and Metallurgy students and new mining and metallurgical Among these young people are those who have Among these young

However, these undergraduates also require a duty Responsibilities around safety, health, and After recently checking, I found that 42 years is For me, this situation was somewhat expected. M these submissions leads me to believe that we are on these submissions leads me to believe that of the the right track in terms of the academic part future training that we provide in developing our mining and metallurgical engineers. need an vocational training, and after graduation, sufficiently to be allowed to register as a professional failing to engineer with ECSA. In this regard, we are teach our youngsters properly. of care for the environment while also regularly targets as transformation and sustainable development graduates from various universities and colleges in the graduates from various southern African region. papers similar to the either authored or co-authored ones in this edition of the opportunity to develop their knowledge and experience opportunity to develop their knowledge and of the time engaging with communities, demand much to meet and attention of our managers, who need well as production targets. Yes, some mining students or companies are still sponsoring individual the employing certain graduates as they enter for our workplace, but the dearth of opportunities the young people to develop themselves under mentorship of experienced professionals and practitioners is huge. now the average age of a SAIMM member who is also registered as a professional engineer. Should this number not be far lower if we are to effectively compete in a fast-changing mineral resource industry where much of the endowment of Southern Africa sits? While working on the mines during the early 1990s I heard the comment, ‘why train when it is probably more cost-effective to simply buy in the skills as and when needed?’ This mindset coincided with a period when South Africa’s large mining houses started unbundling, with the consequence that opportunities for young people to find pre- and postgraduate employment started to dwindle. iv Journal Comment (continued)

resulted in overwhelming agreement on the merits of Tshepo Mmola, Chairman of the YPC, talks of six such an approach. So at the same time, volunteers focus areas covered with the help of three Working were nominated from each of the institutions and on Groups (WGs): 12 September 2014 the SAIMM held a ‘Workshop on One WG for education to represent the interests of Youth Development’ at Sci-Bono to map out a way primarily pre-graduates in basic and higher forward. The outcome exceeded all expectations, with education on matters of career guidance, academic development, and life skills the formation of a Young Professionals Council (YPC), The second WG for career guidance to represent under the umbrella of the SAIMM Council, to the interests of primarily postgraduates in mining effectively replace the long-serving but outdated and metallurgy on matters of training, Career Guidance and Education Committee. professional development, and life skills The YPC’s main focus is to engage with the mining The third, or Enterprise, WG to concentrate on various industry initiatives to serve the interests industry across the SADEC region to assist in finding of our young professionals support for younger members of the Institute. Some It is my hope that senior executives, mine members of the previous committee have stayed on as managers, retired professionals, and entrepreneurs in observers to advise, guide, and assist wherever the mining industry will support this initiative. I know possible in this regard. The YPC is also well positioned that these young people can and, if they are helped, to provide students with a better understanding of: will positively impact the future of our industry. The various career paths that a mining and metallurgy qualification affords them For more information contact the YPC Secretary, The training and registrations that they will Vulani Maseko at [email protected] require early on in their careers The personal development plans or initiatives that graduates can undertake to differentiate themselves in the marketplace. The newly elected members of the YPC know that they can contribute significantly towards appropriate transformation, meaningful succession planning, and a solid portfolio of skills from the next generation. V. Duke

            v    the J.A. Cruise inter alia ger of Ingwe Coal A the development of the  conducting coal-bed methane         Rick was born in Johannesburg in 1947 and died in Johannesburg in March in 1947 and died in Johannesburg Rick was born in Johannesburg Rick started his career with On graduation as a mining engineer in 1972, Richard Peter Mohring It is with great sadness that we announce the passing of Richard Peter Mohring, that we announce the passing of Richard It is with great sadness as ‘Rick’. fondly known by us all education struggle with cancer. He received his formative 2016 after a two-year was also in Johannesburg. Therefore, Rick at King Edward VII School, been during dumps from an early age and it must have surrounded by mine school he crept into his blood, because on leaving these years that mining degree in of the Witwatersrand to read for a Bachelor’s enrolled at the University Mining Engineering. mine, where he progressed Rand Mines on Durban Roodepoort Deep gold Manager. In 1975, Rick was through the ranks to that of Underground where he began his illustrious transferred to the Rand Mines coal division,    Apart from his direct work as a professional mining engineer, Rick was associated with the Engineering Apart from his direct work as a professional He was not only a member of many of ECSA university Rick was also involved with tertiary education. Africa, the Fossil Rick served with many industry associations, including the Chamber of Mines of South been prolific. He With the Southern African Institute of Mining and Metallurgy, Rick’s involvement has Life Fellow of the Rick was the President of the SAIMM for the 1997/1998 term and was an Honorary Rick, we in the Institute will miss you and remember you fondly. Rick was involved with many achievements in the South African coal mining industry, Rick was involved with many achievements African coal mining industry to the inclusion of Black entrepreneurs having a major stake in the industry. African coal mining industry to the inclusion Corporation and then the Chief Executive Officer of NewCoal, an initiative set up by Anglo Coal and Ingwe to Corporation and then the Chief Executive in the coal mining industry. After an 18-month process the create a Black Economic Empowerment entity formed with Rick as the Deputy Chief Executive Officer to largest BEE coal company, Eysizwe Coal, was has played a major role in the transformation of the South oversee a smooth transformation. Thus, Rick drainage tests (the precursor of ‘fracking’), and combining a large export colliery (Middelburg) with an drainage tests (the precursor of ‘fracking’), time he rose to be the Senior Operations Man Eskom supply colliery (Duhva). During this Council of South Africa for many years. He served as a Council Member from 1992 to 2008 and as Chairman Council of South Africa for many years. He ECSA internationally in the negotiation for ECSA’s acceptance in of various ECSA committees. He represented Mobility Forum, which gave rise to the recognition of registered the Washington Accord and the Engineers engineers throughout the world. for mining accreditation teams over the years, but also a member of the Industry Advisory Councils engineering at both the University of Pretoria and the University of the Witwatersrand. Energy Agency, where Fuel Foundation, the International Committee for Coal Research, and the International 2003. he represented South Africa on the IEA Coal Industry Advisory Board from 2000 to – TPC Mining, was a Member from 1971 and a Council Member since 1988. He served on many committees of the SAIMM Publications, Membership, Banquet, and Scrutineers among others, and was a trustee Scholarship Fund. presented to Rick at the Institute. The Institute’s highest honour, the Brigadier Stokes Memorial Award, was 115th AGM in August 2012. Khutala and Majuba collieries utilizing high-capacity continuous miners Khutala and Majuba collieries utilizing high-capacity design and running of Middelburg Mine, a 10 million ton per annum coal mine design and running of Middelburg Mine, a career in coal mining. He underwenr a meteoric rise in the coal division – in 1981 at the age of 34, Rick was career in coal mining. He underwenr a meteoric Exploration Company and in 1984 he was appointed Managing appointed General Manager of Welgedacht Director of Rand Coal. vi President’s Ethics

Corner ‘Never let your sense of morals get in the way of doing what's right’ – Isaac Asimov

ne of the characteristic features of a professional society is that its members are governed by a code of professional ethics. The term ‘ethics’ is derived from the Greek word ethos, meaning ‘character’. Ethics and Omorals both relate to ‘right’ and ‘wrong’ conduct. ‘Morals’ often refers to an individual’s own principles or habits that provide a personal compass regarding right and wrong conduct. ‘Ethics’ refers to the rules of conduct that are provided by an external source within a particular context, and can be considered a social system or a framework for acceptable behaviour. An often-quoted example in the field of law illustrates how professional ethics might apparently conflict with personal morals. A lawyer’s morals may tell him/her that murder is reprehensible and that murderers should be punished, but professional ethics require a lawyer to defend a client to the best of his/her abilities, even if the client is guilty. There are reasons for this ethical requirement, as it helps to build a fair society. Ethics is intended to be practical, and is conceived as shared principles promoting fairness in social and business interactions. However, ethical decisions should recognize the context within which they are set, and must recognize that duties can be ranked in a hierarchy (for example, to stop at an accident to render assistance takes precedence over the promise of meeting for lunch). ‘The word “good” has many meanings. For example, if a man were to shoot his grandmother at a range of five hundred yards, I should call him a good shot, but not necessarily a good man.’ – G.K. Chesterton ‘Right is right, and wrong is wrong, and a body ain’t got no business doing wrong when he ain’t ignorant and knows better.’ – Mark Twain, The Adventures of Huckleberry Finn In South African society in 2016, we are acutely aware of the prevalence of dishonesty and corrupt business dealings around us. The need for integrity in business and politics has never been greater. I would like to live in a world where we all work towards the welfare, safety, and health of all people, and care for our environment. ‘Educating the mind without educating the heart is no education at all.’ – Aristotle ‘Ethics are more important than laws.’ – Wynton Marsalis When people sign up for membership of a professional society such as the SAIMM, it is expected that they will always conduct themselves in a professional manner, and act with integrity and sincerity in all of their work. The SAIMM’s Code of Professional Conduct appears as By-law H in the ‘Constitution and By-Laws’ document in the ‘About SAIMM’ section of our website, and is worth reading as a reminder about our professional obligations. In essence, the code of professional conduct requires Members to eschew fraudulent or dishonest practices, not to conceal unethical acts, and to avoid working with others who behave unprofessionally. A professional should work to the highest possible standards, stay up-to-date with their field, and should undertake only work that he or she is trained for. Conflicts of interest should be avoided, and financial dealings should be open and fair, with no bribery. Honesty and confidentiality are expected. Professional behaviour involves no misrepresentation in advertising or unfair criticism of the work of others. Any transgressions of this code are dealt with in terms of our ‘Complaints and Disciplinary Procedure’ (also on the website) by the Complaints Committee, which gathers facts, and screens complaints to ensure that they are neither frivolous nor malicious, before assessment by the Ethics Committee. The assessment is handled in a firm, fair, and confidential way, and can result in a warning, a reprimand, a requirement for further training, or even suspension, expulsion, or referral to statutory bodies. ‘Live so that when your children think of fairness and integrity, they think of you.’ – H. Jackson Brown, Jr.

R.T. Jones President, SAIMM

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Copyright © 2015, Weir Slurry Group, Inc.. All rights reserved. WARMAN is a registered trademark of Weir Minerals Australia Ltd. PAPERS IN THIS EDITION

Papers — Student Edition–Mining

Improving the ventilation system at Rosh Pinah zinc mine by E. Develo, M. Pillalamarry, and E. Garab ...... 301 A number of options were considered In order to improve the ventilation conditions and these were simulated using an appropriate software package. A workable solution was proposed that could improve the overall ventilation in the mine and lead to significant savings in the cost of providing the ventilation.

Sub-standard practices: effects on safety performance in South African gold mines by G. Kleyn and J.J.L. du Plessis ...... 307 The purpose of this investigation was to establish the root causes of sub-standard practises and the consequent effect on safety performance at an underground production operation of a gold mine in the Free State. The established methods of addressing sub-standard practices and improving safety performance were found to discourage employees from performing work safely and according to procedure.

A critical investigation into tyre life on an iron ore haulage system by G.C. Lindeque...... 317 This investigation compared ‘Best PractiCe’ to the current tyre management strategy at the mine to determine the elements that could be improved. A new Tyre Management Strategy was formulated as a Step-by-Step guide on how to implement the proposed changes.

Review of support systems used in poor ground conditions in platinum room and pillar mining: a Zimbabwean case study by T. Chikande and T. Zvarivadza ...... 323 The results from this study showed that the current support system and mining practices in bad ground areas need to be adjusted to improve safety and productivity. A number of recommendations were made to change the explosive, pillar design, and roof bolting practice.

These papers will be available on the SAIMM website http://www.saimm.co.za Papers — Student Edition–Metallurgy

Slurry abrasion of WC-4wt%Ni cold-sprayed coatings in synthetic minewater by N.B.S. Magagula, N. Sacks, and I. Botef ...... 333 A number of tests were conducted to assess the wear behaviour of mild steel that had been subjected to a low pressure cold gas dynamic spraying to produce a coating deposit of tungsten carbide containing a known amount of nickel.

Matte – tap-hole clay – refractory brick interaction in a PGM smelter by J. Du Toit, R.D. Cromarty, and A.M. Garbers-Craig...... 339 This laboratory scale investigation examined the ability of the tap-hole clay to form a protective layer on the brick which could limit the matte penetration into the tap-hole brick.

Separation of kimberlite from waste rocks using sensor-based sorting at Cullinan Diamond Mine by T. Mahlangu, N. Moemise, M.M. Ramakokovhu, P.A. Olubambi, and M.B. Shongwe ...... 343 This paper describes the initial test work that led to the decision to conduct a pilot scale study. The mineralogical characterization of the feed and product streams, to validate the sorting criteria and the operational data obtained during the pilot plant campaign is shown. An evaluation of the thermal fatigue performance of three alloys for casting mould applications by V. van der Merwe and C.W. Siyasiya ...... 349 The aim of the project was to find an alternative alloy that would outperform the current low alloy cast steel that was experiencing premature thermal fatigue failure of the casting moulds that are used in catalyst production.

The effect of particle size on the rate and depth of moisture evaporation from coal stockpiles by *DE'OEDE "-ULLER Q.P. Campbell, M. le Roux, ANDC.B. Espag de Klerk ...... . .353 The objective of this project was to determine the effect of coal bed particle size on the rate of evaporation as well as the depth to which evaporation extends in a coal stockpile. http://dx.doi.org/10.17159/2411-9717/2016/v116n4a1 Improving the ventilation system at Rosh Pinah zinc mine by E. Develo*, M. Pillalamarry*, and E. Garab† Paper written on project work carried out in partial fulfilment of B. Eng. (Mining Engineering)

drastically and resulted in increasing demands being imposed on the main fan in order to ()&-& supply an adequate air flow. This process also Recent geological exploration at Rosh Pinah mine revealed that the mine’s created more leakage paths between the fan major production is shifting towards the western orefield, which will and the working areas, which has caused the increase the demand for air flow to be supplied to this area. A snapshot of the ventilation survey carried out in December 2014 at the western orefield air to short-circuit before it can reach the drill drive B (WOF-DDRB) showed that the air flow was well below the faces. Consequently, a much larger quantity of required standards. In order to improve the existing conditions, possible air has to be circulated by the fan so that the options were considered and simulated using Ventsim™ software. stipulated quantity reaches the face, which The best option found was to replace the existing western orefield fans increases operating costs (Singh et al., 2004). with the larger fans from the inactive southern orefield workings, to An investigation was carried out to increase the air flow in the DDRB district. Simulation showed that as much optimize the existing ventilation system along as 20 m3/s of air can be received at the working faces of WOF 30, the WOF at Rosh Pinah, in order to 3 compared to the previously received amount of 1.37 m /s. The economic accommodate the growing ventilation demand. analysis indicated that the above option can reduce the ventilation cost by This entailed an evaluation of all the feasible N$1.9 million annually. It was also noticed that after implementing this alternatives available to improve air flow to the option together with other projects, the ventilation conditions in the mine were greatly improved and currently give no cause for concern. working faces (Mukherjee et al., 1982). The current distributions of air flow, pressure, 2.)*!& leakages, and air quality throughout the main mine ventilation, simulation. flow paths of the WOF were quantified by conducting a pressure-quantity survey. Survey data was used to identify ventilation ineffi- ciencies along the WOF drives and also to 1(+*)!'+-)( simulate the current ventilation network. A good mine ventilation system should be Finally, the ventilation network and regulators capable of providing adequate quantity and were modified in order to distribute sufficient quality of air to all working faces, and is fresh air at the working faces in the WOF with critical to the occupational health, safety, and minimum cost. Ventsim™ software was used comfort of underground employees (Luxbacher to simulate the ventilation network. and Ramani, 1977; Exikis and Kapageridis, 2006). No ventilation system can remain 0,#*)'(! adequate indefinitely; as the mine workings Rosh Pinah is an underground mine that are extended, the ventilation characteristics produces primarily zinc and lead. The mine is such as system pressures, air volumes, owned by Glencore and is located approxi- leakages, and airway resistances change mately 360 km southwest of Keetmanshoop in considerably. Continuous improvement of the Namibia. This underground operation is 420 m ventilation system is needed to ensure deep and uses sill-and-bench open stoping compliance with health and safety regulations methods. The mine workings are divided into (Lovejoy, 2010). It also ensures that the right quality and quantity of air is delivered to all the necessary areas at the lowest possible cost. This can be achieved by identifying inefficient airways and poorly ventilated areas in the mine and planning how best to upgrade them. * Department of Mining and Process Engineering, The latest geological exploration shows University of Science and Technology, Namibia, Windhoek. that the focus of production at Rosh Pinah † Rosh Pinah Zinc CORporation, Rosh Pinah, mine is shifting towards the western orefield Namibia. (WOF). As mining progressed, the working © The Southern African Institute of Mining and areas have advanced away from the main fans, Metallurgy, 2016. ISSN 2225-6253. Paper received which increased the resistance to air flow Mar. 2016.

         VOLUME 116    301 L Improving the ventilation system at Rosh Pinah zinc mine different sections according to the location of the orebodies, Access, C-mine entrance, and C5 tunnel. This simulation was which are termed the western, eastern, southern, and simply used to redirect the airflow through the WOF decline northern orefields. Figure 1 shows the layout of the mine by placing a curtain at the entrance to the northern orefield sections at Rosh Pinah. intake tunnel, since no mining is taking place at this location. Rosh Pinah practices very high safety and health A permanent stopping was also placed close to the Quick standards and the ventilation officers are required to conduct Access portals where the air moves towards the workshop daily ventilation surveys before the underground employees and is returned to the Quick Access through a stope. The enter a working area. If these areas do not meet the workshops are dormant and therefore ventilation is not ventilation standards, no personnel are allowed to enter that needed. After the simulation, the airflow distribution was particular area until the conditions are improved by the Rosh analysed. The location of the stopping along the WOF decline Pinah technical team. is indicated in Figure 3.

    3.(+-",+-)(/(.+)*/ Since production is shifting towards the WOF, more air flow The WOF has three major ventilation intakes, namely the will be required in this area. Two J67 Airtec Davidson fans C-mine adit, Quick Access, and the 390 BME adit. The are installed at the southern orefield stope, which will be eastern orefield has one major intake, the eastern orefield mined-out soon (Figure 4). The fan upgrade at WOF adit. The intake to the southern orefield is the C5 access includes removing the existing Howden D7 fans, which tunnel. Figure 2 illustrates the layout of the five main intakes supply 125 m3/s when operating in parallel, and replacing at Rosh Pinah, including the eastern orefield adit. The intake them with the two J67 Airtec Davidson fans from the SOF air is passed through the decline while the exhaust air is (Figure 4). returned to the atmosphere by an exhaust fan connected to a raise. Rosh Pinah has a complex ventilation network requiring efficient use and management of air control within the mine. The deeper sections of the mine are hot and humid, which necessitates the use of auxiliary ventilation. Rosh Pinah currently has five main exhaust fans installed at the top of the worked-out stopes, which are responsible for extracting the return air out of the stopes and to the atmosphere. Maintenance on the main fans is carried out once every three months by the mine mechanics, and once yearly on contract maintenance. The specifications and locations of these fans are detailed in Table I.

- '",+-)(/ )!."& The air flow requirement at the working faces was calculated $-#'*./ ,)'+/)%/)*.%-."!&/,+/)&/-(,/-(/ -(. according to the mine ventilation standards of Namibia (Ministry of Mines and Energy, 1992). The figure includes the requirements for machinery as well as personnel working at the face. Prior to the simulation, the current ventilation model of Rosh Pinah was updated with the new working areas by importing extended level plans (survey plans) as DXF files. The extended branches were drawn and edited in Ventsim. The ventilation network was then simulated with the new ventilation data, using various possible options and different control methods. The changes that could be made to the network were identified from the ventilation survey data. The following two options were considered for simulation.

    The WOF decline intake has three portals, namely, Quick $-#'*./ ./%-./.(+-",+-)(/-(+,.&/,+/)&/-(,

Table I Specifications of main fans used at Rosh Pinah

Fan type Connection Capacity Location

2 × centrifugal Donkin fans Parallel 2 × 160 kW at180 m3/s EOF 310 level 2 × axial flow Howden D7 fans Parallel 2 × 110 kW at 125 m3/s WOF 190 level 1 × axial flow J67 Airtec Davidson fan Series 185 kW at 100 m3/s Surface, SOF L 302    VOLUME 116          Improving the ventilation system at Rosh Pinah zinc mine

newly developed workings, the adequacy of the ventilation under the existing system was surveyed to improve the conditions in this area. However, no production was taking place at this area during the survey, and production will be started only after the ventilation conditions are improved.  The oxygen concentration at all five working faces (no. 1, 5, 6, 8, and 9) in the WOF met the required minimum of 20%. The methane concentration at the working faces was found to be negligible. The nitrogen oxide levels were minimal, and did not cause any major concern.  

$-#'*./ ),+-)(/)%/+. )*,*/,(!/.* ,(.(+/&+)-(#&/,+/$ High temperatures and humidity in an underground workplace may result in reduced performance and impair the attention of workers (Rostami, 2011). Therefore, it is important to study the humidity levels at the working face to ensure comfortable conditions. The humidity measured at all the working faces of WOF 30L was slightly above the maximum allowable level of 85% (Figure 6). A maximum humidity of 90% was measured at working face 8. The humidity at all the other working faces at WOF level 30 was found to be satisfactory.   The air flow required at the working faces of the mine was determined using the mining ventilation standards of Namibia (Ministry of Mines and Energy, 1992). Rosh Pinah $-#'*./ ),+-)(/)%//-*+./,-!&)(/%,(&/,+/$ mine makes use of Cat AD 30 trucks in combination with scoops. Usually, there are a maximum of six personnel at a working face. The cross-sectional areas of the working faces 2 Prior to the fan installation, a bulkhead with a width of 8 are 22.7 m , therefore, the calculated minimum required 3 m and a height of 4 m was drawn at WOF level 30 to locate airflow at the working face is 18.2 m /s. The measured air the fan. The purpose of this bulkhead is to reduce the shock flow at the working faces of the WOF is shown in Figure 7. losses that may occur if the fan was to be located perpen- dicular to the direction of the air flow. Three raises were planned from WOF 30 to WOF 90 to link the new fan location with the return raise at WOF 90. This is shown in Figure 5. The length of the raises from 30 level to 190 level is 163 m. The diameter of the raise that was inserted is 4.0 m. The new airflow distribution along WOF was then simulated. The new location of the fans at WOF is shown in Figure 5

.&'"+&/,(!/!-&'&&-)(  The objective of the survey was to assign resistances to all the branches in the ventilation network by quantifying the air $-#'*./ ./"),+-)(/)%/+.//%,(&/,+/$ flows and pressure drops (Nixon, 1983). Moreover, accurate quantity and pressure measurements are an absolute necessity since the validation of the computer-generated output is heavily dependent on the accuracy of the input data (Gelhn et al., 2008; Rostami, 2011). The characteristics of the existing mine ventilation system were determined by conducting an underground survey. The direction of the airflow and the location of intakes, returns, stoppings, etc. were determined by inspection of the mine plan. The ventilation results below are a snapshot from December 2014. No personnel were allowed to enter the area due to the mine’s safety and health policy. Since these are $-#'*./ .,&'*.!/' -!-+/".."&

         VOLUME 116    303 L Improving the ventilation system at Rosh Pinah zinc mine

Costs of drilling a raise per metre × number of holes × length of raise = N$710 × 21× 160 m = N$2 385 600 Total capital costs to install the fans = costs of drilling and blasting (160 m) raise + installation costs from contractor = N$2 385 600 + N$288 216 = N$2 673 816 Equivalent annual costs are therefore, 320 549×0.1 $-#'*./ .,&'*.!/,-*/%")/,+/+./)*-(#/%,.&/ (EAC) = = N$501 190.81 -1 (1 ) (1.1)8 The annual operating costs for the two fans are   (McPherson, 1993): The air flow entering the working faces was 41.0 m3/s Operating costs (N$) = Pft × Q × e ×24 ×365 ̀ compared to the total air flow of 11.41 m3/s. reaching the  working faces. The volumetric efficiency was therefore where 27.83 %. In addition, the efficiency of the existing Howden Pft = Fan total pressure (kPa), fans during the ventilation survey was found to be only Q = Air flow (m3/s), 67.1%. e = Cost of electricity in kWh (N$) 2×185  Operating costs (N$) = ×0.85×24×365 0.671    =N$4 105842.027 per year Sealing the entrance to the workshop near the Quick Access The total yearly cost is obtained by adding the cost of at level 370 and placing a curtain at the northern orefield fan developing the airways/raises and the annual operating cost tunnel entrance resulted in the air flow at the WOF increasing of ventilation. 3 3 from 60 m /s to 83 m /s. However, air flow at the working Total cost to implement option 2 = N$501 190.81 + faces was still inadequate; this increase in air flow was rather N$4 105 842.027 = N$4 607 032.84 supplied to other areas in the mine. The maximum air flow that was achieved was 11.2 m3/s, and this was at working 4)("'&-)(& face 8. The air flow entering the working faces increased Ventilation survey results revealed that gas concentration and slightly to 44 m3/s. The air flow at the working faces after humidity levels at the western orefield decline met the redirecting is shown in Figure 8. Namibian ventilation standards and did not cause any major    concern (Ministry of Mines and Energy, 1992). Since the By replacing the existing WOF fans with the southern orefield fans, the air flow increased significantly, meeting the regulatory requirements at all the working faces. The air flow entering the WOF was 122 m3/s, and the air flow at working face 8 increased to 25.2 m3/s. The total air flow reaching the working faces was 103.2 m3/s; the volumetric efficiency therefore is 68.8%, and the rest of the air was leaking through the stopping to the return raise. The air flow at all five working faces is given in Figure 9. Working faces 1, 5, 6, 8 at WOF 30 are parallel with working face 9 at WOF 90.

4)&+/)(&-!.*,+-)(&/ $-#'*./ - '",+.!/,-*/%")/ %-."!/ .,&'*. .(+& The costs of making changes to the ventilation network at Rosh Pinah were evaluated for option 2. The costs to replace the two main fans at WOF level 90 with the two fans at southern orefield level 262 (J67 Airtec Davidson fans) were determined. Since the main fans are not new, the capital costs of alteration include the fan installation costs and the costs for drilling the three 160 m raises from 30 level to 90 level of WOF. According to the project planner at Rosh Pinah, the costs of drilling and blasting a raise is N$710 per metre, including labour costs. Hence: Total costs of drilling and blasting the 160 m raise = $-#'*./ - '",+.!/ / .,&'*.!/,-*/%") L 304    VOLUME 116          Improving the ventilation system at Rosh Pinah zinc mine workings are still at the developing stage, the air flow and Environmental Geotechnology (AMREG 2006), Technical University measured at the western orefield decline was below the Crete, Chania. pp. 89–93. GLEHN, F.H., MARX, W.M., and BLUHM, S.J. 2008. Verification and calibration of minimum required. The volumetric efficiency of the western ventilation network models. Proceedings of the 12th U.S./North American orefield decline was found to be 27.3%. The most feasible Mine Ventilation Symposium 2008, University of Nevada, Reno, NV. solution to increase the air flow at the working faces would Wallace, K.G. (ed.). Society of Mining Engineers of AIME. pp. 275–279. be to replace the western orefield main fans with the HARTMAN, H.L., MUTMANSKY, J.M., RAMANI, R.V., and WANG. Y.J. 1997. Mine southern orefield main fans. Along the western orefield Ventilation and Air Conditioning. Wiley, Hoboken, NJ. LOVEJOY, C. 2010. A breath of fresh air. Mining Magazine, July/August 2010. 3 decline, 25.23 m /s of the air is flowing out of the western pp.16-21. orefield into the northern orefield fan tunnels. No mining LUXBACHER, G.W. 2008. Developing input data for computer simulation of mine activity is currently taking place in this area; therefore it is ventilation. Kentucky: Pennsylvania State University. recommended that the flow of air can be controlled by placing LUXBACHER, G.W. and RAMANI, R.V. 1979. Optimization of coal mine ventilation a brattice cloth at the entrance of the fan tunnel. Real-time air systems. AIME Transactions, vol. 286. pp. 1801–1809. MCPHERSON, M. 1993. Subsurface Ventilation Systems. Chapmann & Hall, New quantity and air quality control would reduce the effort of York. pp.25-120. ventilation surveys. The real-time monitoring ventilation MINISTRY OF MINES AND ENERGY. 1992. Mine Health and Safety Regulations, 10th system, together with Ventsim™, could improve the accuracy draft. Windhoek. of the simulation and provide the most accurate results. NIXON, T.R., DEAKIN, J.J., and RALPH, A.M. 1983. Ventilation analysis for mine planning and operation. Computers in Mining Symposium, Southern Queensland Branch, Australasian Institute of Mining and Metallurgy. ()".!#. .(+& pp 231–240. The authors thank Rosh Pinah Zinc Corporation for the ROSTAMI, P., DANKO, G., and BAHRAMI, D. 2011. Ventilation and climate simulation of development ends in metal mines. Proceedings of the SME provision of data and the use of its facilities and ventilation Annual Meeting, Denver, CO. Preprint no. 11–135. pp. 732–735. measuring instruments during the investigation. SINGH, A.K., AHMAD, I., SAHAY, N., VERMA, N.K., and SINGH, V.K. 2004. Air leakage through underground ventilation stoppings and in situ assessment of air leakage characteristics of remote filled cement concrete .%.*.(.& plug by tracer gas technique. Journal of the South African Institute of DUCKWORTH, I.J. and LOWNDES, I.S. 2003. Modelling of auxiliary ventilation Mining and Metallurgy, vol. 104, no. 2. pp 101–106. systems. Transactions of the Institution of Mining and Metallurgy, TIEN, J. 2008. Determining the optimal mine regulator location using computer vol. 12, no. 2. pp. 2–9 simulation. Peabody Coal Company, Kentucky. pp.2-6 EXIKIS, A. and KAPAGERIDIS, I.K. 2006. Simulation of air and contaminant flow in WALLACE, K. and MCPHERSON, M.J. 1983. The efficiency and economics of mine underground mine ventilation networks. Proceedings of the 2nd ventilation systems. TMS/AIME Meeting, Atlanta, GA, 6 March 1983. International Conference on Advances in Mineral Resources Management pp. 2-7. N

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www.worleyparsons.com http://dx.doi.org/10.17159/2411-9717/2016/v116n4a2 Sub-standard practices: effects on safety performance in South African gold mines by G. Kleyn* and J.J.L. du Plessis* Paper written on project work carried out in partial fulfilment of B. Eng. (Mining Engineering)

(Figure 1). These include meeting the Mine Health and Safety Milestones (Department of !+*&/& Mineral Resources, 2011). Sub-standard practices and their adverse impact on safety performance Most South African mining companies remain a challenge in the South African gold mining industry. The purpose have adopted a ‘zero harm’ policy in an effort of this study was to investigate the root causes of sub-standard practices to improve the health and safety of employees and the effect on safety performance in South African gold mines. The at their operations. After the 2003 Mine Health focus of the study was on the underground production operations at a gold and Safety Summit, the following milestone mine in the Free State. The study consisted of three parts: a personal was set with regard to the gold mining investigation into the causes of sub-standard practices at the mine, a industry (Department of Mineral Resources, comparison with the results of a cultural study performed at the West Wits 2011): mines, and a behavioural survey. ‘Achieve safety performance levels The studies described in this article yielded similar results in terms of the key drivers behind sub-standard practices. It was found that sub- equivalent to current international standard practices had a number of causes, and the origin lies within the benchmarks for underground metalliferous habits, attitude, and behaviour of employees. Current methods of mines, at the least, by 2013.’ addressing sub-standard practices and improving safety performance were These milestones were revised in 2014 and found to discourage employees from performing work safely and according new targets for 2024 were set for the South to procedure. African mining industry (Association of Mine It was concluded that the lack of critical behavioural habits for the Managers of South Africa, 2014). The new given work environment and job title could possibly be the primary reason milestones that were set in terms of occupa- for the occurrence of sub-standard practices. tional safety are listed below (Association of 40!*-(& Mine Managers of South Africa, 2014): sub-standard practices, safety, behaviour, habits. ® ‘Every mining company must have a target of ZERO FATALITIES ® Every Fatality is one too many, we will eliminate fatalities by December 2020 ® 3+.-*(,'./*+ Up to December 2016, 20% reduction in Serious Injuries per year Since the implementation of the Mine Health ® From January 2017, 20% reduction in and Safety Act, 1996 (Act 29 of 1996) and the Lost Time Injuries (LTI) per year.’ Mine Health and Safety Regulations, the South African mining industry has been striving to The 2024 targets include new milestones improve health and safety performance and for the implementation of the approved culture has placed great emphasis on adherence to transformation framework (CTF). These mine standards. milestones included the following (Association The Act requires employers in the mining of Mine Managers of South Africa, 2014): ® industry to report accidents, incidents, and ‘By December 2020 there will be 100% dangerous situations to the Regional Principal implementation of: Inspector of Mines in their area. The data provided by employers is captured and analysed by the South African Mines Reportable Accident Statistical System (SAMRASS) and made available for public viewing (Department of Mineral Resources, 2011). A review of the national mine-related * Department of Mining Engineering, University of accident statistics shows clearly that the South Pretoria, South Africa. African gold mining industry has improved its © The Southern African Institute of Mining and safety performance markedly over the past Metallurgy, 2016. ISSN 2225-6253. Paper received decade, but is still facing major challenges Dec. 2015.

         VOLUME 116    307 L Sub-standard practices: effects on safety performance in South Africa

2)'%-*,+( Figure 4 shows the relative distribution of accidents at the study mine between the surface and underground environments. These statistics show that the underground work environment is more hazardous. The question remains: why do employees at the mine still engage in sub-standard acts and how does this affect safety? It is this question that gave rise to this investigation into the root causes of sub-standard practices at the mine. The hypothesis is that sub-standard practices usually have multiple causes on different organizational levels and "/%,-01").)/./0&10-1'*##*(/.!1&0'.*-1/+1*,. 1$-/')1$*-1. 01!0)-& 1.*11 /+010). 1)+(1)$0.!1*,+'/1 have an adverse effect on the safety performance of South African gold mines in general. To understand the current culture and the need to change, an investigation into what causes employees to engage in sub-standard acts and how to change the – The Leadership Pillar of the CTF behaviour at all levels of the organization was required. – The Risk Management Pillar of the CTF – The Bonus and Performance Incentive Pillar of the CTF – The Data Management Pillar of the CTF – The Diversity Management of the CTF – The Leading Practice pillar of the CTF ® After December 2020 the remaining pillars will be implemented: – The Integrated Mining Activity Pillar of the CTF – The Technology Pillar of the CTF – The Inspectorate Pillar of the CTF – Tripartism Pillar of the CTF – Regulatory Framework Pillar of the CTF’ Sub-standard practices compromise the effectiveness of any safety measures, devices, or procedures that have been "/%,-01*(1#/+01)''/(0+.1(/&.-/ ,./*+1 !1& /$. put in place. They create a weak spot in the system that is bound to fail with the slightest amount of interference. Standards and safety are very closely related and standards are necessary not only to maintain the safety of underground employees, but also to improve current safety practices. The information below represents some of the safety performance statistics at the study mine and was compiled from data obtained from the mine’s safety department. From 17 February 2009 to 22 December 2014 a total of 2042 accidents occurred on the study mine. A total of 26 of these accidents led to fatalities. Upon analysis, it was found that the mine experienced approximately 0.94 accidents per day. The accident distribution by shift is shown in Figure 2. Figure 2 shows that the majority of accidents at the mine "/%,-01''/(0+.&1 !1*-)'01).1. 01&.,(!1#/+01  occurred during the morning shift. The average time of occurrence of morning shift accidents was 11:58:17 am. Figure 3 shows that the largest number of accidents at the study mine occurred in the stopes. The second highest number occurred in development, and the third highest in tramming. Not surprisingly, these are also the departments underground that have shown the greatest amount of sub- standard practices. It is estimated that approximately 40–50% of all accidents underground occur as the inevitable result of sub-standard acts. From Figure 1 it is clear that safety performance in gold mining has lagged that in other sectors of the mining industry for the past 10 consecutive years, and despite the "/%,-01,-$)'01)+(1,+(0-%-*,+(1)''/(0+.1*'',--0+'0&1).1. 01&.,(! recorded improvements, further efforts are required. #/+0 L 308    VOLUME 116          Sub-standard practices: effects on safety performance in South Africa

In order to ensure compliance with regulations, the mine conducted on shift bosses in order to determine benchmark has implemented a full compliance policy. However, the sharp attitudes and behaviour for this group of employees. The rest increase in sub-standard practices indicated that the policies of the participants’ habits were then compared to the implemented by the company have not led to the desired benchmark and analysed. result. The results of a cultural survey performed by Dupont Furthermore, a major concern is that the new generation were analysed in order to determine previously known causes of mine employees is adopting a culture where sub-standard of sub-standard practices and their relation to employee practices are the norm. The language barriers that exist behaviour. among the majority of the workforce raise a number of The Society for Mining, Metallurgy and Exploration questions with regards to mine standards in terms of compre- (SME) Mining Engineering Handbook, (1973) states that all hension. mining operations are required to adhere to local, provincial, Figure 5 shows the number of accidents and fatalities and governmental regulations that among other things recorded at the mining operation over the past 5 years. specify mine safety regulations and standards, environmental Although there was a steady decline in the number of protection, and labour relations. The nature, scope, and accidents from 2009 to 2014, this is not reflected in the stringency of these regulations ultimately govern the mining number of fatalities. Thus although the number of accidents operation. has decreased, their severity has not. Over the past three decades, the number and extent of Ideally, the accident statistics should show a steady mining regulations and governing authorities have dramat- decline, indicating that the ‘zero harm’ policy of the company ically increased on an annual basis. The major reason behind is becoming a reality. Unfortunately, the fluctuations in the this is a continuous effort of governments to promote health injury and fatality rates indicate a high probability of and safety standards in the global mining industry (Hansen, recurrence of accidents and fatalities. It is believed that 1973). According to Hansen, (1973), a statistical study that proactive standards have a far greater impact than reactive was performed over a period of 50 years showed that standards. awareness of the effects of sub-standard practices resulted in Firstly, it was necessary to carry out research on a decreased frequency of accidents. The majority of mine accidents related to sub-standard work at the mine. This was health and safety authorities around the world agree that the done in order to identify the root causes of sub-standard major causes of mine accidents and fatalities are unsafe practices in the underground working environment and the conditions, poor management, and especially unsafe effects on safety performance. practices, which according to the SME, is often cited as the The findings of the study at the mine were compared to primary cause (Society for Mining, Metallurgy and those of a cultural study that was completed at mines in a Exploration, 2011). different mining region. The last part of the study involved Due to a combination of sub-standard practices and conducting Shadowmatch surveys on first line supervisors hazardous conditions, one must consider not only the (shift bosses) and making recommendations for further physical causes of sub-standard practices, but also elements studies. such as training of employees, the mental state of employees, A literature study was completed to determine what and employee behaviour (American Institute of Mining, investigations have been completed in South African gold Metallurgical and Petroleum Engineers, 1973) mines, and the safety performance and factors that influence The major shortcoming of most of the approaches used to it. This included a previous cultural study that was performed identify the causes of sub-standard practices is that the at mines in the West Wits region. studies were usually based on hasty investigations, obvious Personal interviews were conducted to try to determine physical factors, and common causes of sub-standard acts the factors that influence sub-standard practices. Production while neglecting the psychological, cultural, and behavioural supervisors were also interviewed in order to compare how drivers. their opinions on sub-standard practices differed from those Poor human behaviour, however, is a known detrimental of the underground employees. Questions were posed in such factor in mine safety. This is evident from the cyclical a way as to determine how the work culture (attitudes and behaviour) influences the implementation of mine standards. recurrence of repeat accidents. The key shortcoming of Towards the end of the study, a Shadowmatch survey was considering only incident and accident frequency rates as the focus of safety performance is that it neglects the root causes of the incidents (American Institute of Mining, Metallurgical and Petroleum Engineers Inc., 1973). The Mine Health and Safety Act (MHSA) aims to enforce health and safety measures and legislation in the South African mining industry (Department of Mineral Resources, 2011). The open question remains whether the implemen- tation of the MHSA was sufficient to create a safety-wise culture in the mining industry. Published fatality and injury rates often reveal a false picture of what is actually occurring in the mining industry. Deep-level mining unfortunately has associated hazards and risks and requires commitment and adherence to health and "/%,-01/+01$).)/./0&1)+(1)''/(0+.&11.*1 safety standards (This is Gold, 2015).

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The published data on mine-related incidents and The different accident causation models often show fatalities (Department of Mineral Resources, 2011) shows conflicting perspectives when it comes to establishing the that conditions in the underground gold mining environment cause of the incident. It is important to understand that there can be extremely challenging. Since most gold mines in South is no single accident causation theory that is applicable to the Africa still use conventional methods (drilling and blasting in mining industry, universally speaking. Some models, narrow-reef stopes) it remains a highly labour-intensive however, enjoy preference due to their simplicity and industry. perspective on what ultimately led to the accident. (Raouf, The CSIR (2013) conducted a study to develop an 2011) accident investigation tool that can be used to determine the The theories that were investigated included: root causes of incidents and which provides better insight ® The Domino Theory into the systematic factors that eventually led to the ® Multiple Causation Theory occurrence of the incident. ® The Swiss Cheese Model The CSIR was of the opinion that the injured person is not ® The Risk Homeostasis Theory the sole cause of the accident, but that a series of events ® leads to such occurrences, and that supervisory and Bird and Germain’s Loss Causation Theory. managerial aspects also contribute either directly or indirectly Research has found (De Villiers, 2009) that many to such events (CSIR, 2013). individuals occupy job positions in which they are extremely It is important to determine the human error aspect of an unhappy. This was also the case with regard to the working accident as well as the path that led to its occurrence (Society environment. The associated problem lies in this: it results in for Mining, Metallurgy and Exploration, 2011). negative implications not only for the individual, but also for It must be realized that the majority of incidents generally the working environment and fellow workers. result from at least one act and one condition. However, the The Shadowmatch system was developed to prevent the majority of mine-related accidents are caused by more than above-mentioned scenario by allocating individuals to one condition or act. If this is not taken into account, the environments that best suit them in order to preserve opportunity to determine the real root cause(s) of the incident harmony between the individual and the environment. The is lost. Shadowmatch system can also be used to identify employees An integrated diagnostic review of cultural transfor- that best suit a specific working environment and specific job. mation was performed at the West Wits gold mines in 2012. The system possesses the capability to provide personal The purpose of the study was to determine employee development programmes for individuals that require specific attitudes and behaviour within the company and the factors habits in order to be successful in their occupation (De that resulted in a certain attitude or behaviour (Gold Fields, Villiers, 2009). 2012). This process is completed by comparing the habits of the The study employed a number of different analysis tools individual concerned to the habits of employees who are in order to identify all the cultural issues and to ensure that deemed successful, based on the performance management all the levels of employment within the organization were system of the company, in performing a specific task within covered. the organization An accident or fatality is usually the outcome of a number The Shadowmatch research team identified a number of of sub-standard practices that ultimately led to the event. The aspects that ultimately define the work environment (a probability of occurrence of the unwanted event (accident or detailed description of each can be found in the Shadowmatch injury) and its severity are increased by sub-standard e-book available at www.shadowmatch.com): practices. As the number of sub-standard practices increases, ® Physical environment the probability of accidents, as well as their severity, also ® Social environment increases. ® Emotional environment It is therefore important to look at accident causation ® Operational environment. theories in order to link the current situation in the South Behaviour, being a complex field of study, can be African gold mining industry to sub-standard practices and motivated by more than one motivator, and a number of their causes. motivators may be present within a single one. Most people A review of the available literature shows clearly that all are uncertain of why they behave the way they do (De accident causation theories have a number of common goals, Villiers, 2009). namely: ® Identifying risks 60&,.& ® Identifying influencing factors ® Attempting to explain why the accident occurred   ® Identifying the root causes of the accident It was found that when employees were interviewed in their ® Using the above knowledge to predict and prevent specific working environment, their opinions differed greatly accidents. from when interviewed on surface. It was therefore decided to The majority of authors, (e.g. Guttierez, 2010; Mol, 2002; conduct all interviews in the appropriate underground Raouf, 2011; Saari, n.d.) agree that there are several theories working environment. of accident causation, and that a single theory is often not Based on the personal interviews with employees at the enough to establish the true cause of the incident. mine and the results of the 2012 cultural survey executed by L 310    VOLUME 116          Sub-standard practices: effects on safety performance in South Africa

Mandala Consulting, (2012), it came to light that accidents Both of these situations could have influenced the and fatalities are in the majority of cases not caused by a findings. After discussion with a psychologist specializing in single event. public health, it was established that in the mining industry, A total of 135 employees were interviewed during the the following behaviour patterns are expected with regard to investigation. The focus of the study was mainly on age and years’ experience in the mining environment (van underground production personnel. The majority of the Zyl, 2015): duration of the study was spent in the stopes, thus the ® Younger employees are more likely to exhibit risk- greatest pool of information was obtained from rock-drill taking behaviour such as engaging in sub-standard operators, winch drivers, team leaders, miners, and shift practices, due to the nature of younger persons’ bosses. The previous general manager at the mine stressed thought patterns that the area of concern with regard to sub-standard practices ® Older employees are the least likely to exhibit risk- and unsafe acts was the production personnel at the mine. taking behaviour due to thought patterns commonly Figure 6 shows the distribution of employees interviewed by associated with age, such as being more careful in the occupation. work environment The mode of the age categories was 46–55 years. The ® The less experience an employee has, the more likely greater amount of employees interviewed were from the they would be to engage in sub-standard practices, higher age categories, and the majority were from the since they have no recollection of previously morning shift. Only six employees interviewed were working encountered dangerous situations or loss of life the night shift. ® Conversely, older employees are seen as the more The final parameter was the number of years’ experience responsible in terms of implementing standards as of employees. This is one of the most important parameters, opposed to risk-taking behaviour. They are more likely since it is generally believed that the more experience an to be focused on issues such as health, job security, employee has, the less likely they are to perform an unsafe and avoiding danger. act or be involved in an accident. Table I shows that the largest category of employees that were interviewed had between 6 and 15 years’ experience in the mining industry. The behaviour of employees during interviews raised concerns in terms of the findings: if employees were too scared to disclose their occupation, how accurate and honest is the information that they have provided in the question- naires and during personal interviews? Honesty and fear of losing employment seemed to be a major problem at the mine. Employees were found to be extremely anxious to voice their opinions while in the presence of their colleagues. On other occasions, some of the ’new ones’ (as new employees are referred to underground) were often silenced by the elder employees when an interview was conducted. The interviewees’ behaviour during interviews also opens a window for speculation that employees are hiding certain things from management as well as their supervisors. It raises the question of complete honesty – some interviewees might have lied and others were maybe too scared to answer the questions honestly. One can thus not conclude that the "/%,-01/&.-/ ,./*+1*$10#*!00&1/+.0- /00(1 !1*'',)./*+ results of this study are absolutely complete and accurate, due to the external influencing factors in the working environment and observed differential behaviour. Despite the occasional behavioural patterns and trust Table I issues, it was possible to determine trends. From the data-set Number of employees by years' experience in the of interviewees it is clear that a greater number of older mining industry employees were interviewed (Table I). The data showed no Years of experience Number of employees correlation between age, years of experience, and the execution of sub-standard acts, which could indicate one of Less than 3 13 two possible situations: 3-5 17 6-10 38 ® The mine currently has a large number of young 11-15 31 16-20 18 employees who do not have many years’ experience in 21-25 13 the mining industry 26-30 4 ® Older people have been appointed in certain 31-35 1 More than 35 0 occupations without a great amount of previous mining Overall total 135 experience.

         VOLUME 116    311 L Sub-standard practices: effects on safety performance in South Africa

There are, however, a great number of factors that could These results prompt the question as to why would influence any employee, irrespective of age category and level employees be willing to take the risk of incurring a loss, if of experience. These factors include mental health, job they understood the probability and severity of the loss? The satisfaction, remuneration, stress, and education, to mention answer lies in the behaviour and mind-set of underground just a few. production personnel. In order to establish and analyse certain trends in Supervisory skills seemed to be lacking in the majority of employee behaviour with regard to sub-standard practices, workplaces that were visited. Due to a lack of respect and no some of the questions in the questionnaire were grouped fixed structure of authority, there was no control over together in order to analyse them for similarities and employees’ behaviour. It was also found that teamwork skills conflicting answers. were not favoured underground. Every employee had the mind-set of ’I’m here only to do my job’. Sub-standard    practices were therefore closely related with communication One group of questions dealt with whether employees had gaps, lack of teamwork, and apportioning blame to younger encountered sub-standard practices, and the other group employees, instead of accepting fault. dealt with whether employees understood what standards It was found that approximately 56% of employees, at were and the necessity for them. some point in their careers, had performed sub-standard More than 80% of the interviewees indicated that they work and approximately 33% of employees also instructed were aware of sub-standard practices in the workplace. This other employees to do so. might show that employees were very aware of what sub- Most of the employees who were interviewed encountered standard practices meant in terms of their occupations. some form of sub-standard practice on a weekly basis. More than 91% of employees that were interviewed felt Surprisingly, some employees felt that they encountered sub- that they were trained to understand why standards were standard practices only on a yearly basis, which is hard to required and needed to be upheld. The result is somewhat believe based on the author’s personal experience at the contradictory, since personal experience and discussions with mine. management indicated that employees often do not Figure 7 shows that 39% of employees said that their understand the implementation of standards. work was always up to standard, while only 5% said that It was found that 89% of the interviewees had a good their work was completely sub-standard. This is, however, a understanding of standards and their importance. The misleading result according to personal investigation. If the correlation between understanding standards and implemen- majority of employees feel that their work is always up to tation is that if employees understand what standards are standard, then why is there a problem with sub-standard and why they are important in the working environment, practices? they should also be able to identify sub-standard practices According to the results, the sub-standard acts that were encountered varied widely, with some types of sub-standard without difficulty. practices mentioned more frequently than others. The general The 22% of employees that said they were not aware of types of sub-standard work that were encountered included, any sub-standard practices could have felt this way due to: but were not limited to, the following: ® Fear of losing their job ® Incorrect procedures when entering and exiting man ® Not understanding the questions carriages ® Not understanding what the standards at the mine are ® Incorrect tramming procedures (speeding, leaving locos A fairly high percentage (11%) of the interviewees were running without an operator inside, attaching too many of the opinion that they were not adequately trained in hoppers etc.) understanding the standards. This shows a strong feeling ® T-sprags almost never in place and ventilation doors among employees that a lack of training and education on always open, since it interferes with tramming standards is a root cause of sub-standard practices. It is clear according to loco guards that an employee who does not understand a standard would ® Unequipped travelling ways (no steps, footwall not be highly likely to implement the standard incorrectly, not be cleaned, no handrails or rope guides, sometimes not able to identify sub-standard practices due to a lack of sufficient support) understanding of the standard itself. 14% of the interviewees claimed that they did not understand the consequences of sub-standard practices. During the interviews, a number of employees often apportioned blame on the ’new ones’ for performing sub- standard acts. The problem here might lie in lack of underground experience. The majority of interviewees were concerned about the consequences of sub-standard acts since they had experienced consequences themselves, witnessed them, or heard accounts of serious injuries from colleagues. Although 86% of employees claimed to understand the consequences of sub-standard practices, a shocking 46% of them were still prepared to perform sub-standard acts if the opportunity was presented. "/%,-01, &.)+()-(1*-1-)./+%& L 312    VOLUME 116          Sub-standard practices: effects on safety performance in South Africa

® Incorrect explosive storage, transport, and handling ® Improve training procedures ® Reward implementation of standards ® Incorrect rigging practices ® Address mental wellbeing of employees ® No supervision ® Address attitude-related issues ® The abovementioned examples of sub-standard acts, Provide education on standards and their importance procedures, and installation are but a few compared to the A factor that stood out was that employees at the mine great number of sub-standard practices that were seemed to lack motivation in performing their jobs. They encountered during the investigation. want to feel part of something larger than themselves and be Employees’ reasons for performing sub-standard work or rewarded for performing a good job. instructing someone else to do so indicated clearly that The level of education of employees influences the engagement in sub-standard practices is a behaviour-based training methods to a great extent. Interviewees felt that on- issue. The majority of employees showed an inclination the-job training in the underground environment would be towards taking matters into their own hands when events did more suited to their level of education than theoretical not go according to their personal plan. It was observed that training in a training centre. The general feeling was that everyone wanted to be leaders, and seldom followers, even there is a major difference between executing tasks in the when it was necessary. training centre and executing the same task a few hundred Many experienced employees were extremely set on metres underground. respect. If they felt that they were not respected, they would Great variation in the origin of sub-standard practices not assist in the task or deliberately work slowly in order to was observed. Some employees believe that this is more of a annoy the person who had assumed seniority in the psychological and behavioural problem, while others tend to situation. A lack of ‘soft’ skills is definitely a major cause of blame management and direct supervisors for the issue. sub-standard practices. Teamwork is essential in the mining The investigation at the mine indicated a number of industry and interpersonal skills are vital; this is an area that potential issues that can be further investigated to determine the root causes of sub-standard acts and their effects on employees at the mine need to be trained in. safety. Perhaps the most interesting question yet to be Ignorance was found to be a major driving force behind answered is if sub-standard acts are largely a result of sub-standard acts. Employees believed that because they human behaviour and individual mentality. This question have never been involved in an accident, it will never happen will be addressed in the analysis of the results from the to them. They have been involved in sub-standard acts for so Shadowmatch survey. long that they are now accepting them as the norm. It was clear that revenge also played a major role in sub-standard procedures and acts. The belief amongst interviewees was *#)-/&*+1 0.00+150&.15/.&1',.,-) that if a colleague has done them wrong, he must pay for it. .-)+&$*-#)./*+1)+(1. /&1&.,(! Sub-standard acts are often the result of payback to try and A number of responses to questions in the gold mine study regain status by being rebellious. revealed that employees were often just there to get the job The results confirmed that production supervisors were done, not willing to go the extra mile with regard to their job often seen as lead agents by not adhering to safe practices as descriptions, lacked a feeling of corporate ownership, and they have instructed to their gangs to do. This behaviour often did not take control of conflict situations. results in a shared anger by production personnel, which The cultural transformation study at the West Wits gold engenders a less motivated work culture. Employees feel that mines yielded the same results. About a quarter of the they can do as they please, since production supervisors do employees that took part in the study were not interested in not care. doing more than what was expected of them. About 70% of Although one might not have expected the physical employees did not want to take control of situations that location and working conditions of stopes to be a leading resulted in conflict. This showed that conflict resolution skills factor driving sub-standard practices, the results clearly were lacking with most employees. showed the opposite. It was found that employees that took part in the cultural Many employees complained about the travel distances study at West Wits also did not feel competent to perform all on foot in order to reach the workplace early enough so that work tasks all of the time. The results also showed that there was still adequate time available for completing mining adaptability, tenacity, and resilience were often a problem for activities. Associated fatigue resulted in employees employees. These findings strongly agree with the results performing work that was of poor quality, as they claimed a obtained at the study mine. lack of energy to perform the tasks correctly. The results indicated a strong similarity in the safety Other employees were of the opinion that they did not culture at the study mine and in the West Wits mines. have the correct tools to perform the given tasks to standard. Employees did not understand the safety vision clearly and A combination of fatigue, incorrect tools, and limited time did not always follow standard procedures. It can therefore be resulted in sub-standard acts. postulated that employees in the gold sector show a general The responses to a question on what employees felt had disregard for safety and standards in the underground to be done to remedy the problem showed a number of working environment. general ideas to remedy sub-standard practices. The Acceptance of teamwork as an inevitable factor in mining suggested actions to take control of the situation can be and safety showed exactly the same trend at the West Wits summarized as follows: gold mines and the study mine. Almost half of the employees

         VOLUME 116    313 L Sub-standard practices: effects on safety performance in South Africa believed that interdependence during teamwork played no 1. Individual inclination role in the quality of work and relationships. Employees 2. Innovation preferred working individually, although this is almost 3. Propensity to delegate impossible in the production environment. 4. Propensity to change When performing teamwork, employees had great Successful shift bosses definitely preferred to work in difficulty in trusting each other. This was the case at both the teams, as indicated by the low score for individual study mine and in the West Wits study. However, trust was inclination. not the only underlying issue. Many employees also felt that Based on the results obtained from the behavioural study they were not fully equipped for performing teamwork and performed at the mine, it was anticipated that employees that they were often not informed on their specific role within would obtain a low score for innovation in a Shadowmatch the team. survey. The reason behind this is that employees showed a From the results obtained in the West Wits study, it was strong inclination towards performing tasks the way they evident that the study mine was not the only operation that were used to, and not to embrace new technology or indicated quality of supervision as a major problem. It was innovative solutions to problems. The group showed a shown that employees did not possess proper supervisory thinking style opposite to an out-of-the-box thinking style. skills, nor did the supervisors themselves. A lack of on-the- As mentioned previously, this type of behaviour could job coaching, lack of motivation and acknowledgement, and hamper safety performance due to the fact that new ways of relationships with supervisors again came up as causes of performing tasks were often deemed as additional work or sub-standard practices. unnecessary change. The studies performed at the study mine and the West The score for propensity to delegate is lower than that for Wits study showed that there were almost no differences in propensity to own. The benchmark group of shift bosses the cultures with regard to safety and sub-standard practices. showed that they preferred to take ownership of problems In fact, most of the influencing factors that were investigated and handle challenges themselves as opposed to getting were similar, and it can be concluded that the findings may another individual to deal with the problem. This habit, in the be applicable to the entire gold mining industry of South opinion of the author, should actually be much more Africa. prevalent, since it reflects the shift bosses’ ability to take control of a situation. 60&,.&1*$1. 01 )(*#).' 1&,- 0! The Shadowmatch results with regard to propensity to A total of 88 shift bosses were selected by senior change confirmed the findings from the study mine as well as management of the company to participate in the the West Wits study. In both of the studies, shift bosses Shadowmatch survey. Included in this number was a found it difficult to adapt to change in their working benchmark study group of 10 shift bosses, who were selected environment. They were not comfortable with new methods based on their performance in terms of safety and production. of performing work, new environments, and new The purpose of the benchmark group was to determine the technologies. habits exhibited by successful shift bosses and enable the profiles of the other shift bosses to be compared with those of     the benchmark group. This was done to determine poor The Shadowmatch attitude analysis delivered results that habits that may result in sub-standard practices and a poor strongly correspond to the critical habits that were identified safety record. within the benchmark group. The majority of participants in The majority of participants were day-shift stoping shift the benchmark group formed part of categories 1 and 2, while bosses. The day-shift vamping shift bosses were the smallest equal numbers of participants formed part of category 3 and group within the data-set. 4. The significance of the attitude distribution is as follows: ® Categories 1 and 2 exhibit a shared habit of    involvement. The Shadowmatch results that were obtained from the ® Categories 2 and 3 share habits of assertiveness and, benchmark group showing the most embedded or critical sometimes, unaggressive behaviour. habits exhibited by successful shift bosses. were identified ® Categories 3 and 4 exhibit a habit of less involvement and are listed below: or complete uninvolved attitude. 1. Team inclination ® Categories 1 and 4 represent a shared attitude of 2. Conflict handling unaggressive behaviour 3. Discipline Figure 8 shows the attitude distribution of the benchmark 4. Resilience group. 5. Altruism As shown in Figure 8, the benchmark group displays a These critical habits correlate well with the problematic strong attitude of involved, unaggressive behaviour. This areas identified at the mine, indicating that the study group showed positive involvement in their work delivered accurate results with regard to the identification of environment. They found it easy to get involved and this the root causes of sub-standard practices. formed part of their natural behaviour. The group thus The benchmark group showed relatively low scores in the showed positivity when working with people and exhibited following habits: optimism. L 314    VOLUME 116          Sub-standard practices: effects on safety performance in South Africa

The attitude scores in the results of the best performer are of particular interest. Although there is a strong correlation with the benchmark group in category 1 and 2 attitudes, the individual showed a significantly stronger category 4 attitude than the benchmark group. As opposed to the best performer, the worst performer showed strong category 2 and 3 attitudes and a low category 1 attitude. The recommended personal development programme (PDP) for the worst performer was problem-solving. As described earlier, the fact that this individual has none of the critical habits of the benchmark group indicates that he/she would be likely to see all aspects of the job as a major "/%,-01../.,(01(/&.-/ ,./*+1*$1. 01 0+' #)-1%-*, challenge. A number of different PDPs were recommended for the study group, based on the habits that were determined as critical habits of the benchmark group. The recommended PDP addresses the habit that needs development. The attitude is associated with altruism since the group Based on the results of the benchmark group, the proved to be unconditional in their actions and willing to Shadowmatch system recommended the following PDPs for make the necessary sacrifices to achieve a greater goal. shift bosses that were not part of the benchmark group Importantly, the benchmark group may be seen as materi- (ranked in terms of number of recommendations from high to alistic, but emphasizing the value of all life. The way they low): perform work is not to serve others, but to drive a certain 1. Handling frustration principle. 2. Routine With regards to conflict handling, the benchmark group 3. Problem solving resolved conflict in a mature way without feeling compelled 4. Propensity to delegate to become aggressive. This type of attitude does not seek 5. Individual inclination revenge or personal gain. 6. Team inclination

      

The purpose of the comparison was to establish any Table II differences and correlations between the habits and Comparison between critical habit scores of behaviours exhibited by the two groups. benchmark group and the best and worst It was decided to compare the ‘worst’ and ‘best’ performing individuals performers in terms of the Shadowmatch study to the data obtained from the benchmark group in order to determine Habit Benchmark Best performer Worst performer any similarities or differences. Team inclination 63 61 46 First, the results of the best and worst performers were Conflict handling 59 67 38 compared to the results of the benchmark group. The best Discipline 58 65 39 performer’s scores with regards to the critical habits showed Resilience 57 57 32 Altruism 57 64 43 a high correlation with the scores of the benchmark group. The comparison of the scores is shown in Table II. The worst performer scored significantly lower in all the critical habits of the benchmark group. This individual had a high likelihood of being extremely problematic in the working environment due to his/her habits. The best performer showed significantly stronger habits than the benchmark group in conflict handling, discipline, and altruism. For this specific individual, it could be said that these three habits are ultimately the drivers behind success. The worst performer scored higher than the benchmark group in only two habits, namely propensity to delegate and individual inclination. However, it is necessary to discuss the possible reasons for these two higher scores. Propensity to delegate is almost self-explanatory. This individual’s critical habits showed very low scores. It may be speculated that he/she would be the type of person who is not involved at all, has no confidence in what he does, showed no altruism, and prefers to give the task at hand to someone else to complete. "/%,-011 1,# 0-1*$1(/$$0-0+.1&1-0'*##0+(0(1$*-1. 01&.,(!1%-*,

         VOLUME 116    315 L Sub-standard practices: effects on safety performance in South Africa

Again, the set of PDPs that were recommended by the to improve on the current situation if the necessary habits system fits the results obtained from the study mine and the such as propensity to change, simplification of problems, self- cultural study extremely well. It further emphasizes the motivation, and team inclination are not addressed. habits and behavioural patterns that were identified that could lead to sub-standard practices in the working 60$0-0+'0& environment with adverse effects on safety. Figure 9 shows the different PDPs that were AMERICAN INSTITUTE OF MINING, METALLURGICAL AND PETROLEUM ENGINEERS. 1973. recommended for the study group as well as the number of SME Mining Engineering Handbook. 1st edn. New York. each recommended PDP. It is clear from the figure that the ASSOCIATION OF MINE MANAGERS OF SOUTH AFRICA. 2014. AMMSA Safety Summit. habit of being able to simplify problems is a major concern. This habit is closely related to the habit of problem-solving CSIR. 2013. Accident investigation practices in the South African mining which was recommended for eight individuals. Frustration industry. Pretoria. handling is the third habit that requires intervention. The underground working environment is full of challenges and DE VILLIERS, P. 2009. Shadowmatch: The Full Story. 1st edn. DBA, definitely requires a radical habit of frustration handling. Johannesburg.

*+',&/*+ DEPARTMENT OF MINERAL RESOURCES. 2011. Mine Health & Safety. Sub-standard practices and their adverse effects on safety remains a challenge in the South African gold mining http://www.dmr.gov.za/ [Accessed 16 February 2015]. industry. Although a number of previous efforts have been FURNESS, J. 2003. Beatrix Gold Mine, South Africa. Mining Weekly, 12 made to determine the root causes of sub-standard practices, December. the results were inconclusive or addressed the same technical issues that have long been present in the mining industry. GOLD FIELDS LTD. 2012. SA Culture Transformation: Integrated Diagnostic The origin of sub-standard practices in the underground View-KDC. working environment was found to be in the habits, attitudes, and behaviour of employees. However, it is GUTTIEREZ, A. 2010. Slideshare: Theories of Accident Causation. important to realize that habits and attitude are not fixed http://www.slideshare.net/yorkypab/theories-of-accident-causation characteristics like personality. Habits and attitude can be [Accessed 27 June 2015]. changed and developed with the correct instruments. The research described in this paper (the study performed HANSEN, L. 1973. Health and Safety. SME Mining Engineering Handbook. at a gold mine in the Free State, the cultural survey conducted Given, I. (ed.). American Institute of Mining, Metallurgical and Petroleum at West Wits, and the Shadowmatch survey) all highlighted Engineers Inc., New York. pp. 3-2-3-10. correlating causes of sub-standard practices which had their roots in the habits and behaviour of employees. The absence MASEKHOA, N.O. 2012. Mine Health and Safety Council. www.mhsc.org.za/ of certain radical habits (such as team inclination, conflict sites/default/files/CTF%20and%20CoE.pdf [Accessed 2 May 2015]. handling, leadership, altruism, discipline, and resilience) for a specific working environment and a specific job title (in this MINE HEALTH AND SAFETY COUNCIL. 2014. Facts and Figures. case underground production employees with the focus on http://www.thisisgold.co.za/downloads/finish/6-presentations/44-mhsc- shift bosses) could be the primary reason behind sub- 2014-zero-harm-presentation [Accessed 21 April 2015]. standard practices.

Aspects such as a lack of education, inappropriate on- MOL, T. 2002. EHSToday: An Accident Theory that Ties Safety and Productivity the-job training, and shortcomings in managerial style were Together. http://ehstoday.com/mag/ehs_imp_35910 [Accessed 25 June found to increase the occurrence of sub-standard practices, 2015]. which in turn had adverse effects on the safety culture at the gold mine. RAOUF, A. 2011. ILO Encyclopaedia of Occupational Health & Safety. The problem extends beyond a specific section at one http://www.ilo.org/iloenc/part-viii/accident-prevention/item/894-theory- mine or a specific shaft, and is most likely an industry-wide of-accident-causes [Accessed 29 June 2015]. issue that needs to be addressed. The best solution would be to determine whether the habits and attitude of an individual SAARI, J. Not dated. Encyclopaedia of Occupational Health and Safety: Part VII- are suited for a specific job position and working Accidents and Safety Management. http://www.ilocis.org/documents/ environment before employing that person. This would avoid chpt56e.htm [Accessed 25 June 2015]. the need for subsequent remedial action on sub-standard practices. SOCIETY FOR MINING, METALLURGY AND EXPLORATION. 2011. SME Mining However, there is no single solution that would alleviate Engineering Handbook. 3rd edn. Littleton, Co. the current problem. In order to address the different aspects of the problem, a number of solutions such as a THIS IS GOLD. 2015. Facts and Figures: Safety Performance February 2015. Shadowmatch survey, improved training, basic education, http://www.thisisgold.co.za/downloads/finish/4-fact-sheets/3-fact-sheet- revision of risk control programs, are suggested. july-2014-safety-performance/0 [Accessed 23 April 2015]. Finally, the gold mining environment in South Africa poses some of the most extreme challenges with regards to VAN ZYL, A. 2015. Clinical psychology of behaviour. [Interview]. 21 March working conditions. Looking forward, it would be impossible 2015. N L 316    VOLUME 116          http://dx.doi.org/10.17159/2411-9717/2016/v116n4a3 A critical investigation into tyre life on an iron ore haulage system by G.C. Lindeque* Paper written on project work carried out in partial fulfilment of B. Eng. (Mining Engineering)

+$  (  " Two main methods of increasing tyre life were identified: A downward trend in tyre life on haul trucks at an open pit iron ore mine prompted an investigation into the current tyre management strategy in ® Method A: reducing the site wear rate of order to improve tyre life. ‘Best practice’ was compared to the current tyre tyres, as measured in millimetres per management strategy at the mine to determine aspects that could be 1000 hours improved. Aspects that showed significant room for improvement included ® Method B: reducing the percentage of employee tyre awareness, tyre pressure maintenance, and road conditions. tyres that fail prematurely. For each of these aspects a plausible alternative was suggested. A new tyre management strategy was formulated as a step-by-step ! !   ! guide on how to implement the proposed changes. Each step introduces The most common reason to scrap a tyre is new initiatives but at the same time builds on the previous step’s success. simply because it is worn out. In 2014 it was A sensitivity analyses was performed to determine the impact of the proposed changes, with the variables being the reduction in the percentage determined that 59% of all tyres scrapped were of premature tyre failure, and the reduction of the site wear rate. classified as worn out. A tyre that is worn out The ‘most likely’ scenario showed an increase in tyre life of 41% for has reached its maximum life achievable due the Komatsu 730 trucks and 105% for the CAT 777 trucks if the entire tyre to a specific wear rate. The wear rate at the management model is implemented. This would result in a possible annual mine in terms of each tyre classification is saving related to tyre usage of R9.2 million. shown in Table II. The data shows that the achievable tyre life for each truck is signifi- *$ # tyre life, tyre management, wear rate, premature tyre failure, tyre cantly higher than the recorded tyre life. This awareness. is due to abnormal wear of tyres or tyres that fail prematurely.

! ! !  ! In 2014 it was determined that 41% of all )$#"$ tyres failed prematurely. This is an increase The study focused on the tyre life on the main of 8% from the previous year. The increasing haul fleet at an open pit iron ore mine. The number of tyres that fail prematurely is the haul fleet consisted of 17 Komatsu 730 (180 t) biggest contributor to the decreasing trend in haul trucks and 12 CAT 777 (90 t) haul tyre life over the last two years. If fewer tyres trucks. fail prematurely, more tyres will be worn out The haulage operation consists entirely of and therefore the overall tyre life will be tyre-based haul trucks. Five per cent of the increased. Figure 2 shows the monthly costs total mining budget is related to tyre costs. associated with each premature failure mode Since 2012 there has been a steady decrease in for a period from 2012 to 2014. In November tyre life as measured in operating hours 2014 the year-to-date premature failure cost (Figure 1) due to the high percentage of tyres totalled R2.5 million (Jordaan, 2014), an that fail prematurely. In 2014 a total of 41% of increase of 92% from November 2013 (R1.3 all tyres failed prematurely and 61% were million). classified as ‘worn out’. The cost associated with tyre failure is based on the value of remaining tread on a $   %!% '$"$ The purpose of this study was to evaluate the current tyre management strategy at the mine and to identify possible aspects that can be altered in order to increase tyre life. A detailed * University of Pretoria, South Africa. breakdown of the objectives and method- © The Southern African Institute of Mining and ologies followed during the project is shown in Metallurgy, 2016. ISSN 2225-6253. Paper received Table I. Jan. 201.

         VOLUME 116    317 L A critical investigation into tyre life on an iron ore haulage system

Table I Objectives and methodologies

Objective Methodology

Quantify the problem The tyre performance history was thoroughly investigated to: • Determine the tyre life trend and outlook • Determine the current tyre-associated targets • Determine the cost of premature tyre failure • Determine the main causes of premature tyre failure through analysing component failure reports and general monthly tyre management reports Identify all the parameters that can influence tyre life A literature survey was conducted to: • Determine the different factors that influence tyre life • Identify the main element of a proper tyre management strategy (best practice) Determine the impact of each parameter on tyre life Each factor that was identified through the literature survey was investigated to determine the extent of the impact if not managed properly Investigate the operational practises. The current tyre management strategy was investigated and analysed through: • On-site observations • Historical tyre failure data • Historical road and pit conditions data Determine which aspects of the current tyre After the evaluation of each aspect of the current tyre management strategy a plausible alteration was management strategy can be altered to comply with suggested, if found unsatisfactory best practice in order to increase the tyre life of both the waste and ore haul trucks Determine the impact of the proposed changes. The qualitative impact of the proposed alterations was estimated and the financial impact thereof was calculated.

Table II Tyre wear rate

Truck Tyre size Target tyre life Tread available Wear rate (mm per 1000 hours Tyre life at actual wear rate (hours) (hours) (mm) To achieve target tyre life Actual

Komatsu 730 40.00×R57 7200 87.0 12.1 9.0 9667 CAT 777 27.00×49 5600 79.0 14.1 8.0 9875

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"#$%  % % %#$!#$%#$%!"#$%% scrapped tyre, which is referred to as lost tread. The lost tread value of scrapped tyres for 2014 was in the range of R5.5–6.0 tyre management strategy has to be aligned with ‘best million. This is the total value of tread left on all the tyres practice’ in order to significantly improve tyre life. The results that were scrapped in the year. Lost tread is caused not only from the literature survey suggested that a ‘best practice’ tyre by the various premature failure modes, but also abnormal management strategy should consist of the key elements that wear of tyres. are summarized in Table III.

! ! ! !    ! From the literature survey it was determined that a single The operational practices at the mine were then evaluated to tyre failure mode cannot be associated with a certain aspect determine whether the following elements were adequately of tyre management. This led to the conclusion that the entire addressed. L 318    VOLUME 116          A critical investigation into tyre life on an iron ore haulage system

Table III Key elements of ‘best practice’ tyre management

Maintenance • Tyre pressure maintenance • Haul road maintenance • Tyre maintenance • Vehicle maintenance Haul road design • Horizontal and vertical alignment • Cross fall • Drainage • Super elevation • Curve radius • Road construction • Road width Loading practice The payload policy of the haul truck manufacturer should be strictly adhered to and monitored Vehicle speed Specific attention to maximum speed, acceleration, and braking Tons-kilometres per hour (TKPH) The TKPH rating of the tyre should never be exceeded due to the site work load (speed and payload) Matching of tyres In order to ensure even wear, tyre assemblies operating as dual pairs must: • Have the same outside diameter • Be from the same manufacturer • Be of the same type (industry code).

   differ if the actual amount of incorrect inflation was known. According to the tyre management contractor (Woodman, The tyre pairs on the rear axle of a truck need to match in 2002), 10% underinflation in very demanding conditions order to ensure even wear of both tyres. The mine does this such as an iron ore mine can lead to a reduction in tyre life of well, as matching spare tyre pairs are kept in a tyre bank. 27%. Another concern is that an individual tyre is only The tyre bank is kept well stocked by replacing tyres on the checked seven times per month, and not the minimum front axle after 30% tread wear with new tyres (Jordaan, required frequency of once a day. 2014). Pairs of equally worn tyres are made up from the replaced tyres and stored in the tyre bank. The mine keeps a  well-stocked tyre bank, with 99 Komatsu 730 tyres and 69 It was found that the mine adheres strictly to the payload CAT 777 tyres recorded during November 2014. policy of Komatsu (2014) in the case of the Komatsu 730   trucks, due to the built-in system on those trucks. This is, however, not the case for the CAT 777 truck. The payload TKPH is a measure of the heat buildup in a tyre due to the study revealed that only 44% of all loads were less than the load it has to carry and the speed at which it is travelling. The optimum load of 90.5 t. Of the 56% of the loads that TKPH is currently not being monitored. A TKPH study was exceeded the optimum, 13% were overloaded more than 20%. done to determine the suitability of the current tyres for the This data is summarized in Figure 3. working conditions. The results are summarized in Table IV. The table shows the average TKPH of the tyres on the axle with the heaviest load, thus showing the average Table IV maximum TKPH of each cycle. From Table IV it is clear that the actual TKPH for tyre types is well below the TKPH rating TKPH study results of the manufacturer. This suggests that the correct tyres for Truck Tyre type TKPH rating Actual site TKPH each truck type in terms of TKPH are being used, and that the tyres are not failing prematurely due to the work load. Komatsu 730E - 7 40.00×R57 960 523.9 Komatsu 730E - 8 40.00×R57 960 785.7      CAT 777 27.00×49 480 386.4 The average vehicle speed is well within the limits prescribed by the mine. There is, however, no means of live monitoring of acceleration and braking. This is where the real danger to tyres lies. Some elements of the mine’s current tyre management strategy showed room for improvement.   Only 90% of tyres are correctly inflated at any given time – thus 20 tyres in the haul fleet are at an incorrect tyre pressure. To what extent these tyres are incorrectly inflated is unknown. A sensitivity analyses was done and the results were based on the assumption that the 10% of tyres that are at an incorrect tyre pressure are 90% inflated. Results would "#$%%% %%! !%" #" " %

         VOLUME 116    319 L A critical investigation into tyre life on an iron ore haulage system

 certain aspects of tyre- and road-related elements. This step involves some capital cost and the associated increased Road conditions can be assessed according to two categories operating costs. Phase 2 builds on Phase 1. The initiatives of road – permanent and in-pit. Currently, the permanent implemented in Phase 1 continue to be practised, with the roads are monitored and assessed using an assessment and additional changes described in Table V. reporting system. This system has a number of drawbacks, the main one being the lack of communication between  !  !  ! assessor and operator who can correct the error. A new Phase 3 is the culmination of the tyre management model. system is proposed (Dust-a-Side, 2013) that will fill the This phase involved the majority of the capital spend and has communication gap. This new system will make continuous the highest additional operating cost. This step can be road evaluation possible, because road defects can be implemented only if Phase 1 and 2 were successful. identified and logged by using a handheld device. This information is immediately shared with the operators of road !   maintenance equipment by using wireless technology. By thoroughly analysing all the results, informed estimations  of the cumulative effect of the various initiatives under each phase could be made. A sensitivity analysis was done to The main challenge at the mine is not the tyre management determine the impact of different scenarios for each step. strategy, but the level of tyre awareness amongst employees. These scenarios were classified as ‘worst case’, ‘most likely’, Figure 4 show the results of a questionnaire completed by and ‘best case’. Each of these scenarios is characterized by a employees of various levels. The employees would have different impact of each step on: known the correct answers to the questions if their level of ® tyre awareness was adequate. The most concerning fact is Reducing premature tyre failure (improvement method that the operators, who have the largest impact on tyre life, B) ® showed the lowest level of tyre awareness. Reducing the site wear rate (improvement method A) If tyre awareness increases amongst employees, common This is demonstrated by Table VI. operator errors would decrease. These include: The results of the sensitivity analysis are shown in ® Reversing onto the muck pile while loading Figure 5 by displaying the calculated savings associated with ® Speeding around corners while loaded each phase. Phase 1 has the largest positive impact on tyre ® Spillage in the loading area life and results in the largest possible annual saving. Phases ® Driving through spillage and water 2 and 3 have a smaller positive impact on tyre life, resulting ® Incorrect loading practices. in less annual saving. This is due to the fact that phases 2 and 3 involve fewer changes to the tyre management system. ! " % %#$  The better the tyre life on a mine becomes, the harder it is to improve it. The results were reworked into a physical and realistic implementable tyre management model. The model consists of a step-by-step strategy, with different aspect of tyre   " %!%#$ $!"  management to be implemented or changed at specific stages. A tyre forum needs to be established at the mine. This forum The model focuses on the three main elements of the current should include representatives from various divisions of the tyre management strategy that showed room for mine. It is recommended that the tyre forum implement Phase improvement. These are: 1 of the tyre management model. The most significant ® Tyre awareness positive impact on tyre life is associated with Phase 1, with an increase in tyre life of 20% for the Komatsu 730 tyres and ® Tyre pressure maintenance 75% for the CAT 777 tyres according to the ‘most likely’ ® Road conditions. scenario. Such an increase in tyre life will reduce the annual The tyre management model consists of three phases. tyre usage and result in an annual saving of approximately Each phase uses different tools to improve tyre management, R6 million. but at the same time builds on the previous phase. Table V describes the initiatives in each phase. It also indicates which tyre life improvement method (A or B) each initiative will have the most significant positive effect on.

 !    !! The employee mind-set and tyre awareness have to change before large sums of capital are spent on technology in an effort to increase tyre life. Phase 1 consisted of most of the changes to the current tyre management strategy, and thus it was estimated to have the most significant positive impact on tyre life.

 !   !   Phase 2 is associated with automated information regarding "#$% $$% %#$%!!#$$ %! %$ $$ L 320    VOLUME 116          A critical investigation into tyre life on an iron ore haulage system

Table V Tyre management model description

Phase Initiatives Method Description BA

1 Tyre awareness campaign Based on similar tyre awareness campaign results at another mine. Cost based on one full-time employee salary to drive the programme Tyre life monitoring Work with people, give information but also hold them accountable. Information is distributed using the and feedback current systems and discussed in the daily 09:00 production meeting and during the daily Operator Caucus sessions Operator education √ In house (no extra cost) Incentives Exact incentive strategy will be designed by a tyre forum but will be based on individual truck tyre performance. This will single out and reward hard-working employees and will serve as extra motivation to take good care of tyres Payload control √ √ Only CAT 777 trucks. Payloads will be manually monitored by operators with much more care Vehicle speed √ Vehicle speed will be manually monitored by all truck operators with much more care Pressure monitoring Manual pressure checks √ √ Increase the number of pressure checks to two per truck per shift. This will require two new employees. (4 per day) Road conditions Site severity survey √ Reinstate the site severity survey as discussed previously. No extra cost Specialist grader √ This requires the training of current grader operators by outside specialist to become specialist graders. operator training R100 000 annual fee converted to a rand per month value. New training and refresher courses would be needed Supervisor application √ This entails the supervisors of grader operators to be trained by outside specialist in order to become engineering training experts in the field of grading (know what to look at in terms of grader performance, advice to give to operators, and how to apply the equipment to achieve the best result). R100 000 annual fee converted to a rands per month value. New training and refresher courses would be needed Total impact 15% 0.1 2 Road conditions Permanent roads √ Implementation of the new monitoring system for main haul roads. Capital cost for units and operating cost for information processing Grader operator made √ Four specialist grader operators are appointed and a new career path is created with the total salary higher level status increased to match that of a haul truck operator. This will ensure that graders are operated only by grader specialists Pressure monitoring iTrack for CAT 777 fleet √ √

Vehicle speed √ iTrack TPMS installed for CAT 777 fleet. Operating cost includes two dedicated employees to monitor the system. TKPH monitoring √ Total impact 2.5% 0.3 3 Pressure Monitoring iTrack for entire fleet √ √ iTrack System for entire fleet. Free trial period is available. Operating cost includes three dedicated employees to monitored and drive the system. Capital cost includes the installation of system on the remaining 17 Komatsu 730 trucks Vehicle speed √ √ TKPH monitoring √ Road conditions Grader operator made √ √ Six specialist graders operators are appointed and a new career path is created with the total salary increased higher level status to match that of a haul truck operator. This will ensure that graders are operated only by grader specialists Total impact 2.5% 0.1

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         VOLUME 116    321 L A critical investigation into tyre life on an iron ore haulage system

Table VI Sensitivity analysis estimations

Phase Tyre life improvement method Scenario Worst case Most likely Best case

1 B 15% 20% 25% A 0.1 0.2 0.35 2 B 2.5% 5.0% 6.5% A 0.3 0.6 0.8 3 B 2.5% 5.0% 6.5% A 0.1 0.2 0.35

The main component of Phase 1 is the tyre awareness & $$$ campaign. The exact details and specifications of this This paper is based on project work carried out in partial programme need to be designed and driven by the tyre forum fulfilment of the degree B Eng (Mining Engineering) to specifically suit the mine. Tyre life improvement needs to be a dynamic and ever-improving process. Due to the capital sensitivity of the current mining +$$#$$ environment, implementation of phases 2 and 3 is optional. DUST-A-SIDE. 2013. Dasmetrics introduction and overview. The sensitivity analysis showed that the largest opportunity http://www.dustaside.com/services/quality-management-systems/das- for savings lies with phase 1, which has virtually no extra metrics cost associated with it. JORDAAN, A. 2014. General Monthly Report-November, Mine X: OTRACO It is the role of the tyre forum to conduct monthly International, Redcliffe, Western Australia. meetings where the newly formulated tyre management JORDAAN, T. 2015. Mining Manager. Personal communication. model is discussed and evaluated, focusing on four major areas: KOMATSU. 2014. About Komatsu. http://www.komatsu.com.au/AboutKomatsu [Accessed 10 December 2014]. ® Conditions ® Operations MICHELIN. 2015. Technical Data- Earthmover Tyres. ® Maintenance WOODMAN, C.A. 2002. Tyre selection, use and operational issues to maximise ® Tyre performance. tyre life. OTRACO International, Redcliffe, Western Australia. N L 322    VOLUME 116          http://dx.doi.org/10.17159/2411-9717/2016/v116n4a4 Review of support systems used in poor ground conditions in platinum room and pillar mining: a Zimbabwean case study by T. Chikande* and T. Zvarivadza* Paper written on project work carried out in partial fulfilment of BSc. (Mining Engineering)

Dyke is almost like a trumpet, comprising layers that dip towards the centre. The reef *;:06=6 exploited at the mine, the Mineralised Sulphide Zone (MSZ), is located in the pyroxenite Falls of ground pose costly hazards to personnel and equipment and thus measures should be taken to prevent them. This study endeavours to improve layer, which is hosted in the ultramafic the support systems used in geotechnically poor ground at a Zimbabwean sequence. The MSZ is a uniform layer about 2– platinum mine by analysing the status quo and recommending an effective 3.5 m thick, dipping at around 10–14° from support system. Various techniques were used to determine the quality of surface outcrop towards the axis of the basin, ground conditions, predict the rock mass behaviour, and to identify the and located between bronzite and websterite appropriate rockbolt type. An analysis of the current ground control methods horizons. The visible disseminated sulphide and their limitations was also undertaken. mineralization shows a typical and consistent The results showed that the current support system and mining practices vertical distribution of platinum group metal in poor ground need to be modified to improve safety and productivity. (PGM) and base metal values. The research Stoping overbreak is influenced by poor ground conditions and the explosives was undertaken to review the current support currently used. The use of emulsion is recommended to replace ANFO. systems used in geotechnically poor ground Redesigning of pillars is also recommended in poor ground conditions. An evaluation of the current roofbolt system indicated an opportunity for conditions in a bid to improve both safety and improvement. With new insight on the performance of the shorter length productivity. roofbolts currently in use, a new support system was recommended taking into consideration cost-benefit analysis. Barring down using pinch bars in ($($)%#") poor ground was seen as a risky and time-consuming exercise, hence the use The mine is fully mechanized and uses the of mechanical scalers is recommended to achieve zero harm and to meet bord and pillar mining method. Access is via production targets. Smoothwall blasting is recommended in poor ground to two declines, one for access of men and minimize excavation damage. Other recommendations include the use of materials and the other for hoisting ore. The hydrological surveys to determine groundwater levels and implement mining layout used in poor ground conditions corrective measures. Both empirical and numerical modelling approaches is shown in Figure 1. need to be utilized in determining the optimum support.

@8* :7.6 ($($)%$(!"$%$#) bord and pillar mining, support systems, pillar design, explosives, roofbolts. The area investigated is characterized by upthrows usually related to sympathetic faults and increased joint frequency. This imposes challenging mining conditions and increases the risk of rockfalls. The reef-subparallel ?;<7:.43<=:; planes in the hangingwall can give rise to The presence of geological discontinuities such unstable hangingwall environments, resulting as faults and joints weakens the rock mass. in block and wedge failures when the planes of Adequate support is critical in achieving zero weakness are intersected by the J1 and J2 joint harm in underground mines. This paper (discontinuity) sets. As the number of joint reviews the current support systems used in sets increases, the strength of the rock mass poor ground conditions at a Zimbabwean deteriorates. There are three prominent joint platinum mine. The area of research is located sets at the mine: on the Great Dyke of Zimbabwe. The mine exploits platinum group elements (PGEs) and base metals. It is shallow, having a maximum depth of less than 300 m. The Great Dyke is the second largest reserve of PGEs, following the South African Bushveld Complex * School of Mining Engineering, University of the (Oberthür et al., 2012). It is a linear layered Witwatersrand, Johannesburg, South Africa. intrusion that extends for about 550 km with a © The Southern African Institute of Mining and maximum width of 11 km (Prendergast, Metallurgy, 2016. ISSN 2225-6253. Paper received 1989). The generalized section of the Great Dec. 2015.

         VOLUME 116    323 L Review of support systems used in poor ground conditions

excavated. Virgin stresses exist in rocks prior to any excavations (Brady, 1985). The magnitude of the vertical component of virgin stress is given (Brady, 1985) by:

virgin = g h [1] where  is the density of the rock mass, g is acceleration due to gravity, and h is the depth below the surface in metres.

&'%')")($'#& ( (# Wood (1987) pointed out that instability can be caused by +=5478>%-=;=;5>29*:4<>=;>0::7>57:4;. the following: ® A decrease in strength to stress ratios, which results in failure of material around the excavation ® ® J1, which trends east-west with an average dip of 70° Geological structures that result in collapse ® and a strike of close to 90° A combination of the above two points ® ® J2, which trends north-south and has an average strike Seismic events. of 008° The authors investigated the strength to stress ratios in a ® J3, which comprises a shallow-dipping plane parallel to bid to determine the factor of safety. There is no history of sub-parallel to the orebody. seismic events in the area of the investigation, hence seismic Talc and serpentine are the common types of joint infill forces were ignored: however, the authors recommended that material. the mine install seismic monitoring devices.

!"% #) & !"$ %%!%')" ) & (#)%'($&#("$)  The company uses a mechanized room and pillar mining Brady (1985) noted that when there is no core available but method. As mining progresses, the intensity of faulting and there are traces of geological discontinuities, Equation [2] jointing increases. This has led to general support failure and can be used to determine Rock Quality Designation (RQD). a challenge in maintaining a stoping width of 2 m. Associated RQD = 115 - 3.3 Jv [2] problems and consequences of this include stoping where J is the sum of the number of joints per unit length for overbreak, grade dilution, unpredictable unravelling of rocks, v all discontinuity sets, and is known as the volumetric joint a decreased factor of safety, increased support costs, and count. failure to meet production targets. RQD is a directionally dependent factor when determined The problems and consequences of poor ground using drill core. The use of volumetric joint count is of conditions led to the need to review the current support paramount importance in reducing this directional system at the mine. Figure 2 shows the mine layout and the dependence (Brady, 1985). RQD is envisioned to indicate the area where the research was conducted. quality of the in situ rock mass. The calculated RQD will then The need to conduct the research is justified by the be used to determine the Q rating and Rock Mass Rating following: (RMR). ® The obligation to improve safety by ensuring that there is adequate regional and local support %"% &$( ') &''(( &#("$))" )&'')&#($ ® The need to improve productivity by meeting  production targets in the required time The RMR system incorporates the sum of six parameters ® The need to minimize PGE grade dilution (Bieniawski, 1989): ® The need to minimize cost of re-supporting ® The opportunity to add value to the company. 1. Uniaxial compressive strength of rock material 2. Rock Quality Designation (RQD) !"% #)" % #(%' 3. Spacing of discontinuities The main objectives were to analyse and improve the current 4. Condition of discontinuities support systems used in poor ground. This was done by: 5. Groundwater condition. 6. Orientation of discontinuities. ® Reviewing the current support system and identifying its limitations ® Designing an effective support system to be used in poor ground ® Making recommendations that can be used to improve the support systems.

=<879<478>78=8 To effectively pin down the research problem and come up with effective solutions, a critical review of relevant literature was undertaken. Rock masses experience primitive stress before mining and induced stresses after openings are +=5478>%-=;8>29*:4<> =<,>9789>:1>7868973,>=;.=39<8. L 324    VOLUME 116          Review of support systems used in poor ground conditions

Table I /:3$>"492=<*>#86=5;9<=:;>

:39<=:; !:&>:1>(:=;<6>=;>6<7=$8 -9& !:&>:1>(:=;<6>=;>.=0> -9&> !:&:1>(:=;<6>=; -9& !:&>:1> /:3$> .=783<=:;> (:=;< .=783<=:; (:=;< ,9;5=;5 922>> (:=;< (:=;<6> "492=<* 087>4;=<>28;5<,6093=;5087>4;=<>28;5<,6093=;5087>4;=<>28;5<,6093=;5087>) #86=5;9<=:;

!:&#=6<9;38 ' !:&#=6<9;38  !:&8=5,<  ))  /"#

66nbg 18 10 1.8 0.3 18.00 7.00 2.6 0.4 9.0 2.3 3.9 100 8.3 88 65nbg 23 11 2.1 0.4 14.00 6.50 2.2 0.2 8.0 2.2 3.6 52 7.9 89 64ntb 18 14 1.3 0.4 15.00 6.00 2.5 0.3 8.0 2.3 3.5 48 7.3 91 64nbg 17 10 1.7 0.30 18.00 6.00 3.0 0.20 9.0 2.0 4.5 98 9.2 85 63ntg 19 8 2.4 0.3 13.00 6.00 2.2 0.5 14.0 2.0 7.0 79 11.5 77 63nbg 25 11 2.3 0.4 18.00 5.00 3.6 0.4 14.0 2.1 6.7 100 12.5 74 62nbg 22 10 2.2 0.4 17.00 6.00 2.8 0.3 15.0 2.3 6.5 100 11.6 77 62ntg 21 8 2.6 0.35 18.00 6.00 3.0 0.30 12.0 2.1 5.7 89 11.3 78 61nbg 23 9 2.6 0.2 14.00 6.00 2.3 0.3 11.0 2.1 5.2 200 10.1 82 67nbg 22 11 2.0 0.2 17.00 6.00 2.8 0.2 13.0 2.2 5.9 87 10.7 80 68nbg 21 9 2.3 0.3 20.00 6.00 3.3 0.5 11.0 2.1 5.2 203 10.9 79 68ntg 22 12 1.8 0.4 18.00 5.00 3.6 0.4 14.0 2.2 6.4 200 11.8 76 82ntg 23 11 2.1 0.2 17.00 6.20 2.7 0.4 13.0 2.0 6.5 96 11.3 78 83nbg 25 11 2.3 0.3 16.00 6.00 2.7 0.3 14.0 2.0 7.0 200 11.9 76 83ntg 22 13 1.7 0.4 15.00 5.40 2.8 0.4 13.0 2.2 5.9 202 10.4 81 84nbg 26 14 1.9 0.3 17.00 6.00 2.8 0.4 12.0 2.2 5.5 97 10.1 82 84ntg 21 9 2.3 0.4 16.00 5.00 3.2 0.3 11.0 2.2 5.0 93 10.5 80 85ntg 22 10 2.2 0.2 19.00 6.50 2.9 0.5 13.0 2.2 5.9 89 11.0 79 81nbg 23 11 2.1 0.3 18.00 6.20 2.9 0.3 11.0 2.1 5.2 55 10.2 81 81ntg 18 6 3.0 0.3 18.00 6.00 3.0 0.3 13.0 2.1 6.2 100 12.2 75 86nbg 17 8 2.1 0.4 17.00 5.40 3.1 0.4 14.0 2.2 6.4 200 11.6 77 86nbg 22 10 2.2 0.3 15.00 6.00 2.5 0.4 13.0 2.2 5.9 102 10.6 80 87nbg 22 14 1.6 0.3 17.00 5.00 3.4 0.3 12.0 2.2 5.5 100 10.4 81 87ntg 21 8 2.6 0.3 18.00 6.50 2.8 0.3 15.0 2.2 6.8 100 12.2 75 88nbg 17 6 2.8 0.3 21.00 6.20 3.4 0.3 14.0 2.1 6.7 58 12.9 72 88ntg 19 6 3.2 0.2 16.00 6.00 2.7 0.4 15.0 2.1 7.1 55 13.0 72 nbg: north bottom gully, ntb: north top gully)

The relationship between RMR and Q is given by (Brown openings, pillar strengths and pillar stresses need to be and Hoek, 1980): determined (Wilson, 1972). After determining pillar strengths RMR = 9ln Q + 44 and stresses, separate pillars and pillar layouts will be designed depending on the degree of stability needed. )''#%       Barton et al. (1974) noted that the Q system classification is The strength of pillars depends on: based on the following three aspects: ® The strength of the intact rock that makes up the pillar ® Block size (RQD/J ) n material, suitably downrated to take into account the ® Inter-block shear strength (J /J ) r a scale effect ® Active stress (J /SRF) w ® The geometry of the pillar, taking into account the RQD J J shape and width to height (W:H) ratio. Q = x r x w [3] Jn Ja SRF For W:H ratios less than 4.5, the strength of hard rock The authors used the Q system to estimate the required pillars is given by: support based on charts, which are discussed under results. 0.5 0.75 Ps = K.Weff /H [4] "!#)''#%' where

A sound strategy for overall mine stability is critical to avoid Ps is the pillar strength accidents or conditions that may give rise to incidents. The K is the design rock mass strength (DRMS) in MPa major hazards addressed by a sound mining method design Weff is the effective pillar width. Weff = 4 × pillar area / pillar and layout include uncontrolled collapses, surface perimeter. subsidence, and major fall of ground incidents.    ( &!)%'($ In situ stress conditions, together with local and regional The pillar support system is the chief basis of support in extents of mining, will determine the stresses acting on a underground mines using the room and pillar mining pillar (Wilson, 1972). For a horizontal mining layout, pillar method. In order to design pillars for supporting mine stress (Pstress) is given by

         VOLUME 116    325 L Review of support systems used in poor ground conditions

, v Pstress = [5] support system, a study was carried out in all sections of the 1-e mine with poor ground conditions, which included Levels 14 where: v is the vertical field stress and e is the extraction to 24. Underground observations, recordings, and data ratio collection were done in these sections. Observations and ( &!)%'($)!" %!% analysis were carried out on the geological structure of the orebody to identify the nature and magnitude of the jointing After determining the pillar strength and pillar stress, the and faulting system. The effects of current mining practices factor of safety (FoS) of the pillar can be calculated as and explosives used were assessed. Interviews were also follows: conducted as part of the study approach. Observations were Pillar FoS = Pstrength/Pstress [6] made in each level and the following parameters were measured and noted: For primary extraction, the minimum design FoS of pillars ® Structural data – number of joints, separation of joints is 1.6. Due to the effect of the explosives used and poor etc. ground conditions, the authors reviewed the current practices ® Pillar dimensions by measuring the actual pillar dimensions in a bid to ® Stope widths of each gully calculate the actual factor of safety. Redesigning of pillars ® Time taken to support one gully was considered where current pillar system is not adequate. ® Fallout heights The conclusion will be drawn after analysis of the results. ® Type of support used.  "'(%)!"%!#(%' The results of these observations were analysed using Ammonium nitrate-fuel oil (ANFO) is a supreme explosive rock engineering principles. used in the mining industry. Its advantages include simple production, low cost, and lack of sensitivity to mechanical   impact during mechanical loading into drill-holes (Mather, This exercise comprised the methodical collection of all 1997). ANFO has also some disadvantages, which include fracture statistics of the underground rock face. The data lack of water resistance and low detonation parameters, collected included joint roughness, joint sets, joint alteration, which reduce its use to dry blast-holes in truncated compact joint water, stress reduction factor, and RQD. These rock masses (Maranda, 2011). Since the type of explosive parameters were used in the calculation of the Q rating of the used has an effect on support systems, the authors reviewed pillars. the literature on ANFO as well as the other bulk explosives, which include emulsion and watergel. The merits of bulk " )&'') &''(( &#("$ emulsion explosives over ANFO and packaged products The determination of the rock mass state was critical to the include easy transportation and handling, increased safety, investigation. Various techniques were applied to determine string charging, low gas emissions, water resistance, full the ground classes in the research area. A comparative coupling, increased velocity of detonation, detonator analysis of these techniques was then conducted to select the sensitivity, and improved work environment (Maranda, most effective method. Substantiated recommendations of the 2011). ANFO generates a lot of gases upon detonation, suitable support to be installed were based on the chosen thereby widening pre-existing cracks. ANFO usage will method. The methods that were used include: therefore result in the formation of keyblocks, which will lead ® The Q system to an unstable hangingwall. In addition, the cut slice will ® RMR increase due to overbreak and more poor hangings will be ® MRMR. formed that require intense barring-down. Barring down becomes a risky operation due to frequent keyblocks and is %!"!&$ %)")($'#& %)'"!#)% %%$#' also time-consuming, leading to failure to meet production Installed support elements used at the mine include rockbolts, targets. shotcrete, and straps. These were analysed for their performance and effectiveness with regard to the fallout /868973,>9007:93, heights and the ground characteristics by means of log data A comprehensive revision of the background literature was and previous reports to ascertain whether failures could be conducted as per the requirements of the project objectives. attributed to the support, the conditions, or both. The The background literature was then combined with contri- analyses included examining situations of failure and of butions from the relevant experts in the field of study, such likely failure. as rock mechanics engineers on a practical level. A field study of the areas of concern was supplemented by the contribution $%'#(&#("$)")#%)%% #(%$%'')")( &!' of experts in order to assemble a system of results that would The pillar strength calculations were carried out through be used for analysis. measurement of pillar heights and widths. The stress acting on a selected pillar was determined by calculation. Pillars are %'%&! ) !(#%!("$ usually less than the designed size due to poor blasting and The research started with the literature review on geological can undergo spalling attributed to poor ground. The and geotechnical factors, underground support systems, frequency of such occurrences was investigated with the view mining methods, and types of explosive used. In order to to highlight the short-term and long-term problems obtain a clear understanding of the existing mining and associated with these practices. L 326    VOLUME 116          Review of support systems used in poor ground conditions

 &'#)%'($)&$)($($)!& #( %' three methods were compared to identify the most suitable method of ground classification. The current blast design and explosives used were analysed to:  ® Attain the planned face advance through efficient Table II shows the data used to calculate Q in each bord. blasting Jx = number of joints per unit distance [7] ® Mitigate overbreak for grade control and mine design purposes where Jx represents Js, Jd, and Jh. ® Reduce damage to rock Jv = Js + Jd + Jh [8] ® Identify the explosives suitable for use in poor ground Using Equation [2], RQD = 115-3.3Jv conditions.   !"% #) "$'#!&($#' Table III shows the RMR calculated from Bieniawski’s six Constrains encountered during the research included the parameters for each gully. following: ® Measuring of pillars was rather dangerous as rockfalls   are mostly from the shoulders of pillars The calculated RMR was adjusted to calculate the MRMR. A ® Difficulties in logging of some ends due to blasting effect adjustment of 97% was used, together with a waterlogging or delays in pumping out water. weathering adjustment of 96%, and 80% for joint orientation. /8642<6> Table IV shows the adjusted RMR to give the MRMR. RMR = 9lnQ + 44 The results are based mainly on geotechnical data collected from the area of research. This includes results from rock The average RMR is below 50, which shows that the rock mass classification methods, numerical modelling, reef- mass is poor. RMR values from Bieniawski are comparable subparallel planes, FoS approach, stoping dimensions, and with calculated values from Q ratings. pillar strength. The current support system data was also Rock-related risks due to the three joint sets are reduced included. by cutting larger pillars and through the use of cable bolts. In Ground Control District-D (GCD-D), the bord is reduced to & &#("$)")!" )&'') &''(( &#("$ 6 m and the in situ pillars are designed to be 3 × 3 m for The rock mass was classified according to each of the three shallower areas (up to 160 m depth) and 3.5 × 3.5 m for systems, which are the RMR, MRMR, and the Q system. The depths greater than 160 m. The main pillars measure 3 ×

Table II /:3$>-966>2966=1=39<=:;> >">6*6<8)

:39<=:; /"# Jn Jr Ja Jw /+ " /-/

66nbg 88 3 1.5 6.0 1.00 7.5 0.97 44 65nbg 89 6 1.5 6.0 1.00 4.0 0.93 43 64ntb 91 6 1.5 6.0 1.00 6.0 0.63 40 64nbg 85 6 1.5 6.0 1.00 8.0 0.44 37 63ntg 77 6 1.5 3.0 1.00 6.0 1.07 45 63nbg 74 12 3.0 5.0 1.00 6.0 0.61 40 62nbg 77 3 1.5 6.0 1.00 10.0 0.64 40 62ntg 78 6 1.5 3.0 1.00 4.0 1.62 48 61nbg 82 4 3.0 6.0 1.00 4.0 2.55 52 67nbg 80 9 1.5 3.0 1.00 10.0 0.44 37 68nbg 79 3 1.5 3.0 1.00 6.0 2.19 51 68ntg 76 6 2.0 2.0 1.00 6.0 2.11 51 82ntg 78 3 3.0 6.0 1.00 8.0 1.62 48 83nbg 76 3 1.5 3.0 1.00 6.0 2.10 51 83ntg 81 4 3.0 6.0 1.00 4.0 2.52 52 84nbg 82 9 1.5 3.0 1.00 10.0 0.45 37 84ntg 80 9 1.5 3.0 1.00 6.0 0.74 41 85ntg 79 9 2.0 2.0 1.00 6.0 1.46 47 81nbg 81 9 1.5 3.0 1.00 8.0 0.56 39 81ntg 75 9 1.5 3.0 1.00 6.0 0.69 41 86nbg 77 4 3.0 6.0 1.00 4.0 2.39 52 86nbg 80 9 1.5 3.0 1.00 10.0 0.44 37 87nbg 81 9 1.5 3.0 1.00 6.0 0.75 41 87ntg 75 9 2.0 2.0 1.00 6.0 1.38 47 88nbg 72 9 1.5 3.0 1.00 8.0 0.50 38 88ntg 72 9 1.5 3.0 1.00 6.0 0.67 40

nbg: north bottom gully, ntg: north top gully

         VOLUME 116    327 L Review of support systems used in poor ground conditions

Table III /:3$>-966>/9<=;5

:39<=:;>  > /"#> 093=;5>:1> :;.=<=:;6>:1> 7:4;. 9<87> .(46<)8;<> /-/ 923429<8.> -9> 79<=;5.=63:;<=;4=<*.=63:;<=;4=<* 79<=;51:7>:7=8;<9<=:; /-/ 79<=;5 79<=;5 79<=;5 79<=;517:)>"

66nbg 53 88 100 mm 1–5 mm Completely dry Unfavourable 47 44 7 17 8 10 15 -10 65nbg 53 89 52 mm 1–5 mm Completely dry Unfavourable 44 43 7 17 5 10 15 -10 64nbg 53 91 48 mm 1–5 mm Completely dry Unfavourable 44 40 7 17 5 10 15 -10 64ntg 53 85 98 1 5 mm Completely dry Unfavourable 47 37 7 17 8 10 15 -10 63nbg 53 77 79 mm 1–5 mm Completely dry Unfavourable 47 45 7178 -1015-10 63ntg 53 74 100 mm 1–5 mm Completely dry Unfavourable 43 40 7 13 8 10 15 -10 62nbg 53 71 100 mm 1–5 mm Completely dry Unfavourable 41 40 7 11 8 10 15 -10 62ntg 53 78 89 mm 1–5 mm Completely dry Unfavourable 47 48 7 17 8 10 15 -10 61nbg 53 82 200 mm 1–5 mm Completely dry Unfavourable 49 52 717101015-10

nbg: north bottom gully, ntg: north top gully

Table IV -=;=;5>/:3$>-966>/9<=;5

:39<=:;> /-/ 89<,87=;5>9.(46<)8;< 296<6>81183<6>9.(46<)8;< :=;<>:7=8;<9<=:;>9.(46<)8;< -/-/>

66nbg 44 0.96 0.97 0.8 33 65nbg 43 0.96 0.97 0.8 32 64ntb 40 0.96 0.97 0.8 30 64nbg 37 0.96 0.97 0.8 27 63ntg 45 0.96 0.97 0.8 33 63nbg 40 0.96 0.97 0.8 30 62nbg 40 0.96 0.97 0.8 30 62ntg 48 0.96 0.97 0.8 36 61nbg 52 0.96 0.97 0.8 39 67nbg 37 0.96 0.97 0.8 27 68nbg 51 0.96 0.97 0.8 38 68ntg 51 0.96 0.97 0.8 38 82ntg 48 0.96 0.97 0.8 36 83nbg 51 0.96 0.97 0.8 38 83ntg 52 0.96 0.97 0.8 39 84nbg 37 0.96 0.97 0.8 27 84ntg 41 0.96 0.97 0.8 31 85ntg 47 0.96 0.97 0.8 35 81nbg 39 0.96 0.97 0.8 29 81ntg 41 0.96 0.97 0.8 30 86nbg 52 0.96 0.97 0.8 39 86nbg 37 0.96 0.97 0.8 27 87nbg 41 0.96 0.97 0.8 31 87ntg 47 0.96 0.97 0.8 35 88nbg 38 0.96 0.97 0.8 28 88ntg 40 0.96 0.97 0.8 30 Average 33

nbg: north bottom gully, ntg: north top gully L 328    VOLUME 116          Review of support systems used in poor ground conditions

10 m and 10 × 3.5 m in most sections. The authors also groundwater. Groundwater reduces the stabilizing normal measured the main pillar dimensions and calculated the stress acting on discontinuity planes, hence weakening the infringements. The actual pillar dimensions of in situ pillars rock. From the results of rock mass classification, it can be were measured and the FoS in the gullies calculated. concluded that adequate support is required for safe mining J3 structures are found in the hangingwall and ground practices. A new roofbolt system envisaged to improve safety penetrating radar (GPR) is used to identify these structures. and productivity is discussed later in this paper. The authors, with the assistance of geotechnicians, took GPR data and assessed the orientations and the average depth !"$)%$%#!&#($)!&&!)  )&$& '(' into the hangingwall. Analysis was conducted to ascertain A slice showing reef-subparallel planes is shown in Figure 3. whether the 1.8 m resin bolts and cable bolts currently used It can be noted that shallow-dipping planes occur at a depth are sufficient. Figure 3 shows a typical slice obtained. A greater than 1.8 m into the hangingwall. The current support clino-rule was used to determine the dip of J1 and J2 system of 1.8 m length is not adequate to clamp these layers, structures. The authors deduced that J1 joint set is the hence a new system that uses longer roofbolts needs to be dominant joint set, with an average strike direction of 088° implemented to reduce the risk of support failure and and an average dip of 70°. The J2 joint set has an average possible injuries, fatalities, and equipment damage. All these strike of 005° and dips at an average of 65°. The J1, J2, and factors lead to heavy cost to the mine, hence it is of J3 joint set data from GPR was used in numerical modelling. paramount importance to improve safety and productivity through the implementation of the new support system. The ;92*6=6>:1>78642<6 authors therefore recommend the use of longer roofbolts in addition to the cable bolts used. #! #!& )&#&)&$& '(' The Q values obtained indicated that the rock is extremely %!( & )"% ($)&$& '(' weak. The values of the measured RMR were comparable JBlock was used to deduce the probability of failure of with the calculated values from the Q values. From this, it keyblocks in the gully. The structural data for the three joint can be deduced that the ground conditions in the area of sets, together with tendon data, was used to simulate research pose a risk due to high probability of potential unstable keyblocks. The authors started by simulating unstable blocks. The authors recommend that the mine uses unstable keyblocks using the current support system of 1.8 m more systems for rock mass classification, since a single roofbolts spaced at 1 m by 1 m. The area simulated is a 6 m system cannot give a clear indication of the quality of the gully in order to check the effectiveness of the current rock due to its inherent limitations. For GCD D, 1.8 m bolts support. are currently used and are spaced at 1 m by 1 m. Barton’s Q Figure 5 shows the probability at which various blocks chart was used to determine the appropriate support system fail using the current support system consisting of grouted for GCD D as shown in Figure 4. tendons 1.8 m in length spaced at 1 m by 1 m in poor ground Based on this chart, the current support system used conditions. From the histograms, it can be seen that the seems to be adequate, although other systems need to be probability of block failure for 1 m3 blocks is 30% and the considered also in the design of the required parameters. The probability of maximum support failure is 16%. The fallout height was found to be 1.8 m in the research area. probability of both block falls and support failure is thus too Roofbolts with a length of 1.8 m are therefore considered high. The current support system is inadequate. Integrating inadequate to clamp the overlying layers, since there will be the results from all the techniques used, longer roofbolts are no bond length. The use of shorter roofbolts has resulted in required to give improved safety. support failure, hence new systems of tendons need to be The new support system designed and simulated by the designed. The issue of reef-subparallel planes and numerical authors consists of grouted tendons with a capacity of modelling will be discussed later in this paper. 160 kN, 2.1 m length, and spaced at 1.2 × 1.2 m. The new All joints in the area of research are currently assumed to system yields the results shown in Figure 6. The probability be dry; however, the authors recommend the use of of block failure for 1 m3 blocks decreases to 11%, and the hydrological surveys to obtain a clear picture of the maximum support failure to 4%.

+=5478>%>6<743<4786>=;>>2882>;:7<,

         VOLUME 116    329 L Review of support systems used in poor ground conditions

+=5478>%97<:; 6>">3,97<>6400:7<>6093=;5>1:7>#>#

+=5478> %7:'9'=2=<*>:1>'2:3$>19=2478>46=;5><,8>34778;<>6400:7<>6*6<8)

+=5478> %7:'9'=2=<*>:1>'2:3$>19=2478>46=;5><,8>;8 >6400:7<>6*6<8) L 330    VOLUME 116          Review of support systems used in poor ground conditions

Taking into account a cost-benefit analysis, a comparison subparallel planes at depths greater than 1.8 m into the was made between the current support system and the new hangingwall implies that the current tendons used will fail to support system Although the 2.1 m tendons are more support keyblocks. The current type of explosives used also expensive than the current 1.8 m tendons, taking into results in stoping overbreak, which decreases the factor of consideration the cost-benefit analysis it can be concluded safety and increases PGE dilution. The ground conditions that the recommended system gives more benefits than the thus require redesigning of the pillars and tendon system to current support system. As well as improved safety, the new improve productivity and safety. The current design assumes system leads to a decrease in support density since the that all joints at the mine are dry, but the effect of tendons will be spaced at 1.2 × 1.2 m as opposed to the groundwater weakens the cohesion of some joints, which current roofbolts spaced at 1 × 1 m. increases the frequency of unstable keyblocks. Barring down using pinch bars is time-consuming and is regarded as a & &#("$)")( &!)%'($)&$) ##($)!& #( %') risky exercise, since the barring team is exposed to unstable The authors evaluated the pillar design and cutting blocks with a higher probability of failure. Because of practices in poor ground conditions. Actual pillar dimensions frequent unstable blocks, barring down using pinch bars in various bords were measured and the resulting factors of wastes more cycle time, which has led to most sections failing safety were calculated (Figure 7). to meet their production targets since fewer faces are The results show that most teams have failed to maintain prepared. the required safety factor of 1.6 due to stoping overbreak. Figure 8 shows how overbreak reduces the FoS. /83:))8;.9<=:;6> Stoping overbreak is caused by poor ground which ® A study of the new support system designed by the unravels unpredictably, and also by ANFO explosive being authors is recommended. Longer roofbolts of 2.1 m used. It is thus critical to redesign pillars so that they are less length spaced at 1.2 × 1.2 m are proposed, as opposed influenced by a small change in overbreak. Pillar robbing also to the current bolts of 1.8 m length spaced at 1 × 1 m. affects the FoS. Zvarivadza (2012) illustrated the relationship The 2.1 m roofbolts are more expensive than the of probability of failure and FoS as shown in Figure 9. current roofbolts; however, there is improved safety From Figure 9 it can be seen that for a FoS of 1.6, the and less support density with the 2.1 m roofbolts. The probability of pillar failure is 0.5%, and at the lowest FoS of extra cost of the roofbolts will be offset by the 1.33 obtained for Bord 66 (Figure 7), the probability of increased spacing, since fewer roofbolts will be used failure increases to 5%. A decrease in FoS therefore increases the probability of failure, hence it is critical to implement a pillar design that is less influenced by overbreak since the ground conditions are poor. Moreover, an alternative to ANFO needs to be considered to reduce stoping overbreak and unravelling of the rocks. Ore dilution occurs as a result of overbreak, as seen in Figure 10, since the grade of PGMs decreases above and below the required slice.

:;3246=:;6 Safe mining practices and installation of adequate support lead to stable excavations. This review of the current support systems used in poor ground at a Zimbabwean platinum mine shows that the current support systems are not adequate in poor ground conditions. The presence of reef- +=5478>%1183<>:1>:87'789$>:;>+: >9<>>)>.80<,

+=5478>%/829<=:;6,=0>'8< 88;>07:'9'=2=<*>:1>19=2478>9;.>+: +=5478>%+93<:7>:1>6918<*>:1>in situ 0=22976 97=9. 9>

         VOLUME 116    331 L Review of support systems used in poor ground conditions

+=5478>%-=;8>579.8>07:1=28>937:66><,8>- 

® A study of alternative explosives is recommended to BIENIAWSKI, Z.T. 1989. Engineering Rock Mass Classification. 1st edn. Wiley, minimize rockfalls. ANFO explosives generate a lot of New York. gases, which widen the joints. The authors recommend

that the mine uses bulk emulsion, which is a low- BRADY, B.H. 1985. Rock Mechanics for Underground Mining. 2nd edn. Allen energy explosive, in poor ground conditions and Unwin, London. ® Additional support is required where there is pillar robbing. The use of timbers and pillar bolting is MARANDA, A. 2011. ANFO detonation parameters. Central European Journal of recommended to improve strength ® The mine should use both empirical and numerical Energetic Materials, vol 8, no. 4. pp. 280–291. modelling to design the optimum support, since relying on one system has limitations MATHER, W. 1997. Bulk Explosives. https://miningandblasting.files. ® The use of hydrological surveys is recommended to wordpress.com [Accessed 13 December 2014]. determine joint water. Hydrological surveys will give an

indication of the exact groundwater conditions within OBERTHÜR, T., MELCHER, F., BUCHHOLZ, P., and LOCMELIS, M. 2012. The oxidized joints, thereby increasing safety by designing for the ores of the main sulphide zone, Great Dyke, Zimbabwe: turning resources actual groundwater conditions into minable reserves – mineralogy is the key. Platinum 2012. ® The use of mechanical scalers is recommended in poor Proceedings of the Fifth International Platinum Conference. 'A Catalyst for ground conditions to improve both worker safety and productivity. Fewer faces being prepared result in Change', Sun City, South Africa, 17–21 September 2012. Southern Afican failure to meet production targets, hence the use of Institute of Mining and Metallurgy, Johannesburg. pp. 647–671. mechanical scalers will improve productivity ® The authors recommend redesigning of pillars to PRENDERGAST, M.D. 1989. The platinum deposits of the, Great Dyke, Zimbabwe. improve safety and production Magmatic Sulphides – The Zimbabwe Volume. Proceedings of the 5th ® Smoothwall blasting is recommended in poor ground Magmatic Sulphide Field Conference, 3–13 August 1987. Prendergast M.D. conditions to minimize excavation damage and Jones, M.J. (eds). 1st edn. Institution of Mining and Metallurgy, ® Adequate training of workers and close monitoring is London. pp. 43–69. required when drilling.

WILSON, A.H. 1972. A hypothesis concerning pillar stability. The Mining /81878;386 Engineer, vol. 131, no. 1. pp. 409–417.

BROWN, E.T. and HOEK, E. 1980. Rock mass classification. Underground

Excavations in Rock. Institution of Mining and Metallurgy, London. WOOD, D. 1987. Support in underground hard rock mines. pp. 40–60. https://rocscience.com [Accessed 10 December 2014].

BARTON, N., LIEN, R., and LUNDE, J. 1974. Engineering classification of rock ZVARIVADZA, T. 2012. Evaluation of pillar design systems for low reef platinum masses for the design of tunnel support. International Journal of Rock mining. MSc thesis, University of Witwatersrand, Johannesburg, South Mechanics, vol. 6, no. 4. pp. 190–235. Africa. N L 332    VOLUME 116          http://dx.doi.org/10.17159/2411-9717/2016/v116n4a5 Slurry abrasion of WC-4wt%Ni cold- sprayed coatings in synthetic minewater by N.B.S. Magagula*†, N. Sacks*†, and I. Botef‡ Paper written on project work carried out in partial fulfilment of BSc. Eng. (Metallurgical and Materials Engineering)

may not have the required mechanical properties (Kim et al., 2006). Low-pressure cold gas dynamic spraying was used to deposit WC-4wt%Ni and WC-4wt%Ni-1wt%Mo coatings onto mild steel. Dense coatings with The WC-based coatings are generally very low porosities were produced. No decarburization occurred during deposited by flame, arc, plasma, or high- deposition and no deleterious phases were formed. The coatings were velocity oxy-fuel (HVOF) spraying, all of subjected to standardized material characterization tests, as well as slurry which require melting or partial melting of the abrasion testing to assess their wear behaviour. The wear tests were feedstock powder constituents (Jacobs et al., conducted in synthetic minewater-silica slurries, while distilled water- 1998; Kear et al., 2000; Zikin et al., 2012). silica slurries were used as a control. The hardness of the coatings, These high-temperature deposition processes 512HV0.3 and 458HV0.3 for WC-4wt%Ni and WC-4wt%Ni-1wt%Mo respec- may adversely affect the properties of the tively, are comparable to those achieved using high-temperature coating coating, as oxidation, decarburization, processes. The abrasion wear rates for both coatings were less than unwanted phase transformations, and tensile 5 mg/min and 10 mg/min in the distilled water-silica and synthetic mine residual stresses may occur. An alternative water-silica slurries respectively. The approximately 50% increase in wear rate in the synthetic minewater slurry is attributed to a synergistic deposition method that claims to reduce and/or corrosive wear mechanism. The predominant wear mechanisms were eliminate these undesirable effects is the cold- identified as binder smearing and delamination, with carbide grain gas dynamic spray process (CGDS) fracture and pull-out. (Champagne, 2007). In this technique, the feedstock powders are heated only to low 51&-/(+ temperatures which are below the melting tungsten carbide, nickel, cold spray, coatings, abrasion, minewater. points of the constituent materials. This process has been shown to produce coatings with low porosity and good wear and corrosion resistance, comparable to HVOF coatings, and 4.,/-(%),0-. may have compressive residual stresses which Slurry abrasion is a common phenomenon in could improve the coating’s mechanical mining operations, particularly in pipelines properties (Lima et al., 2002). Due to the low transporting, for example, sand-water slurries. temperatures employed, this cold spray This type of wear can cause pipeline fracture, technique also has significantly lower energy shortened operational lifetimes, and impede requirements compared to the high- pipeline efficiency. To reduce or limit abrasion, temperature deposition processes, which make thermally sprayed tungsten-carbide-based it attractive in an energy-conscious society coatings are often used as pipe linings (Papyrin et al., 2006). (Kanchan et al., 2010). This is due to their In the current study, the use of a low- attractive mechanical properties, which include pressure cold gas dynamic spray system to high wear resistance, stiffness, hardness, produce WC-4wt%Ni coatings was compressive strength, and tensile strength. investigated. The aim of the research was to These properties are provided by the coating microstructure and composition, which is a blend of hard, wear-resistant tungsten carbide (WC) particles embedded in a fracture-tough metallic binder phase (Brookes, 1997). Cobalt * School of Chemical and Metallurgical (Co) is the most commonly used binder due to Engineering, University of the Witwatersrand, its excellent wetting of the WC phase and Johannesburg, South Africa. moderate mechanical properties; however, its † DST-NRF Centre of Excellence in Strong application is limited to non-corrosive Materials, South Africa. ‡ School of Mechanical, Aeronautical and environments as it has a low corrosion and Industrial Engineering, University of the oxidation resistance (Andren, 2001). Nickel Witwatersrand, Johannesburg, South Africa. (Ni) may also be used as a binder, and has © The Southern African Institute of Mining and been shown to have superior oxidation and Metallurgy, 2016. ISSN 2225-6253. Paper received corrosion resistance, but in some applications Feb. 2016.

         VOLUME 116    333 L Slurry abrasion of WC-4wt%NI cold-sprayed coatings in synthetic minewater produce coatings that have a good resistance to slurry mechanical bonding. The deposition of ceramic materials abrasion, and which may find application in a mining such as WC is difficult. Due to their hard and brittle nature, environment. Nickel was selected as the binder due to its such materials tend to shatter on impact, often leading to superior corrosion properties compared to Co, which would erosion of the substrate and previously deposited layers make it more suitable for mining applications. In addition, a (Karthikeyan, 2007; Ang et al., 2011). For successful small amount of molybdenum (Mo) was added to investigate deposition, hard materials must be co-deposited with ductile its effect on the coating properties. A brief review of the cold binders (Wang and Villafuerte, 2009; Lioma et al., 2015). spray process will be given first, followed by the methodology An additional advantage of the CGDS process over many and results of the research. high-temperature processes is that it may be applied by means of a portable system, which enables on-site repairs to -"(3*2+3(.2$0)3+#/20.* be done. This is more cost-effective than having components disassembled and shipped off-site for repairs. Cold gas dynamic spraying (CGDS) is a process whereby metal powder particles are utilized to form a coating by means of ballistic impingement upon a suitable substrate 2,1/02"+32.(3$1,'-(-"-*3 (Champagne, 2007). The fine powder particles, usually In this study two different coatings were investigated, namely 5–45 m, may be accelerated at supersonic speeds of 300– a WC-4wt%Ni coating and a WC-4wt%Ni-1wt%Mo coating. 1200 m.s-1 towards the substrate, using air or a suitable The coatings were deposited onto mild steel substrates, 20 × carrier gas (Figure 1). The process was first developed in the 20 mm in size, which were grit-blasted with -300+100 μm mid-1980s at the Institute for Theoretical and Applied alumina grit prior to the deposition process in order to Mechanics of the Siberian Division of the Russian Academy facilitate adhesion of the coatings. A low-pressure cold spray of Science in Novosibirsk (Stoltenhoff et al., 2002). The machine (Centreline Series P SST) was used to deposit the discovery began as a study of the erosive behaviour of powder blends onto the mild steel using air as the carrier gas. particle-laden flow on an object in a wind tunnel. Above a Following deposition, the coatings were polished to a 1 m certain minimum particle velocity, the particles adhered to the surface finish for material characterization tests. The target rather than abrading it, leading to the formation of microstructure was studied using a Carl Zeiss Sigma field coatings; a trend found to be characteristic for each of the emission scanning electron microscope (FESEM) coupled with metal powders tested. Further depositions were then made of an energy dispersive X-ray spectrometer (EDS), which was a wide range of pure metals, metallic alloys, polymers, and used for elemental composition analysis and mapping. The composites onto a variety of substrate materials. coating thickness, porosity, WC grain size, and Ni binder Since its initial discovery, CGDS has developed into two mean free path were measured using lineal analysis on the fundamental deposition methods, namely high-pressure cold FESEM images. Phase identification was done using a gas spraying and low-pressure cold gas spraying, in which BRUKER D2 X-ray diffraction (XRD) instrument with Co-K the operational parameters such as pressure, temperature, radiation and PANalytical X'Pert High Score software. Vickers and the carrier gases differ (Villafuerte, 2010). High-pressure micro-hardness tests were done according to ASTM E384 systems typically use nitrogen or helium gas with pressures (2011). reaching approximately 7 MPa to accelerate the gas flow to Slurry abrasion testing of the coatings were conducted the supersonic regime. Low-pressure systems typically use using a modified ASTM G105 (2002) machine. A schematic air (sometimes nitrogen) with pressures between 0.550– diagram of the machine is shown in Figure 2. Three samples 0.695 MPa. Due to the low temperatures used, limited or no were tested simultaneously using an applied load of 22 N per melting occurs during deposition, so that the chemical sample, with the abrasion wheel rotating at 0.66 m.s-1. Silica composition of the coatings typically remains identical to the sand with an angular morphology and an average hardness feedstock powders (Papyrin et al., 2006). of 1084 ± 156HV was used as the abrasive medium. The In order to achieve sufficient adhesion and coating build- silica was mixed with two different liquid media, namely up, the powder particles must undergo severe plastic distilled water and synthetic minewater. The composition deformation on impact; hence the successful deposition of of the synthetic minewater was 37 ppm Ca2+, 1500 ppm Cl-, ductile metals such as nickel, copper, and aluminium. 40 ppm Mg2+, 980 ppm SO2-, and 943 ppm Na+ (Machio et According to Hussain et al. (2009), during impact the al., 2005). The distilled water slurry was used as a control to pressure that is generated causes material interlocking and assess the aggressiveness of the synthetic minewater slurry. The test duration was 60 minutes, with the mass loss of each

0*%/13)'1$2,0)3(02*/2$3- 323)-"(3*2+3+#/23++,1$3 0$23  0*%/13)'1$2,0)3+'-&0.*3,'13+"%//32/2+0-.3$2)'0.13 2)'0-3 !  3 ! L 334    VOLUME 116          Slurry abrasion of WC-4wt%NI cold-sprayed coatings in synthetic minewater coating being measured at 5-minute test intervals for the first average amount of WC retained in the coatings was 41wt%, 20 minutes, and thereafter in 10-minute intervals. The which is low given the original feedstock powder composition abrasion wear rate was calculated as mass loss as a function of 95–96wt%. This is a common phenomenon in cold-spray of time. The abraded surfaces were examined using electron coatings when hard ceramic particles are deposited as microscopy (FEI SEM Quanta 200) in order to identify the mentioned earlier. Due to their hard and brittle nature, a wear mechanisms. certain percentage of the particles will bounce off the substrate during deposition, while some particles fracture on 1+%",+32.(3(0+)%++0-.3 impact. The porosity of both coatings is very low and acceptable, suggesting that fairly dense coatings were     produced. Figure 3 shows the FESEM images of the two coating microstructures adjacent to their respective XRD patterns. An    inhomogeneous distribution of the WC carbide phase within The slurry abrasion wear rates of the two coatings are shown the Ni matrix was observed for both coatings. The smaller in Figure 4. The average wear rate of the WC-4wt%Ni coating WC particles are due to fracturing of the carbide phase during is slightly lower than that of the WC-4wt%Ni-1wt%Mo deposition as the particles impact the substrate. Similar coating in both slurries tested. This concurs with the higher observations have been made by other authors (Bhaumik et average hardness of the WC-4wt%Ni coating, which aligns al., 1991). The XRD patterns show the main phases of WC, Ni, and Mo, and it is noted that no decarburization occurred. A summary of the coating properties is listed in Table I. The WC-4wt%Ni coating has a higher average hardness than the WC-4wt%Ni-1wt%Mo coating. This is due to the smaller average WC grain size measured for the WC-4wt.%Ni coating. It is well known that cemented tungsten carbide materials with finer WC grain sizes have higher hardness values (Brookes, 1997). It was noted that the addition of 1wt %Mo to the WC-4wt%Ni coating reduced the hardness by 10.5%, which is quite significant given the small amount of Mo added. The reason for this effect is as yet unclear. Despite the differences in the carbide grain sizes, the Ni binder mean free path and wt% retained WC of both coatings were similar. The 0*%/13 1/2*13&12/3/2,1+3- 3-,'3)-2,0.*+30.3,'13,&-3+"%//01+

0*%/130)/-+,/%),%/13 &'0,13#'2+13 33*/13#'2+13 30!32.(3 3#2,,1/.+3- 3,'13,&-3)-2,0.*+

Table I Summary of the coating properties

Coating composition Hardness (HV30) WC retained (wt%) DWC (m) Ni (μm) Porosity (%)

WC-4wt.%Ni 512 ± 42 41 ± 1.0 0.71 ± 0.08 0.10 ± 0.01 0.01 WC-4wt.%Ni-1wt.%Mo 458 ± 36 41 ± 4.2 0.78 ± 0.09 0.11 ± 0.02 0.02

         VOLUME 116    335 L Slurry abrasion of WC-4wt%NI cold-sprayed coatings in synthetic minewater with well-established theory that a higher hardness should grains. This leaves the carbide grains unsupported, making provide better resistance against wear (Hutchings, 1992). their removal easier as abrasion proceeds. The removed The wear rates of the coatings in the synthetic minewater material tends to form hard micro-abrasives which then slurries are approximately 50% higher than those in the distilled water slurries. This large increase was unexpected given that the pH of the distilled water was 7, while that of the synthetic minewater was only 6.2. However, these wear rates indicate the extent to which synergistic action between wear and corrosion can lead to high material removal rates. While abrasion may be the dominant degradation mechanism based on the direct contact between the silica abrasive particles and the coating, the breakdown of the coating surface provides access for the liquid medium to attack the subsurface material. Thus while abrasion proceeds on the coating surface in contact with the silica, corrosion of the coating occurs simultaneously at subsurface level. This corrosive process facilitates material removal by preferentially attacking the binder phase, thereby weakening the bonding between binder and carbide, and subsequently making it easier for larger volumes of material to be removed as abrasion continues. Figure 5 is an elemental mapping of one of the WC-4wt%Ni-1wt%Mo coating surfaces exposed to 0*%/133$0)/-*/2#'+3+'-&0.*3,'13&-/.3+%/ 2)1+3- 3 2!32.(3 ! &,032.(3 )!32.(3 (!3&,0&,-3+'-&0.*30.(1/ synthetic minewater. Apart from the expected coating +$12/0.*3*/-- 0.*32.(3)2/0(13*/20.3 /2),%/132.(3#%""-%, elements, traces of sulphur were found on the surface, which are remnants of the chemical salts used to produce the synthetic minewater solution. According to Hutchings (1992), when the ratio of the hardness of the abrasive to the hardness of a surface is greater than 1.2 (Ha/Hs >1.2) then hard abrasion associated with plastic indentation is expected to occur on the surface. In this research, the Ha/Hs ratios for both coatings were 2.1 and 2.4 for WC-4wt%Ni and WC-4wt%Ni-1wt%Mo respectively. Thus both coatings experienced hard abrasion, with the silica particles indenting the coating surface. The precise mechanisms of material removal were identified using SEM, and examples of the worn surfaces are shown in Figures 6 and 7. The predominant mechanisms observed were carbide grain cracking, chipping, and removal, with extensive binder smearing and delamination. Grooving of the surfaces was also observed, which indicates the path followed by the silica particles and wear debris. These wear mechanisms are similar to those typically observed for cemented WC materials 0*%/13 3$0)/-*/2#'+3+'-&0.*3,'13&-/.3+%/ 2)1+3- 3 2!32.(3 subjected to abrasion (Larsen-Basse, 1985). The angularity !3&,032.(3 )!32.(3 (!3&,0&,-3+'-&0.*3)2/0(1 of the hard silica particles facilitated the preferential removal */20.3 /2),%/132.(3#%""-%,32.(30.(1/3+$12/0.*32.(3(1"2$0.2,0-.3 11# of the softer nickel binder phase from between the carbide */-- 0.*30+32"+-3.-,1(

0*%/13 "1$1.,2"3$2##0.*3- 3&-/.3&,0&,-3+%/ 2)131#-+1(3,-3+.,'1,0)3$0.1&2,1/ L 336    VOLUME 116          Slurry abrasion of WC-4wt%NI cold-sprayed coatings in synthetic minewater subject the coating to additional wear, causing fracture of the Abrasion Tests. ASTM International, West Conshohocken, NJ. embedded carbide grains. The wear mechanisms were similar BHAUMIK, S.K., UPADHYAYA, G.S., and VAIDYA, M.L. 1991. Properties and for both slurry types, although larger volumes of material microstructure of WC-TiC-Co and WC-TiC-Mo2-Co(Ni) cemented carbides. were removed from the coatings subjected to the synthetic Materials Science and Technology, vol. 7. pp. 723–727. minewater. BROOKES, K.J.A. 1997. Hardmetals and other Hard Materials. 6th edn. International Carbide Data, UK. -.)"%+0-. CHAMPAGNE, V.K. 2007. The Cold Spray Materials Deposition Process: This research showed that a low-pressure cold gas dynamic Fundamentals and Applications. Woodhead Publishing, Cambridge. spray system could be used to deposit WC-4wt%Ni and WC- HUSSAIN, T., MCCARTNEY, D.G., SHIPWAY, P., and ZHANG, D. 2009. Bonding 4wt%Ni-1wt%Mo coatings onto mild steel. Dense coatings mechanisms in cold spraying: the contributions of metallurgical and exhibiting very low porosities, an average of 41wt% retained mechanical components. Journal of Thermal Spray Technology, vol. 18, WC, and hardnesses comparable to high-temperature no. 3. pp. 364–379. deposited coatings, were produced. No decarburization or HUTCHINGS, I.M. 1992. Tribology: Friction and Wear of Engineering Materials. deleterious phases were formed in the coatings. The addition Edward Arnold, London. of 1wt% Mo to the WC-4wt%Ni coating did not improve the JACOBS, L., HYLAND, M.M., and DE BONTE, M. 1998. Comparative study of WC- hardness or abrasion resistance. Both coatings showed an cermet coatings sprayed via the HVOF and the HVAF process. Journal of approximate 50% increase in abrasion wear rate when Thermal Spray Technology, vol. 7, no. 2. pp. 213–218. subjected to a synthetic minewater-silica slurry. This was attributed to a synergistic corrosive-wear mechanism. The KANCHAN, K., ANAND, K., BELLACCI, M., and GIANNOZZI, M. 2010. Effect of microstructure on abrasive wear behaviour of thermally sprayed WC- predominant wear mechanisms for both coatings are those 10Co-4Cr coatings. Wear, vol. 268, no. 11-12. pp. 1309–1319. typically experienced by cemented tungsten carbide coatings when subjected to abrasion. KARTHIKEYAN, J. 2007. The advantages and disadvantages of the cold spray coating process. The Cold Spray Materials Deposition Process. Champagne V.K. (ed.). Woodhead Publishing Series in Metals and Surface %,%/13&-/6 Engineering, Woodhead Publishing, Cambridge. pp. 62–71.

Although the coatings have shown good abrasion resistance KEAR, B.H., SADANGI, R.K., JAIN, M., YAO, R., KALMAN, Z., SKANDAN, G., and MAYO, under laboratory conditions, further detailed research needs W.E. 2000. Thermal sprayed nanostructured WC/Co hardcoatings. Journal to be undertaken to determine their suitability for industrial of Thermal Spray Technology, vol. 9, no. 3. pp. 399–406. application. This should include field testing on carefully KIM, H-J., LEE, C-H., and HWANG, S-Y. 2005. Superhard nano WC-12%Co monitored slurry transportation pipelines to observe the coating by cold spray deposition. Materials Science and Engineering A, performance of the coatings. As slurries may also have a vol. 391, no. 1–2. pp. 243–248. corrosive nature, corrosion testing should be done on the KIM, H-C., SHON, I-J., YOON, J-K., and DOH, J-M. 2006. Comparison of sintering coatings, with exposure to varying media found in mining behaviour and mechanical properties between WC-8Co and WC-8Ni hard operations. Pipelines have elbows which experience materials produced by high-frequency induction heating sintering. Metals eccelerated erosion, often leading to pipe failure, and and Materials International, vol. 12, no. 2. pp. 141–146. therefore the coatings should be subjected to erosion testing LARSEN-BASSE, J. 1985. Binder extrusion in sliding wear of WC-Co alloys. Wear, at various impact angles and using different slurry media. vol. 105. pp. 247–256. Finally, an in-depth financial analysis should be done to assess the viability of substituting the cold spray process for LIMA, R.S., KARTHIKEYAN, J., KAY, C.M., LINDEMANN, J., and BERNDT, C.C. 2002. Microstructural characteristics of cold-sprayed nanostructured WC-Co some of the high-temperature processes currently being used coatings. Thin Solid Films, vol. 416, no. 1–2. pp. 129–135. to produce wear-resistant pipe linings. LIOMA, D., SACKS, N., and BOTEF, I. 2015. Cold gas dynamic spraying of WC-Ni cemented carbide coatings. International Journal of Refractory Metals and )6.-&"1(*1$1.,+ Hard Materials, vol. 49. pp. 365–373. The authors wish to acknowledge the financial support MACHIO, C.N., AKDOGAN, G., WITCOMB, M.J., and LUCKYX, S. 2005. Performance of received from the Department of Science and Technology and WC-VC-Co thermal spray coatings in abrasion and slurry erosion tests. the National Research Foundation in South Africa. The Wear, vol. 258. pp. 434–442. assistance of Ms D. Lioma, Mr N. Nelwalani, Mr S. PAPYRIN, A., KOSAREV, V., KLINKOV, S., ALKHIMOV, A., and FOMIN, V. 2006. Cold Maqobelane, Professor A. Ziegler, and the workshop staff of Spray Technology. 1st edn. Elsevier Science. the School of Chemical and Metallurgical Engineering, University of the Witwatersrand, is greatly appreciated. STOLTENHOFF, T., KREYE, H., and RICHTER, H.J. 2002. An analysis of the cold spray process and its coatings. Journal of Thermal Spray Technology, vol. 11, no. 4. pp. 542–550. 1 1/1.)1+ VILLAFUERTE, J. 2010. Recent trends in cold spray technology: looking at the ANDREN, H-O. 2001. Microstructures of cemented carbides. Materials and future. Surface Engineering, vol. 26, no. 6. pp.393–394. Design, vol. 22, no. 6. pp. 491–498. WANG, J., and VILLAFUERTE, J. 2009. Low pressure cold spraying of tungsten ANG, A.S.M., BERNDT, C.C., and CHEANG, P. 2011. Deposition effects of WC carbide composite coatings. Advanced Materials and Processes, vol. 167, particle size on cold sprayed WC-Co coatings. Surface and Coatings no. 2. pp. 54. Technology, vol. 205, no. 10. pp. 3260–3267. ZIKIN, A., ILO, S., KULU, P., HUSSAINOVA, I., KATSICH, C., and BADISCH, E. 2012. ASTM E384. 2011. Standard Test Method for Knoop and Vickers Hardness of Plasma transferred arc (PTA) hardfacing of recycled hardmetal reinforced Materials. ASTM International, West Conshohocken, NJ. nickel-matrix surface composites. Materials Science (Medziagotyra), ASTM G105-02. 2002. Standard Test for Conducting Wet Sand/Rubber Wheel vol. 18, no. 1. pp. 12–17. N

         VOLUME 116    337 L SEW-EURODRIVE – Driving the world

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Tel: +27 11 248-7000 Web: www.sew.co.za http://dx.doi.org/10.17159/2411-9717/2016/v116n4a6 Matte — tap-hole clay — refractory brick interaction in a PGM smelter by J. Du Toit*, R.D. Cromarty*, and A.M. Garbers-Craig* Paper written on project work carried out in partial fulfilment of BEng (Metallurgical Engineering)

The amount and positioning of tap-hole clay in the tap-hole and tapping channel affect 5()&/& the shape and length of the tapping channel, Penetration of matte into tap-hole bricks causes detrimental refractory which in turn affect the consistency that can wear, which can lead to furnace breakouts. The ability of the tap-hole clay be achieved in the tapping process (Nelson and to form a protective layer on the brick, thereby limiting matte penetration Hundermark, 2014). Wear of the tap-hole and was investigated by examining the interaction between platinum group metal (PGM) matte, tap-hole clay, and alumina-chrome refractory bricks tapping channel results in less control being on a laboratory scale. possible on the tapping process and less safe Samples containing clay and brick as well as samples containing clay, operating conditions due to the possibility of brick, and matte were heated to different temperatures to establish the burn-through and unintentional reopening of clay-brick interaction and the extent of matte penetration. The greatest the tap-hole. Worn refractories have to be degree of physical contact between the brick and clay was achieved at replaced, requiring significant expenses and curing temperatures of 600°C. Poor clay-brick contact was observed in the downtime (Nelson and Hundermark, 2014). sample that was heated to 900°C. It is generally accepted that refractory wear Matte displaced the clay in the clay-brick-matte sample that was by matte occurs in three steps. Penetration of heated to 1350°C, with significant matte penetration into the brick. Less the matte into the bricks occurs first. matte penetration was observed when the clay-brick-matte sample was heated to 1500°C. Less matte penetration was also observed in the clay- Penetration is followed by corrosion and brick-matte sample in which the clay and brick were pre-baked at 800°C, erosion, during which the worn refractory and the sample then reacted with matte at 1350°C. bricks are corroded and pieces of brick are removed from the tapping channel along with 306),%& molten material (Nelson and Hundermark, tap-hole clay, alumina-chrome refractory bricks, PGM matte, reaction 2014). The extent of refractory wear depends interface, penetration. on the amount of matte that penetrates into the brick and the temperature and viscosity of the matte. An increase in matte temperature (.,)% +./)(11 leads to a decrease in matte viscosity and an Floatation concentrate from ore from the associated increase in matte fluidity and ability eastern Bushveld Complex of South Africa, to penetrate into the refractory brick (Nelson et specifically the Platreef, Merensky, and UG2 al., 2005). reefs, forms the feed to the Polokwane Brick wear may be minimized through platinum smelter (Hundermark, De Villiers, protection provided by the tap-hole clay. and Ndlovu, 2006). The ore from the UG2 Reef Ideally, upon injection of the tap-hole clay into has Ahigh chromite content, which requires the tapping channel and tap hole, interaction high operating temperatures (1500–1700°C) to between the tap-hole clay and brick would avoid chromium spinel build-up in the furnace make matte penetration into the brick more hearth. These high operating temperatures difficult since matte would be required to move lead to matte superheats in the vicinity of 500– through the clay before penetration into the 600°C, which put increased demands on the brick is possible. This interaction between tap- refractory materials (Nelson et al., 2005). hole clay and brick and the associated extent Upon tapping, the matte moves through of matte penetration formed the focus of this the tap-hole, which consists of an alumina- study. chrome refractory brick-lined tapping channel (Hundermark, De Villiers, and Ndlovu, 2006). The flow of molten matte is stopped by the injection of tap-hole clay to form a plug in the tap-hole. The tap-hole clay hardens and * Department of Materials Science and Metallurgical strengthens during curing to obtain the Engineering, University of Pretoria. required hardness and refractoriness against © The Southern African Institute of Mining and penetration, corrosion and erosion (Nelson and Metallurgy, 2016. ISSN 2225-6253. Paper received Hundermark, 2014). Feb. 2016.

         VOLUME 116    339 L Matte — tap-hole clay — refractory brick interaction in a PGM smelter

-.0,/-*& Thermogravimetric analysis (TGA) was conducted on the tap-hole clay to establish the temperatures at which Primary PGM matte was obtained from the Anglo Platinum decomposition of the binder takes place (Figure 2). A 4% Polokwane smelter, while alumina-chrome bricks and tap- decrease in mass was observed between 100 and 200°C when hole clay were obtained from the refractory suppliers to the the sample was heated in both air and nitrogen. An Polokwane smelter1. additional 10% mass loss was observed at temperatures These materials were characterized using X-ray between 450 and 600°C in air. The mass loss between 100 diffraction analysis (XRD), X-ray fluorescence (XRF), and and 200°C can be ascribed to volatiles being driven from the scanning electron microscopy using energy-dispersive X-ray sample. Pérez et al. (2004), obtained similar results through spectroscopy (SEM-EDS). thermogravimetric analysis of pitch binders. The 450–600°C  temperature range correlates to the temperature range at which oxidation of graphite occurs (Xiaowei, Jean-Charles, Quantitative XRD analysis indicated that the nickel-copper- and Suyuan, 2004). The sample heated in air underwent a rich PGM matte consisted of 61.9% (Fe, Ni) S , 13.3% FeS, 9 8 large mass loss in the 450–600°C range due to graphite 6.6% Cu FeS , 6.8% SiO , 6% CaAl Si O , and 3.9% FeCr O . 5 4 2 2 2 8 2 4 oxidation. The mass of the sample heated in nitrogen over      this temperature range remained unchanged, indicating the completion of the pyrolysis of the binder. XRF analysis confirmed that the brick contained 75% Al2O3, 20.7% Cr O , 2.2% P O , and 1% SiO . XRD analysis revealed 2 3 2 5 2 240,/"0(.-* that Al2O3 and the (Al,Cr)2O3 solid solution phase were the major phases present in the brick (56.0% and 40.3% respec- Laboratory-scale experiments were performed to simulate the clay-brick (CB) and the clay-brick-matte (CBM) interactions. tively), while trace amounts aluminium phosphate (AlPO4) In both sets of experiments argon gas was used for purging and cristobalite (SiO2) could also be detected. Microstructurally, the brick consisted of large alumina to avoid the oxidation of sulphur in the matte. grains embedded in an alumina-chrome-based matrix, For the clay-brick interaction a Phasecon tube furnace was used. The furnace was heated to temperatures of 600°C bonded through the formation of the (Al,Cr)2O3 solid solution phase (Figure 1). and 900°C and kept at temperature for one hour. A heating ramp rate of 15°C/min was used upon heating and 50°C/min   upon cooling. Technical-grade argon (99.9% argon) was used The tap-hole clay is an organically bound material. XRD to purge the furnace for the heating, dwell, and cooling analyses were conducted on the raw clay, and on clay periods. samples that were heated to 950°C and subsequently cooled In the clay-brick experiment an alumina crucible to room temperature in an oxidizing as well as an inert assembly, containing a brick core surrounded by clay, was atmosphere. used (Figure 3). The raw clay was found to consist largely of the The clay-brick-matte experiments were done using an crystalline phases corundum and andalusite (55 wt% and induction furnace with a graphite susceptor in an insulated 11 wt% respectively) with some silicon carbide, silicon, gas-tight chamber. An Ambrell Ekoheat power supply was quartz, mullite, and a small amount of graphite. The carbon used and temperature was controlled using a Eurotherm binder present in the clay is an amorphous phase which was temperature controller and a type B thermocouple. not quantified by XRD analysis. Upon heating, graphite is retained in the sample in an inert atmosphere but is oxidized from the system when heated in air. In order to allow comparison between types and amounts of phases under oxidizing and inert atmospheric conditions, the analysis of the sample heated under inert atmosphere was normalized to exclude graphite. It was found that andalusite decomposes into mullite (3Al2O3.2SiO2) and SiO2 or a glassy phase when heated in both the inert and oxidizing /' ,01-+ &+-..0,0%10*0+.,)(1/"-'01)#1-&,0+0/0%1,/+ atmospheres. According to Schneider and Komarneni (2006), andalusite is stable up to temperatures in the vicinity of 780°C, at which decomposition of andalusite into mullite and silica initiates (Schneider and Komarneni, 2006). The decrease in the amount of andalusite in the oxidizing and inert atmospheres is therefore expected with an associated increase in mullite and silica. This agrees with the findings of the XRD analysis, where mullite increased from 5.3% to almost 10% and silica from 6.9% to close to 10% in both samples.

1Names of suppliers omitted for confidentiality reasons /' ,01-$)*01+*-11,0& *.& L 340    VOLUME 116          Matte — tap-hole clay — refractory brick interaction in a PGM smelter

phase) could be distinguished in the solidified matte (Figure 7B), while an Fe-Ni-Cu-based alloy could also be observed. The brick (Figure 7C) was also penetrated by the matte. This was expected, since the matte displaced the clay and no protective layer was present to resist matte penetration into the brick. The sample heated to 1500°C also showed significant matte penetration; although complete displacement of the clay section with matte was not evident. There is a clear distinction between the initial matte section (light grey) and the initial clay section (dark grey), although droplets of matte /' ,01!/(.0,-+./)(1+, +/*01%0&/'(1*0#.1-(%1!/(.0,-+./)( seem to have penetrated into the clay region (Figure 8A). The +, +/*01%0&/'(1,/'$. bright phases in the clay are alloy droplets and not matte. Alloy droplets, however, were not observed in the brick, but only matte droplets. The induction furnace was purged with technical-grade Greater interaction between the clay and the brick was argon for 30 minutes prior to heating to temperatures of observed in the 1350°C CBM sample that contained pre- 1350°C and 1500°C. Purging continued for the duration of baked clay. There was, however, still matte penetration into the experiment. A heating rate of 20°C/min was used, the clay and the brick sections (Figure 9). followed by dwelling at temperature for 60 minutes and then cooling at a rate of 50°C/min. !)(+* &/)(& The crucible assembly consisted of an alumina crucible with a section of the brick placed at the bottom and clay Decomposition of the binder occurs at temperatures up added to the top and around the sides of the brick. Matte was to 600°C with volatiles being driven off in the 100–200°C then added on top of the clay (Figure 3). temperature range. Oxidation of graphite occurs at An additional experiment was performed in which the 450–600°C. CBM set-up was modified by first baking the clay and brick in an alumina crucible in the Phasecon retort furnace at 800°C for one hour. After cooling, the matte was added and the CBM experiment was performed in the induction furnace as described previously. The purpose of this experiment was to establish whether pre-baking would increase the physical contact and extent of interaction between the clay and brick, thereby improving the resistance against matte penetration. The samples were sectioned, and polished samples prepared for analysis on completion of the CB and CBM experiments. Reflected light microscopy and SEM-EDS analysis were used to determine the amount of clay-brick /' ,010#*0+.0%1*/'$.1"/+,)',-$1)#1+*-,/+ 1/(.0,-+./)(1-.1 ! interaction as well as the extent of matte penetration.

0& *.&1-(%1%/&+ &&/)(    The clay-brick interaction was limited, as areas at the clay- brick interface could be distinguished where no direct contact occurred. Areas of poorer and better physical contact were observed, with overall better contact being achieved in the sample heated to 600°C (Figure 4), compared to the sample that was heated to 900°C (Figure 5). The gap between the clay and brick implies that chemical interaction did not occur. /' ,010#*0+.0%1*/'$.1"/+,)',-$1)#1+*-,/+ 1/(.0,-+./)(1-.1 !    The reflected light microscopy images of the samples containing clay, brick, and matte indicate that matte (brightly coloured) penetrated into both the clay (Figure 6A) and the brick (Figure 6B). In the CBM sample heated to 1350°C, the matte seemed to have displaced the clay. The top layer, which initially consisted of matte, contained clay (dark grey, Figure 7A), while the section above the brick, which was initially clay, contained matte only (light grey, Figure 7B). Copper sulphide /' ,01 0#*0+.0%1*/'$.1"/+,)',-$&1)#1&-"*01$0-.0%1.)1! 1 (light sulphide phase) and an iron sulphide (dark sulphide !*-1&0+./)(1)#1.$01&-"*01-(%11,/+ 1&0+./)(1)#1.$01&-"*0

         VOLUME 116    341 L Matte — tap-hole clay — refractory brick interaction in a PGM smelter

/' ,01 -+ &+-..0,0%10*0+.,)(1/"-'01)#1.$01!1&-"*01$0-.0%1.) !1-#.0,1,0- /('1-.1 !11/(/./-*1+*-,/+ 1/(.0,#-+01,0'/)(

Without physical contact, chemical interaction could also not occur. Without clay-brick interaction, the clay provides little protection against matte penetration into the brick. The physical contact between the clay and the brick proved to be better when the clay and brick were reacted at a lower temperature (600°C), rather than a higher temperature (900°C). Matte penetrated through the clay and into the brick in samples heated to 1350°C as well as to 1500°C. Less matte penetration occurred in the 1500°C sample and the 1350°C sample that contained pre-baked tap-hole clay. In the CBM sample that was reacted at 1500°C, matte reacted with the tap-hole clay to form a Cu-Fe-Ni alloy. /' ,01-+ &+-..0,0%10*0+.,)(1/"-'0&1)#1.$01!1&-"*01$0-.0%1.) ! 11(/./-*1"-..01,0'/)( 11/(/./-*1+*-1,0'/)( 1!1/(/./-*1,/+ ,0'/)( + ()6*0%'0"0(.& The authors would like to thank Anglo American (Dr Lloyd Nelson, Rodney Hundermark, and Keith Hines) for supplying the raw materials as well as for technical assistance. A word of thanks also goes to colleagues and analytical staff in the Department of Material Science and Metallurgical Engineering at the University of Pretoria.

0#0,0(+0&

HUNDERMARK, R., DE VILLIERS, B., and NDLOVU, J. 2006. Process description and short history of Polokwane Smelter. Southern African Pyrometallurgy 2006. Jones, R.T. (ed.). Southern African Institute of Mining and Metallurgy, Johannesburg. pp. 35–41.

NELSON, L.R. and HUNDERMARK, R.J. 2014. ‘The tap-hole'— key to furnace performance. Furnace Tapping Conference 2014. Southern African Institute of Mining and Metallurgy, Johannesburg. pp. 1–32.

NELSON, L.R., STOBER, F., NDLOVU, J., DE VILLIERS, L.P., and WANBLAD, D. 2005. Role of technical innovation delivery at the Polokwane Smelter. Nickel and Cobalt 2005. Challenges in Extraction and Production, Calgary. Donald, J. and Schonewille, R. (eds.). CIM, Montreal. pp. 91–116.

PEREZ, M., GRANDA, M.S., MORGAN, T., and MENENDEZ, R. 2004. A thermoana- lytical study of the co-pyrolysis of coal-tar pitch and petroleum pitch. Fuel, /' ,01 -+ &+-..0,0%10*0+.,)(1/"-'01)#1.$01!1&-"*01$0-.0%1.) vol. 83, no. 9. pp. 1257–1265. ! 11(/./-*1"-..01-(%1+*-1,0'/)(& 11/(/./-*1,/+ 1,0'/)(

SCHNEIDER, H. and KOMARNENI, S. 2006. Mullite. Wiley, Weinham.

Interaction between tap-hole clay and brick does not XIAOWEI, L., JEAN-CHARLES, R., and SUYUAN, Y. 2004. Effect of temperature on occur extensively at either 600°C or 900°C. Regions of poor graphite oxidation behaviour. Nuclear Engineering and Design, physical contact between the clay and brick were observed. pp. 273–280. N L 342    VOLUME 116          http://dx.doi.org/10.17159/2411-9717/2016/v116n4a7 Separation of kimberlite from waste rocks using sensor-based sorting at Cullinan Diamond Mine by T. Mahlangu*†, N. Moemise†, M.M. Ramakokovhu*, P.A. Olubambi‡, and M.B. Shongwe* Paper written on project work carried out in partial fulfilment of BTech. Eng. (Metallurgical Engineering)

Salter and Wyatt, 2009; Death et al., 2009). In sensor-based sorting, materials are mechan- .2353 ically sorted based on certain physical Near-infrared (NIR) spectroscopy sorting technology is incorporated in an properties that are detected by a sensor (Dalm, automated optical mineral sorter that can discriminate between materials 2013). Research has found that with NIR using the differences in characteristics when exposed to near-infrared scanners it is possible to obtain a ‘fingerprint’ radiation. During September 2014 to April 2015, a pilot plant that utilized of a sample that is directly related to its NIR technology to discriminate between kimberlite and waste materials mineralogical composition. According to was commissioned to determine the viability of including this technology Woutruba et al. (2009), molecules absorb NIR in the diamond winning process flow sheet at Cullinan Diamond Mine. The radiation by means of electronic and plant was used to minimize the waste content in the size fraction -70+35 vibrational transitions. Nowadays, there are mm that reports to the crushing section and then to the dense media many sensors available in the market that separation process. This paper describes the initial test work, conducted at Mintek, that led to the decision to conduct a pilot-scale study. The utilize different material properties; the choice mineralogical characterization of the feed and product streams to establish of a sensor is dependent on the mineralogy of the sorting criteria and the operational data obtained during the pilot plant the ore. campaign are described. The results indicated a good possibility of discrim- Traditional metallurgical techniques for inating between the kimberlite and waste material using NIR technology. diamond winning from kimberlitic ore involve However, the consistency of discrimination was not good enough to avoid size reduction, dense medium separation the risk of potential diamond loss. Furthermore, a lower than expected (DMS), and final recovery by X-ray technology availability of the machine reduced the throughput capabilities. (Ketelhodt et al., 2013). These techniques !724#3 have no ability to remove waste rocks that are sensor-based sorting, NIR spetroscopy, kimberlite, preconcentration. often associated with the kimberlite. The kimberlite orebody at Cullinan Diamond Mine (CDM) is intruded by sills and dykes of waste rock, and the current mining method cannot separate the waste material (Bartlett, 1994). .642#*)652. Waste hoisted from underground is mostly Using near-infrared spectroscopy (NIRS) from development areas. This paper evaluates technology for ore sorting is a new concept for the viability of the new COLOR/NIR sorting the mineral processing and mining industry. technology to remove the waste rocks from the NIRS has been used for decades in the kimberlite ore stream, thus reducing the laboratory for the identification of pure amount of waste going into the DMS process. minerals, and has its roots in the recycling, food, and pharmaceutical industries (Salter and Wyatt, 1991; Robben et al., 2009). Ore sorting in itself is not a new concept; it was introduced during the Stone Age with hand- sorting being the first method to separate valuable materials from gangue (Wills and Napier-Munn, 2006; Sassos, 1985). However, * Institute for NanoEngineering Research, over the years the scale of mining has Department of Chemical, Metallurgical and increased and hand-sorting has become Materials Engineering, Tshwane University of challenging to implement (Joensson, 2014). Technology, Pretoria, South Africa. Sensor-based sorting is an advanced † Cullinan Diamond Mine, Petra Diamonds technology that can help overcome problems Southern Africa (Pty) Ltd. ‡ Department of Chemical Engineering Technology, such as ore dilution experienced in mineral University of Johannesburg, Johannesburg, processing operations. The benefits are lower South Africa. energy and water costs, reduced ore dilution, © The Southern African Institute of Mining and lower environmental impact, and improved Metallurgy, 2016. ISSN 2225-6253. Paper received profit margin (Mathew, 1974; Jonsson, 2014; Feb. 2016.

         VOLUME 116    343 L Separation of kimberlite from waste rocks using sensor-based sorting

:;745+7.61/842)7#*473   In order to provide background information for sensor-based sorting, mineralogical characterization of a run of mine (ROM) sample from CDM was performed by X-ray diffraction (XRD). The primary use of XRD is for the identification and characterization of compounds based on their diffraction (a) patterns.The sample, which had a top size of -70 mm, was reduced using a single toggle jaw crusher followed by ball milling. The XRD results are shown in Figure 1 and Figure 2. Both the kimberlite (Figure 1) and the waste (Figure 2) were found to contain NIR-active minerals, and there is thus the possibility of using NIR technology to discriminate between the two streams. Images (Figure 3) extracted from the classifier also showed a very good possibility of (b) separating kimberlite from the associated waste materials. Classifiers are part of the NIR technology programme and are used to classify materials (Korsten, 2014).

      Tests work was conducted with the Pro Secondary COLOR/NIR sorter illustrated in Figure 4. The sorter uses a combination of a high-resolution line camera and NIR scanner to provide accurate detection of the mineral fingerprint of each rock (Ketelhodt et al., 2013). The working (c) width of the COLOR/NIR sorter is 1200 mm. The technical set-up of the sorter is shown in Figure 5. %50*478 +10738'42+86(78 83246748)/1335'57483(25.08#53)45+5.1652. The sorter used was a chute-type sorter, with the material fed &7677.8$5+&74/56781.#8,1-801&&428,&-8.2456781.#8,)-8'7/3567 by a vibratory feeder and accelerated down a chute under gravity. Scanning is done by means of an NIR and a colour sensor on the free-falling stream of particles. Prior to the sorter, a washing/sizing screen with a 10 mm aperture size was installed for the purpose of particle preparation. Sizing was done to obtained a size ratio of 1:3, because research on

%50*478 4287)2.#148   83246748'42+82+4182465.0 2/*652.3

%50*478 8+5.741/205)1/8)(141)6745 1652.82'8$5+&74/567

%50*478 7)(.5)1/8376*82'86(78   83246748,!767/(2#68et al. %50*478 8+5.741/205)1/8)(141)6745 1652.8'7/35678,1367- - L 344    VOLUME 116          Separation of kimberlite from waste rocks using sensor-based sorting sensor based technology has shown that the sorting results sensitivity reduces the aggressiveness of the machine with can deteriorate at a particle size ratio greater than three respect to its ejecting potential. In both the rougher and (Woutruba and Riedel, 2005). scavenger stage the kimberlite recovery was calculated to be The material that was supplied for the test work was a above 95%, which clearly indicates that the COLOR/NIR 12 t sample of Cullinan ROM material. The waste rocks at sorter is able to discriminate between the CDM kimberlitic CDM comprise of gabbro, norite, felsite, and quartzite. The and waste rocks. sample, which was collected by means of a belt cut, was within the size range of -70+35 mm. The sorter needs to be programmed with information obtained from a pre-classified sample. Thus, a 10 kg sample of the kimberlites and waste material was collected from underground at Cullinan. Groups were formed by statistical means and applied into the sorting algorithm, called the classifier, for bulk sorting. The process flow diagram configuration shown in Figure 6 was tested with the aim of maximizing overall kimberlite recovery with a target of 5% kimberlite loss to the waste stream.

     

  The overall results of the tests that were carried out only in the rougher stage are shown in Table I and Figure 7. The average kimberlite recovery was calculated to be 97.8%, while the average waste removal was calculated to be 90.2% %50*478 %/28#51041+8*37#8'2486(786736824$8,!767/(2#68et al.8-    The scavenger stage was used to recover the kimberlite misclassified into the waste stream from the rougher stage. Approximately 4.1% of the kimberlite is calculated to be lost at the rougher stage. Table II and Figure 8 show the results for the scavenger stage. The average kimberlite recovery was calculated to be 99.8% and the average waste removal was calculated to be 93.1%. The results clearly indicate that the introduction of a scavenger stage improves the separation efficiency and minimizes the potential for diamond loss. It is also seen that the kimberlite recovery decreases at a low classifier sensitivity. This is due to the fact that low classifier %50*478 !5+&74/567847)2"748  1367847+2"1/8,42*0(74836107-

Table I 73*/6382'842*0(74836107832465.0

736 /1335'574837.3565"56 %77#8,$0- !5+&74/56785.88 136785.8 !5+&74/5678/236 !5+&74/567847)2"74 1367842+2"1/ 37665.08,- '77#8,$0- '77#8,$0- 2*08,- )1"8,- ,$0- ,- ,$0- ,-

1 50 958.0 457.1 509.9 1.03 - 452.0 98.89 480.0 94.13 3 55 1220.0 616.5 603.5 5.64 -583.0 94.57 560.5 92.87 4 65 1149.0 600.0 549.0 1.76 - 591.5 98.58 474.5 86.43 5 60 1376.0 685.0 691.0 2.93 - 666.0 97.23 629.0 91.02 6 50 1189.0 581.1 607.9 4.28 - 579.1 99.66 525.5 86.44

Table II 73*/6382'83)1"7.074836107832465.0

736 /1335'574837.3565"56 %77#8,$0- !5+&74/56785.88 136785.8 !5+&74/5678/236 !5+&74/567847)2"74 1367842+2"1/ 37665.08,$0- '77#8,$0- '77#8,$0- 2*08,- )1"8,- ,$0- ,- ,$0- ,-

2 45 1268.0 589.0 679.0 5.87 0.24 587.5 99.75 622.0 91.61 7 45 1047.0 535.2 511.8 4.83 0.34 533.6 99.69 473.4 92.50 8 50 992.0 505.8 486.2 6.34 0.22 504.8 99.80 463.0 95.23

         VOLUME 116    345 L Separation of kimberlite from waste rocks using sensor-based sorting

5/268/1.68473*/63 Figure 11 shows the average tons treated through the pilot plant for a period of 6 months (November 2014 to -April 2015) when the plant was running at full production. The total tonnage fed to the pilot plant was lower than the design tonnage of 50 000 t/ month, due to the fact that the availability and utilization of the pilot plant was lower than expected. The availability of the pilot plant was critical for successful assessment of the sensor-based sorter and economic evaluation. Throughout the duration of the project the tailings stream was sampled to monitor the average kimberlite loss. %50*478 !5+&74/567847)2"748  1367847+2"1/8,3)1"7.074836107- Kimberlite loss is an indication of potential diamond loss, and should be kept at a minimum. The acceptable kimberlite loss was set at a target of below 5%. Figure 9 compares the kimberlite loss in the rougher and Figure 12 shows the kimberlite loss during the pilot plant scavenger stages against the target kimberlite loss of 5%. The campaign. It was possible to keep the kimberlite loss below kimberlite lost to the waste stream was monitored to prevent 5% for several months, but in January 2015 a high loss of ore the risk of diamond loss. occurred. It was decided to stop the sorter until the problem There is a relatively high loss of the kimberlite ore when was found and rectified. The sorter was found to have lost using only a rougher stage. However, introducing the programming and had to be re-programmed with pre- scavenger stage minimized the risk of kimberlite loss to an classified samples. It was also realized that the kimberlite average of 0.3%. The kimberlite lost was above target for loss was above target when the screen sprays were blocked tests 2, 3, and 8 because the agressiveness of the machine and the feed coated with mud. After the problem was rectified was kept low.

5/268/1.6842#*)652. The feed to the pilot plant was the discharge from the scrubber, screened to -70+35 mm size. The main goal of the sorting in this case was to preconcentrate the -70+35 mm material prior to the DMS process. A lower waste content in the DMS feed would reduce the impact of near-density waste material on the cyclone dynamics; with the benefit of the reduction of waste material reporting to the DMS concentrate, which could have a detrimental impact on the subsequent X- ray sorting processes. The pilot plant was run from September 2014 to April 2015. The commissioning process was complete within a month. Figure 10 illustrates the pilot plant flow sheet, where only the single pass configuration was implemented. %50*478 !5+&74/5678/23686286(781367836471+8  6140768/233

%50*478 5/268/1.68'/283(776 L 346    VOLUME 116          Separation of kimberlite from waste rocks using sensor-based sorting

BARLETT, P.J. 1998. Premier Mine. Proceedings of the 7th International Kimberlite Conference, Cape Town. pp. 39–49.

BERRY, L.G. and MASON, B. 1959. Mineralogy: Concepts, Description and Determinants. Springer, San Franciso. pp. 296–298.

CHADWICK, J. 2008. Process progress. International Mining, May 2008. pp. 24–40.

CHRISTON, J. 2014. Sensor based sorting technology implementation in the mining and mineral processing. Lund University, Sweden.

%50*478 2..10738647167#86(42*0(86(785/268/1.6 COMMODASTULTRASORT. 2009. Sorters reduce mining costs and increase profits. pp. 34–36.

DALM, M. 2012. TA3690 – Project on sensor based sorting of copper- molybdenum ore. pp. 1–4.

DEATH, D.L., CUNNINGHAM, A.P., and POLLARD, L.J. 2009. Multi-element and mineralogical analysis of mineral ores using laser breakdown spectroscopy. Spectrochimica Acta Part B. Atomic Spectroscopy, vol. 64, no. 10. pp. 1048–1058.

HARMON, R.S., DELUCIA, F.C., MCMANUS, C.E., MCMILLAN, N.J., JENKINS, T.F.,

WALSH, M.E., and MIZIOLEK, A. 2006. Laser-induced breakdown spectroscopy – an emerging chemical sensor technology for real-time field- %50*478 !5+&74/5678/2337386286(78615/5.038  6140768$5+&74/5678/233 portable, geochemical, mineralogical, and environmental applications. Applied Geochemistry, vol. 21, no. 5. pp. 730–747. the kimberlite loss was acceptable, as can be seen in HOLLAS, J.M. 2004. Modern Spectroscopy. 5th edn. Wiley. Chapters 1–3. Figure 12. ROBBEN, M., WOTRUBA, H., BALTHASA, D., and REHIMANN, V. 2009, NIR spectral imaging in the mineral processing industry. RWTH Aachen University, 2.)/*352. Germany. pp. 2–5. Based on the test work, the COLOR/NIR sorter is generally a good tool to separate Cullinan kimberlite from waste rocks. ROBBINSON, D.N. 1973. Magnetite-serpentine-calcite dykes at Premier Mine and The introduction of a scavenger stage will improve the aspects of their relationship to kimberlite and to carbonatite of alkali kimberlite recovery and also minimize diamond loss. The carbonatite complexes. Physics and Chemistry of the Earth, vol. 9. pilot plant test work results were not consistent since the pp. 61–70. sensing technology is based on the surface properties of the SALTER, J.D. and WYATT, N.P.G. 1991. Sorting in the mineral industry: past, material, hence the feed needs to be clean and free of dust or mud prior to sorting. However, this is not always the case in present and future. Minerals Engineering, vol. 4, no. 7. p. 779–796. a production environment, particularly for kimberlite ores, Sassos, M.P. 1985. Mineral sorters. Engineering and Mining Journal, vol. 186, which have a high content of clay material. Due to the risk of no. 6. pp 68–72. diamond loss as a function of kimberlite lost, it is recommended that a scavenger stage be implemented in SMITH, C.B. 1983. Pb, Sr, and Nd isotopic evidence for sources of southern further kimberlite preconcentration processes using the same African Cretaceous kimberlites. Nature, vol. 304, no. 5921. pp. 51–54 sorting system. TONG, Y, 2009. Technical amenability study of laboratory scale sensor-based 9)$.2/7#07+7.63 ore sorting on a Mississippi Valley type lead-zinc ore, MASc thesis, Department of Mining Engineering, University of British Columbia. The author wishes to express her gratitude to Cullinan pp. 19–20. Diamond Mine (Pty) Ltd for the opportunity and funding for the project. The deepest thanks are extended to my mentor WAGNER, P.A. 1914. The Diamond Fields of South Africa. Transvaal Leader, and supervisor for their guidance and technical input, and to Johannesburg. 347 pp. the CDM laboratory personnel for their assistance during the test work and analysis. The inputs from Mintek and Tomra WESTHYZEN, P., BOUWER, W., and JAKINS, A. 2013. Current trends in the Sorting (Pty) Ltd, South Africa, are also acknowledged. development of new or optimization of existing diamond processing plants, with the focus on beneficiation. Journal of the Southern African 7'747.)73 Institute of Mining and Metallurgy, vol. 114. pp. 539–545.

ASD Inc. 2010. Fieldspec3 User Manual, WILLS, B.A. and NAPIER-MUNN, T. 2006. Mineral Processing Technology. http://support.asdi.com/document/documents.aspx [Accessed 28 May 7th edn. Elsevier Science & Technology, Brisbane. Chapter 14, 2015]. pp. 372–377. N

         VOLUME 116    347 L Learn more: www.geobrugg.com/rockfall

GBE rockfall barriers made of high-tensile steel wire FOR AN ECONOMICAL SOLUTION TO ROCKFALL

Geobrugg Southern Africa (Pty) Ltd | Unit 3 Block B Honeydew Business Park | 1503 Citrus Street | Honeydew 2170 | South Africa | T +27 11 794 3248 | [email protected] | www.geobrugg.com http://dx.doi.org/10.17159/2411-9717/2016/v116n4a8 An evaluation of the thermal fatigue performance of three alloys for casting mould applications by V. van der Merwe* and C.W. Siyasiya* Paper written on project work carried out in partial fulfilment of B. Eng. (Metallurgical Engineering)

the highest temperature fluctuations. This ')67-898 suggests that the cracks are caused by thermal fatigue during the casting process. A petrochemical company experiences premature thermal fatigue failure of In order to prolong the life of the mould the casting moulds used in catalyst production. The aim of the project was and improve the operational efficiency, a to find an alternative alloy that would outperform the current low-alloy cast steel used for the moulds. Based on their thermo-fatigue properties, recommendation for a new alloy or an 3CR12 ferritic stainless steel and H11 tool steel were chosen for testing improvement of the existing casting mould had and comparison with the currently used BS3100 B7 cast steel. Samples of to be made. each material were subjected to temperature cycling in a Gleeble 1500TM In many instances, there are no service life thermo-mechanical processing simulator, followed by surface analyses. records for specific moulds to track their life The main parameters derived from the test work were the total true strain, span, as well as no records regarding the the hot strength of the materials, and the number of cycles to failure. surface temperatures of the mould during the Additionally, the coefficient of thermal expansion for each material was heating and cooling cycle. The operating measured using a Bähr dilatometer. H11 tool steel yielded the best conditions and safety concerns make it performance by way of having the fewest surface cracks, the lowest total impossible to measure the surface temper- true strain per cycle, the most cycles to failure, the highest hot strength, and the lowest coefficient of thermal expansion. atures. Therefore, the temperature fluctuations can only be estimated. =)7;+8 On average, the casting moulds last about thermal fatigue, fatigue failure, casting moulds, thermal expansion. 6 months in this operating environment. One of the primary indications that the mould has reached the end of its life is the sticking of the catalyst to the mould due to the enlarged ?6<;7+35<976 surface area caused by the surface cracks, as The Catalyst Manufacturing Plant (CMP) is a seen in Figure 1. This type of surface is called dusty environment with temperatures higher the ‘elephant skin’ and is caused by thermal than ambient. Molten mill scale (magnetite, fatigue.

Fe3O4) is tapped from the electric arc furnace into the casting moulds at temperatures close ,=;1:4>.:<9/3=>.:943;= to 1600°C. After 10 seconds the magnetite is All materials of construction are affected by quenched with a water spray for 50 seconds to thermal fatigue. This is a result of cyclic a minimum temperature of 400°C. Sometimes stresses caused by variations in temperature. there is residual water in the pans from the The damage occurs under repeated thermal cooling fog process (water sprays) in the cycling in the form of cracking in the metal, empty mould. In a typical plant, the factory specifically where relative movement (differ- produces 40–44 batches a day containing ential expansion) is constrained (American between 150–300 moulds, depending on the Petroleum Institute, 2011). time required for the specific batch (Buchholz, The failure of the moulds in the current 2014). The typical batch in the CMP usually investigation can be classified as a low-cycle weighs about 6 t. The thickness of the tap, high-strain fatigue problem, typically with N < speed of the casting belt, and tilting angle all 104 cycles. The number of cycles to failure is affect the number of moulds per batch. One of the main problems faced during the molten mill scale casting is the premature failure of the casting moulds. Cracks initiate on the surface of the mould, which is in * University of Pretoria, Department of Materials contact with the hot catalyst, and propagate Science and Metallurgical Engineering, Pretoria, into the interior of the mould. Cracks are South Africa. generally concentrated in the middle area of © The Southern African Institute of Mining and the mould where the catalyst makes first Metallurgy, 2016. ISSN 2225-6253. Paper received contact with the mould, and which experiences Apr. 2016.

         VOLUME 116    349 L An evaluation of the thermal fatigue performance of three alloys

[2]

where p is the plastic strain range, Nf is the number of cycles to failure (fatigue life), C2 is a constant and  is the fatigue ductility exponent (generally -0.5 >  < -0.7) (Coffin Jr., L.F., 1954; Manson, S.S., 1954)

-=;91=6<:4>-;75=+3;= The physical properties of the three steels that were investigated are given in Table I. The selection of 3CR12 and %9/3;=>2#,=;17.:<9/3=>83;.:5=>7.>:>('&200>(>1734+ H11 steels was based on their melting points, coefficients of thermal expansion, and thermal conductivities. The chemical compositions of the steels are given in Tables II. The thermal fatigue simulation was carried out in a fewer that in typical high-frequency low-cycle fatigue. In Gleeble 1500TM thermo-mechanical processing simulator. these casting moulds, the thermal fatigue failure is controlled This apparatus enables the specimen to be subjected to either by a cyclic plastic strain rather than a cyclic stress. The cyclic isothermal compression or tensile tests at elevated plastic strain results from the thermal stresses, which are a temperature. However, in this investigation, the specimens consequence of the temperature fluctuations during the were subjected to temperature cycling without constraint. casting process. The number of cycles to failure, Nf , for this Three samples, 10 mm in diameter and 116.5 mm in type of fatigue failure can be predicted by the Coffin-Manson length, were prepared of each material (Figure 2). The test equation. zone at the centre of each sample was milled to a thickness of This approach is similar to what is known as the Paris 7 mm for entire gauge length of 50 mm so as to create sharp equation for the stable crack growth regime. The Paris corners simulating the edges of the mould. Two K-type equation for high-frequency low-cycle fatigue is

[1] where

C2 = Constant  = Cyclic strain amplitude. Low-cycle fatigue test data are often represented as a plot of the plastic strain range versus cycles to failure. When plotted on log-log coordinates, a straight line is obtained, which is represented by the Coffin-Manson relation: %9/3;=>#'5,=1:<95>94438<;:<976>7.>8:1-4=>.7;><=8<96/

Table I ,)895:4>-;7-=;<9=8>7.><,=><,;==>8<==48>

:<=;9:4 =4<96/><=1-=;:<3;=> * ,=;1:4>=-:68976>57=..959=6<> 11  ,=;1:4>576+35<99<)> 1 

BS 3100 B7 - 11.9 42 H11 tool steel 1427 13.3 28.6 3CR12 ferritic stainless steel 1430–1510 12.8 40

Table II 447)>571-789<9768!>

**;679*3*7'9 94  $*:' (

BS 3100 B74 0.17 2.25 0.75 1.00 0.4 - - 0.35 - - - 0.025 - 2 3 0.02 - - 3CR12b 0.019 11.01 0.81 0.03 - 0.1 0.02 0.72 0.13 0.017 0.08 0.022 0.012 0.001 - - - 0.001 H11c 0.37 4.95 0.36 1.26 0.22 0.13 0.01 1.08 - 0.019 0.95 0.023 - - 0.0014 0.003 0.04 -

*Balance Fe aBuchholz, 2014 bASTM A240 and EN 10088-2 (Columbus Stainless, 2015) cDu Toit, 2015 L 350    VOLUME 116          An evaluation of the thermal fatigue performance of three alloys

thermocouples were spot-welded onto each specimen: one As expected, the surface of BS3100 B7 was heavily in the middle and one further away from the centre of the oxidized. After removing the oxides, cracks were exposed specimen, to measure the temperature. Each test was run for and were visible in the centre area in both longitudinal and 100 cycles over approximately 3 hours. In a case where the transverse directions (Figure 3). 3CR12, in contrast, cracks appeared before 100 cycles were completed, the exhibited less oxidation than BS3100 B7. However, cracks experiment was stopped prematurely. The temperature was were visible in the transverse direction in Figure 4. Strain fluctuated between 400 and 1200°C. In the first 50 seconds, marks (material flow lines) in the lengthwise direction were the specimen was heated to 1200°C at a heating rate of also present. No visible cracks or irregularities like strain 20°C/s, followed by another 10 seconds of soaking at the markings or necking were observed in H11 (Figure 5). The elevated temperature. The specimen was then cooled to 400°C specimen was still in sound condition after 100 cycles. at a cooling rate of 20°C/s. This cycle was repeated 100 times. Figure 6 shows a summary of the total plastic strain for After completion of the test, the surface of each specimen each steel after 100 thermal fatigue cycles. The total true was examined for cracks or other irregularities. Photographs plastic strain per 100 cycles for BS3100 B7, 3CR12, and H11 of the surface were taken, before and after cleaning with was 0.148, 0.182, and 0.058 respectively. The total plastic Hibatex solution to remove oxides, using a stereo microscope strain represents the measure of resistance to thermal fatigue. at magnifications of 12× and 15×. The data generated was used to calculate the total plastic strain in 100 cycles. Three tests were conducted for each steel, and an average value for the total plastic strain after 100 cycles was obtained. Equation 3 was used to calculate the total plastic strain, , after 100 cycles.

[3]

where L is the change in length (m) and Lo is the gauge length of the specimen (m). The hot strength of the steels was determined at 1100°C through an isothermal hot compression test, see Figure 7. The strain was limited to 0.8 to avoid barrelling effects. The coefficient of thermal expansion was determined using the Bahr dilatometer. This test was done in accordance %9/3;=>&#('&200>(>8-=591=6>83$=5<=+><7><,=;1:4>5)5496/>:.<=; with ASTM E831-14 specifications. The thermal expansion 54=:696/!>8,796/>476/9<3+96:4>:6+><;:68=;8=>5;:5 8 coefficient  is a material constant. It is the amount of expansion or contraction a material undergoes per kelvin during heating or cooling and is given by the following equation:

[4] where dL = Change in length (m) dT = Change in temperature respectively (°K) L = Total length of the specimen (m)  = Thermal expansion coefficient (m/m.°K) The thermal expansion coefficient should be as low as possible when the material is used to make moulds used in %9/3;=> #&*"2>8-=591=6>83$=5<=+><7><,=;1:4>5)5496/>:.<=;>54=:696/! the casting process. 8,796/><;:68=;8=>5;:5 8 The specimens were 5 mm in diameter and 10 mm long. Three of these specimens were machined for each alloy. The sample was heated to 1220°C (above AC3) at a heating rate of 0.25°C/s. The specimen was then soaked for 60 seconds and afterwards cooled to room temperature at a cooling rate equivalent to that of the heating rate. Lastly, Ac3 is the temperature at which ferrite completes its transformation to austenite during the heating up cycle.

"=834<8>:6+>+985388976>    Figures 3, 4, and 5 show stereo micrographs for BS3100 B7, 3CR12, and H11 after 100 thermal cycles between 400 and 1200°C. %9/3;=>#22>8-=591=6>83$=5<=+><7><,=;1:4>5)5496/>:.<=;>54=:696/

         VOLUME 116    351 L An evaluation of the thermal fatigue performance of three alloys

Table III 8<91:<=+>631$=;>7.>5)54=8><7>.:943;=>.7;>&*"2 :6+>22>3896/><,=><7<:4><;3=>8<;:96>-=;>200>5)54=8

'<==4><)-= ":<97>$:8=+>76><,=><7<:4>8<;:96>  -;=+95<=+

- >-=;>200>5)54=8

3CR12 1:1.3 13 931 H11 1:3.1 35 478 %9/3;=> #*71-:;9876>7.><,=>;=834<8>7.><,=><7<:4><;3=>8<;:96>-=;> 200>5)54=8 Table IV       ":>1:<=;9:4>578<8>.7;>('&200>(> :6>:;+=! The average number of cycles to failure for BS3100 B7, based 02 >:6+>22><774>8<==4> 49$:$:>;73-!>02 on the industrial data, is 11 340 i.e. Nf (BS3100 B7) =11 340 cycles. The cycles to failure for 3CR12 and H11 are unknown. '<==4><)-= ":>1:<=;9:4>578<> "<76 However, the ratios of the cycles to failure for BS3100 BS3100 B7 9 500 B7:3CR12 and BS3100 B7:H11 can be determined based on H11 32 550 the total true strain per 100 cycles. The number of cycles to failure for 3CR12 and H11 can then be calculated by multiplying the respective ratios by Nf (BS3100 B7). The results are shown in Table III. Although H11 tool steel looks promising, it is more expensive than BS3100 B7. Therefore, before H11 can be recommended as an alternative material, a comprehensive cost benefit analysis would be required. Based on a rough calculation regarding the raw material cost, the cost of H11 is 3.5 times higher than that of BS3100 B7 (Table IV).            %9/3;=>#76>98=8><;3=>8<;=88>><;3=>8<;:96>53;=8>.7;>('&200>(! Figure 7 shows the Von Mises true stress versus true strain &*"2!>:6+>22>:<>2200*>:6+>8<;:96>;:<=>7.>00028 for the three steels. H11 exhibited the highest hot strength of 31 MPa. The hot strengths of 3CR12 and BS3100 B7 were lower than H11, and similar i.e. 16 and 18 MPa respectively.       Figure 8 shows a typical dilatometer-generated plot of change in length versus temperature. The  values for BS3100 B7, 3CR12, and H11 were found to be 15.8, 13.1, and 12.8 m/m°.C respectively.

*7654389768 %9/3;=>#*,:6/=>96>4=6/<,><=1-=;:<3;=>53;=>.7;>('&200>(>.7;><,= The thermal fatigue behaviours of BS3100 B7, 3CR12, and +=<=;196:<976>7.> H11 were compared under similar conditions. H11 had the lowest total true strain of 0.058 per 100 cycles, indicating that it had the highest resistance to thermal ASTM International. 1980. Metals Handbook: Properties and selection on tool fatigue compared with 3CR12 and BS3100 B7. The mould life steels. Benjamin, D. (ed.). Materials Park, OH. would be longer than for the other two steels, and was ASTM INTERNATIONAL. 2015. ASTM E831. Standard test method for linear estimated to be about 35 478 cycles. thermal expansion of solid materials by thermomechanical analysis. Materials Park, OH. However, before H11 tool steel can be recommended as AZO MATERIALS. 2014. Investigation of fatigue crack propagation in polymers. an alternative material, a comprehensive cost analysis is http://www.azom.com/article.aspx?ArticleID=11114 [Accessed 17 March required. Based on a rough calculation regarding the raw 2016]. BUCHHOLZ, H. 2014. Catalyst Manufacturing Unit, Secunda. Personal communi- material cost, the cost of H11 is 3.5 times higher than that of cation and unpublished results. BS3100 B7. COFFIN JR., L.F. (1954), A study of the effects of cyclic thermal stresses on a ductile metal, Trans. ASME, vol. 76, pp. 931–950. "=.=;=65=8 COLUMBUS STAINLESS. 2015. Unpublished results. Middelburg, South Africa. DU TOIT, W. 2015. Orion Engineering, Pretoria. Unpublished results. ALIBABA GROUP. 2015. Minerals & Metallurgy. http://www.alibaba.com/showroom/alloy-raw-material-price-h11-tool- HERTZBERG, J.L. 2013. Deformation and Fracture Mechanics of Engineering steel.html [Accesed 18 October 2015]. Materials. 5th edn. Courier Westford, North Chelmsford, MA. MANSON, S.S. (1954), Behaviour of materials under conditions of thermal AMERICAN PETROLEUM INSTITUTE. 2011. API recommended practice 571: Damage mechanisms affecting fixed equipment in the refining industry. 2nd edn. stress, NACA TN-2933, National Advisory Committee for Aeronautics API Publishing Services, Washington. STUMPF, W. 2014. Department of Materials Science and Metallurgical Engineering, University of Pretoria. Unpublished results. ASTM INTERNATIONAL. 1978. Metals Handbook: Properties and selection on irons steels. Benjamin, D. (ed.). Materials Park, OH. pp. 114–116. VAN AARDE, B. 2015. Steloy, Johannesburg. Personal communication. N L 352    VOLUME 116          http://dx.doi.org/10.17159/2411-9717/2016/v116n4a9 The effect of particle size on the rate and depth of moisture evaporation from coal stockpiles by J. de Goede*, B. Muller*, Q.P. Campbell*, M. le Roux*, and C.B. Espag de Klerk*, Paper written on project work carried out in partial fulfilment of B.Eng. (Chemical Engineering with specialisation in mineral processing)

J.F. and Szladow, A.J. 1973) – as well as by 1"' #(# the porosity, heat conductivity, and chemical nature of the coal particles (Karthikeyan, M., Excessive amounts of moisture in product coal can influence the efficiency Zhonghua, W., and Mujumdar, A.S. 2009). of downstream utilization processes due to a decreased calorific value and handling problems. Stockpiles can be used to decrease the moisture Moisture from a coal stockpile surface will content of coal by means of gravity drainage and evaporation. This paper evaporate until equilibrium is reached between is focused on the evaporation of moisture from a coal stockpile surface the ambient atmosphere and the coal particles. with the aim of investigating the effect of particle size on the rate of When the relative humidity increases as the evaporation as well as the depth to which evaporation extends. temperature decreases, the coal particles can It was observed that moisture initially evaporates at a higher rate from reabsorb moisture to re-establish equilibrium a stockpile consisting of fine particles (-6.7 mm) than from coarser (de Korte, G.J. and Mangena, S.J. 2004; particles (-13.2 mm +6.7 mm). This high rate of evaporation is restricted to Karthikeyan, M., Zhonghua, W., and the outer shell of the fine coal stockpile. However, for coarse coal, the Mujumdar, A.S. 2009). This process of porous nature increases the depth at which evaporation occurs. desorption and reabsorption can be repeated Evaporation of moisture was observed up to the fourth day of each experi- mental run, after which steady state was obtained. It was shown the on a daily cycle(de Korte, G.J. and Mangena, water can evaporate from the surface into the body of the stockpile, S.J. 2004). depending on the coal particle size and void spacing. An experimental reclaim depth of 0.4 m was achieved after 4 days. 1& !)* $) &$&%('" .)'$# Washed South African bituminous coal from coal, stockpile, dewatering, depth of evaporation, rate of evaporation. the Witbank No. 2 seam was used for the experiments. The proximate analysis of the coal can be seen in Table I. The coal was used as received and was -"%$'%('" sieved into three size ranges: fine (-6.7 mm), Coal stockpiles serve as surge capacity for total range (-13.2 mm), and coarse (-13.2 mm downstream utilization processes and can also + 6.7 mm). be used for moisture reduction by means of gravity drainage and evaporation. Excessive , )$( )"%&!* )%' amounts of moisture in coal can cause The objective of this investigation was to handling problems and, most importantly, will establish the effect of coal bed particle size on decrease the calorific value, leading to inefficient combustion. Research has shown that evaporation by Table I means of wind and solar action is considerably more effective than gravity drainage(Williams, $' ( &%)*&"&!#(#*&($$()*&#(# D.J. 2006), but the effect is limited to a restricted depth from the exterior of the ' '")"% )$)"%&)**)(% stockpile (Boyapati, E. and Oates, A. 1994; Inherent moisture content 2.6 CSEM-UAE, 2010). The effectiveness of wind Ash content 15.9 and solar action can be improved by orienting Volatile matter 25.2 Fixed carbon 56.4 the stockpile perpendicular to the predominant wind direction, maximizing the surface area of the pile, and reclaiming the coal from the pile gradually in shallow cuts over a large area (Williams, D.J. 2006). * School of Chemical and Minerals Engineering, The extent of evaporation is mainly North-West University, Potchefstroom, South influenced by the weather – in particular solar Africa. radiation, temperature, wind strength, and © The Southern African Institute of Mining and Metallurgy, 2016. ISSN 2225-6253. Paper received relative humidity (Deodhar, M.J. 2008; Fryer, Feb 2016.

         VOLUME 116    353 L The effect of particle size on the rate and depth of moisture evaporation from coal the rate and depth of moisture evaporation. The investigation oven at a constant pressure of 101.3 kPa and temperature of was divided into two parts. In both cases saturated samples 105–110°C. for 6 hours. The inherent moisture content of the of the three different size ranges were prepared. The first coal was determined by difference. experiment was designed to determine the depth to which The evaporation rate (experiment 2) was determined by evaporation extends. The samples were loaded into sectioned analysing the data from the data logger of the load cells and PVC pipes, using 12 pipes for each size range, and placed the weather station. outside for 10 to 12 days and exposed to ambient conditions to facilitate the process of evaporation. In the second 0)#!%#*&"*(###('" experiment, coal samples were placed in three shallow containers to investigate the rate at which moisture        evaporates from a coal stockpile surface. These samples were From Figure 3, a sharp decrease in total moisture content is exposed to ambient conditions while the masses of the noted from start-up to day two. This is due to drainage of containers were continuously measured. The experimental moisture under gravity . From day two to day four, set-up included a weather station that continuously measured evaporation occurred from the top 0.2 m below the surface. temperature, relative humidity, and wind speed and direction. From Figure 3 it can be seen that the coal samples reached steady state at day four, after which the total moisture  content remained relatively constant until day twelve. This is The PVC pipes for the first experiment were cut into seven an indication that no surface moisture is available to 0.1 m sections and connected with duct tape as seen in evaporate into the atmosphere. The void spacing of the coal Figure 1. bed had a major influence on the depth to which evaporation The shallow containers for the second experiment, with occurs. The coarse (-10 mm +6.7 mm) coal bed was more dimensions of 34 cm × 25 cm × 20 cm, were placed on load porous than the fine (-6.7 mm) coal bed. It was found that cells that continuously recorded the weight of the containers. evaporation took place up to 0.4 m below the surface of the This set-up can be seen in Figure 2. Both structures were coarse coal bed, and that only the surface of the fine coal bed covered with Perspex roofs. showed signs of evaporation.

          To determine the depth to which evaporation occurs, one PVC Figure 4 illustrates the cyclic behaviour in the mass loss pipe containing each particle size of coal was removed on a profile of each size range. Evaporation generally occurred daily basis for moisture analysis. The coal samples from each from 09:00 to 17:00 when the temperatures were high and section of the three pipes were removed and weighed, then the relative humidity low. As evening fell, the temperature dried for 72 hours in a climate-controlled room at a constant decreased and the relative humidity increased, resulting in temperature of 22°C and a constant relative humidity of 40%, the reabsorption of moisture into the porous coal particles as and re-weighed. The samples were then placed in a vacuum the particles tried to stay in equilibrium with the atmosphere.

($)* !%( !)*)& '$&%('"* ( )#*) '#)*%'*& ()"%*'"(%('"# ($)*'%&!* '(#%$)*'"%)"%*'*'&!* &$%(!)*#()** **  ("*&*'! "*&%*()$)"%*) %#*')$*%( )

($)*'"%&(")$#* !&)*'"*!'&*)!!# ($)* &##*!'##*)*%'*)& '$&%('"*'* '(#%$) L 354    VOLUME 116          The effect of particle size on the rate and depth of moisture evaporation from coal

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It can be seen that all coal samples reached the same University (NWU). The research was supported by the South moisture content by the end of the experimental run. The African Research Chair’s Initiative of the Department of coarse coal sample reached the final moisture content first. Science and Technology and the National Research To compare the effect of particle size on the rate of Foundation of South Africa (NRF). Any opinion, finding, or evaporation, the daily rates of evaporation were calculated for conclusion or recommendation expressed in is that of the each size range as shown in Figure 5. It can be seen that authors and the NRF does not accept any liability in this moisture initially evaporates faster from the fine coal sample regard. (-6.7 mm) than from the other coal samples. After two days, the surface of the fine coal sample was dry and the rate of evaporation decreased. The same phenomenon was seen in 0))$)")#** the experiments that investigated the depth to which BOYAPATI, E. and OATES, A. 1994. A mathematical model for stockpile evaporation occurs. This is attributed to the porous structure management. 6th International Working Conference on Stored-product of the coarse sample. Protection, Canberra, Australia, 17–23 April 1994. pp. 684–688. During the investigation, it was found that the initial moisture content had an influence on the rate of evaporation. A lower initial moisture content resulted in a lower maximum CSEM-UAE INNOVATION CENTER. 2010. Water evaporation rate at Ras-Al- rate of evaporation. Khaimah, UAE. http://www.csem-uae.com/pdfs/Water%20Evaporation% 20rate%20%20in%20Ras-Al-Khaimah,%20UAE [Accessed 18 June '"!#('"# 2014]. This study showed that bed particle size affects the extent of moisture evaporation, and that the porous structure of a DE KORTE, G.J. and MANGENA, S.J. 2004. Thermal Drying of Fine and Ultra-fine coarse coal stockpile aids the process. Experimental results Coal. CSIR.Fryer, J.F. and Szladow, A.J. 1973. Storage of coal samples. indicate that moisture drainage takes place within the first Alberta Geological Survey, Edmonton. two days of exposure to environmental conditions. Evaporation of moisture can be seen up to the fourth day, but DEODHAR, M.J. 2008. Elementary Engineering Hydrology. Pearson Education, this is a function of the initial moisture content of the coal. India. Dorling Kindersley. Coal with a higher initial moisture content will take a longer time to lose all surface moisture. It was shown that water can evaporate from underneath KARTHIKEYAN, M., ZHONGHUA, W., and MUJUMDAR, A.S. 2009. Low-rank coal the surface of coal stockpiles. Increased void spacing has a drying technologies-current status and new developments. Drying positive influence on the effectiveness of evaporation for coal Technology, vol. 27. pp. 403–145. stockpile drying. The results obtained in this study can be used to manage stockpiles efficiently. Up to 0.4 m of coal can PRIYAL, D. and TOERIEN, A. 2010. The effect of salinity on evaporation rates of be reclaimed from the stockpile surface and the remaining coal can be left to dry for another four days – if no rain brines resulting from the treatment of mine occurs. water.http://www.google.co.za/url?sa=t&rct=j&q=&esrc=s&source= web&cd=1&cad=rja&uact=8&ved=0CCcQFjAA&url=http%3A%2F%2Fww +/"'!) )"%# w.ewisa.co.za%2Fliterature%2Ffiles%2F200_150%2520Dama-87 The authors would like to thank the following institutions for Fakir.pdf&ei=7I6LU5TcFqzA7AaH6oF4&usg=AFQjCNForf8NhQQ3zVqS90 their contributions towards this project: GVcrPPBldPQw&bvm=bv.67720277,d.ZGU Date of access: 18 June 2014. ® Coaltech ® NRF (National Research Foundation). WILLIAMS, D.J. 2006. Application of Unsaturated Soil Mechanics to Product Coal This paper is based on project work carried out in partial Dewatering. Australian Mining Technology Conference, Hunter Valley, fulfilment of a degree in Chemical Engineering at North-West NSW, 26–27 September 2006. N

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