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By C. M. Rule

Stirred milling using either horizontal or vertical mills has made a rapid entrance into PGM ore and tailings concentrator flow sheets. Currently there are in excess of 40 units installed in either mainstream, ?MIG? or intermediate concentrate regrind, ?UFG?, applications in PGM, primary ore treatment plants or in tailings scavenging and reclamation treatment plants. This represents a total of approximately 70 MW of installed fine grinding equipment. This paper outlines the reasons why the technology take-up has been rapid and illustrates the advantages of this technology over conventional milling. Keywords PGM, platinum group metals, UG2, Merensky, platreef, stirred milling, MIG?mainstream inert grinding, UFG?ultra fine grindingof intermediate flotation concentrates, IsaMill?, Metso SMD?, Deswik, ceremic grinding media, QEMSEM, MLA.

Jan 1, 2011

Gravity-driven rock falls account for a large proportion of all fatalities and injuries in underground mines. Potentially unstable blocks of rock are found in the hanging wall of excavations, which may be delineated by natural joints or stress fractures. These blocks, referred to as keyblocks, will fail if their weight exceeds the support capacity or if they are located between support units. This paper describes a computer program which simulates blocks in the hanging wall of an excavation based on measured properties of fractures and joints. Keyblocks are identified and placed at random locations in a predefined excavation. The keyblocks are tested against the support to determine whether they fail the support, drop out between the support or are stable. By repeating the procedure several thousand times, statistics of the probability of failure of the keyblocks are obtained. This approach allows the relative hazard associated with different types of support or excavation orientations to be obtained. It is concluded that a probabilistic approach is suitable for the evaluation of supports effectiveness in situations where large numbers of discontinuities or stress fractures are exposed in excavations.

Jan 1, 1998

By D. J. Greeff

By making use of genetic programming, empirical models for metallurgical processes can be evolved that are more cost-effective than models determined by means of classical statistical techniques. These methods explore populations of candidate models assembled from sets of variables, parameters and simple mathematical operators, and do not require explicit specification of model structures. The application of the proposed strategies is illustrated by means of a case study pertaining to the leaching of nickeliferous chromite ores. Modelling of the nickel and cobalt extraction from the ores yielded models of similar accuracy compared to those obtained by non-linear regression and artificial neural networks. However, in the case of the iron extraction from the ores, the genetic programming model was significantly more accurate than both the regression and neutral network models.

Jan 1, 1998

By V. Bari?ic

The scheduled power cuts of early 2008 were a disturbing reminder that South Africa needs to expand its power-generating capacity. Low-grade and discard coals, of which South Africa has much, are a source of energy and amenable to combustion in circulating fluidized beds (CFBs). Foster Wheeler (FW) has a long record in developing this technology in boilers. The technology is flexible in burning a variety of fuels; low-grade, high-ash coals, good quality bituminous and anthracite coals, and biomass and waste fuels have all been used. CFB boilers are efficient, reliable and can be designed to meet tight emission standards. In recent years once-through supercritical (OTSC) CFB technology has been developed. It enables the next stage in CFB development to proceed to a medium-scale (500 MWe) utility in such projects as Lagisza, which runs at a net efficiency of nearly 44%. Scaling the technology up to 800 MWe with a net efficiency of>45% is planned to be commercial during 2009. CFB technology can reduce CO2 emissions in the repowering of coal-fired and greenfield power plants. It does so through greater efficiencies and by co-combusting coal with biomass. FW has also developed CFB technology for the gasification of biomass, as, for example, in a pressurized gasifier to produce syngas, which can be used for the production of biodiesel, thereby reducing CO2 emissions from vehicles. Carbon capture and storage (CCS) can potentially cut CO2 emissions in the generation of power from fossil fuels in the short term, provided that it gains public acceptance, that the required regulatory framework is created, and that emission-trading mechanisms or other incentives provide a solid return on the major investments required. Oxyfuel combustion is an option in CCS; Foster Wheeler is adapting its CFB combustion technology for oxy-fuel combustion to meet this challenge. It is developing Flexi-burn?, which enables a plant to be operated either with or without carbon capture. This paper describes the status of CFB technology in terms of boiler efficiency and fuel flexibility. It highlights the advantages of CFB technology for oxyfuel combustion, presents a development plan for Flexi-burn?, and discusses a pressurized gasifier for biodiesel applications.

Jan 1, 2009

By Ö. Uysal

This study deals with the presentation of the mechanized longwall mining project introduced some years ago to increase productivity and output of Aegean Lignite Establishment (ELI) owned by Turkish Coal Enterprises (TKI.) and the comparison of this method with a planned alternative new mining method called ?shortwall mining? where continuous miners will be introduced as primary coal excavation machines. Following the planning phase, production costs have been calculated for both mining methods on the basis of a panel having a height of 7.5 m. In addition to cost analysis, both methods have been evaluated using ?the multi-dimensional objective system?. In this evaluation the value synthesis has been carried out according to scoring models. Lastly, the advantages and disadvantages of both production methods have been stated by analysing them according to related criteria. In the light of outputs gathered from the analyses, it has been determined that the shortwall mining method will out perform the longwall method. Keywords: continuous miner, shortwall mining, longwall mining, multi-dimensional objective system.

Jan 1, 2006

Assuming that a gold ore has been effectively ground to ensure maximum economic liberation of gold, the circuits that will have the most effect on the successful operation of a gold plant will be that of the leaching and carbon-in-pulp circuit (CIP). The reagent and utilities operating costs associated with leaching, adsorption, elution and regeneration would typically make up some 15% of total operating cost, whilst the capital costs associated with these areas is about 16% of the total. Although not largest (capital and operating costs associated with comminution are generally dominant) these items represent a significant proportion of capital and operating cost. Much more importantly, these plant areas represent the primary gold recovery process and their technical and operational efficiencies will have a significant impact on overall plant efficiency. The objective during process design of these sections is thus to develop a design which provides maximum technical and economic efficiency and which is robust to potential changes in ore throughput, mineralogical characteristics and head-grade. Experience has shown that, particularly for longer life and higher-grade projects typical of the South African underground gold mining industry, small changes in recovery and efficiency have a significant value over the life of the project.

Jan 1, 1999

By E. S. Schubert

Keywords: co-generation, furnace CO-gas cleaning, disintegrator scrubber, Theisen In a closed, electric, reduction furnace, no oxygen enters the furnace from the surrounding environment. The off-gases are thus not ?burnt? and therefore contain a considerable amount of CO and H2. Traditionally these gases have been captured and burnt in a flare stack. Recent developments have led operators of such furnaces to revise this strategy and to consider utilising these gases as a fuel for gas-fired generator sets to produce electricity, thus becoming more energy efficient. On 31 March 2010 the new emission standards, in accordance with the Air Quality Act, Act 39 of 2004, were promulgated. The minimum emission standards according to the act require that the particulate matter emissions from the primary fume-capture systems on closed furnaces for ?new plants? in ferroalloy and calcium carbide production not exceed 50 mg/Nm³ and 25 mg/Nm³, respectively. By implementing co-generation, the producer automatically complies with the new environmental emission standards for an off-gas. As much as 30% of the electrical power cost, which is set to double in the near future, can be saved by partly generating one?s own electrical power. In December 2010, the National Treasury published a discussion paper for public comment, one entitled ?Reducing greenhouse gas emissions: The carbon tax option?. Irrespective of how the tax is finally implemented, it will result in an increase of production costs in affected industries. This paper focuses on the characteristics of a furnace-off-gas cleaning system for closed ferroalloy smelters, characteristics that meet the requirements of both reducing solid-matter emissions and operating a safe and reliable gas plant.

Jan 1, 2011

By L. Lehasa

The purpose of the project was to investigate the challenges faced by Khutala Colliery pertaining to underground road construction and maintenance. Furthermore the influence of these challenges on productivity and safety requirements were taken into consideration. The operating standards required for the construction and maintenance of the 2 seam road transport infrastructure was investigated, together with reasons why the standards of operating procedure are not met. The Code of Practice put in place by Khutala Colliery was used to view the standard operating procedures. Leading practices on underground road construction were researched. The project aims to discover the gaps that Khutala Colliery must bridge to implement enhanced practices with regards to underground road construction. During the period of study, observations were carried out to determine whether the road construction standards of operating procedure were being adhered to at all times for both road construction and road maintenance. Khutala Colliery has put in place a traffic management plan, which includes safety practices and work policies that must be adhered to while travelling on underground transport roads.

Jan 1, 2012

By J. N. Van der Merwe

Due to the approaching depletion of reserves in the Witbank Coalfield, and the fact that the Waterberg Coalfield is as yet under developed, there is increasing pressure to extend the lives of the operating coal mines in the Witbank Coalfield. One potential source of coal is the old pillars, often small and at shallow depth, that were not left with secondary extraction in mind. At face value, some of these pillars appear to be suitable for secondary mining due to their high safety factors. However, it is known that over time, these pillars have scaled and the current sizes are smaller than the as-mined dimensions. It is also known that at shallow depth, the overburden is often less likely to fail during secondary mining, resulting in high abutment loads on the unmined pillars. The paper proposes a systematic method to pre-evaluate those old pillars for the possibility of stooping. The method consists of elements of fundamental methods and newly developed technology. In essence, it revolves around using empirical methods to estimate current pillar dimensions, followed by numerical modelling to investigate the probability of progressive pillar failure and then fundamental methods to determine the limits of applicability of the numerical model.

Jan 1, 2012

By S. Read, G. Cook

The Hoek-Brown failure criterion is often applied to a wider range of rocks than the isotropic rock masses to which it is strictly applicable. This paper evaluates the patterns of defects in rock masses using spherical projection contour plots of samples of randomly-generated orientations and datasets from mapping of New Zealand closely-jointed greywacke rock masses. Two indices from the contour plots - the area within the 1% contour (A1%) and maximum concentration (Cmax) are introduced for distinguishing uniform (isotropic), random or regular defect patterns. The indices provide a potential extension to current guidelines on the use of the Hoek-Brown failure criterion. The paper also outlines kinematic checks to assess the influence of defect clusters on rock mass strength. Das Hoek-Brown Bruchkriterium, das strikte nur fuer isotrope Gefuege gilt, findet oft einen viel weiteren Anwendungsbereich. Diese Arbeit bewertet diverse Dispersionsmuster der Defekte einer Gesteinsmasse. Wir vergleichen in sphaerischer Projektion (1) Beispiele zufaelliger Orientierung von Defekten und (2) Felddaten ueber neuseelaendisache engstaendig geklueftete Grauwacken. Die Projektionen werden durch die Indices A1% (Flaechenanteil des 1%-Bereichs) and Cmax (Hoechstkonzentration) gekennzeichnet, welche isotrope, zufaellige und regulaere Muster unterscheiden und die aktuellen Richtlinien zum Hoek-Brown Kriterium ergaenzen. Wir testen ferner Defektgruppen der Gesteine kinematisch auf ihren Einfluss auf Massenfestigkeit. Le critère de rupture de Hoek-Brown est souvent utilisé sur une variété de roches plus étendue que les masses rocheuses auxquelles il est strictement applicable. Ce travail évalue la distribution des défauts au sein d'une masse rocheuse en utilisant une projection sphérique des contours d'échantillons d'orientations générées aléatoirement et de données de cartographie provenant de greywackes à joints rapprochés de Nouvelle Zélande. Deux indices de cette projection - la zone des contours en dessous de 1 % (A1%) et celle de concentration maximum (Cmax) sont introduites pour distinguer les répartitions uniformes (isotropes), aléatoires ou régulières. Ces indices fournissent une extension potentielle aux règles d'utilisation du critère de rupture de Hoek-Brown. Ce travail utilisent également les contrôles cinématiques pour évaluer l'influence des groupes de défauts sur la résistance de la masse rocheuse.

Jan 1, 2003

By R. Heuberger

South Africa?s Mining Industry operates in an uncertain world. The industry is buffeted by problems regarding retrenchments, unemployment, low productivity, rising costs, volatile exchange rates, commodity prices and government regulations. With these uncertainties facing the decision makers, what does applied technology offer the industry?s management? Modelling languages with risk analysis have been available for decades, but in the past their use has been very expensive, requiring large mainframe computers and lots of computer time. Today, PCs and laptops have incredible power, which makes interactive risk analysis affordable and viable for all enterprises, whether small or large. ?What is risk analysis? ?What is Monte Carlo simulation? ?What kinds of computer models need to be created to use risk analysis and Monte Carlo simulation effectively? This paper addresses these questions and illustrates, with a practical example in the mining industry, how risk analysis techniques can be used to support decisions in the climate of uncertainty.

Jan 1, 2005

By Valérie Léveillé

As new legislation drives to lower SO2 emissions from metallurgical plants, plant managers face the challenge of keeping their costs under control. The Cansolv® SO2 Scrubbing System has been broadly adopted in the non-ferrous industry as a cost effective solution for smelter operators to meet the new SO2 emissions targets. The Cansolv® SO2 Scrubbing System is an amine-based regenerable process that selectively absorbs SO2 from a variety of gases, including dilute smelter gases, such as furnace and converter gases. The system produces a pure, water-saturated SO2 byproduct stream, which can then be directed to the front end of a sulfuric acid plant for conversion to sulfuric acid. When deployed in a smelter complex, the Cansolv® SO2 Scrubbing System may also be used to process acid plant tail gas, allowing single absorption sulfuric acid plants to achieve emissions an order of magnitude lower than that of a double absorption acid plant with a lower capital investment. Depending on inlet gas temperature SO2 emissions in the treated gas can be controlled to as low as 55 mg/Nm3. This paper will describe some of the applications where customers have or are planning to use the Cansolv® SO2 Scrubbing System and what as well as which features and cost advantages for the treatment of smelter gases were key to the technology choice.

Jan 1, 2009

By N. Anacleto, S. Ganguly

Reduction of Groote Eylandt (Australia) and Wessels (South Africa) manganese ores using CH4-H2-Ar gas mixture was investigated in a fixed bed laboratory reactor in the temperature range 1000?1200oC. The extent and kinetics of manganese ore reduction as a function of gas composition and temperature were determined by on-line off-gas analysis using mass-spectrometer and dew point sensor. Morphology of ores and its change in the course of reduction was examined by optical and scanning electron microscopy. Phases of raw materials and reduced samples were analysed by XRD and EPMA. Manganese oxides were reduced to carbide Mn7C3. High extent and rate of reduction by methane-containing gas in comparison with carbothermal reduction were attributed to high carbon activity in the reducing gas, which was in the range 15 - 50 (relative to graphite). The reduction rate of Wessels manganese ore increased with increasing temperature. Reduction rate and extent of Groote Eylandt manganese ore achieved maximum at 1050oC. The decrease in rate and extent of reduction of Groote Eylandt ore at higher temperatures, particularly at 1150-1200oC, was due to sintering and formation of semi-liquid silicate slag. The optimum conditions for the reduction of manganese ores were established as follows: a) temperature: 1150-1200oC for Wessels and 1050-1100oC for Groote Eylandt ores, b) methane concentration: 10-15 vol%, c) hydrogen concentration: above 30 vol%, (d) size: 1-3 mm. An addition of lime (10-15 wt% CaO) to the Groote Eylandt manganese ore increased melting temperature of slag and significantly increased the rate and extent of reduction at elevated temperatures.

Jan 1, 2004

The current methodology to design stope support systems in South African gold and platinum mines is based upon the tributary area concept. The discontinuous nature of the hangingwall rock is not adequately addressed, and mechanisms leading to rock mass failures between adjacent support units are poorly understood. The work reported here aims to formulate a basis for quantifying support mechanisms and gain insights into the influence of rock discontinuities on stable hangingwall spans. Numerical models are used to qualitatively investigate the stress transfer from the support units to the discontinuous hangingwall. Stable hangingwall spans are quantified by considering two failure mechanisms, namely (i) beam buckling, and (ii) shear failure due to slip at the abutments. The output of the proposed design methodology is appropriate site specific support spacing, based on discontinuity spacing and orientation. The method is particularly suited to mines at intermediate and great depth, where typically the hangingwall is highly discontinuous due to face parallel mining induced fractures. Results of parametric studies show that with increasing in situ compressive hangingwall stress, beam thickness and friction angle, hangingwall stability is increased, leading to wider stable hangingwall spans between adjacent support units.

Jan 1, 2000

By J. -W. Kim, Y. -B. Kang, H. -G. Lee

The effect of SiO2addition on the decomposition of Li2CO3was investigated at temperatures up to 1000ºC. It was found that addition of SiO2greatly enhanced the decomposition of Li2CO3. The main decomposition reaction started at around 600ºC, and completed just above the melting point of Li2CO3. The major decomposition product was Li2O?SiO2irrespective of the Li2CO3to SiO2mixing ratio while both reactants were available. It was ascertained that a liquid layer betweenLi2CO3and SiO2particles formed and facilitated the decomposition reaction. The governing reaction of the decomposition was the one between the dissolved Li2CO3and SiO2in the liquid layer to form Li2O?SiO2. The decomposition rate was independent of the Li2CO3/SiO2mixingratio until either one had been completely exhausted. When excess Li2CO3existed, it further reacted with the initial product of Li2O?SiO2to form 2Li2O?SiO2. When SiO2was found in excess, on the other hand, no further reaction took place. This is attributed to the fact that uponLi2CO3exhaustion there is no liquid phase available to facilitate further reaction. The apparent activation energy of the decomposition of Li2CO3in existence with SiO2is 198 kJ mol-1.

Jan 1, 2004

By M. Bwalya, L. Mabokela, L. C. Woollacott

This paper presents a study on the ability of the King stratification modelto describe density stratification patterns that are achieved under idealizedconditions. Tests were conducted in a batch jig using artificial particles inseven density classes. All particles in a density class had essentially thesame density, size, and shape. Tests were conducted for particle systemsinvolving from two to seven components. Good agreement was obtainedbetween measured and modelled data to an extent that gave strongendorsement of the mathematical appropriateness of the core equation inthe King model. Somewhat ambiguous results were found with regard toclaims about the independencies of the single experimentally-determinedparameter required by the model.

Jan 1, 2015

By M. Sibanda

The diffusion of carbon in Co-5% Fe alloy was studied in a belt-type pressure system at temperatures of up to 1330°C and press loads or nominal pressures of 7 020 tons or 42±3 kbar. Under these conditions, this alloy is in the solid state. Discs of graphite and prealloyed Co-5%Fe were used to make up the diffusion couple. The diffusion coefficient increased with increasing press load due to the tendency of the low density graphite to dissolve in the metallic phase reducing the overall volume and increasing the density of the system. Furthermore, inhomogeneous plastic deformation may have promoted diffusion by creating defects in the alloy. Diffusion couples treated at atmospheric pressure exhibited graphite particles in the metal, while those treated at high pressures exhibited carbide in the form of Widmanstatten laths. Carbon analyses indicated increased carbon solubility with increasing pressure. This was confirmed from calculated high-pressure phase diagrams.

Jan 1, 2005

By H. Yavuz

Closed form solutions assume opening shape to be circular to simplify the calculation of the ground response curve for the design of underground openings. However, in mining and civil engineering works, non-circular openings are commonly excavated. Therefore, there is a need to estimate the ground response curve for such openings. In this respect, a simple model for circular, arch and rectangular shape underground openings subject to a hydrostatic stress field is the aim of this study. A comprehensive numerical modelling, using the finite difference method, based on numerical modelling code FLAC version 4.0, was carried out. In addition to shape of an opening, the effect of rock mass strength, opening size, in situ stress on strain (tunnel deformation to tunnel radius) of the opening in response to applied support pressures was investigated parametrically by developing models for each specific condition. The strain results for each excavation shape obtained from this large number of models against the normalized strength of rock mass and internal support pressure with in situ stress magnitude were evaluated by multiple regression analysis. As a result, a model that was well correlated to data was developed for an overall estimate of the ground response curve depending on relevant effecting parameters. The regression coefficients of the model were given for estimating both roof and sidewall response curve of each excavation shape. The model was verified by statistical tests and by an analytical solution. Diagrams were also established to highlight the influence of relevant parameters and to estimate the support pressure for a stable opening staying within the acceptable limits of strain. Strains occurring in a rectangular opening are found to be larger than those in the arch and circular openings for the other fixed parameters. In the mean time, larger strains occur around an arch shape opening than a circular opening.

Jan 1, 2006

By I. A. Mwamba

Titanium sponge, which is almost pure titanium, is extremely ductile and not easily processed into titanium powder. One method of producing powder is the hydride-dehydride (HDH) process, where titanium sponge is hydrided to form brittle titanium hydride (TiH2). Titanium hydride is easily milled to produce powder and is then dehydrided to form Ti powder. In this work, titanium hydride powder obtained from titanium sponge was used as a starting material for blending and mechanical alloying with elemental powders. Firstly, titanium hydride powder was blended with aluminium elemental powder to produce a homogenized powder, which was then compacted and sintered to produce powder metallurgy compacts. Secondly, titanium hydride powder was mechanically alloyed with aluminium elemental powder and then compacted. The mechanically alloyed powder was characterized in terms of particle size distribution, morphology and microstructure. In both blending and mechanical alloying, the green compacts were characterized by assessing the green density, while the sintered compacts were characterized by their sintered density, microstructure, and hardness. The two processes have resulted in the formation of TiA13 intermetallic compound. It was established that by simple mixing and homogenizing, titanium hydride can be used as a starting material to produce powder metallurgy components in which porosity is a benefit rather than a problem, much akin to metallic foams. From the products obtained in the TiHz-Al system, it appears that titanium hydride can be used as a precursor in mechanical alloying. However, the possible formation of complex hydrides may introduce detrimental properties, and needs to be further investigated. For the production of non-porous components, it would be advisable to dehydrogenate the TiH2 powder before milling i.e. producing titanium powder by the hydride-dehydride (HDH) method. Keywords Mechanical alloying, titanium hydride, titanium aluminide and blending

Jan 1, 2011

By W. P. Erasmus

This paper will focus on the use of the ?wet-mix? steel fibre re-in forced shotcrete as a permanent lining in deep shafts, assessing gold bearing reef. It will cover all aspects relating to the choice of this material covering the geological conditions through to the final quality control. All procedures are in line with ISO 9001,as JCI projects who manage the project, are an approved company therof.

Jan 1, 2001