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By J. N. Van der Merwe

Due to the approaching depletion of reserves in the Witbank Coalfield, and the fact that the Waterberg Coalfield is as yet under developed, there is increasing pressure to extend the lives of the operating coal mines in the Witbank Coalfield. One potential source of coal is the old pillars, often small and at shallow depth, that were not left with secondary extraction in mind. At face value, some of these pillars appear to be suitable for secondary mining due to their high safety factors. However, it is known that over time, these pillars have scaled and the current sizes are smaller than the as-mined dimensions. It is also known that at shallow depth, the overburden is often less likely to fail during secondary mining, resulting in high abutment loads on the unmined pillars. The paper proposes a systematic method to pre-evaluate those old pillars for the possibility of stooping. The method consists of elements of fundamental methods and newly developed technology. In essence, it revolves around using empirical methods to estimate current pillar dimensions, followed by numerical modelling to investigate the probability of progressive pillar failure and then fundamental methods to determine the limits of applicability of the numerical model.

Jan 1, 2012

By J. H. Zietsman, M. W. Erwee, P. J. A. Bezuidenhout, Q. G. Reynolds

"Pyrometallurgical furnaces are tapped through tap-holes that are opened with drills and oxygen lances. The lance is often used on its own or as the last step of opening the tap-hole. Interaction of oxygen with molten material inside the tap-hole can occur, and is a phenomenon that is not well understood. As part of a study that focuses on the effect of lancing on flow inside and around the furnace tap-hole, a cold-model validation was done. The validation study focuses on validating the MULTIPHASEINTERFOAM multiphase flow solver in OpenFOAM® for the problem involved. The sensitivity of the model to different materials properties (viscosity and density in particular) is presented with both cold models and the results from flow simulations in OpenFOAM®. IntroductionMany pyrometallurgical operations are carried out in furnaces where molten material accumulates continuously. Once enough material has accumulated and is ready to be removed from the furnace, material is tapped through one or more tap-holes in the furnace. Tap-holes differ significantly in both geometry and materials of construction, depending on the process involved – examples of different types of tap-hole configurations can be found in, for example, Nelson and Hundermark (2014). Tapholes all share one common feature: they are high, wear areas of the furnace. Molten material at high temperature flows through these areas, after which the tap-hole is sealed, usually using tap-hole clay. The purpose of the tap-hole clay is to harden inside the tap-hole and seal it until the next tap.Once ready to tap, a pneumatic drill and/or oxygen lance is used to open the tap-hole. The extent of lancing a furnace tap-hole depends strongly on the type of furnace. In, for example, many blast furnace operations lancing is limited as much as possible, and done only if drilling was not effective. In other operations, such as on small-scale pilot furnaces with short tap-holes, only lancing is used to open the tap-hole."

Jun 1, 2019

By M. Kawakami, K. Suzuki, T. Takenaka, S. Yokoyama

Molten NaNO3-NaNO2-KNO3mixture is used as a heat transfer medium at high temperature. One of the most important properties of this mixture is the heat capacity. In the present work, the enthalpy change with temperature was measured by the drop calorimetric method to evaluate the heat capacity. The results are summarized as follows: The enthalpy of the mixture increased linearly with the temperature. From the slope of the line, the heat capacity was evaluated. The heat capacity of pure NaNO3, NaNO2and KNO3was 0.129,0.110 and 0.142 kJ/mol/K, respectively. These values are in fairly good agreement with the published data. In the binary and ternary systems, the molar additivity of heat capacity, which is well known as Neumann-Kopp’s law, was obtained. The heat capacity of HTS1and HTS2, which are well known ternary mixtures of practical use, were in the range of published data.

Jan 1, 2004

By R Kroukamp

Horizontal belt filters are typically used for separation of relatively free filtering solids where good post treatment is required. He horizontal belt filter is a continuous filter with an endless cloth supported on a grooved carrier belt. The belt and cloth are driven around two rollers across a series of evacuated suction boxes. The feed suspension is introduced at one end of the filter and deliquored to produce a cake at the other end. The benefits of using horizontal belt filters are good cake washing, continuous and visible processing, fully automatic operation, flexibility, high capacity and relative high speeds of operation. If required, horizontal belt filters enable efficient counter-current washings to minimize the usage of wash liquid. The horizontal belt filter has applications in the following: [? Metal concentrates ? Mineral sands ? Tailings ? Coal ? Iron ore ? Alumina ? Chloride processing ? Nickel and Cobalt refining ? Platinum group metals ? Zinc processing ? Many other applications in the Mining and Metallurgy industries ] 2. Operating Principle of a Horizontal Vacuum Belt Filter 2.1 Cake Forming The slurry to be dewatered is evenly distributed onto the filtering surface. Gravity assists the cake formation and the feed can be introduced in multiple stages. 2.2 Cake Washing Once the cake is formed, wash liquor/water can be introduced onto the top of the cake via a wash launder or sprays. Multiple wash stages, co-current, counter-current or direct washing can be added by increasing the length of the filter.

Jan 1, 2007

By P J. Fourie, J R. Walklate

Gravity separation techniques have been in use in the mineral sands industry for decades; from the Reichert cone to Wilfley tables, Wright sluices and the Kelsey Jig, all attempting that elusive perfect gravity separation. Just as the gravity separation industry evolved, Richards Bay Minerals also evolved in their use and approach to gravity separation. This paper discusses the history of gravity separation at Richards Bay Minerals and briefly comments on future developments. History Primary Concentration Richards Bay Mineral?s (RBM) first mining concentrator and mineral separation plant commenced operation in 1977 to process ilmenite, rutile and zircon bearing dunal deposits along the northern Natal coast. The orebody contained a greater proportion of non-valuable magnetic heavy mineral in the SG range of 3 to 4 compared to West Australian and Florida USA deposits, making mineral separation more difficult(1). The deposit was mined using two dredges feeding a floating 2000 tph concentrator. Concentrator feed was screened and fed to two four-stage circuits consisting of primary, scavenger, cleaner and recleaner Reichert cones [see Figure 1]. The primary units were fed at a rate of 80 tph and a density of 60% solids by weight.

Jan 1, 2006

By J J. McEwan

Silver tarnishes readily in common atmospheres and is accelerated in humid atmospheres. Tarnish is the formation of silver sulphide on the surface of silver when it is exposed to a wide range of sulphur-containing atmospheres. Tarnish is unattractive and highly undesirable, and can be removed either with a silver polish or a chemical dip. Dips are generally only recommended when heavy black tarnish cannot be removed with a polish, and care must be taken during cleaning because these can contain aggressive chemicals and give off hazardous and unpleasant smelling fumes. Polishes work best for large areas of plain undecorated silver, and form part of a regular cleaning programme. Some polishes contain chemicals that inhibit tarnishing, but these generally only have a short life. Several methods have been developed to reduce tarnish formation on Silver; these include alloying, surface treatment, and coatings. The authors evaluated a range of self-assembled monolayer (SAM) surface treatments and coatings in earlier research. Four treatments/coatings increased the time to noticeable tarnish by more than ten fold, and the results were reported at the International Corrosion Congress (ICC) in 2005, and at the Mint Directors Conference (MDC) in 2006. SAM treatment using 95% 1-hexadecanethiol (C16H34S) was found to give good anti-tarnish performance and showed potential for the commercial treatment of Sterling silver. Therefore research was performed to optimise the methods of application of this type of coating to provide an easier, faster, and more-user friendly technique to provide an anti-tarnish treatment. Keywords: silver, tarnish resistant coatings.

Jan 1, 2006

By B. Andresen, S. T. Johansen, H. Tveit, S. Grådahl, B. Ravary

The Norwegian ferroalloy industry has high ambitions regarding environmental standards. Basic research work has been performed to improve the fundamental understanding of ferroalloy processes and the environ-mental aspects. This paper will present work dealing with the understanding of formation and control of NOx, PAH and dioxins. During this work various techniques and methods have been applied, such as comprehensive industrial measurements, laboratory experiments, model development and application of Computational Fluid Dynamics (CFD). The main goal has been to reduce the environmental impact of ferroalloy plants, by means of improving the combustion processes done by introducing new charging routines and optimized furnace operations, instead of installing expensive gas treatment systems. The Norwegian obligations in accordance with the Gothenburg protocol are to reduce the NOx emissions by 30%, compared with the 1990 level within 2010. Measures developed in this work have resulted in 40-60%reduction in NOx emission, and major reductions in PAH and dioxins for ferrosilicon and silicon metal plants. This has been achieved by introducing semi continuous charging and improved furnace operations. Semi continuous charging and optimized furnace operations are shown to reduce the blowing activity (i.e. emission of large quantity of SiO over the charge by direct channelling from the crater zone). It also reduces variation in off-gas temperature and dust production. To understand the processes and to achieve our results we have used online equipment, with fast sample rates and response times, to measure the off-gas compositions and temperatures. Most of the measuring techniques used are based upon optical principles making use of the absorption- and emission spectrum of the gases. In addition a new prototype instrument is developed for continuous measurement of off-gas characteristics, total dust amount and off-gas temperature. The presented work is a result of a long term co-operation research and development teamwork, between the industry and the research community, and has improved both the process and reduced the emissions. The work has introduced new process design and operation standards, and has resulted in ferroalloy production with better environmental standards.

Jan 1, 2007

By H. Jalkanen, L. Holappa

The main role of slag in oxygen converter processes is to absorb the non-volatile oxidation products of hot metal impurities, Si, P, Mn, Ti, V, etc. The importance of converter slag as deP and de Smedia has ceased with implementation of special pre- and post-converter treatments. The transfer from top blowing (LD) to combined blowing converters has decreased the amount of slagged iron that, together with the tendency towards lower silicon and manganese contents, has decreased slag to steel ratio. Still the control of slag forming and behaviour during the blow is of great importance. In this paper the thermodynamics of the slag forming reactions, the role of slag in the modern oxygen converter process for impurity elimination, splashing, lining wear, dust formation and post combustion are discussed on the basis of common knowledge and experience of Finnish steel plants.

Jan 1, 2004

By Q. Cheng

This paper introduces the multi fractal interpolation method (MIM)developed for handling singularities in data analysis and for data interpolation. The MIM is a new moving average model for spatial mapping and interpolation. The model decomposes the raw data into two components: singular and nonsingular components. The former can be characterized by a localized singularity index that quantifies the scaling invariance property of measures from a multifractal point of view. The latter is a smooth component that can be estimated using ordinary kriging or other moving average models. The local singularity index characterizes the concave/convex properties of the neighbourhood values. The paper utilizes a binomial multiplicative cascade model todemonstrate the generation of one- and two-dimensional data with multi-scale singularities which can be modelled by asymmetrical multifractal distribution. It then introduces a generalized moving average mathematical model for analysing and interpolating data with singularities. Finally, it is demonstrated by a one-dimensional case study of de Wijs’ data from a profile in a zinc mine, that incorporation of spatial association and singularity can improve the interpolation result, especially for observed values with significant singularities.

Jan 1, 2015

By P G. Gaylard

The minerals Industry carries out over US$ 2 billion of R&D annually. The R&D is performed at three levels ? in house research facilities; on a one-on-one basis with a research provider; as syndicated (collaborative) research. The key to a successful R&D programme is project selection. It is suggested that at this time of ?bounty? for the minerals industry the research portfolio should contain some ?blue sky? but potentially long term significantly beneficial projects. This said, the projects should align the technical concepts with the business imperatives. AMIRA has found the ?Road Map? concept has assisted in defining areas for R&D. Examples of this methodology using a Copper Road Map developed by AMIRA for the copper producers operating in South America is presented. The benefits derived from syndicated research are also discussed.

Jan 1, 2007

By M. K. Sichone

Anglo Platinum?s Waterval smelting complex based in South Africa operates the Anglo Converting Process (ACP) that produces SO2 offgas. This SO2 offgas is treated in a double-contact, double-absorption acid plant allowing for conversion efficiencies higher than 99.90 %. The catalytic converter used in the acid plant to convert the SO2 to SO3 is a 4-bed reactor loaded with a combination of cesium-promoted and conventional vanadium pentoxide catalysts. In June 2008 there was a shutdown, in which one of the main activities was to screen the catalyst. Before this shutdown, the operator would control the converter pass temperatures manually, via the SCADA, especially during plant start-ups after which some of the automatic temperature controllers were used. After the shutdown, the control philosophy was revisited and all temperature controllers were put on auto mode during plant start up. Furthermore the set points of the pass inlet temperatures were reduced to maximize conversion in the first two passes. The result has been a reduction of SO2 emissions, from a daily average of 50 ? 70 ppm to as low as 20 ppm for similar sulphur dioxide and oxygen concentrations. Further work has been done to maintain high bed temperatures in the third and fourth passes at low SO2 strengths by splitting the gas stream between pass 1 and 2 thus increasing the SO2 content in the gas to pass 2. This increases the temperature of the gas exiting the second pass, which results in higher temperatures in passes 3 and 4. Comparison of the converter performance prior to and after the changes is made. The benefits of partially bypassing the first pass to increase the SO2 content in the gas to the second pass are shown. Conclusions and scope for further work have been drawn from the comparisons.

Jan 1, 2009

By Chad W. Brown

"A study of five commercially available solvent-extraction diluents in combination with three commercially available extractants under sub-Saharan African copper solvent-extraction conditions yielded intriguing results. A variety of physical and chemical property analyses showed that the diluents have some property differences, but overall the properties are similar and provide comparable solvent-extraction performance. Although each physical chemical property technique provides useful information, no individual test result suffices for prediction of diluent performance. Furthermore, a diluent should be evaluated within the conditions for which it is targeted to determine a true measure of performance. Overall, the diluents studied possess appropriate physicochemical properties for sub-Sahara Africa copper solvent-extraction conditions and can be utilized to achieve efficient, safe and reliable operations. INTRODUCTION Background Today, commercial SX diluents are available globally from a limited number of manufacturers. Production quality and consistency of these diluents have improved tremendously over the past 20 years. For example, diluent flash points have been increased incrementally to improve transport and handling while reducing fire hazards. In addition, properties have been successfully modified to minimize evaporative losses, ultimately reducing SX plant raw material costs. Diluent manufacturers have also focused on meeting performance requirements of SX plants, including eliminating components detrimental to SX operations, such as olefinic groups that can react with various species resulting in changing phase-disengagement properties over time, as well as ensuring that proper hydrocarbon components are present within diluent mixtures to maintain good reagent–metal complex solubility. These challenges have been met in the midst of ever-increasing stringent environmental regulations. Sub-Saharan Africa copper SX operations pose a unique set of conditions for diluents due to inherent ore compositions and the associated high reagent concentrations required for complete copper extraction. Chevron Phillips Chemical Company, LP has been manufacturing hydrocarbons and hydrocarbon-based diluents since the mid-80s, applying this experience to identify the physical properties considered crucial for proper performance in SX operations. This paper documents the findings of a study utilizing commercially available diluents in combination with extraction reagents commonly utilized in African SX operations to evaluate the relative performance of the diluents under sub-Saharan Africa copper SX conditions."

Jan 1, 2015

By Rajendra Singh

Underground depillaring of contiguous coal seams/sections is a difficult problem, which becomes even more complex if the interburden/parting between them is thin. Conventionally, the depillaring with caving of contiguous seams/sections is done in descending order. However, if the parting is thin, the influence of the top sections/seams working over the standing pillars of bottom the sections/seams becomes extremely important for the safety and optimal exploitation of coal. Field investigations were carried out at Nowrozabad East mine where superimposed pillars of the Johilla top section were depillared above the developed pillars of the Johilla bottom section with a 3 m thick parting between the two sections. The competency of the 3 m thick parting (which consists of alternate layers of shale, sandstone and shaly sandstone) was improved by reinforcement (underpinning). The strata control investigations did not show any considerable instability problem of the 3 m thick reinforced parting and pillars of the bottom section due to top section depillaring. On the basis of this field investigation and a laboratory study on simulated models, simultaneous extraction of both the sections, along with reinforcement of the parting, was suggested for the geomining conditions of the Johilla top and bottom sections. Adopting the suggested simultaneous depillaring process, two sub panels of Johilla top and bottom sections have successfully been extracted without any strata control problem. This paper presents this case study along with the results of the strata monitoring conducted to evaluate performance of the underground structures during the field trial.

Jan 1, 2004

By A. Basçetin

Equipment selection in mining engineering is one of the most important decisions that affects the mine design, production planning and economic parameters in open pit and underground mining. Mine planning engineers generally use their intuition and experiences in decision making. Mostly, linguistic variables (the weather is raining, soil is wet, etc.) come into question and decision-makers may not know how these variables are computed. Since the advent of the fuzzy set theory, these uncertainties are easily interpreted in the decision-making process. The development of computer technology and programming of colloquial language with expert systems have considerably reduced decision-makers? burden. This paper reviews the development of a computer programme software called EQS (EQuipment Selection) that automates equipment selection in mining engineering using fuzzy set theory. The EQS with an introduction of the concepts and theories of multiple attribute decision-making, the fuzzy set theory, and EQS applications to mining industry problems with case studies are presented

Jan 1, 2006

By K. Schwerdtfeger

Data are presented on the effect of iron oxide on the electrical conductivity of CaO-SiO2-FeO-Fe2O3melts, and on limiting current and impedance in direct current or alternating current charge transfer at iron electrodes. The strong influence of iron oxide content can be utilized for in situ determination of total iron oxide content and Fe3+/Fe2+ratio. The possible probe designs are presented and the principles and procedures of the measurements are explained. Keywords: in situ probe for iron oxide determination in steelmaking slags, electrical conductivity of CaO-SiO2-FeO-Fe2O3slags, direct current over voltage and alternating current impedance at iron/slag electrodes.

Jan 1, 2004

The effect of composition on electrical conductivity (resistivity), viscosity and liquidus temperature of the slags encountered in electric smelting of PGM-containing suphide concentrates is reviewed along with the relationsip between slag composition, slag-matte separation and metal losses to slag. Optimization of slag composition at furnace temperature is attempted on the basis of opposite and parabolic trends of the viscosity-conductivity relationships of the slags. The importance of surface tension of slags is emphasized using available and estimated information, which are grouped into a useful correlation. These values are coupled with or incorporated into slag viscosity plots to illustrate the correlation between the two factors which influence slag-matte separation as well as refractory attack. The electrode in the slag-resistance furnace is the central factor in the design and operation of the furnace by its role of conveying the smelting power. The obvious parameters are the size and positioning in the slag bath, which are defined by slag resistivity, furnace resistance, cell constant and power input. The flow of heat generated by the electrode current determines the energy distribution and furnace dimensions creating viscosity profiles, which in turn affect flow conditions. Thus the flow of slag and matte isdiscussed in conjunction with the furnace geometry, stirring action of the electrodes, buoyancy and electromagnetic effects. The action of the electric furnace as a settler is discussed. The rectangular furnace is considered as a channel reactor in this analysis and the action of the electrodes is described to indicate a balanced settling rate in the area of electrode action. Discussion of the design and production capacity of the electric furnace with reference to operating current, power input, furnace dimensions and electrode size are based on considerations derived mainly from slag properties such as its resistivity, viscosity and liquidus temperature.

Jan 1, 2004

By R. Hansson

Zincite and spinel phases are present in the complex slag systems encountered in zinc/lead sintering and zinc smelting processes. These phases form extensive solid solutions and are stable over a wide range of compositions, temperatures and oxygen partial pressures. Accurate information on the stability of these phases is required in order to develop thermodynamic models of these slag systems. Phase equilibria in the Fe-Zn-O system have been experimentally studied for a range of conditions, between 900 and 1580°C and oxygen partial pressures (pO2) between air and metallic iron saturation, using equilibration and quenching techniques. The compositions of the phases were measured using Electron Probe X-ray Microanalysis (EPMA). The ferrous and ferric bulk iron concentrations were determined using a specially developed wet-chemical analysis procedure based on the use of ammonium metavanadate. XRD was used to confirm phase identification. A procedure was developed to overcome the problems associated with evaporation of zinc at lowpO2s and to ensure the achievement of equilibria. An isothermal section of the system FeO-Fe2O3-ZnO at high ZnO concentrations at 1200°C was constructed. The maximum solubilities of iron and zinc in zincite and spinel phases in equilibrium were determined at pO2=1*10-6atm at 1200and 1300°C. The morphology of the zincite crystals sharply changes in air between 1200 and 1300°C from rounded to plate-like. This is shown to be associated with significant increase in total iron concentration, the additional iron being principally in the form of ferric iron. Calculations performed by Fact Sage with a thermodynamically optimized database have been compared with the experimental results. Keywords: Phase Equilibria, Fe-Zn-O, Quenching, Wet-Chemistry, EPMA, XRD, ISP.

Jan 1, 2004

By F. T. Cawood

The distinction between real estate ownership and that of interests in the property is fundamental to the appraisal of mineral properties. This distinction affects the nature and understanding of security of tenure and, consequently, the perception of what constitutes fair value. Legal matters are a particular concern because of their influence on security of tenure, ownership definition and use restrictions. The dynamics of the market and the complex interrelationships between the factors of production define value at a specific point in time for the bundle of rights, interests and assets that constitute a mineral property. Because each mineral property is unique, physically immobile and of a wasting nature, its usefulness to its owner and society must be optimized. The US Appraisal Institute (2001) classified the forces that affect land use as the cultural, political and economic attitudes of society. These forces culminate in laws that often dictate the purposes for doing appraisals. Once the legal definition of the asset is understood, valuers can decide on the valuation process that will support the final valuation approach.

Jan 1, 2004

Mineral Resource Throughput Management is based on the extraction of the maximum potential value from an ore reserve with the emphasis to generate maximum ROI and ROR (return on reserve). A steel producing company in India implemented MRTM to significantly improve their ROI and ROR. The value chain of this company consists of their own iron ore and coal mines, ore washing plants, sinter plants, steel plants, and sales and marketing division. The target for the mines was to produce at a stable and predictable rate and at specific quality requirements. These requirements were set to improve productivity and ROI of the steel plant. The implementation constituted the alignment of the reserve potential, total production chain, human resources and management culture at the mines with the requirements of the steel plant. Many typical mining practices were challenged and changed. Production targets regarding lump vs. fines ratio, consistent product tons, quality targets such as Fe, Al content and moist, and standard deviation on the quality targets were not achieved. A reverse distribution model with release mechanisms to satisfy the demand were developed and implemented at the mines. A stable and predictable flow of mine product with quality standards well within the required standard deviation targets were achieved. The contribution from the mines to significantly improve the Net Profit, ROI and ROR of the company were reached.

Jan 1, 2007

By R. Weideman, M. Le Roux, F. B. Waanders, Q. P. Campbell, E. Fosso-Kankeu, D. Moyakhe

"*Paper written on project work carried out in partial fulfilment of B.Eng (Chemical Engineering) degreeSynopsisSpent coffee grounds were transformed into biochar using a hydrothermal method. Some of the biochar product was pre-treated through surfactant impregnation with sodium dodecyl sulphate (SDS) to enhance its adsorption capacity. The non-treated(NT) and pre-treated(PT) biochars were characterized using FTIR spectroscopy and SEM-EDS analyses, which revealed that the products had the potential for adsorption of heavy metals from solution and confirmed the successful impregnation of biochar with SDS surfactant. The two adsorbents were then used for the removal of cadmium from solution and the adsorption behavior and capacity determined through adsorption isotherm, kinetic, and thermodynamic studies. It was found that the cadmium was adsorbed in several concentric layers on the surface of the adsorbents through a chemisorption mechanism. The PT biochar was identified as a superior adsorbent, with a capacity of qe = 10.67 mg/g compared to the NT biochar with qe = 4.82 mg/g. The adsorption of cadmium onto the PT biochar was further determined to be spontaneous and endothermic. It was therefore concluded that the PT biochar shows potential as an adsorbent and could be considered for implementation in the treatment of metal-polluted effluents. IntroductionCoal mining operations are notorious for producing large amounts of waste tailings, which are disposed of in the form of a slurry on tailings dams. This inadvertently contributes towards environmental problems (Jin, Mansour, and Thomas, 2017). Heavy metals are one of the most common pollutants that originate from solid mine waste disposal facilities, and these can leach into groundwater supplies, contaminating them and rendering the water unsuited for human consumption (Salomons, 1995). Cadmium occurs in conjunction with metalliferous ores and can cause severe damage to agricultural soils and drinking water supplies in the vicinity of mining sites (Dudka et al., 1995). It has a tendency to migrate into the surrounding vegetation, which in turn can cause harm to humans and animals when consumed (Marquez et al., 2018)."

Jul 1, 2019