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By D. D. Hawat

The locations of potential reserves of chromite ores throughout the world are discussed. Reference is made to the marked changes in international trade in chromite ores during the past ten to fifteen years, and to the change in locality of the production of ferochromium aloys, which is curently largely carried out in the country of origin of the ores. The influence of these changes has been very profound in South Africa, which has the largest smelting capacity and the largest production of ferochromium aloys in the world. A proportion of South African ore is stil exported to meet the demands for the production of chromium chemicals and refractories, including a large tonnage of foundry sands. Ferochromium smelters in South Africa have a capacity of virtualy 1 Mt of aloy per annum. Nearly al this development has taken place since the introduction of the argon-oxygen decarburization (A.O.D.) process for the smelting of stainless steels. Formerly, expensive Iow-carbon ferochromium aloys were required as raw materials, but the AO.D. process, which is being used world wide, permits the use of high-carbon ferrochromium, the main product of the smelters in this country. The production in South Africa of chromium-containing corrosion- and heat-resistant steels is stil on a relatively smal scale, but serious atention is being paid to the exploitation of low-carbon weldable feritic chromium steel.

Jan 1, 1986

By Stephen Hughes

Ausmelt Top Submerged Lancing (TSL) Technology has gained widespread commercial acceptance in the lead and zinc industries, as an efficient and highly flexible pyrometallurgical reactor with accompanying excellent environmental performance. For the processing of lead and zinc bearing feed materials twenty one (21) Ausmelt furnaces are now in operation, under design or under construction. With recent increases in the value of both lead and zinc and an ever increasing focus on the sustainable use of resources, interest in the processing of secondary feed material sources as well as metal containing residues has substantially increased. Ausmelt Technology has proven to be well suited to the economic recovery of values from such sources. This has for example culminated in Ausmelt?s commitment to the Whyalla Zinc project as the owner/operator of a facility for the treatment of zinc bearing secondary feeds. This paper describes Ausmelt?s recent developments in the fields of lead and zinc processing, as well as further investigations into new processing areas, including the direct smelting of zinc concentrates. Ausmelt?s TSL Technology can now be regarded as Best Available Technology (BAT) for metal production.

Jan 1, 2008

By W. D. Grimsley, R. P. King, J. B. See

Samples (15 to 20 g) of pre-calcined Mamatwan manganese ore or pure Mn 304 smaller than 48 mesh were reacted at temperatures in the range 1000 to 1300°C with samples of spectrographically pure graphite smaller than 325 mesh. Samples (1 g) of ore or pure Mn02 smaller than 48 mesh were reacted at temperatures of 1000 and 1200°C with pure graphite fines in argon, with graphite in carbon, .'1onoxide, and with carbon monoxide alone. In each case, the loss of mass as a function of time was recorded with a hermobalance. The rate and degree of reduction were found to increase with additions of carbon and with increasing temperature up to 1300oC, when they reached their maximum. The shape of the reduction curves, together with the results obtained from examination of the products of reaction by microscopy and X-ray diffraction, were used as the basis for a postulated reduction mechanism. Some details are given of an initial kinetic model that was used to verify the proposed mechanism. It was found that the reduction of Mamatwan ore by graphite at temperatures in the range 1000 to 1300°C occurs in two stages: (i) an initial stage during which the higher oxides of manganese are rapidly reduced to MnO with concurrent formation of CaMn2O4 and (ii) a longer stage during which CaMn2O4 and MnO are reduced to carbides by carbon dissolved in the ferromanganese phase.

Jan 1, 1978

By J. M. Musadaidzwa

Skorpion Zinc is located 25 km north-west of the small settlement of Rosh Pinah in southern Namibia. Commissioned in early 2003, Skorpion Zinc became the first mine-to-metal operation to commercially apply a purely hydrometallurgical process route to exploit a zinc oxide orebody. The novel technology, known as The Modified ZincexTM Process patented by Tecnicas Reunidas, comprises sulphuric acid atmospheric leaching, zinc solvent extraction (SX) and electrowinning (EW) to produce London metal exchange (LME) Special high grade (SHG) zinc. Forming the core of the process, the SX step has thrived in its role as a barrier to impurities and also in the upgrading of the pregnant liquor solution (PLS), converting it into a loaded electrolyte (LE) sufficiently rich and pure for EW. Against this successful run, a number of challenges have, however, been encountered in SX due the emergence of upset conditions largely emanating from upstream processes. This paper outlines some of the major deviations that have beset the SX process in its first five years of continuous operation. Impurity excursions, temperature depressions, changes in phase continuity, excess aqueous entrainment, the effect of colloidal silica and the accumulation of rare earth elements on the organic phase will be discussed in detail. Keywords: skorpion zinc, solvent extraction, the Modified ZincexTM Process (MZP) DE2HPA, aqueous entrainment (AE), loaded electrolyte (LE), standard liquid validation (SLV) test, organic continuity, aqueous continuity (AC), electrowinning, colloidal silica, phase disengagement time (PDT), rare earth elements (REE).

Jan 1, 2009

By R. Hoare

TSG Consulting works with many of the major global mining companies using simulation modelling as an integral component in their development team's processes to determine which combination of infrastructure options, operating performance and operating rules best achieve project goals. All systems can be divided into a series of subprocesses. Conventional management and design practices focus on the optimisation of these system components. However, the interaction between subprocesses means that improvements made to the individual components do not necessarily translate into total system performance improvement. TSG Consulting advocates a `total integrated system approach' to understanding the behaviour and performance of complex interacting systems. In a constraint-based integrated set of processes, the instantaneous system capacity is limited by the subsystem component capacity that is the bottleneck at that point in time. Additionally, real world stochastic and dynamic influences tend to have knock-on effects across subsystem boundaries. This necessitates the requirement for simulation modelling to develop and validate solutions that are sufficiently robust to deliver sustainable outcomes. The key to maximising production is to understand the causes and effects the inherent variability has on component performance, subprocess performance and most importantly, the total integrated system performance. The correct use of simulation modelling techniques allows study teams to evaluate the relative merits of different capacity enhancement proposals. Put simply, when done well, simulation modelling provides a quantitative and rational process to enhance the knowledge and insight needed to make informed decisions.

Jan 1, 2007

Mixtures of MnO and graphite were reacted under argon at temperatures ranging from 1200 to 1425°C, and the loss in mass of the mixture was recorded continuously. The results showed that the rate of reduction of MnO increased as the temperature increased and the ratio of MnO to C decreased. The effect of the particle size of MnO and of graphite on the rate of reduction at I350°C was very small in the range 63 to 250 µm for MnO and 45 to 355 µm for graphite. The rate of reduction at I350°C was increased markedly by the addition of Na2CO2 and K2CO3, was slightly increased by the addition of Fe2O3, was unaffected by the addition of CaO, MgO, and AI2O., and was decreased by the addition of SiO2. Some CO2 was always present in the effluent gas, and this was taken as evidence that the reduction of MnO occurred by way of CO2 as an intermediate product. The activation energy of the ratecontrolling step was 57,5 kcal, and this was similar to the measured activation energy for the gasification of graphite by CO., namely, 61,S kcal per mole of graphite. A simple kinetic model was derived on the assumption that the gasification of graphite was the ratecontrolling step, and the results over the temperature range 1200 to I425°C, when plotted in the appropriate form, yielded straight lines as predicted by the model.

Jan 1, 1980

By D. G. Davies

Colloquium on the construction of Slimes dams The following contributions to the discussion at the above Colloquium were received for publication. D. G. DAVIES* This contribution is really a follow up on Mr H. E. Cross's paper on the conversion of a uranium plant to the recovery of zinc (published in the Journal, November 1973). Ecological aspects of slimes-dam construction by H. T. CLAUSEN C. M. VAN STADEN* Published in the Journal, December 1973 I should like to thank Mr Clausen for his paper and to congratulate the Research Laboratories and the Vegetation Unit of the Chamber of Mines on the excellent work they have done in the past, are still doing at present, and, we hope, will continue to do in future, on the testing of various methods for the covering of slimes dams and specifically on the vegetation of dams. The impact of slimes-dam formation on water quality and pollution by R. T. RUDD* C. M. VAN STADEN Published in the Journal, December 1973 I should like to congratulate Mr Rudd on the paper he presented. Congratulations are also due to the Department of Water Affairs for the practical attitude they have taken in implementing the Water Act. Slimes-dam construction in the gold mines of the Anglo American Group by W. T. RUHMER W. R. FLOOK* Published in the Journal, February 1973 Methods for the construction and operation of slimes dams in the gold-mining industry do not appear to have changed much for some considerable number of years.

Jan 3, 1974

By C. Clark, P. Patton, B. M. Stewart

Handling materials in underground mines continues to be a major safety problem. To help reduce materials-handling injuries, the National Institute for Occupational Safety and Health (NIOSH) at the Spokane Research Laboratory is developing, modifying, and testing equipment to replace the necessity of doing lifting tasks manually. To reduce single-event lift injuries, equipment having mechanical automatic weight sensing and balancing control was investigated. The Coleman manipulator was selected for testing. Modifications to the Coleman manipulator to make it more suitable for underground mine use included mobilization, self-containment, all-purpose gripper attachment, and support jacks. To reduce or eliminate the need to clean off manually the materials that commonly plug grizzly openings (timbers, wire mesh, roof bolts, and other debris), a track-guided pincher arm device was developed. The TGPA attaches to an impact hammer head, and the pincher arms are controlled by the operator of the hammer. Oversized rock can be broken with the pincher arms in the up position; the arms can then be lowered to grab and remove debris. Sweeping action to remove cohesive fines bridging grizzly openings is also greatly improved. This device is especially useful in recessed grizzlies. An industrial gun was tested to evaluate its effectiveness in breaking oversized rock. Boulders up to 76 cm in diameter were successfully broken to minus 33 cm. Although methods to control flyrock need to be developed, an industrial gun may be a safe and inexpensive alternative to breaking oversized rock in certain underground mining situations. Keywords: Mining, materials handling, over-exertion, injuries

Sep 1, 2001

The Copperbelt areas of Zambia and the Democratic Republic of Congo (DRC) have recently been seeing the development of a significant number of new projects. Due to the current economic climate, some of these projects have been delayed but the region remains an important resource for copper and cobalt for future years. Many of these projects will utilize an agitation leach followed by solvent extraction and electrowinning to recover both copper and cobalt. The flowsheet route for copper is fairly well established while the processing options for cobalt vary considerably depending on the final product (metal or salt) the operator wishes to make. The mineralogy of ores in the area is typically associated with high gangue acid consumption during the leaching process. This has resulted in acid availability to the area being constrained and acid prices have risen accordingly. Agitation leach circuits, typically, have a tight water balance which needs to be maintained and a bleed of process liquor needs to be continuously removed from the circuit in order to maintain this balance. This bleed, typically, contains fairly high levels of acid and requires neutralization prior to tailings disposal or secondary metal recovery. It is, therefore, desirable to minimize the acid concentration in this bleed stream in order to decrease total acid requirements and neutralization costs for the process plant. An in depth case study by Cognis and Bateman Engineering evaluated three different flowsheets with the aim of determining relative operating costs between the three alternatives, together with differences in plant capital cost requirements.

Jan 1, 2009

By G. G. Rogers, A. Vna Der Linde, N. B. Strydom, W. H. Van Der Walt

Changes in the level of serum vitamin C in mineworkers by N. B. STRYDOM, M.Se., Ph.D. (Illinois) (Fellow), G. G. ROGERS, M.Se. (Pta) (Visitor), W. H. VAN DER WALT, B.Se. (Poteh.) (Visitor), and A. VAN DER LlNDE, B.Se. (O.F.S.) (Visitor) The levels of serum vitamin C in the blood of mineworkers were determined on the first and fifth days of the normal heat-acclimatization period (i.e., before and after exposure to heat) and again after I, 2, and 4 months of underground employment. Supplementary vitamin C was administered to the men during the heat-acclimatization period. Six groups of 20 men featured in the study and, except for one of the two 4-month groups, all the values were obtained after a full shift of underground work. It was found that adequate levels of serum vitamin C were maintained during the heat-acclimatization period, and the 250 mg of vitamin C given daily to each man must therefore be regarded as sufficient. The serum vitamin C decreased significantly with time of exposure to underground conditions, showing that the vitamin C utilized during heat stress is more than that provided in the men's diet. At the end of 4 months, not a single subject had more than 0,4 mg of serum vitamin C per 100 ml, most of them having only 0,3 mg per 100 ml; 90 per cent of the men had had more than 0,4 mg per 100 ml during the acclimatization period. It is therefore recommended that the mineworkers' diets should be supplemented with 100 to 200 mg of vitamin C per man per day.

Jan 5, 1977

It is desirable to have a model, or method, for major project development, which will enable flexible modelling of separation circuits. This ability improves the understanding of circuits and how they should be operated, especially in a design phase, where various options are evaluated and decisions are made on the required number of stages and configuration. This paper describes existing gravity separation circuit modelling theory and concepts, as defined by Holland-Batt1 (separation window, separation efficiency and proportionality of efficiency). The crux of the paperis the application of numerical analysis to fit raw separation data by means of a modified Bézier-Spline. The paper proposes an alternative to the theory developed by Holland-Batt that provides more flexibility in the modelling of separation stages and curves, which include S-shaped curves. The paper proposes a solution to the challenge of continuously extrapolating data, and the first difficulty normally encountered, which is the fitting of an appropriate empirical formula to raw data.

Jan 1, 2007

By P. R. Jochens

SYNOPSIS This review article first highlights the past performance of the industry and discusses the manner in which the development of the industry has followed a logical progression from mining to the production of mineral and metal products of specification purity. Then the numerous constraints against a greater contribution by the industry are enumerated. Attention is drawn to the extent of further processing that can be undertaken in the context of mining and metallurgical processing, not only to indicate the benefits that can be derived from the added-value conferred on a mineral or metal commodity during each stage of its further processing, but also to point out some important corollaries of further processing. The many opportunities and challenges for an increased contribution by the minerals and metals industry are then reviewed. This major section includes a list of commodities for which increased penetration of export markets could be sought because the increasing resistance level (a term developed in this paper) has not been attained; a list of commodities that are imported at present, many of which could be produced locally on the basis of identified resources and expertise; a list of commodities for which additional uses should be developed so that South Africa, which possesses the largest reserves and is the largest exporter, can increase its production rate; and examples of commodities for which further processing is still at an early stag*..

Jan 1, 1985

By J. Levin

The Bond standard grindability test provides a Work Index that is widely used to estimate the energy required for grinding, but the test cannot be applied to fine materials such as plant tailings and middlings. For such materials, a comparative grinding test must be used in which a reference material from an operating plant is ground in a laboratory mill to determine the 'equivalent' energy consumption per revolution of the laboratory mill. As the Bond grindability test mill and its operating conditions are specified, its equivalent energy consumption per revolution should be a constant, here designated as B. Once B has been determined, the mill can be used to estimate the grindability of fine materials without the need for reference materials. A value of B can be calculated from any Bond grindability test, and 245 tests that were conducted at Mintek were examined to determine its value. A wide range of values was found, but most of them were grouped around 198 x 10- 7 kWh/rev, which is taken as the best estimate of B that is available at present. Values of B that are not close to this figure are obtained from materials for which the Bond grindability test gives misleading or 'spurious' Work Indexes. These spurious Work Indexes lead to the apparent departure of B from its true value. Some limitations of the Bond grindability test arise from its use of a mill without litters and of screening, instead of classification, to close the circuit.

Jan 1, 1989

By M. L. Young, J. B. See

Effective thermal conductivities of packed beds of chromite ores by M. L. YOUNG, B.Se. (Rand), M.Sc. (Rand) (Visitor) and J. B. SEE, B.Sc. (Hons), Ph.D. (New South Wales), M.I.M., M.I.M.M. (Member) The effective thermal conductivities in stagnant air of packed beds of fines, lumps, and indurated and pre-reduced pellets of two chromite ores with different chromium-to-iron ratios were determined in the temperature range 300 to I 100°C by the heat-sink technique. Packed beds of fines, whether of the size fraction between 20 and 65 mesh, between 65 and 100 mesh, or between 100 and 150 mesh, were found to have the same values of effective thermal conductivity. For one ore, the effective thermal conductivities of packed beds of fines between 20 and 48 mesh at tem peratures above 600"C were higher than those for finer particles. This difference is explained as being due to the increase in importance of radiation heat transfer, but no definite conclusions are reached about the relative contributions of conduction and radiation heat transfer to the effective thermal conductivities of packed beds of fines between 20 and 48 mesh. Two published models were used for the theoretical prediction of values for thermal conductivities of the indurated and pre-reduced pellets as well as of lump ore. The experimental and theoretical results were in good agreement in view of the uncertainties in the assumed values of emissivity and thermal conductivity of the chromite ore.

Jan 12, 1976

By L. W. Helle

In this investigation, which was conducted at the Metallurgical Research Plant, Lulea, Sweden, a series of experiments were carried out using a water-model to simulate the gas rinsing of a ladle containing liquid metal. The factors examined include the effect of gas flowrate, the position of a porous plug or lance, the immersion depth of the lance, and the geometry of the bath at the time of complete mixing. Mixing times were recorded by conductivity measurements. The results showed that there is a threshold level for mixing above which no advantage is to be gained from an increase in the gas flowrate. It is suggested that the results can be applied to rinsing ladles in working situations, the levels being approximately 270 dm3/min for 40 t ladles and 780 dm3/min for 150 t heats. The optimum siting of the lance or porous plug is a position that is three-quarters of the internal radius from the centre of the ladle with the lance penetrating as deeply as possible into the ladle. The best design of liquid bath is that having a diameter-to-height ratio of I. An equation was developed for the calculation, by dimensional analysis, of the time required for mixing during gas rinsing, and a comparison of the calculated mixing times with the results from production trials shows a satisfactory agreement (with a correlation factor of 0,91). Thus, an equation is available for the calculation of the stirring time needed to completely mix the bath in production situations.

Jan 1, 1981

By P. R. Jochens, D. D. Howat, A. A. Hejja

The effect of the reactivity of lime on desulphurization efficiency in the basic oxygen furnace A. A. HEJJA, Dipl. Ing. (Budapest) (Visitor) D. D. HOWAT, B.Sc. (Glas.), Ph. D., F.I.M. (Fellow) P. R. JOCHENS, Pr.Eng., M.Sc. (Eng.) Rand, Ph.D., A.I.M. (Member) The iron charged to the basic oxygen furnace at the steel plant of Highveld Steel and Vanadium Corporation has a relatively high sulphur content. Considerable emphasis is therefore placed on the reactivity of the lime. An investigation of the lime used at the steel plant showed that its reactivity had deteriorated considerably both during transport from the supplier (Northern Lime Company) and during storage and handling at the steel plant. The deterioration on the steel plant is the more severe, and is due to hydration and carbonation. Rapid deterioration is a characteristic of highly reactive lime when exposed to the atmosphere. Plant tests showed that the desulphurization efficiency decreases with a decrease in the reactivity of the lime. The addition of slag rich in manganous oxide to the furnace considerably improved the efficiency of desulphurization that can be achieved with limes of lower reactivity and with lime that has deteriorated. A decrease in particle size of lime of lower reactivity greatly increased the desulphurization efficiency. Less lime of higher reactivity is required for the same degree of desulphurization to be achieved. Lime of higher reactivity gives rise to slags with lower ferrous oxide contents and hence the steel yield is increased.

By P. J. Petit

The strategic mission of the South African mining industry is to extract the mineral assets in an energy efficient, economical and safe manner. Drilling has received particular attention in the last few years. As the operations move away from the power source, conventional and old drilling technology result in poor penetration rates, increased drilling shift lengths, slow face advances and limited stope efficiencies. The need for an alternate mining method, performed by a skilled workforce, to increase productivity, has led to the development of the electric rock drilling system for in-stope mining operations. The focus of this paper is a systematic evaluation of the electric rock drilling system as a function of production and technical parameters, in the platinum orebody. The particular electrical reticulation system is illustrated. Power usage, problems experienced, and solutions are described. The safe use of the recently developed drill is elaborated upon by describing protection devices. The testing and certification process, for approval by the recognized authorities, are documented. The testing and certification process, for approval by the recognized authorities, are documented. The human factor is also considered. Known detrimental factors of high noise exposure, vibrations levels and oil emissions are reviewed. In conclusion, recommendations on future strategies for the implementation of electric drilling technology within the mining and construction industries, is included.

Jan 1, 2006

Performance testing is often used by project owners and financiers to provide protection from, or assessment of, technical aspects of project design, procurement, construction and commissioning. The performance tests can range from comprehensive performance warranties relating to process performance and production in the case of lump sum turn key (LSTK) projects to less onerous demonstration tests for cost reimbursable contracts. This paper will discuss performance testing from both the contractor's and owner's perspectives and focuses on: ? when performance tests are required, ? what type of performance test/warranty is optimum for each type of project, and ? how project performance should be evaluated. The requirement for performance testing can be driven by the project financiers, particularly in the case of smaller resource development companies. In such cases, differentiation between owner's risk and contractor's risk can become contentious. At the other end of the spectrum, larger mining houses may choose to heavily influence the engineering and design process with the contractor supplying services on a reimbursable basis. In that case, the performance testing process is often limited to demonstration tests that validate performance for the owner's corporate governance requirements. This paper was prepared due to the lack of published benchmarking of performance testing and the resultant differences in expectations between a contractor and a project owner that often surface late in the contract negotiation process. The paper provides a checklist of requirements for both the owner and the contractor that may be used to provide `common purpose' early in the contract negotiation process.

Jan 1, 2007

Orebody modelling and reserve estimation are now subject to sophisticated procedures, but folded stratiform and stratabound deposits present particular problems in transforming coordinates of samples and blocks into their correct relative positions prior to deformation. In this paper an approach is taken whereby a geologically interpreted reference plane is used as a control. The study area is the Rio Tinto Minera copper mine near Santiago de Compostela, Spain. The transformation procedure on the 'unfolded' state is described, its limitations assessed and advantages considered.

Jan 1, 1987

By V. M. Lovell, N. P. Finkelstein

The concepts involved in flotation research are discussed and aims are presented. Three different method. of investigation can be used, all of which are applied at the National Institute for Metallurgy (N.I.M.), and these are the empirical, trial and error method, the chemical engineering method, and the physicochemical approachs This paper is devoted to the last of these. Because of the complexity of the physicochemical interactions involved, the work has, to a large extent, been concentrated on only one aspect, viz. the interaction between the mineral surface and reagents in solution, which was considered of major importance in the understanding of the process. The aspects on which work has been done are the concentration of uranium, the reaction between salt minerals and fatty acids, mixed xanthate-cationic collector systems, and the reaction between sulphide minerals and thiol reagents. Selected problems from the first two of these are discussed in some detail and deal with the agglomeration flotation of uranium and the chemical control of the flotation process for phoscorite. A detailed discussion is also presented of the progress made in the understanding of the interaction between sulphide minerals and thiol reagents, which is of more general application. Finally, an indication is given of the future direction of physicochemical research at the N.I.M.