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By M. D. Dolan

In this study, the development of a new method for investigating the diffusion of metal cations in multi-component slag systems, using microprobe analysis is discussed. This method allows the analysis of the diffusion of multiple species within a single system. This project has focused on the diffusion characteristics of manganese, iron, calcium and silicon in silicate slags, in order to simulate industrial steel and ferromanganese production. The diffusion behaviour of transition metals is of particular interest because of the effects of their variable valence. This study identified the variation in diffusivity of slag components with changes in composition and temperature of multi-component slag systems. The molecular structure of the experimental calcium-aluminosilicate slags was investigated to determine the chemical and physical properties that influence diffusion behaviour. This experimental data was used to develop predictive models for diffusivity. These models enable the estimation of the diffusivity of many slag components in complex slags, over a range of compositions.

Jan 1, 2004

By B. P. Watson, A. Carpede, W. O. Kekana, N. Fernandes, W. Theron, M. P. Mahlangu, G. Betz

The research described in this paper was done to confirm the Upper Group 2 (UG2) PlatMine peak pillar strength formula (Watson et al., 2007), which was determined from a back-analysis of failed and unfailed pillars. Underground measurements were made on a stable pillar that was loaded by firstly reducing it’s length and then by mining the surrounding pillars until pillar failure took place. The pillar was instrumented with suitably positioned strain cells and closure meters, which allowed both the average pillar stress and strain to be determined. The paper describes the methodology applied to identify a suitable position for the instrumentation, as well as the results. A stress/strain curve is presented for a UG2 pillar with a w/h ratio of 2.0, at Booysendal Platinum Mine. The measured pillar strength was similar to the predicted strength using the PlatMine pillar strength formula for UG2 pillars. The PlatMine formula has been successfully implemented on Booysendal Platinum Mine, and about 3 670 pillars have been cut without a single failure. An additional revenue of US$1.3 billion was calculated for the 25-year life of the mine as a direct result of the improved pillar design, given the January 2020 platinum group metals basket price. An extended life of mine and better mining efficiencies will also be realized.

Aug 1, 2021

By A. J. Van Der Merwe, N. A. Barcza, M. Boyes, N. R. Clarke

Oriel Resources has with the support of SRK (Cardiff) and DRA and Mintek (South Africa) carried our a Definitive Feasibility Study (DFS) to recover high grade chrome ore from its Voskhod deposit very close to Chromtau that is near to Aktobe in Kazakhstan. Voskhod is a large podiform ore body that contains nearly 20million tons of chromite grading about 48% Cr2O3 and with a Cr/Fe ratio of over 3/1. Selected bore hole core samples were obtained from the confirmation drilling programme during the DFS phase of the project in 2005 for pilot plant test work to design the mineral beneficiation plant. The chrome ore is characterised by four main types, namely high grade lumpy and chip sized ore, high-grade fine ore, lower grade (subordinate) lumpy ore and lower grade fine ore. Gravity separation tests carried out by Mintek showed that the large density difference between the high grade (at over 3.7t/m3) and lower grade ore (at less than 2.97t/m3 ) should ensure very good separation in the DMS drum and DMS cyclone stages resulting in high recoveries of Cr2O3 - rich chromite ore products. Very high chrome ore grades of up to 64% Cr2O3 and Cr/Fe ratios of 4 to 1 were obtained at an 80% mass yield from selected samples of lumpy and chip ore size fractions. The overall predicted recovery from the design work on the mine and plant is expected to be closer to about 70% of the ROM (Run of Mine) feed. DRA has completed the design of the mineral processing plant to recover about 900 kt/a of chrome ore from the 1.3 Mt/a of ROM feed. The plant has been sized to handle up to 1.5 Mt/a and will also be able to address the variability in ore feed as different regions in the deposit are mined. The lumpy high-grade product and the chips size fraction is expected to grade around 48% Cr2O3 and the fine concentrate between 56 and 58%Cr2O3 The ratio of products is expected to be about 70, 15 and 15 percent respectively but will vary to some extent during the expected 20 year life of the mining operation based on including the associated adjacent Karaagash deposit together with the Voskhod deposit. The prediction of the product split from the processing plant depends on many factors such as the geology, mineralogy, mining, handling and metallurgical processing. An overall process flow model has been developed that covers the ROM ore, the various types of chrome ore feed to the mineral beneficiation plant, the projected products and the subsequent smelting of the chromite ores to produce High Carbon Ferrochromium. The model allows the optimisation of the quality of the chrome ore in terms of Cr2O3 content, Cr/Fe ratio and recovery to be studied. This information can also be evaluated in terms of the economic requirements for smelting High Carbon Ferrochromium (HCFeCr) at a given location. Oriel is planning to supply chrome ore to Ferrochrome plants mostly in China and Russia. The use of the model will assist to maximise the value of the Voskhod project to its owners and also assist the users of the chrome ore in selecting the appropriate supply quality to meet their needs for a given smelter operation. The smelting of high grade Voskhod ore requires a limited addition of about 5 to 7% quartz to flux the MgO and Al2O3 and about 25% coke as a reducing agent to produce an alloy containing from about 65 to 74%chromium depending on the Cr/Fe ratio.

Jan 1, 2007

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 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 D. G. Krige

For the purpose of determining confidence limits for ore grade estimates, an extensive simulated database was used, which included 1728 ore blocks with ?actual? grades and the corresponding estimates based on ordinary and simple kriging. The practical results show that conditional unbiasedness is essential and that acceptable confidence limits can then be set using Normal theory for the simulated error distribution based on the logarithms of the ratios of ?actuals?/estimates with a variance related to the kriging variance. The mean of the data used to prepare the variogram and the estimated block grade are to be used properly in this approach. A practical analysis was also done of the actual point and block data from a very large mined out Carbon Leader area. The distributions of the actual grades for two levels of block sizes with different levels of variability were fitted using three models, ie. two three and compound lognormal. The trends of tonnages, grades and relative profits for a range of pay limits, as well as the usual tonnage-grade curves, show a practical insensitivity for the choice between the three lognormal models considered.

Jan 1, 2004

The practice of pumping gases which inhibit combustion for purposes of controlling or extinguishing mine fires is now universally accepted. The practice has been used many times in coal mines in India and the experiences are reviewed. The procedures relating to a membrane based nitrogen generator and to a combustion gases generator are described. The physical properties, practical requirements and economic implications of using different gases is briefly reviewed. Some aspects of the practice as related to mine fires in certain collieries in other countries are dealt with.

Jan 1, 2000

By N. Ogbonna

A mathematical model for bioleaching at the agglomerate scale is developed. The agglomerate is defined as a unit volume of a heap which contains a solid phase (a size distribution of ore particles), a liquid phase (stagnant and flowing leaching solution) and a gas phase (flowing air and air pockets). Leaching at the level of an ore particle is modelled using a diffusion-reaction equation, and oxidation by attached and detached microbes is treated separately. With the aid of the mathematical model, the effect of particle size distribution on the bioleaching of an ore containing a mixture of chalcocite and pyrite, and a culture of iron oxidizers, is investigated.

Jan 1, 2006

By J. W. Drelich, H. Zeng, L. Xie, X. Cui, Z. Gao, M. Tian, Y. Hu, W. Hu, W. Sun

Flotation is a mineral separation technology that uses the surface hydrophobic difference of valuable minerals and their associated gangue minerals to separate them. The flotation collector adsorbs on the valuable mineral surface to improve its hydrophobicity, and metal ions are usually used as activators to enhance the collector adsorption. Different mineral surfaces show different charging properties and adsorption behaviours with the collector or metal ions. Moreover, the order of adding metal ions and the collector also show significant and different flotation performance for the same mineral. The adsorption or flotation behaviour or both are governed by mineral surface chemistry, such as surface charging and reactivity. In our recent studies, force measurement using atomic force microscopy (AFM) was employed to study the surface charging and adsorption mechanism of metal ions and collectors. By preparing collector-functionalised AFM tips, AFM can directly measure the adsorption strength of the collector on the mineral surface to determine the anisotropy of mineral surface reactivity. The preparation of collector-functionalised AFM tips provides the foundation for further study of the activation role of metal ion in the collector adsorption. The application of AFM for force measurement in the surface chemistry of mineral flotation can provide important information on developing flotation reagents and lays the foundation for the specific regulation of mineral surface characteristics. Keywords: Scheelite; flotation; surface chemistry; AFM force measurement

Jan 1, 2020

This paper pays tribute to the pioneers in geomechanics, and addresses some of the most pressing issues of our time related to deep mining, and how to mitigate these issues. Solutions developed by our predecessors seem to have reached their limits as mines continue to go deeper. The International Society for Rock Mechanics (ISRM) guidelines for rock mass characterization for excavation design also require re-thinking to reflect current knowledge and experience. Thus, a whole new approach is urgently required to increase mine safety and productivity. The paper will draw on the challenges and experiences in medicine and science that have been overcome through genuine collaboration, advances in technology, and impressive funding, which can be adopted to provide solutions to contemporary geomechanics challenges for increased safety and productivity as mines continue to go deeper.

Jan 1, 2014

By H. Pei

PZH (Pan Zhi Hua) Iron and Steel (Group) Corporation, the biggest steel company in southwest China, has been using titanium-vanadium-magnetite as the main raw materials for blast furnace iron making processing for over 30 years. One of the problems that has a negative affect on the blast furnace operation is slag foaming. Based on the chemical components of the blast furnace slag-bearing higher TiO2, the foaming properties were studied. The TiO2content, which is calculated according to the total titanium content in all the forms of titanium compound in the slag, in this research is 30% weight per cent. Different forms of titanium compounds have different actions on the slag foaming behaviour that depends on the reduction condition in the blast furnace. The relationships among slag foaming performance and the binary alkalinity of the slag, the content of CaF2, MnO in slag, and the amount of gas injected in slag are investigated. The results show CaF2 and MnO have a stronger anti-foaming affect on the slag, even in the lower percentage. The way to measure high TiO2slag foaming performance and how to eliminate foamy slag are also discussed. Keywords: blast furnace slag bearing TiO2, foamy slag, foaming performance

Jan 1, 2004

By J. Nell

An overview is given of the matte melting process used for the beneficiation of South African Platinum Group Metal (PGM) ores. Most producers use six-electrode furnaces to melt the concentrate and Pierce Smith converters to oxidize excess iron sulphide from the furnace matte. Concentrates from two reef-types (the so-called Merensky and UG-2 reefs) dominate the feedstock supply. Concentrate from the Merensky reef is low in chromium and do not pose significant melting problems. Concentrates from the UG-2 reef contain much higher levels of chromium, which results in the formation of chromium-rich spinels during melting. This is attributed to the low solubility of chromium in furnace slag under typical operating conditions (an oxygen partial pressure of 10-8-10-9bar at temperatures of 1550°C to 1600°C). During the converting process care is needed to avoid excessively oxidizing conditions, which result in cobalt, nickel and copper losses to the slag. High nickel losses result in the formation ofFe2NiO4(trevorite), which often forms solid solutions with FeCr2O4and Fe3O4. In future, the main challenge in the processing of South African PGM ores will be to cope with ever increasing levels of chromium in the concentrate. A short-term solution to the problem would be to melt the concentrate under slightly reducing conditions to promote the formation of CrO, which is more soluble in the slag than Cr2O3. A longer-term solution to the problem would be to abandon the current matte-smelting process in favour of an alloy-based process, which would offer total flexibility with respect to the amount of chromium that can be tolerated in the feed. Key words: Merensky, UG-2, furnace, slag, matte, converting, spinel, chromium.

Jan 1, 2004

By M. Syamujulu

In 1994, Nkana smelter commissioned a multimillion US Dollar Chilean Teniente converter (CT) in its operations in order to improve its smelting technological base. The main objective was to reduce the overall smelting energy costs and increase the sulphur capture for sulphuric acid production to support the company?s leaching operations at Nchanga tailings leach plant. A decade of CT operations have since ensued following its installation and start-up. This paper provides a technical and operational audit of the performance of the CT in the first 10 years of its operations at Nkana smelter.

Jan 1, 2005

By L. S. Jeffrey

Estimates for South Africa?s coal recoverable reserves made in 1999range from nine to 59 billion tons; latest estimates by the Minerals Bureau suggest that 33 billion tons is a more likely figure. As much as 70% of that coal is located in the Waterberg, Witbank, and Highveld coalfields, as well as lesser amounts in the Ermelo, Free State and Springbok Flats coalfields. However, the Witbank and Highveld coalfields are approaching exhaustion (estimated 9 billion tons of recoverable coal remaining in each), while the coal quality or mining conditions in the Waterberg, Free State and Springbok Flats coalfields are significant barriers to immediate, conventional exploitation. New extraction technologies, technologies exploiting the energy content of the coal in situ, as well as suitable uses and markets for low-grade, high-ash coal are required before the country can utilize its admittedly vast coal resources. Major challenges for exploiting some Limpopo province coalfields are severe water shortages, insufficiently developed infrastructure, fragile environments and poor roof conditions due to the depth and complex geology. In the Central Basin (Witbank, Highveld and Ermelo coalfields) technical innovations for thin seam extraction, economic mining of both pillar coal and intrusion-fragmented resource blocks and the utilization of lower-grade coals are required. The success of the fluidized bed combustion technology is necessary to utilize the low-grade coals of the Free State and Molteno coalfields, while environmental exemption for past problems, together with strategies for mining small, disjointed thin-seam resource blocks, is required in KwaZulu-Natal. Clean coal technologies, coal cost and quality, environmental considerations, sustainable development, the growth of the South African economy and Government?s regulation of the electricity industry are the main challenges to the continued use of coal as South Africa?s primary energy source.

Jan 1, 2005

By A. W. Breed

The bioleaching of arsenopyrite, the oxidation of arsenate and the precipitation of ferric arsenate are competing reactions, hence their rates depend on the relative concentrations of the respective species, and the activity of the bacterial culture. Bacterial arsenic resistance may be attributed to the Pst+Pit-mutation and an energy dependent efflux pump. Pst+Pit-mutations result in a reduced uptake of arsenate. This enables the bacteria to survive in solutions in which the arsenate concentration is significantly higher than the arsenite concentration. However, the excretion of arsenate requires energy. Therefore, in the absence of an energy source or during periods of reduced bacterial activity, the inhibitory effect of arsenate may manifest at concentrations to which the culture has been adapted. The chemical ferric leaching rate of pyrite and arsenopyrite decrease with a decrease in the solution redox and may be described using a modified Butler-Volmer equation. The bacterial ferrous-iron oxidation kinetics of L. ferrooxidans also depend on the redox potential, and can be described using a Michaelis-Mententype model modified to account for both temperature and pH. A model developed using the independently determined ferric leaching, and ferrous-iron oxidizing kinetics, has been shown to compare well with the experimental data for the continuous bioleaching of pyrite. Keywords: Leptospirillum ferrooxidans, arsenopyrite, bioleaching, sulphide minerals ferrous-iron oxidation kinetics, ferric leaching kinetics, redox potential

Jan 1, 2000

By D. Xie, S. Sun

An overview of recent development of CSIRO?s Multi-Phase reaction models will be presented with examples comparing the calculated physico-chemical properties of metallurgical slags with the existing experimental data. The paper will also outline the development of a kinetically based model for molten bath reactors and its application to submerged combustion of coal in a slag bath as well as the reaction between the slag and injected coal particles. The plume model combines established models for the combustion of pulverized fuel with models for the growth and rise of bubbles from a lance or tuyere. This model predicts the extent of de-volatilization and combustion of the coal in the plume, the utilization of oxygen and the exchange rate of oxygen between the gas and the bath as well as the heat transfer rate between the gas bubbles and the bath. The slag reduction model brings together the recently measured rate data and fundamental understanding of the kinetics of CO-CO2reaction with iron oxide containing slags and predicts the changes resulting from injection of coal particles into molten slags. The top-space model covers reactions between gases and molten droplets in the post-combustion zone, where heat and mass transfer between phases results in higher utilization of the fuel values in the partly oxidized gases and transfer of heat to the molten bath. Keywords: Phase equilibria, viscosity, electrical conductivity, slags, kinetics, reaction rate.

Jan 1, 2004

By J. F. Curtis

In the synopsis, the author concludes that ?high levels of seismicity do not coincide with high rockburst rates?. Implicit to an appreciation of this statement is the necessity of a common understanding of what is understood by the terms: ?high level of seismicity? and ?high rockburst rates?. With respect to the former term there is no difficulty in that the level of seismicity is traditionally measured in terms of the Richter Scale. The latter term however presents a problem in that the author defines it as a particular sort of seismic event?viz: ?Rockburst? is understood as a seismic event that causes damage to an underground excavation with subsequent injury, loss of material/equipment or production shifts? (p. 322). No scale is given of the amount of: ?excavation damage ?level of injury ?material/equipment loss ?production shifts lost whether separate or cumulative, for a particular seismic event to be classified as a rockburst. A further difficulty arises in that in common usage the words ?rockburst?, ?seismic event? and ?earthquake? are all used to describe the same event.

Jan 1, 1999

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 F. T. Cawood

The new South African Mineral Policy has major implications on the way mineral rent will be collected and shared between the stakeholders in future. Although the policy does not supply details on how this will be done, drastic departures from practices under the previous dispensation require a new approach. For example, there introduction of the ?right to mine? principle implies that the repealed lease consideration concept will be expanded to all minerals. The new policy also makes provision for predetermined standard terms and conditions for all prospecting and mining permissions. It also states that, regardless of whether the mineral rights are state or privately-owned, all prospecting fees and mineral royalties will be determined by state officials after consultation with the registered holder of the mineral rights. This paper proposes a standard mineral royalty formula that complies with the principles mentioned in the White Paper and has been shown to be internationally competitive.

Jan 1, 2001

By J. P. Bergh

The advent of low-quality export coal demand has brought a new range of possibilities to the South African coal industry. Products that traditionally were only of value to the domestic or combustion industry sectors now have the potential to be exported, with only minor amounts of upgrading required through beneficiation. Comparatively high steam-coal export prices can be obtained for lowquality export coal, which enhances the economic feasibility of expanding low-quality thermal coal exports. There are, however, increasing concerns about the feasibility of lower quality thermal coal exports and the broader implications. These concerns relate to the environmental impact of low-quality thermal coal production for export and the inherent threat to the security of domestic thermal coal supply in South Africa. Against this background, this paper serves to explain the extended value chain in the production of export coal. The technical and economic advantages and disadvantages of low-grade exports versus coal production for domestic use are evaluated. The value chain estimation is calculated by the beneficiation modelling and characterization of two coals. Based on the value estimation, the lowgrade export production scenario, and finally the modelling of potential pollutant distribution, are described. Keywords coal beneficiation, techno-economics, thermal coal, dense medium processing, dry processing, fine coal processing, environmental impact.

Nov 1, 2013