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The environmental impact of solid waste materials is closely linked to their potential to produce a hazardous leachate once deposited in a landfill. This potential is conventionally assessed with simple laboratory batch leach tests, which find more and more frequent application also in the minerals and metals industry. Such tests are intended to help distinguish between high and low risk wastes, but are completely unsuitable to allow quantitative prediction or modelling of the long-term leachate generation potential. In the present approach the leachate generation process is perceived as a combination of bulk convective transport, stagnant zone and inner particle diffusion, as well as reaction kinetic effects. Model equations are formulated accordingly. A modelling frame work, WASTESIM, has been developed at UCT, which allows flexible combination of the model components and simulation of leach scenarios. Quantitative model parameters are obtained from a systematic laboratory study on the waste material in question. The combined assessment and modelling approach is demonstrated with a study on Cr (VI) leaching from a ferro-chromium slag material. Although not straightforward, the approach is particularly useful in determining long-term liabilities in the context of waste disposal sites with considerably more reliability than has previously been possible. Keywords: waste deposits, waste leaching, heap leaching, environmental, risk assessment, Cr (VI), ferro-chromium, slag.

Jan 1, 2000

By M. Gous

Namakwa Sands is a heavy minerals mining and beneficiation business in the Anglo Base Metals Division, and operates along the West Coast of South Africa. The business encompasses mining, mineral concentration, separation, and smelting operations. The smelting process comprises the carbonaceous reduction of ilmenite to produce titania slag with a TiO2 content of 86%, and iron with a carbon content of 2.5%. The Namakwa Sands smelter, situated near the Saldanha Bay harbour, commenced smelting operations in 1994, when a 25 MW DC-arc furnace was commissioned. The smelting operations were expanded in 1999, with the commissioning of a second 35 MW DC-arc furnace. Despite the fact that ilmenite smelting poses a technical challenge in terms of the high temperatures required, the physical characteristics of the slag, the constraints placed on the feedstock, and the tight product specifications, Namakwa Sands has continually increased slag production since 1995. High furnace feed-on utilization and furnace stability, complemented by continuous improvement drives, will be thevehicle to drive performance in the short-term, with longer-term performance enhancements due to strategic process development. Keywords: Pyrometallurgy, Namakwa Sands, ilmenite, DC-arc furnace, titania slag, pig iron

Jan 1, 2006

The processes by which particles and bubbles interact capture many of the central concepts of colloid science and hydrodynamics. This area of research embraces hydrodynamics, interfacial(including capillary) forces, particle and bubble behaviour and solution chemistry. In this review, we discuss collision, attachment and stability efficiencies. We deal with the identification of a flotation ?domain?, the deformation of a bubble surface upon interaction with a solid surface, the kinetics of three phase contact line expansion and the determination of attachment efficiencies through to the direct measurement of bubble-particle interaction forces. We have recently carried out a test of collision theory where the latter embraces both inertial and centrifugal forces. The real challenge is now to quantitatively describe the behaviour of real systems and to incorporate a reliable description of the behaviour of particles in flotation froths. The approach described is very robust when applied to flotation, both from qualitative and quantitative points of view, providing an intellectual foundation for understanding this complex process in separation science and technology.

Jan 1, 1999

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

This paper presents an initial investigation into the viability of co-kriging the grades of multiple mining cuts in a two dimensional, thin reef scenario. Deposits with gradational mineralized zones, in the perpendicular sense, are not as well served by the use of reef accumulation and thickness as deposits characterized by a sharp distinction between ore and waste rock. South African Bushveld Complex platinum deposits and Witwatersrand gold deposits are examples of this distinction. The calculation of an optimal mining cut is of paramount importance in the mining of Bushveld platinum. Two-dimensional kriging of a constant stoping width mining cut is an effective method for resource calculations once a cut is decided, but this begs the question of how to decide on the cut. Comparison of multiple cuts is used as a way of achieving this decision on many of Anglo Platinum’s operations. Although the kriging of each cut is valid in isolation, occasional negative values occur when incremental grades between overlapping cuts are calculated. Negative incremental grades cannot reflect reality. They are thought to be related to the inability of the method to include the strong continuity in the perpendicular direction demonstrated by the relevant variograms. Co-kriging of related variables has been investigated as a potential means tore impose this inherent order relationship. Various co-kriging options have been investigated. The method has been tested on a real data set from an established platinum operation. One of three types of anomaly has been investigated so far. The results show that co-kriging the mining cut grade as the primary variable, with just one secondary variable, the reef thickness, eliminates most occurrences. Severe anomalies remaining are arguably indicative of population mixing and might be more effectively treated by rezoning the data. Aim—To investigate the viability of co-kriging the grades of multiple mining cuts as a method for resolving anomalies in the estimation of such cuts on Bushveld platinum deposits, with applicability to other thin reef type deposits with a gradational not sharp cut-off between ore and waste in the direction perpendicular to the reef. Keywords: co-kriging, cross variograms, ordinary kriging, platinum, two-dimensional, grade profile

Jan 1, 2003

By R. M. Jara

This work evaluates and characterizes the impact of the support size and mining dilution of a block model in the operation and selection of equipment at an open pit mine. An exploratory analysis and geostatistical modelling of the grades assayed on a set of drill hole samples is performed, which allows constructing a grade model on a dense grid by means of a conditional simulation. The grades are then averaged to greater selective mining unit supports in order to proceed with the study and methodology. First, the metal-tonnage curves are used to analyse the loss of selectivity on the in situ resources caused by a change of support. Concerning the ore reserves and their mining sequence, defined in the pit optimization and analysis process, the same curves prove that the loss of selectivity is more accentuated. Second, the importance of the block boundary dilution produced during mining operations is assessed. Its value depends on the amount of ore in contact with waste, on the loading error of the equipment and on the ore loss/waste dilution criterion assumed by the planner. The dilution percentage and the differences between waste and ore grades become higher when the block size decreases. For these reasons, considering the dilution in the production plans makes mining a small support more constraining. An adequate delimitation of the orebody can improve the mining selectivity, leading to greater income. Finally, a study of the increase in mining cost that provides a zero difference in NPV between the different block size options is carried out, in order to determine the maximum increase in mining costs for which it remains profitable to mine at a smaller block size. Keywords: Mining selectivity, support effect, block boundary dilution, selective mining unit size, block model.

Jan 1, 2006

By R. G. Tarr

During an intense and accurate study of initiation systems used on an AngloGold mine, Mine A, poor drilling practices were revealed. Graphic results of all actual measurements taken are shown below. [ ] Accurate drilling of shot holes will determine whether a mining operation is payable or not and at what pay limit mining can take place. Losing 30 cm of a potential 120 cm-hole length will result in a number of consequences, i.e.: ?Higher stoping costs ?Drilling of one shot hole twice in every five shifts ?Increased explosive cost as a result ?Excess stress on hangingwall and footwall due to bad face shape ?Excessive blast damage before the area is worked out. No wonder we have such a high-risk operation. Drilling accuracy is crucial to the profitability on any mine as profits are directly related to the quality and utilization of the drilled shot holes.

Jan 1, 2000

By N. Kornelius

In recent years there has been an increased focus on corporate governance matters worldwide. The duties and responsibilities of directors of companies have come under close scrutiny, with shareholders increasing their demands for greater responsibility and accountability. Media attention and pressure groups have also had their effect. Governmental actions have supported these demands and directors have witnessed sweeping legislative changes imposing more onerous duties and liabilities than formerly imposed upon them at common law and in terms of the Companies Act. At the same time, the power of regulatory bodies has been increased to enforce this legislation and make someone pay to remedy an alleged infringement. Breach of such duties may incur personal or criminal liability, or both. Environmental protection legislation has become a particularly prevalent feature in this regard, and the number and complexity of statutes concerning the environment have increased over the past few years. Directors of South African companies will be familiar with relevant acts such as the National Environmental Management Act 107 of 1998; Conservation of Agricultural Resources Act 43 of 1983;Hazardous Substances Act 15 of 1973, as well as the National Water Act 36 of 1998. Now the directors of mining companies are faced with the Mineral and Petroleum Resources Development Act 28 of 2002.

Jan 1, 2003

By S. Mundike

A scraper-based block cave method has been successfully applied to extract the Lower orebody at Nchanga since the 1950s. Since inception, scraper drifts and service ways have been supported using steel arch sets fabricated to a specific design from high strength manganese steel To reduce costs and to improve productivity, trials commenced in 2002 using fibre reinforced shotcrete as an alternative support method. One of the areas, the 2420 8E 1C trial drift, was subjected to abutment loading for several months prior to undercutting and cave mining. Shotcrete installed exhibited minor cracking shortly after application but very little deterioration thereafter. Following the success of the trial, the application of fibre-reinforced shotcrete was extended to other drifts. This paper describes the application of fibre-reinforced shotcreteat Nchanga and outlines design and quality assurance methods employed.

Jan 1, 2005

Leinster Nickel Operations, located in Western Australia, consists of an underground and three open pit mines in relatively adverse ground conditions. This paper reviews our ground control practices in the open pits, covering aspects of ground support, wall control and monitoring. These methods have been effective in allowing mining operations to continue beneath unstable slopes. In particular, the use of Ground probe?s slope stability radar has enabled the Harmony open pit to safely operate for months following indication of failure from traditional methods. This case study highlights the benefits of investing in appropriate slope stability monitoring systems.

Jan 1, 2006

By J. L. Deutsch

Block model estimates are commonly calculated by the well-established technique of kriging. The mathematics are well established, but implementation details require site-specific considerations. Checking and measuring the performance of the estimates is important to ensure the block model is suitable for its intended purpose. There are different criteria for long-term planning and short-term planning. The implementation of kriging should be checked with cross-validation and assessed for conditional bias and departure from theoretical optimality with the calculation of kriging efficiency. A new expression of kriging efficiency, which compares the kriging variance with the theoretically optimal kriging variance, is developed to aid in this assessment. The assessment tools presented here can be applied in a number of situations; however, ordinary kriging with a reasonably large search performs well in most cases.

Jan 1, 2014

In extracting base metals from orebodies, sulphide as well as oxide, the main environmental concern is sulphur, whether in the form of sulphurous gases or sulphate in liquid form. Generally sulphur is in over supply in developed countries mainly because of strict legislation to capture it. In developing countries, on the other hand there is usually a shortage of sulphur because of less strict environ-mental legislation. Africa falls in this second category and the African continent imports substantial amounts of sulphur, despite the fact that large quantities of sulphur are emitted by smelters, thermal power stations, coalmines, fertilizer manufacturers and others. Other than making acid from gaseous emissions, existing methods to capture sulphur from gaseous and liquid effluents are uneconomical and it ends up in the environment either as ammonium sulphate (from gaseous effluents) or as gypsum (from liquid effluents). The CSIR?s Environmentek and Key Structure Holdings have developed a process whereby gaseous sulphur emissions and sulphates in liquid effluents can be economically captured and converted into elemental sulphur and metal carbonates. The elemental sulphur is of high purity as it is precipitated from a gas stream and is readily marketable. The metal carbonates (barium or calcium) can be recycled back to the process or marketed. The only harmful by-product of the process is carbon dioxide. Should natural gas or methane be available, the carbon dioxide could be reduced by about one third. Should solar, wind or hydro energy be available to generate hydrogen, the carbon dioxide emissions would be zero. Employing this technology could make Africa independent of sulphur imports and furthermore reduce the impact of acid rain and seepage of sulphate from gypsum and other waste dumps into the environment.

Jan 1, 2005

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

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 R. Scott

This article describes and evaluates the establishment of Kuyasa Mining including the search for a suitable deposit, the ongoing lack of finance, and market constraints. Despite the dramatic initial growth and success of their Ikhwezi Colliery near Delmas, Mpumalanga, Kuyasa?s experiences offer some sobering arguments for significant changes to mineral rights ownership, the attitude of financial institutions and government policy if South Africa is to have a dynamic and successful junior and small-scale mining sector.

Jan 1, 1998

The coal-based power generation industry faces increased pressure from all sectors to improve its environmental performance. This is due to increased awareness of and concerns regarding greenhouse-and acid-gas emissions, toxic metal releases (to both air and water) and water availability. A methodology to assess this industry?s environmental performance is needed. Such a methodology should assess all environmental impacts accurately, recognizing the irspatial and temporal dependence, and taking into account the social acceptability of technologies employed. Here, we develop a methodology to determine the environ-mental impact associated with solid wastes generated by this industry, and apply this to the specific case of ash management. More specifically, the case study compares the environmental footprint of an ash deposit for a number of operational water management scenarios. The methodology considers leachate generation processes from ash impoundments to obtain a time-dependent concentration profile of mobile constituents at the interface between the ash impoundment and the surrounding environment. This leachate prediction modelling is subsequently linked to plume dispersion modelling tools to determine the fate and transport of leached components, predominantly salts, into groundwater. Together, these provide a measure of the extent to which a land mass is affected by leachate migration from the deposit. To determine the exact boundary between regions of acceptable and unacceptable risk to the environment, we use Ecological Risk Assessment concepts. In this way it is possible to obtain a time dependent affected land footprint which could be used as an indicator of the environmental impact of solid waste management practices. This information can be included in a set of environmental criteria which form the basis of an overall environ-mental impact assessment, using tools such as Life Cycle Assessment (LCA). The value of LCA is that its structure is consistent with accepted models of environmental decision making, where different approaches to valuation in impact assessment assist in prioritizing impacts on the basis of their perceived significance. The proposed ?affected land footprint? metric represents a significant improvement over current LCA impact indicators for solid waste management practices. Keywords: Environmental Impact Assessment, Environmental Risk Assessment; Life Cycle Assessment; coal ash; leachability; salinity

Jan 1, 2002

It is well known that the electrochemical precipitation of metals from aqueous solutions is conducted by the electrochemical standard potential scale. This scale indicates the order of nobility of different metals. Consequently, the standard potential scale shows the nocivity of metals when they are present as impurities in aqueous solutions containing metals. In the hydrometallurgy of cobalt, nickel and zinc are co-deposited during cobalt electrodeposition. Nickel has almost the same chemical, physical and electro-chemical properties as cobalt. Furthermore, the electrochemical potential of nickel is relatively higher than that of cobalt. For this reason nickel is preferentially reduced at the cathode in the presence of cobalt. The presence of small amounts of zinc in solution leads to contamination of cobalt electrowon. In spite of its lower electrochemical potential in comparison to cobalt, zinc is reduced on the cathode because of its higher hydrogen-overvoltage. But, in the hydrometallurgy of zinc, small amounts of cobalt present solution will contaminate the zinc reduced at the cathode. This is easily explained by the fact that cobalt is more electropositive than zinc. The co-deposition mechanism of sulphur at the cathode is not yet well understood. Great attention has to be paid to the mechanism of co-deposition of sulphur during cobalt electrolysis. This work aimed to investigate the influence of some parameters on the co-deposition of nickel, zinc and sulphur during cobalt electrowinning. The following parameters have been investigated: Co2+concentration in the electrolyte, current density and ammonium sulphate (NH4)2SO4additions. It has been established that important nickel, zinc and sulphur co-deposition takes place at relatively low Co2+ concentration in solution. The behaviour of these elements with regard to the cathodic phenomena has been established.

Jan 1, 2005

By C. F. Vos

Small replacements of C12-trithiocarbonate (C12-TTC) for dithiocarbonate (DTC)/dithiophosphate (DTP) in a reagent suite for the flotation of platinum group metals (PGM) have significantly improved the rejection of gangue. Coupled to this is an improvement in kinetics, grade and recovery of PGMs. In a pilot-plant trial, after a 5 mole per cent replacement of the current DTC/DTP collector combination by C12-TTC, large opaque bubbles were replaced by small clear ones. In addition, a similar flotation response was realized with one-third of the current depressant dosage. During a preliminary plant trial on underground UG2 ore, the initial rougher concentrates were characterized by higher PGM concentrate grades and this was in part due to improved chromiter ejection. The concentrate produced from the TTC trial also exhibited a much finer particle size distribution. The overall circuit performance, which included secondary regrind and flotation, showed an increase in concentrate grade of approximately 44% while the tailings grade remained unchanged

Jan 1, 2007

By Manoj Kumar, S. Ranganathan, S. N. Sinha

The reducibility of three different manganese ores with coke was studied. The three ores were reduced to different extents under the same experimental conditions. The investigations showed that in the temperature range of 900-1000 ×C, Fe2O3 in the ore was reduced to metallic iron. MnO2 was reduced to Mn3O4 in all cases except one in which it was reduced to Mn2O3. The kinetics of reduction was controlled by different mechanisms in the different ores. Temperature had a significant influence on the reducibility of the ores.

Jan 1, 2007

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