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By P. den Hoed, R. I. Rambiyana

"Four sulphide minerals - pyrite (FeS2), pyrrhotite (Fe1-xS), pentlandite ([Ni,Fe]9S8), and chalcopyrite (CuFeS2) - contain the base metals and most of the iron in concentrates of platinum group metals (PGMs). In the pyrometallurgical processing of PGM concentrates these sulphides form a matte during smelting, and iron and sulphur are removed from the matte during the converting process. This paper discusses the roasting of Merensky concentrate in air before smelting, with the purpose of reducing the matte load to the converter.Roasting tests were conducted in a bench-scale rotary kiln at temperatures from 350°C to 700°C. The concentrate tested contained 17.4% sulphur and consisted of 23% pyrrhotite, 16% pentlandite, 11% chalcopyrite, and 2% pyrite. The particles were fine (d50 = 22 µm), and all the sulphide particles were liberated. Roasting in air at 550°C and 650°C for 20 minutes removed respectively 60% and 70% of the sulphur. The iron in the sulphides was oxidized to Fe3O4 (magnetite) at temperatures below 500°C and to Fe2O3 (haematite) at temperatures above 550°C. At 700°C the bed sintered and copper oxides formed. At temperatures below 450°C oxidation was incomplete: pyrrhotite remained and only 30% of the sulphur was removed. Smelting tests were conducted to assess matte fall and the deportment of copper and nickel to matte. It was evident that roasting resulted in lower matte falls (a drop of approximately 60%) compared with matte falls from unroasted concentrate. The iron and sulphur levels in the matte were reduced to below 3.5% and 22% respectively.This paper also briefly describes the mechanisms by which pyrrhotite, chalcopyrite, and pentlandite are oxidized during roasting. For chalcopyrite, the mechanism proceeds through an intermediate solid solution phase, which extends from Cu1.02Fe1.04S2 to Cu2.04Fe0.72S2 to a copper-rich solid solution of bornite (Cu4Fe1.4S4-Cu2S). The oxidation of pentlandite proceeds through a monosulphide solid solution (Ni0.39Fe0.53S-Ni0.74Fe0.15S) to a solid solution of heazlewoodite ([Ni,Fe]3}xS2). These mechanisms are explored in relation to chemical thermodynamics and microstructures."

Jan 1, 2015

By W. Mbhalati

"Conzal Mine was not meeting production targets in 2013, and it was established that this was caused by the inability of the load haul dump machines (LHDs) to tram the required tonnages. An investigation of the LHD productivity was therefore conducted to identify the inhibiting factors. This was accomplished by carrying out a literature review on LHD operations to gain in-depth knowledge and conducting observations in the working environment. The relevant information and data on the LHD type used at Conzal was also acquired.The major inhibitor was found to be excessively long tramming distances in all the sections of the mine. The one-way tramming distances were all significantly greater than the 90 m set in the mine’s code of practice (COP), with the Main Shafts section having the longest average one-way tramming distance of 260 m. The other inhibitor was LHD utilization, which in 2013 was only 47% against a target of 70%. Simulation of the LHD operation, taking these two factors into account, showed that production could be increased by more than 100%. As a result, it was recommended that conveyor belts should be extended regularly in order to keep tramming distances within the recommended one-way distance of 90 m. In addition, utilization can be improved by minimizing employee absenteeism as well as by modifying the travelling routes such that LHDs do not encounter unnecessary delays.Paper written on project work carried out in partial fulfilment of BSc. (Mining Engineering)"

Jan 1, 2015

Often plant performance suffers as a result of poor control. Poor control leads to low mill throughputs, poor classification and less than satisfactory concentrate grades and overall recoveries. By using the appropriate control tools, substantial gains in plant performance can be made. Mintek?s MillStar and FloatStar controllers have been implemented at various sites across the world. The MillStar controller incorporates leading technology that controls process units from the mill feed through to the flotation feed. Typical results show that milling circuit throughput is increased by 6-10 % and the final product grind size is tightly controlled, thereby enhancing flotation performance. The FloatStar controller is aimed at stabilising and optimising flotation circuits. Through improved level control alone, recovery improvements of up to 1 % have been achieved. Furthermore, by using on-line grade analysers, the controller stabilises final concentrate grades, whilst maximising flotation recovery.

Jan 1, 2005

By M. Castelli, C. Scavia, S. Marello, A. Allodi

ABSTRACT – This paper investigates the possibility of interpreting the shear band evolution in hard soils and soft rocks as the result of shear propagation from pre-existing natural defects. Thesis done through the application of the principles of Fracture Mechanics, a Slip-Weakening Model(SWM) being used to simulate the non-linear zone at the tips of the discontinuity. Experimental observations have been carried out on prismatic samples of Beaucaire marl through biaxial compression tests in plane strain conditions. A numerical simulation confirms the validity of the proposed approach. RÉSUMÉ – Cet article présente la possibilité d’interpréter l’évolution des bandes de cisaillement dans les roches tendres et les sols raides comme le résultat de la propagation pour cisaillement à partir d’un défaut préexistant. Le Slip-Weakening Model (SWM) a été employé pour modéliser la zone non linéaire a l’extrémité d’une discontinuité. Nous présentons des observations expérimentaux obtenues à travers des essais de compression en déformation plane sur des échantillons prismatiques de marne. La simulation numérique d’un essai confirme la validité de la méthode proposée. KURZFASSUNG – Die vorliegende Arbeit versucht die Ausbreitung von Scherzonen in(bindigen) Böden und im Lockergestein anhand der Entwicklung von Scherrissen ausgehend vonexistierenden Schwachstellen zu erklären. Die Umsetzung erfolgte mit Hilfe der Bruchmechanik,für die Modellierung der nichtlinearen Zone an den Rissenden wurde ein Slip-Weakening-Modell(SWM) eingesetzt. Es wurden zweiaxiale Druckversuche an prismatischen Probekörpern vonBeaucaire Mergel unter der Bedingung eines ebenen Verzerrungszustandes durchgeführt. Dienumerische Untersuchungen bestätigten die Annahmen der untersuchten Theorie.

Jan 1, 2003

By H. H. Einstein

This paper reviews how uncertainty has been dealt with over the past 40 years using the decision making cycle as a frame of reference. The review of the phases of this cycle, as applied to rockmechanics and rock engineering, namely characterization, performance analysis, updating and decision making shows that in each, progress has been made over the past 40 years, although most of the basic concepts existed already in the 1960’s. Characterization is the area in which the greatest scientific steps were taken, this phase and performance analysis also gained from the tremendously expanded computational capabilities which allow one to use both more complex and more practically oriented models. The greatest practical advance is without using any doubt in risk based decision making although its acceptance shows interesting differences between different professions. Dans l’article suivant on utilise le cycle de décision pour illustrer le développement du traitement des incertitudes en mécanique des roches et en construction en roche dans les quarante années passées. La revue des phases du cycle de décision montre qu’on a fait du progrès dans chaque phase du cycle de décision, c’est à dire dans la caractérisation, dans l’analyse et la prédiction du comportement, dans l’actualisation et dans l’acte de décision, même si les concepts fondamentaux existaient déjà dans les années 1960. Les plus grands avancements scientifiques se trouvent dans le domaine de la caractérisation tandis que l’analyse prédictive profitait du développement de l’informatique qui a mené à des modèles plus complexes mais aussi plus pratiques. Le plus grand progrès est sans doute dans le domaine de l’acte de décision sur la base des risques. Ce procédé est devenu assez commun même s’il y a encore des différences d’acceptation entre différentes professions. Im vorliegenden Artikel wird der Entscheidungszyklus gebraucht, um darzustellen wie sich derUmgang mit Unsicherheiten im Felsbau während der letzen 40 Jahre entwickelt hat. DerÜberblick über die Phasen des Entscheidungsprozesses zeigt, dass bei der Anwendung in derFelsmechanik und im Felsbau, in allen Phasen d.h. bei der Charakterisierung, bei der analytischenVorhersage, beim Aktualisieren und bei der Entscheidungsfindung Fortschritte gemacht wurden,obwohl die grundlegenden Konzepte bereits in den 1960er Jahren existierten. Im Gebiet derCharakterisierung gab es wohl die grössten wissenschaftlichen Entwicklungen, während dieanalytische Vorhersage vor allem von den Fortschritten der Informatik profitierte, welchekomplexere wie auch praktischere Modelle möglich machte. Der grösste Fortschritt ist ganz sicherin der Entscheidungsfindung zu beobachten, wo Risikobetrachtungen gang und gäbe sind, obwohlhier noch einige Unterschiede zwischen verschiedenen Berufsgattungen zu finden sind.

Jan 1, 2003

By J. N. Van der Merwe

The principal goal of the research described in the paper was to determine, by measurement of pillar scaling on pillars that have not failed, whether the pillar life prediction method developed by van der Merwe (2003) was valid as it stood or whether adjustments were necessary to the rates indirectly derived from observation of failed pillars. To this end, measurements were taken on over 350 pillars at 13sites on 6 mines. The project was done as a collaborative effort between the University of Pretoria, the Nancy School of Mines and CSIR Miningtek. During the course of the investigation, it was found that the majority of pillars display maximum scaling at mid height, that there was no clear preferential direction of pillar scaling, and that pillar corners do not scale significantly more than the mid pillar areas. The most important conclusion was that the scaling rates found by measurement agreed with the inferred rates found in the previous work. The previously developed procedure for the prediction of pillar life spans consequently requires no adjustment, although the error span is in the region of 20%. It is recommended to do further research into the effect of sealing of panels and, possible chemical changes taking place in the pillars as they age on the scaling rate.

Jan 1, 2004

By C. Sima, M. Legoabe

Keywords: Pyrometallurgy, furnace, platinum Mortimer Smelter is one of the three smelting operations in the Anglo Platinum Group. It is located in the Limpopo Province, approximately 100 km north of Rustenburg, and approximately 15 km west of Northam. The smelter operation is the smallest of the three smelting operations in the group, with a smelting capacity of 170 kt/annum. The operation consists of a Larox filtration plant, a Drytech flash drying plant, a modified Elkem / Hatch 19.5 MVA furnace, and a 60 t/h matte crushing plant. The operation does not convert its furnace matte, and hence the final sulphide rich matte is transported to and processed further at the Anglo Platinum Converting Process (ACP) within the Waterval Smelter Complex in Rustenburg. Furnace slag is granulated, and processed through a slag mill, or transported to a slag dump.

Jan 1, 2006

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Jan 1, 2009

By P Papanastasiou, J Hadjigeorgiou, E Kyriakou

The south west area of Cyprus has a long history of slope instability problems. The location and extent of these landslides has been influenced by ground morphology, geological structure and the presence of weak rocks and cohesive soils. The main triggering mechanisms have been precipitation and/or seismic events. Landslides have contributed to the decision to relocate villages and considerable efforts have been put into maintaining the integrity of the local transportation network. This paper uses a recent case study of road embankment failure near Pentalia in southwest Cyprus to review the available tools for the analysis of slope instability. It further demonstrates how the shear strength reduction technique can be used in a finite element analysis to better visualise the slope instability mechanism of a road embankment and provide a reliable tool in selecting appropriate remedial measures.

Jan 1, 2006

By A van Jaarsveld

Environmentally-friendly, safe and cost-effective technology for stope drilling has successfully been introduced at TauTona mine. It has enabled the problem of inadequate compressed air pressure and its downgrading impact on production capability to be overcome. The paper traces the development process which culminated in the conversion of the entire stoping operation at TauTona to electric drilling. Background work which took place at other mines is also described. Statistics of performance improvements are provided. 1. Introduction Holman?s Silver series and the Seco S215 were drills that had a measurable impact on the South African gold mining industry. It is too soon to say whether Hilti will join those great names. However, there is no doubt that the introduction of electric drills into the harsh and unforgiving world of deep level gold mining is a significant development. History has shown that being the first to enter a new technology is no guarantee of long-term success. The pain and suffering which accompany the birth of anything new can deplete the energy of the innovator while at the same time creating opportunities for competitors to leapfrog him. In addition to commitment and enthusiasm, the innovator must therefore also possess, or have access to stamina and resourcefulness to overcome the unexpected difficulties which will inevitably arise. All of these were needed for the Hilti project.

Jan 1, 2008

By C. Legote

"This paper investigates the conditions leading to the indefinite termination of production in four critical primary panels at an underground coal mining operation, the observed shortcomings in the mining approach, and the proposed strategy to mine through the affected panels. Initial assessment of the abandoned panel conditions indicated time-dependent strata failure,(i.e. bolted roof failure overrunning intersections), which occurred from mere minutes to up to four weeks post-production, with and without prior warning of failure. This prompted the constant re-supporting of back areas, which raised safety and productivity concerns. Investigation of the initial mining conditions revealed that the failures were due to a critical combination of factors, the chief of which was isolated horizontal stress. Other factors that were initially overlooked by the mine (i.e. influence of hydraulic stress, misinterpretation of borehole data), resulted in the conditions being described as abnormal. Remedial actions were determined, and in so doing, a new strategic approach was formulated to thoroughly address all failure concerns. The four panels were explicitly planned to serve as the main intake and return airways for the recently commissioned secondary ventilation shaft, as well as providing access to millions of tons in proven coal reserves. It is thus imperative to mine the panels. A feasibility study showed that the proposed strategy set for implementation would be financially viable. Paper written as project work carried out in partial fulfilment for BEng(Mining Engineering) degree"

Jan 1, 2015

By F. M. L. Mulaudzi

Behaviour studies of metal dusting processes and associated filamentous carbon formation were undertaken on Alloys 600, 601, and 800 using a simulated metal dusting environment of 25C0-70H2-5H20 (vol.%) at 650°C. These samples were studied visually and by optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy with energy-dispersive X-ray spectroscopy (TEM-EDX) and x-ray diffraction (XRD). Visual examination and SEM surface observation showed that Alloy 800 suffered metal dusting attack at an early exposure reaction period. The coke deposit amounts increased significantly with reaction time from 168 hours to 336 hours in Alloys 600, 601, and 800. Alloy 800 showed pitting after 168 hours' exposure, and the degree of pitting increased after 336 hours. XRD showed all these alloys had a common austenitic phase, with Alloy 800 also having ferritic metal particles. Alloy 800 after 168 hours' exposure had a complex phase mixture on the surface, consisting of ferritic Fe and austenitic FeNi phases. For coke deposit, there were also Fe304, Fe3C and graphitic carbon. The existence of Fe, Ni, and Cr metal particles, and also graphitic carbon in coke deposits, was confirmed by EDX analyses.

Jan 1, 2013

By R. Hummel

When the slope angles of the southern side of the Venetia open pit were required to be flattened by some 20 degrees after an analysis completed by De Beers geotechnical engineering in conjunction with SRK, the additional waste stripping tonnage generated was in the order of some 70 million tons. The potential cost of having to move this tonnage had a significantly negative effect on the Net Present Value of Venetia Mine, challenging the viability of the third pushback and rendering a potential fourth pushback completely uneconomic. This paper details some of the innovation that went into the design and planning process undertaken to virtually negate the instantaneous effect of the flattened slope angles and the associated waste tonnage as well as further improve the NPV of Venetia Mine and bring the fourth pushback back into economic viability. This process has become known as NPV+ and is anon going exercise in waste reduction/deferment and revenue advancement.

Jan 1, 2001

By H. E. Bartlett

In the operation of some flotation plants treating platinum ores it was found that there were imbalances between the inputs and outputs. The inputs and outputs were sampled as slurries and it was determined that the imbalances arose from biases in the sampling, despite the samplers having been designed according to well-established rules. The launders feeding the sample cutters, and the sample cutters themselves were redesigned using finite element analysis to model the flows. A new set of design rules were formulated. The application of a Components of Variance Analysis, to determine the variance of primary and secondary sampling and of analysis in the lab for a concentrate is presented to illustrate the need for frequent sampling of process streams.

Jan 1, 2002

By S. M. Spottiswoode

Much as one hopes to predict whether damaging seismicity might occur somewhere in the next shift, this is not possible at present. Recently, an analysis of seismicity at two mines has shown that a small increase in seismicity occasionally occurs before both large and small events. This analysis is extended here to five mines, with the same results. Earthquake seismologists forecast hazard in terms of the average incidence of earthquakes over the last 50 years, adjusted on an hourly basis according to the possibility of aftershocks of events that have happened. The rate of seismicity in any area remains approximately constant when expressed as seismicity per area mined, or better still, per unit of elastic strain energy released. It is suggested that seismic hazard in mines be estimated using historical seismicity and forward modelling, adjusted according to the possibility of aftershocks. In summary, medium-term forecasting of seismicity is viable; short-term prediction of large events is not.

Jan 1, 2010

By C J. de Beer

The Kwaggashoek East pit is one of the four production areas of Thabazimbi Iron Ore Mine. The Kwaggashoek East Open pit mines through the abandoned sublevel caving operations of the Kwaggashoek East underground workings. A risk assessment indicated that the primary risk is the occurrence of surface subsidence. Based on local knowledge, a hypothesis, that most of the cavities were filled with broken rock as a result of roof collapse and bulking of failed material was formulated. To test the hypothesis a number of geophysical methods as well as probe drilling was utilized. The results of the resistivity, gravity and ground penetrating radar surveys were inconclusive in determining the position of voids. Either there were no voids present or the resolution of the surveys was not high enough to pick it up. It is accepted that only small voids remained, and that the supported roof hypothesis is valid. As a precautionary measure all the production blast holes within the caving area were over-drilled by forty percent. This would collapse the roof of any small voids or tunnels immediately below the block. This operation proved to be successful as two of the three underground levels have been mined out with no subsidence occurring in the pit floor.

Jan 1, 2006

By J. Kempken, T. A. Schreiter, R. Degel, H. Schmieden

Keywords: Pyrometallurgy, SMS Demag, Germany, submerged arc furnace, ferro alloys, non-ferrous, FeCr, FeNi, FeMn, copper, cobalt, slag cleaning, PGM, rectangular furnace After a short summary of the SMS Metallurgy part of the SMS group, the paper will focus on Submerged Arc furnace technology. After general aspects of furnace design, the focus will shift to different applications and their specific furnace requirements. Finally, a state-of-the-art design tool as well as a new invention to improve slag-cleaning technology will be featured.

Jan 1, 2006

By D. Tsweleng

In the Evraz Highveld production process, iron ore is prereduced in rotary kilns prior to charging into submerged arc furnaces (SAFs). Owing to the highly aggressive slags that are formed within the combustion zones of these kilns, chrome-oxide-containing lowcement castables have been used for some years in the kiln lining. Due to concerns around the potentially harmful effects should Cr(V1) be present in the spent linings, Highveld and its suppliers of kiln castables devoted time to developing alternative chrome-free lining materials. Such materials needed to be cost-effective and ensure good performance and improved kiln availability. This paper discusses all the parameters surrounding this development. Keywords Low-cement castable, chrome-oxide free, chrome (VI), titaniferous magnetite ore, rotary kiln, submerged arc furnace, open slag bath furnace, Evraz Highveld Steel & Vanadium Limited.

Aug 1, 2013

By Gift Chisakuta, Bravo Mbao, Nils Schwarz, Angus Feather, Anthony Mukutuma

Bwana Mkubwa is a 50 000 tons per annum copper cathode producer, owned by First Quantum Minerals and located in Ndola, on the Zambian Copperbelt. The Bwana Mkubwa solvent-extraction circuit was started up in 1997. In 2002, the plant began treating ore from First Quantum?s Lonshi mine located in the Democratic Republic of Congo. The Lonshi ore is exceptionally fine and the amount of solids in the feed solution reporting to the solvent-extraction feed solution increased dramatically. Initially, crud was filtered in a filter press, but this rapidly blinded and seldom produced anything better than a wet sludge containing large quantities of organic. In December 2003 the decision was made to install a Flottweg Z4E-3/441 Tricanter® centrifuge to recover organic from the crud. The installation was completed in June 2004 and has since led to significant improvements in plant operability and savings in organic consumption.

Jan 1, 2007

By M. C. Bhulose

Paper written on project work carried out in partial fulfilment of B. Eng (Mining Engineering) degree The purpose of this project was to identify constraints that could occur in the current sub-decline shaft at Turffontein Shaft should an increase in production take place. Particular attention was to be paid to the transportation of men and materials and to the broken rock and ventilation capacity of the shaft. This project is an in-depth evaluation of the logistic capacity of the sub-decline system at Turffontein Shaft in order to determine by how much production can be increased in this area to replace tonnages from the vertical shaft area, where ore reserves are rapidly becoming depleted.

Jan 1, 2004