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By R. Dass

Paper written on project work carried out in partial fulfilment of B. Sc Eng (Extractive Metallurgy) degree Screening is an industrial process that splits material at a specific cut size into one fraction of particles larger than the cut size and another fraction of particles smaller than the cut size. Particles are vibrated to increase the probability of them being accurately classified and to move the oversize particles off the screen surface. In conventional screening, the screen mesh vibrates with a single frequency and the particles on the screen are all exposed to this same frequency. The Ultimate Screener (see Figure 1) is a new screen technology that imparts multi-frequency vibrations to the screen mesh so that different parts of the screen surface vibrate at different frequencies. The Ultimate Screener incorporates an additional deck that holds the multi frequency adapters as shown by Figure 2. These special adapters can transform single frequency vibrations into multi frequency vibrations. When the screen motors are switched on they begin to vibrate. This vibration is transmitted to the adapters via the body of the machine. The adapters then modify the vibration to have multiple frequencies, which are transmitted to the screen surface via resonating rings.

Jan 1, 2004

By J. M. Font, R. G. Reddy

Jan 1, 2004

By K. M. Li, Y. D. Zhang

The selection of stripping dragline is a complicated problem. Several factors, such as the deposit buried conditions, the demand of mine production rate, cast blasting result, the mining/stripping operation method and parameters, etc. may comprehensively influence the optimal selection of technical specifications of the dragline. Under these circumstances, the basic thinking and procedures for dragline selection are put forward as follows. •Step 1—Initially estimate the dragline annual stripping rate and stripping bench height according to the annual coal production rate and advancing speed of mining front. Then the feasible alternatives of dragline sizes can be calculated and selected from the existing dragline series. •Step 2—A computer simulation model is developed to simulate the dragline stripping operation, to obtain a series of working face parameters, then to select the best dragline alternative. This step can be interactively iterated until the satisfactory results are obtained. •Step 3— Sensitivity analysis can be done with the systems simulation model by changing the stripping bench parameters, e.g. stripping bench height and cut width, etc. to verify and modify the selection results if necessary. The mathematical model for dragline stripping simulation has been set up. The flowchart of the model is shown. A case study for a large surface coal mine with annual production rate of 16 Mt/a is followed. The dragline bucket capacity and operation radius, stripping bench height and cut width as well as other parameters are comprehensively optimized and selected. Keywords: Open cast, dragline, specification, selection, cast blasting

Jan 1, 2003

By H. Krogerus, P. Jokinen, T. Lintumaa

The energy consumption and recovery of chromium are important economic factors in ferrochrome production. Outokumpu has a lot of experience of the reduction behavior of the sintered pellets in industrial-scale furnaces and also on the grounds of numerous laboratory and pilot-scale investigations. Sintered pellets have shown a superiority over lumpy ore and briquettes made of the same chromite grade. The good performance of the pellets has also resulted in investigations on the reasons for such a performance. In this study, the factors affecting pellet behavior in smelting furnace were investigated. This study is divided into two sections, i.e. the investigations were on the factors affecting solid state reduction and on the factors affecting reduction under melting. These tests were performed by means of thermo gravimetry and by smelting tests. The correlation between the pellet characteristics and reduction behavior was shown and its influence on industrial-scale furnaces was discussed. Factors worth of consideration are for instance, the extent of oxidation during sintering, slag formation and chemistry in respect of molten state reduction, and the grain size of the chromite mineral in the raw material in respect of kinetic reasons (retention time in smelting).

Jan 1, 2007

By O. I. Ostrovski, D. K. Belashchenko

The aim of this paper is the construction of models of systems with ionic and ionic-covalent bonds (molten salts) using experimental diffraction data and the calculation of their structure and thermodynamic and transport properties. Modelling was performed using algorithm BELION, in which the non-coulomb part of interaction potential between ions in the model was determined by the method of iterative simulation which targeted agreement between calculated and experimental partial pair correlation functions (PPCFs). The ionic charges in salts, which can be fractional, were determined by minimization of internal energy. In this paper, the algorithm BELION is applied for chlorides of alkaline-earth metals. Pair potentials, PPCFs, atomization energies, self-diffusion coefficients and electric conductivity are calculated. The charge of alkaline-earth metals was in the range of 2.0-2.1, slightly increasing from Mg to Ba. Partial pair correlation functions and atomization energies of models agree well with experimental data for MgCl2, SrCl2and BaCl2. Keywords: molten salt, molecular dynamics, partial pair correlation function, ionic charge, atomization energy, diffusion.

Jan 1, 2004

By A. V. Pavlov, A. V. Dubachev, K. L. Kossyrev

The purpose of the given research was to investigate the possibility of high-carbon ferrochromium refining to remove harmful impurities as a result of metal treatment by slag mixtures on the basis of the CaO-MgO-SiO2system. The final conclusions were drawn from experimental results. It was shown that the treatment of high-carbon ferrochromium by SiO2-MgO-CaO slag mixtures with additions of chromium sinter or iron-ore concentrate removes carbon, sulphur and phosphorus from the metal. A mechanism of phosphorus removal from a melt to a gas phase is proposed.

Jan 1, 2004

By R L. Langak, R A. Heins

The use of differences in specific gravity between minerals to separate them has long been utilized in the extractive industries. The environmental and cost benefits of the commercialized forms of these processes are well understood and widely used. Gravity concentration is used inter alia in the primary beneficiation of gold, diamonds, coal, tin, ferrous metal ores and andalusite. The potential for economic loss due to poor performance of these gravity processes is significant, but diverse in manifestation and regular process monitoring can prevent or at least reduce these losses. The measurement of performance of gravity processes has always presented a challenge, due primarily to the masses of material involved and the physical nature of the processes, generally typified by long reporting time, and hazardous materials (such as Tetrabromoethane) for float and sink type tests. The development of density tracers has improved this situation, however recovery of these tracers from the process streams created the next set of challenges, requiring significant manpower to physically remove tracers from product dewatering screens. Additions to these tracers (magnetic or x-ray fluorescent) eased the recovery mechanism issues but made them much more expensive to produce, hence operators became concerned about losses during process testing. In addition, magnetic recovery of smaller size tracers by a magnet suspended above a loaded screen panel is still problematic. The development of new low cost magnetic tracers has improved statistical significance of tracer tests, as the tracers themselves can be bought and used in much larger quantities, whilst still remaining economically viable. Coupled with the development of effective magnetic recovery technology, such as the Gekko MagScreen, for even fine sized tracers, on-line, continuous tracer testing is now becoming a reality. Whilst the development of high technology radio frequency detection tracer systems continues, enabling the real time measurement of the process and interpretation of results, miniaturization and recovery of these tracers, which is critical given their costs at present, remains an issue. Keywords: Gravity, process measurement, tracers, magnetic recovery

Jan 1, 2006

By A. F. Lee

A pick-up apparatus capable of yielding quantitative results has been described. Studies of some collector-mineral systems have been presented to illustrate the versatility of the apparatus and prove the validity of results.

By M. Maleki

Variogram analysis and kriging lack robustness in the presence of outliers and data with long-tailed distributions, which often arises when estimating grades in precious metal deposits. The capping technique, consisting of truncating the data to some top-cut grade, is widely used in order to mitigate the influence of the values in the upper tail of the distribution. However, this procedure omits part of the grade variability and is likely to provoke a bias in the estimates. To avoid these issues, a recently proposed approach is to decompose the grade of interest into three components (the truncated grade, a weighted indicator above the top-cut grade, and a zero-mean residual) and jointly estimate the truncated grade and the indicator by cokriging. This approach is attractive as it provides unbiased grade estimates, allows choosing the ?optimal? top-cut value, and essentially works with truncated and indicator data, thus avoiding the use of outlying values for calculating sample variograms and performing spatial interpolation. This work presents an application of this approach to a disseminated gold deposit that has been identified through exploration drilling. The effect of using an indicator covariate is assessed through leave-one-out cross-validation, by comparing the grade estimates with the true grades and with the grade estimates obtained with the conventional capping approach, which considers only the truncated grade as the variable of interest. As a result, cokriging the truncated grade and the indicator above top-cut grade outperforms the conventional capping approach, yielding significantly more accurate estimates. A few complementary guidelines are provided for validating the model hypotheses and for the implementation of cokriging.

Jan 1, 2014

By J. Björkvall, S. Ångström, L. Kallin

In this paper results from industrial trials of CaC2 injection during stainless steel production in an electric arc furnace at Sandvik Steel is presented. The main purpose of the investigation was to analyse the effect of the injection on slag foaming and final chromium oxide concentration in slag. The results show that both an increase in slag foaming and a decrease of the final chromium oxide could be obtained during the charges with CaC2injection. On the basis of the results, the economical requirements are also discussed. Both the technical and economical requirements could be achieved for steels alloyed with Mo. In order to secure the economical requirements for all steel grades of interest, the injection technology must be further developed. It would also be important to utilize the positive effect of the slag foaming on the electric energy consumption. The work has been performed as a part of MEFOS frame research programme with participants from Sandvik Steel, AKZO Nobel and Avesta Polarit. Keywords: stainless steel, EAF, slag foaming, injection, CaC2

Jan 1, 2004

By V. Labiouse, P. K. Kaiser, F. Descoeudres, F. Rojat

In this paper some failure phenomena observed in the crossing of brittle rock formations at the Lötschberg base tunnel are presented. A brittle failure criteria, recently developed by Canadian researchers, is applied through finite element calculations together with a semi-empirical failure criterion, to explain these behaviours. Good agreement is found between predicted and observed failures at the tunnel walls. This study also shows some of the limitations of this approach. Dans cet article sont présentés certains phénomènes de rupture observés durant la traversée de zones de roches fragiles lors de l’excavation du tunnel du Lötschberg. Un critère de rupture développé récemment par la recherche canadienne est utilisé à travers des calculs par éléments finis. En parallèle, les résultats sont comparés avec ceux d’un critère semi-empirique. Au niveau des parements, l’ampleur des ruptures observées est assez proche des résultats de calcul. Cette étude a également permis de mettre en avant certaines limites de l’approche choisie. In diesem Artikel werden verschiedene Brucharten dargestellt, die bei der Durchfahrung von sprödem Gestein im Rahmen des Ausbaus des Lötschberg-Basistunnels beobachtet wurden. Zur Erklärung des vorliegenden Verhaltens wurden die erst kürzlich in Kanada entwickelten Theorien zur Beschreibung von Sprödbrüchen herangezogen und bei der Berechnung mittels der Finite-Elemente-Methode und eines semi-empirischen Kriteriums angewendet. Die so vorhergesagten Versagenszonen an den Tunnelwänden stimmen mit den Beobachtungen gut überein. Die Studie hat auch dazu beigetragen, die bei der Anwendung des Lösungsansatzes angetroffenen Schwierigkeiten aufzuzeigen.

Jan 1, 2003

By M. K. Elmouttie, G. V. Poropat

The analysis of structure using joint set statistics is well known. Other data such as the position of discontinuities and the contacts between rock mass units cannot be easily incorporated in simple statistical analysis based on orientation alone. Algorithms to model the structure of rock slopes using measurements of the orientation and position of discontinuities are being developed by CSIRO Exploration and Mining. These algorithms provide a capability to model the structure of a rock slope and estimate the likelihood of the formation of hazardous blocks in existing or proposed rock slopes and identification of the location and size of these blocks. The algorithms provide the basis of structural modelling to identify potential failure mechanisms in rock slopes.

Jan 1, 2006

By T. Lindstad, V. Myrvågnes

In the production of high silicon alloys, carbonaceous materials like coal, coke, charcoal and woodchips are utilized as reducing agents. Primarily based on historical prices of charcoal compared to fossil reduction materials, the Norwegian Ferroalloy Industry has mostly been using coal and coke (char) as carbon source. The most important role of the carbonaceous material is to react with the SiO gas to produce SiC. The ability of the reduction materials to bind SiO gas can be measured and the value is recognised as the reactivity of the carbon source. This reactivity is one of the most important parameters in the smelting process in order to obtain a high yield of metal. The reactivity of the carbon materials is directly correlated to the material properties. It is known that the rank of the coal influences the SiO reactivity where low rank is beneficial. Coals of the same rank have however proven to have varying reactivity. In order to investigate how the micro-constituents of coal influence the reactivity towards SiO gas, three single seam unwashed coals of different origin which fulfil the requirements of the Norwegian Ferroalloy producers have been chosen. As the structure in the carbonized product is a function of petrographic constitution and carbonization parameters, the coals have been separated into different density fractions. The various density fractions of the same coals proved to have significantly different petrographic composition. The coals were carbonized according to a procedure simulating the conditions the coals experience when charged to an industrial furnace. Chemical-, physical- and petrographical properties of both the coals and the resultant chars have been thoroughly examined and correlated towards the SiO reactivity.

Jan 1, 2007

By V. Tathavadkar

Worldwide TiO2is extracted from natural ilmenite, rutile, and anatase minerals via the sulphateand chloride processes. The sulphate process generates large volumes of less toxic wastes, whereas the chloride process, including the ilmenite-chloride process of DuPont, yields much lower volume of wastes, which are highly toxic and hazardous. The treatment and disposal of such hazardous chloride wastes is both expensive and difficult in terms of long-term monitoring. Besides the waste management and disposal, there is also a shortage of high-grade titanium dioxide minerals in nature, which consequently yields much larger tonnages of sulphate and chloride wastes. In the present investigation we report the results of an alternative titaniferous mineral beneficiation process based on soda ash roasting of minerals. Compared to the conventional processes for beneficiation of TiO2- ores, the alkali roasting of titaniferous offers several advantages including the zero process wastes. In the soda ash roasting process, the mineral is mixed with sodium carbonate and heated above 1023 K in air. The oxidative roasting of ores yields several complex alkali compounds, some of which produce a liquid mixture above 1123 K. In this paper, we have attempted to characterize the composition and physical chemistry of alkali-rich liquid phase. The phase equilibria in the Ti-(M:Fe)-Na-O system are evaluated and compared with the phases formed as a result of roasting reaction. The experimental results revealed that the composition of complex alkali liquid at the reaction interface plays an important role in determining the transport of O2-ions and decomposition of ilmenite. The roles of the crystal structure of mineral phases and their energetics are also emphasized in controlling their decomposition during alkali roasting. The presence of molten alkali in controlling the partitioning of water-soluble alkali salts and insoluble sodium titanate is also explained. Keywords: ilmenite, anatase, alkali roasting, phase equilibria.

Jan 1, 2004

By P. Gonzalez, C. Ariyo, L. Holappa

Oxidation state of titanium was determined in CaO-SiO2-TiOxslags in the composition range25–53 per cent CaO, 27–46 per cent SiO2, 10–55 per cent TiOxat 1873K using gas equilibration method. In the experiments, slags with different titanium oxide contents were equilibrated with a known carbon monoxide and carbon dioxide ratio. The results were used to determine the Ti3+and Ti4+contents as well as the activity coefficient ratio of corresponding oxides in the slag. The dependency of the activity coefficient ratio as a function of oxygen partial pressure was determined. Keywords: titanium, titanium oxide, activity, activity coefficient, slag iron, carbon monoxide,carbon doixide, gas, equilibrium.

Jan 1, 2004

By R. D. Hull

Paper written on project work carried out in partial fulfilment of B.Sc. (Eng.) (Mining) degree As a partial fulfilment for the degree of B.Sc. (Eng) (mining) at the University of the Witwatersrand, a dissertation was to be completed in the mining industry. This was done at Finsch mine, with the purpose of determining the best solution to the required secondary breaking problem. In order to complete the study of the secondary blasting method available for use in the new block 4, cave mining method at Finsch mine the following problem statement was identified and solved ?The methods currently in use, for the secondary breaking of oversize rocks at their source in the current production levels, are to be investigated, and their applicability to the new block 4mining project determined?. To effectively achieve this problem statement above; time was spent researching and investigating, in depth, the methods that are currently in use at both Finsch and Koffiefontein mines; so as to gain practical knowledge of these. The methods were identified and independently evaluated, taking into consideration factors such as costs of the equipment, time to break oversize rocks, advantages, disadvantages, safety and labour requirements, etc. This in turn then allowed for a direct comparison between the methods and the decision as to the best to apply to the new block 4 production level. The methods that were investigated included: ?Concussion blasting, where concussion bombs and lay-on charges are used to break hang-ups and boulders. ?Drill and blast methods, where holes are drilled in large rocks and charged manually with explosives. ?Emulsion secondary blasting, which is a new project in use at Koffiefontein mine from African Explosives Limited. ?The Ro-BustTM breaking system, a hydro-fracturing breaking system. Once all the methods had been evaluated and compared it was found that the Ro-BustTM Breaking system was the most applicable for the breaking of boulders, with, the Emulsion Blasting System being used for hang-ups. Further information and the more in-depth version of this report, is stored in the resource centre at De Beers?Finsch Mineand the School of Mining Engineering WITS University.`

Jan 1, 2002

By H. Sekimoto, T. Matsuoka, K. Yasuhara, M. Ota, S. Akutagawa

A magnetic anisotropy sensor is used for nondestructive measurement of stress on surfaces of a ferromagnetic material, such as steel. The sensor is built on the principle of the magneto-strictive effect in which changes in magnetic permeability due to deformation of the material is measured in a nondestructive manner, which then can be translated into the absolute values of stresses existing on the surface. This technique was applied to measure stresses of H-beams used in tunnels. The results show that this method could be one of the promising technologies for non-destructive stress measurement for safe construction of underground structures. Une sonde magnétique anisotropique est utilisée pour des mesures non-destructives de stress sur la surface d' unmétal ferromagnétique, comme l'acier. La sonde est construite sur le principe de l'effet magnéto-strictif dans lequel les changements dans la perméabilité magnétique due à la déformation du metal est mesurée avec une manière non-destructive, qui peut être alors traduite en valeurs absolues des stress existants à la surface. Cette technique a été appliquée pour la mesure de stress des poutres en H utilisées dans les tunnels. Les résultats montrent que cette méthode peut être l'une des technologies promet tantes concernant les mesures non-destructives de stress pour des constructions sûres de strcutures souterraines. Ein magnetischer Anisotropie-Sensor wird für die zerstörungsfreie Messung von Spannungen an Oberflächenvon ferromagnetischen Materialien wie z.B. Stahl verwendet. Der Sensor kann Änderungen in der magnetischen Durchlässigkeit auf Grund von Verformungen des Materials erkennen, die dann in Absolutwerte der Spannungen an der Oberfläche umgerechnet werden können. Die Methode wurde auf Messung von Spannungenvon H-Balken in Tunnels angewendet. Ergebnisse zeigen, dass dies eine vielversprechende Methode für diezerstörungefreie Messung im Tiefbau ist.

Jan 1, 2003

By I. A. Minaev

The conditions of a stability of metallurgical films on a surface of solid on the basis of classical regularities of a thermodynamics are considered. For specific conditions of metallurgical processes the basic equations relevant to non-metallic inclusions (product of steel killing) migration and transfer through the interface boundary of metal-slag are obtained. The basic criteria equations of conditions of stability of metallurgical dispersed systems are developed in view of films formation. The probable thermodynamics reason of wetting due to formation of stable films are discussed. The experimental measurement of thin and thick films elastic resistance for metallurgical systems are carried out and the results are discussed. The presence of a wetting thick film increases stability of dispersed systems (facilitates an inverse implication of non-metallic inclusion in a melt) due to a barrier effect of wetting films. The quantitative evaluations of non-metal inclusion stability for steel in contact with any metallurgical slag are carried out. The results are in accordance with technological experience. Keywords: Inclusion removal, Film thermodynamic, Slag-metal dispers system

Jan 1, 2004

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

By SDN Wessels, WA Naismith

On 16 July 2004, at 07:10 a collapse of about 1.8 million m3 (about 4 ½ million tonnes) took place on the north wall on Nchanga Open Pit This collapse was the result of a developing instability that was first identified when the benches in this area were exposed during September 2002. The NOP Geotechnical and Survey Departments closely monitored the development of the failure. Control measures were implemented to reduce risk to men and equipment. These measures were continually improved and adjusted in reaction to observations and changing conditions. The purpose of this paper is to describe in detail the monitoring results that were obtained both by traditional methods and the novel Slope Stability Radar System (SSR). Difficulties encountered in establishing critical deformation levels and deformation rates that can be used to predict the onset of collapse are described. Details of the monitoring and control measures, which led to the successful completion of mining in the area, are also described in this paper.

Jan 1, 2005