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By T. Ertekin, X. Dong

This paper identifies the need for the development of specialized inverse solution techniques for the analysis of pressure transient data for the characterization of the transport and sorption properties of coal seams. Central to the proposed inverse solution technique is a specially structured artificial neural network (ANN). The most important transport and sorption characteristics of coal seams are butt and face cleat permeabilities, macropore porosity, Langmuir volume constant, Langmuir pressure constant, and sorption time constant. Conventional methods, such as type curve matching techniques and laboratory-derived measurements are handicapped in terms of being representative over the entire domain of interest. In this paper, we utilize analytical forward solution techniques for various combinations of characteristics of coal seams to generate training and testing patterns. These training patterns are shown to an ANN structured to learn the ubiquitous non-linear relationships that exist between coal seam properties, input conditions and the pressure transients measured. The trained networks are then extensively tested to ensure that they have effectively learned the training patterns. In the final stage of the development, the networks are run in the prediction mode. The responses of the networks are found to be in agreement with the input data. The developed networks are able to generate results generally within 5% error margin for permeability and porosity and 20% error margin for the sorption characteristics of coal seams. A number of examples highlighting the capabilities and degree of effectiveness of the network in characterizing the coal seams areincluded. Keywords: artificial neural networks (ANNs); coal seam characteristics; pressure transient analysis

Jan 1, 2003

The 108th Annual General Meeting of The South African Institute of Mining and Metallurgy was held at The Country Club, Johannesburg, Napier Road, Auckland Park on Thursday, 11 August, 2005. Welcome The President extended a special welcome to the guests and representatives of our sister institutes and other associations, also to recipients of awards, senior members of industry, Honorary Life Fellows, past-presidents, our members and other guests, among them the following: Dr Con Fauconnier, President, Chamber of Mines of South Africa Prof. Jay Barton, President, The Geological Society of South Africa V. Townshend, President, Institute of Certificated Mechanical and Electric Engineering, South Africa M. Livingstone-Blevins, President, Institute of Certificated Mechanical and Electrical Engineers, South Africa Prof. B. Lacquet, President, South African Institute of Electrical Engineers Dr F. Malan, President, South African National Institute of Rock Engineering

Jan 1, 2005

The functional design of a pavement relates to the selection of appropriate wearing course materials which optimise the trafficability of a pavement. Trafficability is dictated to a large degree by the choice, application and maintenance of locally available wearing course materials. Poor functional performance results in decreased safety and operational efficiency and increasing road and vehicle maintenance requirements. An optimal functional design will include a certain amount and frequency of maintenance (watering, grading etc.) and thus maintenance itself can be planned, scheduled and optimized within the limits of required road performance and minimum vehicle operating and road maintenance costs. Since no wearing course material selection guidelines, tailored to the specific needs of surface mines, were available, there was the need to identify appropriate selection guidelines for the range of materials commonly encountered for road building on South African mines. The aim of this paper is to present an overview of the functional design method for mine haul roads and, through an analysis and quantification of existing wearing course material performance, to recommend appropriate wearing course material selection guidelines. The functional design technique has been applied at a number of mines and is illustrated by an application case study which demonstrates the potential reduction in total transportation operating costs associated with the optimal functional design.

Jan 1, 2000

By S-L. Weeber

Ash fusion temperature is the temperature at which the mineral matter in coal begins to soften, flow and fuse. It is an important parameter relating to coal utilization. Optimum ash fusion temperatures derived from coal in the Witbank Coalfield region are approximately 1400°C, and higher, although temperatures above1300°C may be deemed acceptable. This study attempted to determine which factors, mineralogical or inorganic-chemical, influence variations in the ash fusion temperatures in certain coals. Coal was sampled from the Number 2 coal seam at opencast and underground workings at New Clydesdale Colliery, Witbank Coalfield, South Africa. The samples represented known low and high ash fusion temperature coal. Analyses performed included proximate analyses, calorific value determination, percentage sulphur, ash fusion temperatures, ash analyses (composition of ash), X-ray diffraction, scanning electron microscopy and petrographic studies. Results show that although a complex relationship exists between ash fusion temperature and the various geological and coal parameters, some positive correlative results were obtained. These indicate a possible relationship between low ash fusion temperatures and i) finer size fractions, ii) an increase in iron content present in the form of pyrite and iii) the form in which pyrite is present, namely cleats. High ash fusion temperatures tend to correlate with i) the absence of pyrite or ii) pyrite present as framboids.

Jan 1, 2000

By J. D. Steenkamp

Southern Africa has a history rich in the pyrometallurgical processing of ores. Two of the alloys produced are high-carbon ferromanganese (74?83 per cent Mn) and silicomanganese (59?67 per cent Mn and 14?31 per cent Si). The largest land-based manganese ore deposit in the world is based in the Northern Cape Province of South Africa. In 2010, 6.3 Mt of ore from the deposit was exported, mainly to China, Norway, Japan, and India, and an estimated 1.1 Mt beneficiated locally to produce manganese ferroalloys. In southern Africa the producers of manganese ferroalloys are Metalloys and Assmang, and of silicomanganese Transalloys, Mogale Alloys, and Match Corporation. Submerged arc furnace technology is utilized in the production of high-carbon ferromanganese (HCFeMn) and silicomanganese, applying the discard slag practice in both instances. The carbon content of HCFeMn is reduced using converter technology and that of SiMn using the Perrin process. Ninety per cent of the world?s manganese ferroalloys production is consumed by the steel industry. The consumption (and production) of manganese ferroalloys therefore closely follows worldwide steel production. From 2001 to 2010, the doubling of the worldwide production of manganese ferroalloys can be attributed to an increase in production capacity in Asia and Oceania, with the largest increase in the production of SiMn. Manganese ferroalloys produced in Asia and Oceania are mainly for the local market, with North America, Europe, Russia, and Turkey the major markets for alloys from southern Africa. The major challenges faced by the southern African manganese ferroalloy producers are increasing electricity tariffs and productivity of labour, which require a concerted effort by all parties involved to achieve a satisfactory solution. Keywords manganese ferroalloys, ferromanganese, silicomanganese, southern Africa, South Africa, manganese ore, high-carbon ferromanganese, refined ferromanganese, refined silicomanganese.

Aug 1, 2013

By J. Wills

The use of drilling rigs to increasingly mechanize stope drilling has been acknowledged as important for the S.A. mining industry in it ís efforts to tackle the challenges of low productivity, AIDS and an ageing driller workforce. The spin-offs of increased safety, cost-effectiveness and better mining performance provide advantages to all?from the driller to the shareholder. However, implementation or product rollout has varied from outright success to dismal failure. A study of various cases by Novatek and Anglogold TDS showed clear reasons for these differences. Whereas the successes were characterized by clear objectives, accountability, user buy-in, a commitment to make the technology work and no-nonsense reporting, these were typically absent in failed implementations. The attitude at unsuccessful mines was to ?trial? the equipment?even subconsciously, a ?trial? is a test where failure becomes an acceptable outcome. During the study it became clear that mining management are not adequately trained to manage the often-tricky rollout process. They are often also not empowered or clearly mandated to deal with the organizational, human and technical issues that must dovetail to create a success. The output of the study was to develop a basic rollout process that could be used to formally manage the implementation of new drilling technology. Creating an alignment between the mine, workforce and supplier promotes a win-win situation that will not otherwise spontaneously arise.

Jan 1, 2002

By J. D. Stone

This paper briefly reviews the adequacy of existing management theories and practices and the managerial proficiency or competency in the South African mining industry. The investigation revealed that existing management practices are totally inadequate to enable all employees on all the levels of the mining industry to achieve the results required from them, in all aspects, at all times. As a result, the South African mining industry is gradually losing its long standing reputation as a relative cheap, competitive, and reliable supplier of minerals to the local and global markets. According to some prominent management authors and theorists, an all-inclusive unified management theory does not exist at present. In this paper the authors summarize the main aspects of a newly developed comprehensive, practical, and integrated management method. It is believed that the application of this method would significantly improve the future performance and competitiveness of the South African mining industry

Jan 1, 2010

The aim of this investigation was to study the influence that varying production rates have on iron sinter quality. This was done by performing sinter pot tests at different pressure drops over the sinter bed, namely 11 kPa and 15 kPa (for 500 mm total bed depths). During each of the sintering processes temperature-time profiles were recorded of the top, middle and bottom layers of the sinter bed. On completion of the sinter process the sinter cakes were divided into top, middle and bottom layers. The physical properties of each layer were subsequently characterized by performing a tumbler test and a sieve analysis. A comprehensive mineralogical study was also conducted on each layer. This study revealed that sinters of similar cold strength could be produced under the examined production rates. However, a higher production rate was accompanied by an increased amount of fines. The cold strengths of both sinters significantly increased from the top layer to the bottom layer of the sinter bed. This strength variation is not related in any simple way to the phase composition. Keywords: Sinter, sinter bed, production rate, phase composition, cold strength, tumbler index, sieve analysis, temperature-time profile

Jan 1, 2003

By L. J. Leach

Quench and tempered Cr-Mo plate steel was found not to contain a fully martensitic structure as a result of either slow slack quenching or insufficient hardenability at the cooling rates used. The resulting microstructure contains bainite in combination with martensite. It is necessary to examine the implications of bainite for the toughness of the final product. Loss of toughness arises primarily from the inter-lath carbides that typically form in upper bainite. An investigation into the effect of upper bainite in a martensitic matrix of a steel grade containing 0.17% C, 0.1% Cr, 0.54% Mo, and 20 ppm Bindicated lower toughness than in a fully martensitic structure.

Jan 1, 2013

By A. M. Bryukhanov, A. G. Mnukhin

The report states accident rates for gassy/dusty coal mines represented as an ergatic system "man – machine - environment" with further analysis by the method of conditional probabilities. A coal mine has been analyzed with allowance for the attending personnel, equipment and environment as a sequence of events and states. Probabilities of operational states have been determined and prediction of mine behavior has been made on the basis of investigation findings for equipment and the personnel states, and analysis of the environment (i.e. mine and mining conditions). Utilization of expert estimation methods has been considered for determining major operational parameters of gassy/dusty mines. The importance of standardized values of permissible occupational risks (permissible probability of accident, PA) is demonstrated. It is also stated that a procedure is essential to determine these values, involving regular check-ups of the integral safety criterion at all mines and further development of customized recommendations for individual mines on efficient improvement of accident situations. Methodology to determine the assessment criteria has been developed and scientifically substantiated for permissible accident rates in hazardous industries.

Jan 1, 2003

By M. K. Pelser

The purpose of this paper is not so much to provide a scientific study of the selection process for the perusal of other psychometrists or industrial psychologists?the purpose is to provide line management with a practical, relatively user-friendly guide to fair and scientific selection. The main areas that are to be covered are: ? Why fair and scientific selection? ? Job analysis ? The job requirement?selection technique circle ? Assessment centres in the mining industry?the Tavistock Collieries Ltd experience. Why fair and scientific selection? Seen from a line manager?s perspective, fair and scientific selection should be pursued for two main reasons: ? to remain within the ambits of the law ? to maximize the probability of selecting the potentially most productive and efficient candidate for the job.

Jan 1, 1997

By A. Krause

Shovel-truck systems for loading and hauling material in open pit mines are now routinely analysed using simulation models or off-the-shelf simulation software packages, which can be very expensive for once-off or occasional use. The simulation models invariably produce different estimations of fleet sizes due to their differing estimations of cycle time. No single model or package can accurately estimate the required fleet size because the fleet operating parameters are characteristically random and dynamic. In order to improve confidence in sizing the fleet for a mining project, at least two estimation models should be used. This paper demonstrates that the Machine Repair Model can be modified and used as a model for estimating truck fleet size in an open pit shovel-truck system. The modified Machine Repair Model is first applied to a virtual open pit mine case study. The results compare favourably to output from other estimation models using the same input parameters for the virtual mine. The modified Machine Repair Model is further applied to an existing open pit coal operation, the Kwagga Section of Optimum Colliery as a case study. Again the results confirm those obtained from the virtual mine case study. It is concluded that the Machine Repair Model can be an affordable model compared to off-the-shelf generic software because it is easily modelled in Microsoft Excel, a software platform that most mines already use. This paper reports part of the work of a MSc research study submitted to the University of Witwatersrand, Johannesburg, South Africa. Keywords: simulation, bunching, probability distributions, cycle time, queuing, matching, shovel-truck, OEM.

Jan 1, 2007

By J. W. Klokow, K. L. Riemer, R. I. L. Ferreira

As a result of the increased depth of mining in the South African gold mining industry mining induced seismicity is a severe problem. One of the strategies within the industry to contain the problem is to incorporate a system of regularly spaced stabilising pillars into mine layouts. At the Driefontein Gold Mine a system of closely spaced dip pillars is used to contain seismic energy emissions. Comparisons of seismic data for several mining clusters initially indicated a possible measure of success in the containment and occurrence of larger events. A detailed analysis of data over a 5-year period since the start of mining however, has revealed a delayed seismic response to the increasing strike spans. Significant changes marked by an increase in certain seismic variables have been observed at mining spans of between 100 to 120 meters and could be of significance to pillar spacing in the design of deep level mining layouts. La sismicité occasionnée par l’exploitation minière est un problème grave dans les mines profondes de l’industrie minière aurifère en Afrique du Sud. Une des stratégies utilisées dans l’industrie a été de maîtriser le problème en incorporant un système de piliers de stabilisation régulièrement espacés dans la disposition des mines. A la Driefontein Gold Mine, un système de piliers de pendage proches les uns des autres est utilisé pour contenir les émissions d’énergie sismique. Au début, des comparaisons de donnés sismiques pour plusieurs groupes d’extraction ont indiqué un succès possible dans la limitation et l’occurrence d’évènements sismiques. Cependant, une analyse détaillée des données sur une période de 5 années a révélé un délai entre la progression de l’extraction et une réponse sismique accrue. Des changements considérables dans les variables sismiques ont été observés dans des intervalles d’extraction entre 100 et 120 mètres, ce qui pourrait être significatif pour l’espacement des piliers dans la conception de la disposition des mines de fond. Resultierend aus den zunehmenden Tiefen des Bergbaus in der südafrikanischer Goldbergbauindustrie stellt sich die vom Bergbau hervorgerufene Seismizität als bedrohliches Problem dar. Es war eine der Strategien innerhalb der Industrie, das Problem dadurch einzudämmen, daß regelmäßig plazierte Stabilisierungspfeiler in den Bergbaulayouts inkorporiert wurden. In der Driefontein Gold Mine wird ein System von knapp aneinandergesetzten im Abfallbereich befindliche Pfeiler benutzt, um seismische Energieemissionen einzudämmen. Vergleiche der seismischen Daten für mehrere Bergbaugruppen zeigten anfangs ein mögliches Maß von Erfolg in der Eindämmung und im Auftreten von größeren Fällen an. Eine ausführliche Analyse von Daten über einen 5jährigen Zeitraum hat jedoch ergeben, daß eine Verzögerung zwischen der Progression des Bergbaus und einer erhöhten seismischen Reaktion besteht. Bedeutende Änderungen in den seismischen Variablen wurden an Bergbauspannen von 100 bis 120 Metern beobachtet und könnten für Abstandsbemessung von Pfeilern im Design des Tiefbergbaulayouts von Bedeutung sein.

Jan 1, 2003

By Luthie Els, Chris Coetzee, Roedolf Koekemoer, Casper Els, Olof Vorster, Frank Fereday

Three electric arc furnaces (EAFs) were constructed by Union Carbide at Tubatse Ferrochrome (TFC) in1975. This plant was expanded to four furnaces at the East Plant in 1985 and the gas cleaning system was enlarged without taking flow dynamics into consideration. In order to improve competitiveness, TFC has increased furnace capacity, partially substituted coal for coke, and changed the charge mix. These changes increase the heat and dust load into the air pollution control (APC) system. TFC embarked on a project to improve the APC capacity by: ?Quantifying the required off-gas capacity ?Optimising the aerodynamic flow through the system by means of Computational Fluid Dynamics (CFD) ?Converting the old Brandt Koyo top entry baghouses to bottom entry ?Upgrading the cleaning system ?Installing Gore-tex® ePTFE membrane filter bags The estimation of required off-gas capacity is traditionally done by rule-of-thumb methods such as specific extraction. A more elegant evaluation method was developed for simulating the effects of changes in charge mix on the furnace reaction gas volume and the APC system. Reaction gases are calculated by modelling the reactions taking place in the furnace and off-gas volumes are compared to both fan and baghouse capacity. This enables identification of bottle-necks in the off-gas system. CFD techniques were utilized to evaluate geometric imbalances and propose solutions to ensure optimal use of off-gas capacity. The system modifications were completed over several months and the modified equipment went into service in May2006.

Jan 1, 2007

By S. Uludag

Spontaneous combustion of coal has been studied by laboratory techniques using an apparatus in a small-scale laboratory testing. Coal?s inherent characteristics can be measured using Differential Thermal Analysis (DTA) and Crossing Point Temperature (CPT) methods. The DTA curve obtained after testing is compared with actual inherent moisture and its effect on spontaneous combustion has been investigated. It has been found that the Wits-Ehac Index increases as the inherent moisture of the sample increases. Therefore it can be deduced that liability to spontaneous combustion increases with increased inherent moisture. In addition, volatiles have a catalytic affect on self heating immediately after the inherent moisture is reduced. This is identified as stage two in the thermogram. The inherent moisture has a cooling effect during the initial stages of testing and is visible in the DTA thermogram. In addition, while an increase in carbon content means an increase in Wits-Ehac Index value, an ash content decreases the likelihood of on spontaneous combustion. Keywords: Spontaneous Combustion, Differential Thermal Analysis, Crossing Point Temperature, Moisture, Coal, Laboratory Testing.

Jan 1, 2007

By G. C. Smith

Process control applications in the minerals processing industry have grown extensively over the years due to the many benefits derived, both financially and operation-wise. Although control theory is widely known, conventional control does not address many of the problems posed by minerals processing circuits. Some of these problems include interactions between process units, large dead times, few and sometimes unreliable measurements of process variables, non-linear systems, disturbances entering the process, processes with varying dynamics, and many more. For the past 26 years Mintek has been active in the field of providing specific, customized solutions for the minerals processing industry. This paper focuses specifically on applications in milling and flotation control. The underlying control principles have been applied to a wide range of other processes including submerged arc furnaces. Advanced control application is implemented on a common advanced control platform, called the PlantStar. Much innovation has been brought to the fore in terms of adapting theoretical techniques and developing new methods to resolve specific milling and flotation circuit issues by using process control. The general approach adopted by Mintek when implementing advanced control is to enforce stabilization of the process as a solid foundation for optimization strategies to be built upon. In doing this, a robust control solution is presented, and the end result is flow and level stability, better product quality regulation, increase in throughput and a stable feed to downstream processes. The MillStar advanced milling control system ensures that the milling circuit is at all times easy to operate while achieving optimum product quality and throughput. Stabilization should include product size regulation and sump level control. Another important aspect of stabilization control is the handling of milling circuit constraints without introducing cyclical behaviour and with minimal disturbance to the final product quality. Process constraints may include factors such as process water limitations, cyclone feed density, and cyclone underflow angle. An optimization strategy should be developed to increase the mill throughput without affecting product quality or introducing mill overloads. The relationship between solids feed and power draw is examined and manipulated for optimization. The interactive nature of flotation circuits and the presence of recirculating streams tend to make satisfactory control almost impossible with conventional techniques such as PI (Proportional plus Integral) or PID (Proportional, Integral and Derivative) control. The FloatStar Level Stabilizer simultaneously considers all the flotation levels in a circuit by use of a multivariable algorithm, and takes compensating action in anticipation of disturbances. The FloatStar Flow Optimizer is an optimization strategy that controls the concentrate flow rate between various sections of a flotation circuit (e.g. Rougher ?Cleaner; Cleaner ?Recleaner). By controlling the concentrate flow between the sections, the mass pull, circulating loads and residence times of the circuit can be stabilized, thereby enhancing the performance of the flotation process. Optimizing grade and recovery are coupled with the dynamic optimization of circulating flows. The FloatStar Grade-Recovery Optimizer will maximize the grade in a section, whilst ensuring that recovery or any other process specific limits remain within predefined limits. With successful applications on several milling and flotation plants worldwide processing amongst others PGMs, gold, copper and nickel, Mintek has shown that it is a leader in milling and flotation control innovation

Jan 1, 2004

By R. E. Wilmot

This paper is based on the experiences, over many years, of numerous authors in the South African mining industry and of the hot dip galvanizing process and its application as a corrosion protection system. The paper sets out the extensive development, financial resources and stringent operating requirements of the South African mining industry. After many years of research and operational experiences, hot dip galvanizing and, when necessary, duplex systems, have been found to meet the demanding requirements of this particular industry. The paper sets out the requirements from the standpoint of corrosion criteria and is followed with a case where the corrosion protection properties of hot dip galvanizing are demonstrated. This case history traces the early investigation of the expected corrosive conditions in a new mining operation and concludes with two follow-up visits to the mine in order to examine actual performance of the corrosion protection system after ten years in service.

Jan 1, 2007

By R Ratlou

Increased contamination due to sand in spiral feed has had a negative effect on the efficiency of spiral concentrators at Navigation Plant. The no. 1 seam at Kromdraai opencast, which was previously mined by underground bord and pillar methods, is now susceptible to spontaneous combustion because of air ingress into the old workings which are exposed in the opencast high wall. This posed a risk in the loss of reserves to burnt coal. As solutions, buffer blasting of the preceding cut to collapse bords and soft overburden dressing of un-collapsed bords were implemented to prevent air entering the workings. The latter remedy resulted in increased contamination due to addition of sand in Run of Mine. After evaluating alternatives, a low capital option was selected. The 110t/hr Teetered Bed Separator (TBS) has been installed, primarily to desand and upgrade the feed to the spiral concentrators. The unit indicated an upgrade with a yield increase of 0.4% during test work and is currently showing an overall plant yield increase of 0.97%.

Jan 1, 2006

By Y. M. Chen, H. L. Zhang, W. U. Bing, C. Q. Zhou

Multiphase flow in the widely used Vanyukov furnace was numerically studied. An unsteady three-dimensional and three-phase flow model was firstly built using the computational fluid dynamics (CFD) software ANSYS FLUENT®, and then solved with the volume of fluid (VOF) and k - ??model. The results showed that the proposed model could be used to predict the multiphase movement, the slag/air fluctuation, the vortex formation, and effects of structural and operational parameters. By fast Fourier transform (FFT), the dominant frequency of density with time signal was calculated as 0.29 Hz. The analysis of different injection flow rates of enriched air indicated that this variable has a major effect on the mean slag velocity. The peak mean velocity increased from 2.17 to 4.99 m/s while the flow rate of enriched air varied from 70 to 160 m/s. The proposed model provides a method to optimize the furnace structure and operating conditions for the best furnace performance and lowest energy consumption.

Jan 1, 2015

Common practice in mineral resource estimation consists of partitioning the orebody into several domains defined by grade intervals, prior to the geostatistical modelling and estimation/simulation at unsampled locations. This paper shows the pitfalls of grade domaining through a case study in which we compare the performance of several estimation schemes and demonstrate that the use of domains defined by grade cut-offs implies a deterioration of the resource estimates, mainly in what refers to precision and conditional bias. Then, several conceptual limitations of the grade domaining approach are stressed, in particular the fact that it does not account for the spatial dependency between adjacent domains and for the uncertainty in the domain boundaries. Also, this approach is shown to be sensitive to the cut-offs that define the domains, to provoke artifacts in the kriging maps, histograms and scatter grams between true and estimated grades, and to lower the kriging variance, a feature that may impact the mineral resource classification. An alternative approach is finally proposed to overcome these limitations, based on a stochastic modelling of the grade domains and a co-kriging of the grades using information from all the domains. Keywords: geostatistics, kriging, conditional bias, geological control, grade zoning.

Jan 1, 2005