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By J. Maiti

This study examined the group differences in accident susceptibility among underground coal mine workers accounting for their personal and workplace characteristics. A logistic regression model was used for this purpose. Data were collected from five underground coal mines for a period of four years. The case study results revealed that different age and experience groups of workers bear no significant differences in their accident susceptibility; however, the workplace location and occupation groups show significant differences in their risk of injuries. It is inferred based on the logistic model results that among the three occupation groups, the face workers are more susceptible towards accidents/injuries compared to the haulage and other workers. Key Words: Mine Safety, Accident Susceptibility, Group Differences, and Logistic Regression.

Jan 1, 2001

By T. R. Roy

A prediction model, developed by Central Mining Research Institute (India) for evaluation of fire risk rating of underground coal mine panels in bord and pillar working in respect of their proneness to spontaneous heating, is presented in this paper. The concept used in this model is innovative and user friendly. This model may be applied to a panel where extraction is carried out using any of the techniques: i) depillaring with formation of small pillars as final operation, ii) extraction by broadening of galleries, iii) depillaring with hydraulic sand stowing, and iv) depillaring with caving. Here, major fire risk parameters are short-listed and divided into three broad groups in accordance with the nature of their contribution to the spontaneous heating of a mine panel. The paper describes the procedure for estimating the fire risk rating of individual groups using separate objective type models developed for this purpose. Then it evaluates the overall fire risk rating of the panel by combining the fire risk ratings of all the three broad groups. The model is tested with the field data collected from different collieries spreading across the country and with the laboratory data for critical assessment of fitness. Keywords : prediction model, fire risk rating of panel, spontaneous heating of coal, underground panel, bord and pillar working.

Jan 1, 2003

By J. N. Van der Merwe

The results of over 900 coal strength tests done during the period 1993?1994 for the SIMRAC project COL021A were re-analysed with a view to find a method to delineate areas or seams that can be grouped together for analyses of coal strength and strength decay characteristics. It was confirmed that the strength of a coal specimen increases linearly with increasing diameter-to-length ratio and decreases exponentially with increasing size of specimen. However, by extrapolation of the data, it was shown that beyond a diameter of approximately 2 m, the size effect is insignificant. For larger specimens, the diameter-to-length ratio (referred to as the width-to-height ratio for full scale mine pillars) alone continues to influence the strength. The slope of the linear strength vs. diameter-to-length ratio relationship is independent of the size of the specimen and is not unique for coals from different mines. However, the intercept of that relationship is unique and is a function of specimen size. This offers a previously unknown method to distinguish between the coals from different mining areas and coal seams. Ranked from weakest to strongest, the samples tested from the different mines are in the order shown below, which roughly corresponds to the judgement of practising rock engineers in the field: ?Sigma ?ZAC ?Goedehoop ?Kriel ?Bank ?Blinkpan ?Secunda ?Greenside Arnot ?Khutala ?Delmas

Jan 1, 2003

By I. V. Lunkin, E. B. Rakishev, B. R. Rakishev

In mining the method of statistical tests is used by solving of problems, exposing to influence of random factors. Such problems are: rational selection of equipment set; co-ordination in time of different processes; interaction between some processes and kinds of works. Usually it is considered that Monte Carlo method proves its value in the first place in that problems, which allow theoretical-probabilistic description. Analysis of numerical solution of mining-economic problems shows that the method of statistical tests may be used successfully by solving of determinate problems, which are solved usually analytically or by the methods of mathematical programming. We are talking about the problems of optimal use of resources, expedient placing of equipment, effective use of investments, rational planning of stripping and extracting works, groups of mining enterprises and about different variants of transport problem. In the report possibility of the method use is studied at an example of typical technical-economic problems solving. By solving of these problems the variant of the method with uniform distribution of random quantity had been applied and built-in random number generator of visual modelling system VisSim had been used. By algorithms elaboration it seems very perspective to use combination of the Monte Carlo method with traditional methods of numerical solving of the problems (methods of linear, nonlinear and dynamic programming and so on). Keywords: method of statistical tests, mining-technical problems, diapason of random number sample, efficiency function and its extremum.

Jan 1, 2003

By A. B. Fox, R. P. Thackray, K. C. Mills

The role of mould fluxes in continuous casting is reviewed. The main functions of the flux are described and the importance of the flux in providing lubrication and the right level of heat transfer between the shell and the mould is described. The major problems of longitudinal, transverse and star cracking, gas and slag entrapment and deep oscillation marks in the steel product and ?sticker breakouts? are analysed. The important physical properties of the flux in combating these various problems are identified. Physical property data for the fluxes are given.

Jan 1, 2004

By J. M. A. Geldenhuis

This work is concerned with studying possible reactions in the ilmenite furnace which may control the product quality of both slag and metal. Two different approaches were followed: comparing actual furnace slag compositions with the calculated equilibrium values and using commercial oxygen probes to measure the effective partial oxygen pressure in the slag and metal. It appears from a comparison of actual furnace slag compositions (in terms of the distribution coefficient of vanadium) with equilibrium values, that the TiO1.5-TiO2reaction may fix the effective partial oxygen pressure for the vanadium reaction. This possibility was tested using commercial oxygen probes (traditionally applied during steelmaking) to measure the effective oxygen partial pressure of both the slag and liquid iron in Iscor?s 3MVA pilot plant ilmenite furnace. From these measurements, it appears that commercial oxygen probes containing zirconia solid electrolytes can be used to measure the effective oxygen potential of both the slag and liquid iron. This oxygen activity correlates well with the FeO content of the slag. The results, furthermore, clearly illustrate that equilibrium conditions are not attained in the ilmenite furnace during the production of high titania slags, since the effective oxygen potential of slag and metal differ substantially.

Jan 1, 1999

By G. Bacon

The past decade has witnessed unprecedented growth in the development and implementation of solvent extraction technology in the extractive metallurgy of nickel and cobalt. Solvent extraction is proving to be a powerful tool, opening new opportunities for simpler, more cost efficient and environmentally sound metal refining processes. These advances, however, could not have been possible without the cooperative efforts between the nickel industry and the people and organizations involved with reagents, materials and equipment development and supply as well as solvent extraction research, aided by the accumulated knowledge and practical experience from the copper and uranium solvent extraction operations. This paper provides an overview of these developments and some of the challenges ahead.

Jan 1, 2002

By L. R. Nelson

A review is presented of the furnace cooling system design and operating developments since the initial furnace start-up in January 2001 of the Chambishi DC-arc furnace to produce ferrocobalt alloy. The furnace operating conditions present a number of challenges to the furnace designers and operators, in particular, to provide a sustainable lining that can withstand the highly corrosive siliceous slag (roughly 50% SiO2). This is exacerbated by the dual requirement of operating this slag in a relatively highly superheated state (?T ?400°C when tapped at 1550°C) to ensure that the ferroalloy can be tapped (estimated 1370°C alloy liquidus temperature) prior to atomization. The core design challenge occurs at the alloy-slag interface, where a single refractory type cannot simultaneously meet the dual requirement of both adequate alloy and slag corrosion compatibility. Progression by the fourth furnace campaign to involve a retrofit of the bath sidewall to HATCH high-intensity, water-cooled, copper Waffle coolers and tap blocks is described. This involves operation of the entire slag bath, the slag-alloy interface and a portion of the alloy within a more chemically compatible refractory/slag (and possibly at times even an alloy) freeze-lining. Due to the high furnace power density employed (up to 500 kW/m2 hearth area), coupled with the large slag superheat needed, the resulting imposed peak bath sidewall heat fluxes are substantial, especially in the alloy (typically averaging 170 kW/m2), and on occasion have exceeded 1000 kW/m2. The performance of the HATCH Copper Waffle coolers under such aggressive process pyrometallurgical conditions is described. Aspects of the design and especially operating strategies to effect sustained production at up to 38 MW power input are also discussed.

Jan 1, 2004

By J. R. Cole-Baker

An independent technical audit by a consultant is part of the accountability process of publicly owned or publicly quoted companies when raising finance through share issues or loans or the sale of equity, and of banks or development funds when granting loans. Africa is undergoing a renaissance in investment in its mining industry. It is forecast that capital investment, in major mining projects in Africa, will be over US$ 4.4 billion, in the next few years. Most, if not all, of the capital to be raised will require an independent technical audit. The aim of this paper is to assist the management of mining companies seeking finance in appreciating the role of such technical audits. The reasons for such audits, especially to attract international investment, are listed. The role of the audit is explained in assessing the underlying robustness of the company as ?a going concern? and the viability of any ?expansion plans?. Its use is emphasised in establishing the underlying value of the company based on the mine life as supported by the mineral reserves. The independent consultant role is stressed as a representative of the parties in a finance deal who cannot, in practice, carry out their own detailed and specialized technical due diligence. The various components of a typical audit are examined with examples of critical matters which may require resolution. The definitions, which are used commonly in audits, in respect of competence and reserves and resources, as stated by various regulatory bodies, are compared.

Jan 1, 1998

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 M. Olper

The zinc recycling is assuming more and more importance. A lot of zinc secondaries and wastes are ready to be collected and converted to zinc metal. The impurities present in these materials and the technical and economical problems that some traditional ways of treating these materials are facing, call for new technologies. The EZINEX Process, a fully hydrometallurgical process industrially proven to convert oxidised zinc bearing materials directly to zinc cathodes, is an innovative process that can deal with any kind of zinc waste/secondaries in a very powerful way. In this paper the highlights of this process will be shown and discussed to demonstrate the robustness of the process and its economic viability.

Jan 1, 2008

By M. Sanchez, C. Morales, J. Palacios

The slag produced in the Peirce Smith converters at the Ilo smelter of Southern Peru Copper Corporation has shown a wide range of magnetite content, which introduces an additional problem in the smelting units due to materials? recirculation. However, the operation data analysis and the application of thermodynamic concepts have made it possible to produce slag with magnetite content between 18 and 20%. The results have suggested that matte grade enhances magnetite formation while silica controls its precipitation, and they are also influenced by the increasing temperature of the slag. Thus, in order to obtain the required magnetite content in the slag, matte grade is gradually enriched in equilibrium with slag containing from 25 to 32% silica.

Jan 1, 2004

By J. P. Theron

Paper written on project work carried out in partial fulfilment of Phd.(Process Engineering) degree Process modelling is an essential element in the development of advanced (model-based) process control systems, accounting for up to 80% of the cost of development. Often, models based on historic process data are the only viable option when dealing with processes that cannot be modeled cost-effectively from first principles. Despite major advances that have recently been made in the field of nonlinear process modeling, some basic idea of the dynamic behaviour of a process system is important prior to system identification. While many process systems seem unlikely to be linear, the possible nonlinear aspects of their dynamics are not necessarily supported by the data. This may have significant implications for subsequent system identification or interpretation of the data. For example, it is quite possible that an underlying nonlinear deterministic signal may be obscured by a high degree of measurement or process noise, to the extent that it may be critical in the choice of model to fit to the data. The method of surrogate data analysis has recently been proposed as a means to classify the underlying dynamics of complex systems, and in this paper the use of Fourier transform surrogates to classify process systems is explored. Keywords: modelling, process control, simulation, surrogate data analysis, nonlinear systems.

Jan 1, 2004

The major proportion of South African coal is extracted by the bord-and-pillar mining method which requires that the overlying strata be supported by pillars of coal. The stability of the pillars is a major safety concern. One of the factors which affects the strength of coal pillars is the intensity and nature of discontinuities in the coal seams. Current design methods for pillars assume that al the coal seams have equal strength and are equally disturbed by natural discontinuities, resulting in over-designed pillars in some cases and potentially unstable pillars in others. Research was carried out to determine the nature of discontinuities in coal seams and to assess their potential effect on pillar strength. It was found that large variations exist in the intensity of discontinuities in the different coal seams being mined. In addition, numerical model studies showed that the discontinuities could significantly reduce pillar strength if the width-to-height ratio of the pillars is small, but the effect decreases as the width-to-height ratio increases.

Jan 1, 1997

By P. J. D. Lloyd

At first I read this paper with interest, which grew to fascination, and ended up with horror. Such reactions to a supposedly scientific contribution are rare, and I believe the coal mining community must be warned in the strongest possible terms against the recommendations that this paper makes. The paper purports to have assessed statistically two sets of data on methane concentrations recorded in the return air from Turkish longwalls. The first set of data, from their Table I, is reproduced in Table I below. The data have been rearranged in classes to indicate the underlying distribution. While there is only limited data (N=33), the distribution looks as if it could be the sum of two normal distributions with means around 0.5 and 0.8, or possibly a log-normal distribution. What is quite clear is that it is nota single normal distribution.

Jan 1, 2004

By Wayne Burmeister, Danie Benade, Louis Meyer, Hugo Joubert

What is not measured cannot be managed. This is true of most things, including a furnace lining. This paper describes a Lining Management System used for this purpose. It provides the operations staff with a management tool to predict long term lining life and acts as a process optimisation tool. It alarms and records upset furnace conditions. Outputs from the system are described as presented through a specially developed software package and interface. It includes vertical and horizontal furnace sections showing estimated isotherms through the lining as well as the furnace bath. It also shows calculated heat flux values, estimated lining wear and the freeze layer profile. A novel three-dimensional display is described which provides the operator with a big picture view of the furnace crucible profile under real time operating conditions. The powerful trending facility for analysing both measured and calculated values is discussed. The required instrumentation hardware as well as the installation thereof is described, with special reference to an electrically insulating thermocouple socket design. Finally feedback is provided on the first year?s performance of the system installed on an open ferrochrome furnace at Assmang Chrome, Machadodorp, South Africa.

Jan 1, 2007

By B. Samanta

A quality characteristic analysed through construction of the Shewhart control chart is required to be normally distributed. In mining applications, this assumption is often violated as many quality characteristics follow skewed or lognormal distribution. In this paper, two methods were investigated using a heuristic approach for setting up the control limits for a skewed population. Based on these approaches a Mode chart, and a Weighted Variance (WV) control charts were constructed. The performance of the proposed methods was compared with the normal based Shewhart method through a case study conducted in a surface mine supplying iron ore to a steel plant. A simulation study was also conducted to evaluate the effectiveness of the proposed methods over the Shewhart method. The study revealed that the Shewhart control charts generated more out of control alarms compared with the Mode and Weighted Variance control charts for a skewed population of Fe%. The simulation results also revealed that for extremely high skewed population, the WV control chart and Mode control chart provided higher probability of coverage than the Shewhart method; although the detection rate (probability of detection) of out of control condition for these methods was slightly reduced compared with Shewhart method.

Jan 1, 2004

A physical modelling study has been carried out to simulate the slag-metal dispersion induced by a high-strength bottom gas injection. Water and kerosene were utilized to simulate metal and slag respectively. A water model of CLU (Creusot-Loire Uddeholm) vessel was used with three different nozzle orientations, namely, off-centre, triangular off-centre and centre. The gas flow rates changed from 0.00599m3/sec to 0.01081m3/sec. Height of heavy and light phases was kept fixed at 0.23 m and 0.02 m respectively. The dispersed phase holdup was determined at various axial and radial distances, gas flow rates, and tuyere configurations. The observations revealed that at a fixed gas injection rate, as the vertical distance increased in the centerline, straight off-centre orientation resulted in greater dispersed phase hold up values than those of the centre configuration and the triangular off-centre orientation. The dispersed phase holdup was found to increase with gas injection rate and decreased with axial distance. The variation of the dispersed phase hold up with the dimensionless axial distance and the gas injection rate was correlated by using the Modified Froude Number. The experimental values of the dispersed phase holdup were found to be in good agreement with the correlated values obtained from the modelling equations. The findings of the present study may be utilized in the ferroalloy refining vessels in terms of designing tuyere locations for optimum processing conditions.

Jan 1, 2004

By R. Boom, L. Holappa

In the present paper, microstructure changes of solid-state reduction of industrial chromite pellets and lumpy ore were investigated with SEM/EPMA. To simulate the reactions in the packed bed zone of the Submerged Arc Furnace (SAF), carbon monoxide was used as the reducing agent, with the presence of graphite in proximity to chromite. The experiments were carried out at 1500 °C. Scanning electron microscopy was used to observe and analyse the structure and composition changes of the chromite samples. It was found that reduction of lumpy ore generally took place slower than that of pellet. In all samples, chromite reduction proceeded faster in the outer part of the sample than in the centre part. The reaction mechanism is discussed on the basis of experimental results and earlier investigations. The possibilities to optimize the FeCr production process are also discussed.

Jan 1, 2007

By P. He

Abstract This paper introduces the test results of dark-gray calcium-shale, discusses the infection of strength characteristic and deformation characteristic due to the angle between structural planes. Keywords calcium-shale, failure form, strength, deformation characteristic, structural planes. Zusammenfassung: basier auf der Anwendung von Problematik des Felsenbauprojektes und Beschaffenheit Felsen unter Beaugnshme auf den Zustand des Druckes von einzeler Welle legt dieser Text dar, wie der Winkel der Schichtstrukturflaeche des schwarzgrau kalziumhaltigen Schieferblocks auf die Zerstoerungs-, Intensitaets- und Deformationseigenschaften einwirkt. Schluesselwoerter: schwarzgrau kalziumhaltigen Schiefer, Zerstoerungseigenschften, Intensitaetseigenschften, Deformationseigenschaften, Flaeche dar Schichtstruktur. Résumé – En fonction de la configuration du massif rocheux sous l’état de la contrainte de pression axiale simple et de la pratique de l’ingénierie de roches, le présent article fait la déscription concernant l’influence de l’inclinaison ? de la couche de structure stratifiée du bloc de schiste calcaire gris noir sur ses caractéristiques de destruction, sa spécificité de résistance ainsi que sa nature de déformation. Mot clés – Schiste calcaire gris noir, Caractéristiques de destruction, Spécificité de résistance, Nature de déformation, Couche de structure stratifiée

Jan 1, 2003