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By M. Verri

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Jan 1, 2009

By M. J. Lukhele

Paper written on project work carried out in partial fulfilment of B. Tech (Mining Engineering) degree A number of high wall mining methods were developed over the years to mine coal reserves exposed on the high walls created during surface mining. The auger mining system was initially developed in the early 1940s in the United States of America. High wall mining is a method of recovering coal from seam exposed either by mechanical excavation methods or natural erosions. This is usually associated with strip-mining (opencast) where the stripping ratio is high and uneconomical to mine using the opencast mining method. This paper discusses the surface auger mining as deployed at Rietspruit Mine Services Proprietary Limited.

Jan 1, 2002

By M. -O. Suk, S. -K. Jo, S. -C. Shim, J. T. Kim, S. -H. Kim, C. -W. Seo, J. -S. Kim

An equilibrium study was carried out at 1873 K to ascertain the effect of carbon in CaO-SiO2-Al2O3-MgO-MnO-FetO slag systems on their FetO and MnO activity coefficients, representing the slag?s thermodynamic potential for steel reoxidation. Both ?FetOand ?MnO showed not only a sharp increment, but also a simultaneous slow decrement by increasing carbon content in slag, suggesting opposite roles of the carbon according to its stable forms. XPS (X-ray photoelectron spectroscopy) was introduced to clarify the stable forms of carbon in slag. XPS results prove that carbon dissolves in slag as carbonate, and carbide ions under oxidizing and reducing atmospheres, respectively. It was concluded that carbonate ions increase ?FetOand ?MnO, and that carbide decreases them. This paper suggests an application method of the present results to actual ladle refining processes, in order to enhance steel cleanliness without decreasing (FetO + MnO) content in slag. Keywords: carbon, slag, activity coefficient, FetO, MnO, carbonate, carbide, XPS, reoxidation, cleanliness

Jan 1, 2004

Recent studies on the physico-chemical properties of molten slags and oxide solid solutions of interest are reviewed. The review covers redox and phase equilibria in slags, viscosity, diffusivity, electrical conductivity, kinetics of interfacial reactions between slags and CO-CO2, interfacial properties and phenomena. Some highlights from ongoing work on modelling phase diagrams, component activity, viscosity and electrical conductivity of multi component slags will be presented and results compared with published experimental data on slags with or without suspended solid phases.

Jan 1, 2004

The Mineral Density Separator (MDS) was developed by Mintek to predict mineral separation in a plant, evaluate efficiencies and develop scale-up parameters. This study investigated the influence of particle size on the results of the MDS, the misplacement of material in the MDS and the possibility of replacing heavy liquid float and sink analyses of coal with MDS analyses. Six tests were done with coal of different size ranges. Each MDS layer was subjected to a float-sink analysis whereafter each float fraction was screened to determine the particle size distribution. The results indicated that MDS results represent float-sink analyses when compared to an ash curve. There is some misplacement in the different MDS layers, but this does not seem to influence the results negatively. Keywords Mineral density separator, sink-float analyses, heavy liquid analyses, washability curve

Jan 1, 2006

By L. Jeffrey

The Waterberg Coalfield has vast potential to become a significantmining and industrial centre in South Africa. Its future developmenthinges on a number of critical decisions that must be made jointly by government, power utilities and industry, and on some technical and economic challenges that must initially be overcome. Sufficient water is the primary key to enabling exploitation, together with an adequate market for the large volumes of low-grade coal. As the most likely consumer of this coal will be either a power station or a petrochemical complex, the need for additional energy will be a driving force in the development of this coalfield. Conventional mining methods can exploit the shallow coal resources in both the Grootegeluk and the Vryheid formations, but alternative technologies such as coalbed methane extraction and underground coal gasification are the only currently known technologies that may be able to exploit the deep Grootegeluk Formation resources. However, extensive research is still required into these procedures, particularly with respect to the Waterberg coals. Transport infrastructure to the region is currently not sufficiently well developed to support large-scale exploitation of the region?s coal resources. In particular, the railway line would have to be extensively upgraded to allow the increased export of coal. Alternative transport methods such as pipelines would also have to be pursued to serve a large Sasol-type petrochemical complex or coal gas extraction. The road network would also require improvement, as only the roads between the main commercial centres are currently tarred. Dr Con Fauconnier, Kumba CEO, concluded his presentation to the Investing in African Mining Conference 2004 with the words: Again, it?s all about infrastructure? when it?s there, it enables the development of bulk mining projects which attract the resultant economic benefits for the region and country as a whole. These words aptly sum up one of the stumbling blocks to the future development of the Waterberg Coalfield.

Jan 1, 2005

By B Vorster

Falls of Ground is one of the highest causes of incidents, accidents and fatal injuries in our mines today. These falls of ground may occur as soon as the face is exposed after blasting or after machine cutting. The falls of ground can also occur after support has been installed. There are many reasons why these falls occur before and after supporting of the face. It is therefore important to support the exposed face as soon as possible to prevent the falls of ground. It is also very important to support the face with the correct support products and to support the face as designed and required by the mining engineers. The possible reasons for falls of ground, possible support methods and the products available will be discussed in this presentation. In typical conventional narrow vein stoping operations, the use of conventional temporary support components to offer some support to workers, whilst the permanent and generally more elaborate support system gets installed or constructed, still results in injuries to people. The author wishes to discuss the following items in this paper:- ? Introduction ? Basic face behaviour after exposure ? Controllable Parameters ? Mining Engineers support designs ? Primary and Secondary Support ? Products available for prevention of falls of ground

Jan 1, 2008

By S. Kamalpour

It has been observed that the productivity of ferromanganese furnaces, and the stability of metal and slag compositions, vary considerably according to the type of coke used as reductant. However, the desired properties of coke for optimum furnace performance are not well understood. In this investigation, the behaviour of four cokes, which exhibited a wide range of performance in ferromanganese production, was investigated by means of laboratory simulations of reducing conditions in the furnace. The Stationary Charge in Controlled Environment (SCICE) technique was used to simulate the conditions in the furnace shaft. Batches of raw materials, mixed in the same proportions as used in practice, were heated at fixed rates to 900, 1100 and 1300°C then cooled. The mass loss was used as a measure of the degree of reduction. Conditions in the lower part of the furnace were simulated by means of melt-reduction experiments in which lumps of coke were drilled out to form crucibles in which enriched ferromanganese slags were reduced at 1500 and 1550°C then cooled. An examination of the raw materials and the cooled, reacted charges using a variety of analytical and characterization techniques enabled the sequence of reaction and changes in morphology of the raw materials to be followed. This enabled an understanding of the behaviour of the cokes during reduction to be developed, which was then used to explain the observed performance of the cokes in practice. By relating the observed behaviour of the cokes in the laboratory tests to measurable properties of the unreacted cokes and to their observed performance in practice, it was shown that to achieve high productivity and good furnace performance, cokes should be selected to have moderately high reactivity towards CO2 (Boudouard reactivity) relative to conventional iron blast furnace cokes.

Jan 1, 2004

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. S. Raseroka

An experimental rig has been constructed to produce chloride stress corrosion cracks in Type 304L stainless steel tube samples. The samples are to be used to test possible in situ repair methods in future work. The factor which influences the time to failure most strongly is the sample temperature; the distribution of cracks within the sample is affected by local temperature variations and by the position of the water line. Low-frequency oscillations in stress, caused by the on-off temperature controller, did not appear to influence cracking in these tests.

Jan 1, 2009

By L. Uotinen, M. Rinne, R. Mishra

Underground mining gives rise to geotechnical hazards. A formal geotechnical risk assessment can help to forecast and mitigate these hazards. Frequentist probability methods can be used when the hazard does not have many variables and a lot of data is available. However, often there is not enough data for probability distributions, such as in the case of new projects. The risk assessment is often subjective and qualitative, based on expert judgement. The purpose of this research is to present the use of Bayesian networks (BNs) as an alternative to existing risk assessment methods in underground mines by combining expert knowledge with data as it becomes available. Roof fall frequency forecasting using parameter learning is demonstrated with 1141 sets of roof fall data across 12 coal mines in the USA. The prediction is nearly identical for individual mines, but when multiple mines are evaluated it is difficult to find a single best fit distribution for annual roof fall frequency. The BN approach with TNormal distribution was twice as likely to fit the observed data compared to the Poisson distribution assumed in the past. A hybrid approach using BN combining multiple probability distribution curves from historical data to predict annual roof fall is proposed. The BN models can account for variability for multiple parameters without increasing the complexity of the calculation. BNs can work with varying amounts of data, which makes them a good tool for real-time risk assessment in mines.

Jun 1, 2021

By M. F. Handley

Sequential grid mining has been employed as the primary mining strategy at the AngloGold West Wits Elandsrand Mine since the inception of stoping operations from the sub-vertical shaft system in 1988. Little has been published on sequential grid mining as a mining strategy since, and the purpose of this paper is to describe sequential grid mining, its history, its implementation at Elandsrand, and the outcome to date. The results obtained using sequential grid mining have been evaluated from seismic data, productivity statistics, and rock related accident statistics. Comparisons with neighbouring mines namely Western Deep Levels and Deelkraal, have been made to substantiate the improved conditions observed at Elandsrand, and to compare sequential grid mining directly with longwall mining in similar conditions and at similar depths. Sequential grid mMining is shown to be cost-effective, more flexible, and safer than long wall mining in similar conditions, at least on the Ventersdorp Contact Reef in the western part of the Carletonville Goldfield. More work is necessary to establish it as the favoured mining strategy at depths exceeding 3000 metres, and for reefs other than the Ventersdorp Contact Reef.

Jan 1, 2000

Publications on hard rock tunnel support design in the South African mining industry have originated primarily from the goldmines during the past 50 years. Little has been published to date on the platinum and chrome mines of the Bushveld Complex. This paper covers the search for a suitable design methodology for off-reef tunnels at Impala Platinum Mine, situated on the Western Lobe of the Bushveld Complex. The fall of ground accident statistics for off-reef excavations of the mine are presented and the available rock mass quality evaluation systems are reviewed. The Q-Tunnelling Quality Index (or Q-Index) is selected because it assesses the important driving factors behind falls of ground at Impala. Two off-reef excavations are evaluated using the Q-Index, and it is shown that minor modifications are required for implementation at Impala. It will take some time before support design throughout the mine is based on the outcome of proper geotechnical investigations based on the Q-Index. Widespread implementation of such support designs should help to solve the fall of ground problem in off-reef excavations while at the same time reducing support costs.

Jan 1, 2002

By T. Struminski

The paper is aimed to assess the possibilities of usage of pyrometers and thermal cameras to study ventilation and environmental conditions in underground mines. Surface and underground thermovision tests were carried out in the Rudna mine and included channels and diffusers of some selected fan stations, shaft crest closures, engines of central fans and their instrumentation. The thermovision underground tests in the Rudna mine consisted of ventilation barriers, underground fans, temperature of rocks, ventilation machines, parts of belt-conveyors and electric machinery.

Jan 1, 2003

By M. M. Manamela

Paper written on project work carried out at the University of Pretoria in partial fulfilment of the requirements of the B Tech degree at the Tshwane University of Technology This work tested whether ore particle size affects the carbon-based pre-reduction of titaniferous magnetite. Pre-reduction is performed at a temperature of some 1100°C in a rotary kiln, in the Highveld Steel process. Laboratory isothermal reduction measurements were performed with ore-coal mixtures at this temperature, to test the effect of ore particle size. The results show that size does limit the degree of reduction for particles larger than 15 mm.

Jan 1, 2005

By J. S. Harington

Our purpose is to record and to explain the widely changing numbers of the huge total of black workers on the gold mines of South Africa over the century from 1896 to 1996. These men were recruited from up to twenty territories, and their contributions are examined. The major areas providing labour over this long period have been Lesotho, the former Transkei within South Africa and Mozambique. From 1989 to 1996, for instance, these three areas accounted for over sixty per cent of the total labour force (tlf). Our principal Figure 1 shows the tlf fluctuating through time to reach a peak of 480 000 in 1988. Irregular falls are also documented with the most serious in 1995 to 180 000. Based on this graph we consider the political, economic, sociological and historical reasons behind these changing employment opportunities. These have included external world-scale events such as war or depression, as well as internal changes of national economy and policy. We show the importance for numbers employed of the discovery of gold in the Orange Free State in 1946, the influence generally of the ?Winds of Change? and the firm maintenance by the State of law and order. Varying gold production costs and profitability against high tax rates, allied with increasing wages and a lack of development capital, have led in the last decade to employment falling by fifty per cent, despite an actually higher value of gold output. Finally, this analysis considers the role of the migrant labour system as it affects, and is affected by, conditions in the gold mining industry, with special reference to its less than humane consequences in the numerically dominant territories of Lesotho and Transkei.

Jan 1, 2004

By A. Lane

The socio economic risks of mining in South Africa have been emerging for some time now, and have been brought into sharp relief by recent events in the platinum sector. The slow pace of social upliftment in the country has lead to widespread social unrest with consequent calls for different forms of resource nationalism. Fundamentally, the key stakeholders are not fully aligned, and are not engaging productively. This poses significant above-the-ground risk to mining companies. Measuring social impact, deploying inclusive solutions and engaging effectively with stakeholders are three ways in which mining companies can mitigate this risk. Keywords platinum, mining, community, socio-economic impact, stakeholders, conflict, labour unrest, social licence to operate, investment, Africa.

Mar 1, 2013

By J. M. Richards

For most of the 20th century optical petrography has been the primary petrological and mineralogical tool used to characterize coal. The development of quantitative SEM-based techniques, e.g. QEMSCAN®, for coal began only about a decade ago. The application of these techniques for coal lagged behind other commodities, but they are currently being developed with the aim to provide ?one complete analysis? for coal. Quantitative SEM-based techniques are supplemented by quantitative X-ray diffraction (XRD). Recent indications are that these more modern techniques cannot replace the ?standard? petrographic and chemical evaluations, but rather complement them where and when required. The great advantage of quantitative SEM-based techniques is that they are very rapid, with the result that large volumes of samples can be processed on a routine basis. This is ideal for coal type identification, since the results can be used in the creation of ?intelligent? composites. This can lead to the more speedy evaluation of coal deposits by reducing the number of samples on which detailed metallurgical and characterization test work is required, without an increase in the overall statistical error of the resource model. Coal petrography, however, remains important for the prediction of the coking characteristics of certain coals and coal products. As a consequence it is therefore important that any coal laboratory be able to produce data with confidence. This requires strict quality control and assurance protocols that adhere to international standards. Keywords coal petrography, coking strength, scanning electron microscopy, QEMSCAN®.

Nov 1, 2013

By M. R. Samis

The great variability of mineral and energy prices has motivated some governments to incorporate a windfall profits tax into their mineral taxation regimes. Windfall profits taxes are a means for governments to capture additional mineral revenue when mineral prices are considered higher than some historic level. Governments need to be aware of the effects of such contingent taxes on the exploration, development and operating decisions of mining companies. Mining companies need to be able to calculate the full impact of windfall profits taxes on the economics of their projects. This paper examines the valuation of a multi-phase copper-gold project in the presence of a windfall profits tax. Real options Monte Carlo simulation is used to characterise the different exposures of the mine owner and of the government to the risky cash flow streams that they receive from the project. The results highlight that Monte Carlo simulation paired with the real option valuation method is able to account appropriately for the differing risk exposures, while the traditional discounted cash flow valuation model is not. Our key conclusion for governments and mining companies is that the impact of contingent tax and royalty terms can and should be assessed using advanced valuation techniques, and the results used to improve contract designs under the constraint of actual and perceived fiscal system stability.

Jan 1, 2007

By A. Tor, M. Borowski, N. Szlazak, D. Obracaj

This article presents possibilities of reducing methane emission to the atmosphere in working mines in Jastrzebie Coal Company by means of proecological solution. They form a new approach towards the problem of rational and effective use of natural resources both in economical and environmental respect. Power and thermal energy for underground air conditioning in mining excavations are produced from the methane, which is drained out of the mine for safety reasons.

Jan 1, 2003