Search Documents

By A. Singh

The control of flotation plants is by no means trivial. Flotation is one of the most interactive minerals? processing operations. The interactive nature of flotation circuits results in oscillations of levels and hence of grades and recoveries. Also, poor level setpoint tracking and disturbances have negative influences on grades and recoveries. The result is an unstable plant with limited scope for optimization. An advanced controller, FloatStarTM, has been developed to provide tight control and to reduce the amount of disturbances in flotation levels. It has been shown on a number of plants that the system results in faster and better setpoint tracking, better regulatory control and faster settling times after start-ups and disturbances. The successful stabilization provided by FloatStar has made it easier to investigate the area of optimization on flotation circuits. Mintek has identified the need for a more meaningful set of setpoints or aeration rates to use as a basis for control than levels and have advocated flow control by looking after residence times. When the feed conditions change, the ideal solution would be an algorithm or strategy that finds the new optimum conditions rather than just having an unguided hunt from the previous point. A multivariable flow-optimizing algorithm, a new module in FloatStar, has been developed to calculate optimum level setpoints and/or aeration rates that will aim to optimize the residence times, mass pulls and circulating loads within a flotation circuit. Keywords: flotation, regulatory, FloatStar, start-up, disturbance, residence times, circulating loads

Jan 1, 2003

By I T. Tshabalala

In typical conventional narrow vein stoping operations, the use of temporary support components to offer some support to workers, whilst the permanent and generally more elaborate support system gets installed or constructed, still results in injuries to people. The authors wishes to explore the probability and practicality of making use of new generation support products to make the support operations safer as well as enhance productivity in the stope face. This paper will examine the use of Autorock Drills as a means to drill roof support holes and install appropriate support components into these holes, as well as the application of ?Thin Spray Liners?, commonly called TSL?s as an additional means of creating a safer operating environment. The installation of netting as a means of roof protection and other support aspects such as cemented roof-bolts will also be explored. These proposed items are envisaged to improve the safety of our people and reduce production down time and increase production and productivity.

Jan 1, 2008

By T. Khumalo, L. P. Coetzer

This paper addresses the impact of the variable speed drive on the particle size distribution in the product of a fully autogenous UG2 grinding circuit. It further discusses the impact of a varying particle size distribution in the product of the mill on the downstream classification and milling circuits. An industrial case study was used and data is presented to illustrate the techniques applied to identify the root cause of the shift in operational efficiency. The results achieved from both the investigation into the shift in plant efficiency and the sub-sequent corrective action taken illustrate that the root-cause methodology used in advance control can be effectively applied on production sites to both detect the shift and identify probable root-causes. The industrial example used confirms that the variable speed drive in a UG2 autogenous milling operation is a critical control parameter to ensure that the plant operates to design specifications.

Jan 1, 2006

By L. Holappa

Ferroalloys like FeCr and FeMn are mostly produced in submerged electric arc furnaces. Typical for these processes is that the amount of slag is quite high. The role of slag for the process is thus very essential and specific chemical, physical and electrical properties are required. Slags in FeCr process are Al2O3-MgO-SiO2based with minor contents of CaO and CrOx. Slags in FeMn process are principally similar originating from silicate minerals but can have quite a large composition range depending on the manganese ore and its gangue minerals. Characteristic for FeMn process is that the slag is rich in manganese oxide up to above 30%. A common feature is that the ?ore oxides?, CrOx and MnOxin slag are not only divalent oxides but also containing some higher valent of Cr3+ and Mn3+, respectively. In FeMn production conditions the slag consists mainlyMn2+. This is a clear difference from CrOx containing slags in which both two and three valent coexists in slags in FeCr process conditions. Oxidation state of the slag depends on the ambient oxygen partial pressure and temperature in the examined process. Thermodynamics of slags in ferroalloys production are discussed in terms of phase diagrams, activities and oxidation state of chromium and manganese oxides. Further, slag properties influencing reduction kinetics and furnace operation i.e. viscosity and electrical resistivity are discussed. Keywords: review, slags, ferroalloys, ferrochromium, ferromanganese, thermodynamics, physical properties.

Jan 1, 2004

By J. Xiao, Y. Jiang, Y. Tanabashi, Z. Song

Modelling the effect of blasting-caused damage, anisotropy of rock masses and excavation sequence on deformational behaviour and stability of large-scale underground caverns is important in the design and information-oriented construction of the pumped storage power plant. A powerful three-dimensional numerical method that can be applied for that purpose is presented in this paper. Damaged range caused by blasting and mechanical properties of rock masses near to the walls of caverns are determined by using the back analysis approach in which three lines of the measurement results during the arch part excavation process were used to verified the simulations. Finally, applying the improved model and properties of rocks, the cavern stability and reinforcement effect of the preliminarily designed support system are also estimated for the safety in the bench excavation process. La création de modèles des effets relatifs aux dommages résultant des explosions, à l’anisotropie des masses rocheuses et à la séquence d’excavation quant au comportement à la déformation et à la stabilité des cavernes souterraines de grandes dimensions est une étape importante dans l’étude et la construction sur ordinateur de centrales hydrauliques à accumulation par pompage. Cet article traite d’une méthode numérique tri-dimensionnelle puissante applicable à cet effet. La gravité des dommages résultant des explosions et les propriétés mécaniques des roches à proximité des parois de la caverne sont déterminées par une analyse du fond dans laquelle les simulations sont vérifiées à l’aide de trois lignes de résultats de mesures prises durant le processus d’excavation de la partie arche. Finalement, la stabilité de la caverne et les effets du renforcement du système de support préalablement conçu sont estimés par application du modèle amélioré et des propriétés de la roche, pour application à la sécurité durant le processus d’excavation en gradins. Nachahmung der Wirkungen von durch Explosionen hervorgerufenen Schäden, Anisotropie der Gesteinsmassen und der Ausschachtungssequenz auf das Verformungsverhalten und die Stabilität großräumiger Untergrundhöhlen ist für das Design und den informationsorientierten Bau von Pumpenkraftwerken wichtig. Entsprechend der Vorgaben in dieser Arbeit kann ein leistungsfähiges, dreidimensionales numerisches Verfahren für diesen Zweck eingesetzt werden. Der durch Explosionen und die mechanischen Eigenschaften des Gesteins bedingte Schadensumfang im Bereich der Höhlenwände kann mit Hilfe eines retroversen Analyseansatzes bestimmt werden, bei dem die drei bei der Ausschachtung resultierenden Messlinien dazu genutzt wurden, die Simulationen zu bestätigen. Abschließend wurde außerdem durch Einsatz verbesserter Modelle und Gesteinseigenschaften die Auswirkungen vorläufig entworfener Unterstützungssystem auf die Höhlenstabilität und Verstärkungswirkungen hinsichtlich der Sicherheit bei Böschungsausschachtung abgeschätzt.

Jan 1, 2003

By H. Urata, K. Ishii

To determine the effect of F ions in the molten alkali silicate systems on their structures, quenched Na2O-SiO2-NaF systems were investigated by Raman spectroscopy and molecular dynamics simulation. The systematic increase of 1100 cm-1band intensity in the Raman spectra of the silicate melts accompanying the replacement of F for O provides the evidence for concomitant polymerization of melts. From the molecular dynamics simulation, it was confirmed that most of substituted F was mainly coordinated to Na+ ions but not Si4+ions. These results were consistent with the mechanism in which F associated with otherwise network-modifying Na rather than with network-forming Si. Since F was associated to Na+ ions, the replace of O ion by two F ions promote the polymerization of silicate melts. Keywords: fluorine; molten flux; slag structure; molecular dynamics simulation; Raman spectroscopy.

Jan 1, 2004

By P. M. Cole

An unprecedented expansion of the global zinc industry is currently under way. While most new projects and plant upgrades remain committed to traditional processing technologies, recent advances in zinc solvent extraction (SX) have created opportunities for new process routes for both primary and secondary materials. The first commercial plant to use zinc SX for the mainstream processing of a low-grade ore is under construction and promises to become one of the lowest cost zinc producers. Several other oxide and sulphide projects in various stages of feasibility are considering the inclusion of SX in their process flowsheet. Zinc SX has also proved advantageous in the reprocessing of secondary materials, particularly for the treatment of zinc residues and furnace dusts. This review focuses on recent installations and projects underdevelopment that feature zinc SZ as the key separation step.

Jan 1, 2002

By M. Görnerup, A. Kapilashrami, Seetharaman. S., A. K. Lahiri

Simultaneous reduction and foaming of chromium-rich slag have been studied in a laboratory furnace equipped with X-ray image analysis. Reduction of the metal oxides by graphite generated CO, which caused the melt to foam. The slag composition continuously changed due to reactions and dissolution of lining. Gas generation rate, foam height, and gas bubble size were studied and correlated to slag composition. Viscosity increased significantly during the experiments due to a change in slag composition. Bubble sizes varied little during the progress of reactions but differed considerably for different slags. Bubble sizes were largest for V2O5 containing slag, which is contrary to the general understanding that the presence of strong surface active agents reduces the bubble size. The foaming index did not follow expected trends for bubble size and viscosity, suggesting that foaming index is not a suitable parameter for discussion of foams under dynamic conditions. Keywords: slag, foaming, dynamic conditions

Jan 1, 2004

By D. Fukahori, K. Sugawara, A. Sato

X-ray Computed Tomography (CT) is a nondestructive imaging technique, and its efficiency is widely recognized. In the present paper, X-ray CT is successfully applied for the visualization of water permeation process in rock. A new experimental technique using a tracer, which mainly consists of Potassium Iodide (KI), is proposed, together with the analysis method of the velocity field. The permeation process and the velocity field in rock are concretely visualized and analyzed by considering the conservation of mass of the tracers. La tomographie calculée aux rayons X est une technique de la prise d'images non-destructive et son efficacité est largement reconnue. Dans le présent exposé, la tomographie calculée aux rayons X Radio est appliquée avec succès à la visualisation du procédé de perméation de l'eau dans la roche. Une nouvelle technique expérimentale, se servant d'un identificateur principalement constitué d'iodure de potassium (KI), est proposée avec la méthode de l'analyse du champ des vitesse. Le procédé de perméation et le champ des vitesse dans la roche sont visualisés concrètement et analysés en considérant la conservation de masse des identificateurs. Röntgen-Computer-Tomografie (CT) ist eine nicht-destruktive Bildverarbeitungstechnik, deren Effizienz weit anerkannt ist. In der vorliegenden Arbeit wird Röntgen-CT erfolgreich für die visuelle Darstellung des Wasser-Durchdringungsvorgangs im Fels eingesetzt. Eine neue experimentelle Technit mit einem Tracer, der hauptsächlich aus Kaliumiodid (KI) besteht, wird vorgeschlagen, zusammen mit der Analysemethode des Geschwindigkeitsfelds. Der Durchdringungsprozess und das Geschwindigkeitsfeld im Fels werden konkret visualisiert und analysiert, wobei die Bewahrung der Masse des Tracers berücksichtigt wird.

Jan 1, 2003

By M. Magnelöv, Du Sichen, U. Sjöström

An experimental study has been performed to investigate the behaviour and separation of inclusions at the interface between steel and slag. The study has been limited to liquid inclusions because they can be a potential problem in transient situations such as ladle changes in continuous casting of steel. Model experiments with water and silicon oils have been carried out to study the kinetics of separation of simulated inclusions at an interface. The properties of the inclusions and the slags have been varied by using different oils with different viscosities, densities and surface tensions. The effect of temperature of the liquids has also been examined. Measurements of the terminal velocity, rest time and the behaviour of the liquid inclusions at the interface have been recorded using a video camera. It has been found that the inclusions reach their terminal velocity early in the vessel and the experimental velocities differ somewhat from the values evaluated using ?intermediate law?. The results from the experiments have shown that the size of the inclusions has no appreciable influence on the rest time. Droplets of AK50 oil have been found to have considerably long rest time. A water film surrounding the droplet has been expected to be the main reason for the long rest time. The present study has also shown that the viscosity of the oil has certain effect on the rest time, but only to some extent, since viscosity has double functions. A higher viscosity provides higher resistance to the droplet entering the oil phase leading to longer rest time and at the same time damps the lateral movement of the droplet along the interface, leading to easier stabilization and shorter rest time. On the other hand, a high viscosity of the oil phase results in slow dissolution process. It has been concluded that a meaningful model of inclusion separation at the metal-slag interface must take the interfacial phenomena into consideration. Keywords: Inclusions, terminal velocity, rest time, dissolution.

Jan 1, 2004

By J. Lehmann, H. Gaye

A brief review of Computational Thermodynamics software concerning the modeling and prediction of reactions involving metals, slags and fluxes is presented. Their application for various steelmaking treatments is discussed. Examples concern phosphorus removal in BOF and EAF, ladle steel desulfurization, and specific treatments for inclusions control in semi-killed or Al-killed carbon and stainless steels.

By J. -Y. Jia, G. -B. Qiu, C. -G. Bai, D. -F. Chen

Due to the great importance of the smelting process, it is essential to establish a calculation model on the viscosity of the slag system containing titania. In this paper, the calculation models of mass action concentrations and viscosity for the CaO-SiO2-TiO2slag system have been established according to the coexistence theory of the slag structure, as well as the referenced viscosities ofCaO-SiO2-TiO2at different temperatures and TiO2compositions. With the two models, corresponding calculated programs are made by means of programming language Matlab5.3, and the curves of viscosity of the TiO2concentration (?TiO2/%) at 1400°C, (R=0.9~1.0) are plotted. The results show that mass action concentrations of TiO2increases with increasing percentage ofTiO2, while the viscosity of CaO-SiO2-TiO2system is decreased. The results show that the models are in good agreement with the experimental and referenced data. They also shows that the models are reasonable for the CaO-SiO2-TiO2slag system. Keywords: coexistence theory; CaO-SiO2-TiO2slag system; viscosity ; calculation models.

Jan 1, 2004

By J. Hop, A. Støre, T. Foosnæs

The carbon cathode for aluminium electrolysis is also part of the container of the process. In order to understand the behaviour and possible failure of the cathode, detailed material properties under operating conditions are needed. The paper reports experimental studies of bath and sodium in filtration, graphitization with time, loss of strength due to sodium, sodium expansion as function of pressure, as well as creep due to the developed stresses. As an example, sodium and thermal expansion data are used to calculate strain-stress models of realistic cell designs, and possible design weakness can be pointed out. Keywords: carbon, cathodes, sodium expansion, strength, graphitization, creep

Jan 1, 2004

By S. Matsuyama, S. Tomita, H. Kawahara, G. Deguchi

A proper management system of coal mine methane gas associated with underground mining activities is essential for the mine safety due to its nature of explosion. Optimum design of the mine ventilation and gas drainage need accurate prediction of gas flow rate emitted by mining activities. Permeability to gas, which is affected by stress conditions of surrounding rock mass, governs the emission rate of the gases. JCOAL has developed a three dimensional FEM simulation program named Mine Gas Flow 3D (MGF-3D). MGF-3D is designed to predict the volume of methane gas emitted from surrounding coal and rock seams based on stress distribution and permeability change which are determined by 3D stress analysis. In MGF-3D, stress change and/or expansion of fractured zone affected by mining is calculated at the first and then gas emission into roadways and longwall panels under the determined stress conditions is calculated using Darcy’s law. MGF-3D also can set up a number of pre-drainage holes and estimate drainage gas volume from each hole. This function makes MGF-3D remarkable program. These simulations for gas emission can contribute to mine gas utilization plan. Comparison between actual measurement of gas emission in the underground mine and simulation results has been performed and availability for the mine safety and problems with MGF-3D are discussed in this report.

Jan 1, 2003

Council for 1996/97 President Dr N.A. Barcza President Elect R.P. Mohring Vice Presidents Senior J.R. Dixon Junior M.H. Rogers Immediate Past President D.A.J. Ross-Watt Honorary Treasurer J.A. Cruise

Jan 1, 1997

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 B Vorster

Falls of Ground is one of the highest causes of incidents, accidents and fatal injuries in our mines today. These falls of ground may occur as soon as the face is exposed after blasting or after machine cutting. The falls of ground can also occur after support has been installed. There are many reasons why these falls occur before and after supporting of the face. It is therefore important to support the exposed face as soon as possible to prevent the falls of ground. It is also very important to support the face with the correct support products and to support the face as designed and required by the mining engineers. The possible reasons for falls of ground, possible support methods and the products available will be discussed in this presentation. In typical conventional narrow vein stoping operations, the use of conventional temporary support components to offer some support to workers, whilst the permanent and generally more elaborate support system gets installed or constructed, still results in injuries to people. The author wishes to discuss the following items in this paper:- ? Introduction ? Basic face behaviour after exposure ? Controllable Parameters ? Mining Engineers support designs ? Primary and Secondary Support ? Products available for prevention of falls of ground

Jan 1, 2008

By S. E. Olsen, K. Tang

Slag-metal and slag-metal-gas heterogeneous equilibria involving MnO-containing slags have been simulated using recently developed Mn-based alloy and IRSID oxide thermochemical databases. A large number of experimental equilibrium data have been used to verify the calculation results. The experimental slag-metal and slag-metal-gas equilibria in MnO-SiO2binary, MnO-SiO2-CaO and MnO-SiO2-Al2O3ternary, MnO-SiO2-CaO-Al2O3quaternary andMnO-SiO2-CaO-Al2O3-MgO higher-order system can be reproduced within experimental uncertainties. The influence of temperature, CO partial pressure and slag chemistry on the Mn-and Si-distribution equilibria have been quantitatively evaluated. This leads to a sound basis for optimizing the manganese ferroalloy production processes. Key words: MnO-containing slag, manganese ferroalloy, equilibrium simulation, thermochemical database

Jan 1, 2004

By I. Benning

Since the dismal performance of the Rand Mines management was called to account by its shareholders in 1994, the waves of change have continued to ripple across the South African mining industry .The number of listings on the gold board of the Johannesburg Stock Exchange, that once numbered 40 or 50-odd, have now dwindled to no more than a handful as unprecedented restructuring has taken place. The redefining of the industry has not been limited to the gold sector, but across the base metal, coal, diamond, platinum and industrial mineral sectors as well. At the same time the Mining Houses began to reconsider their funding strategies. Originally established in the early part of the century to ensure the long-term sustainability of their group mining operations by providing substantial financial muscle and technical support, the Mining Houses were faced with a rapidly changing political environment, which proved to be a critical catalyst in giving momentum to the change. Furthermore, the significant development costs and increasing risk profile for new projects, coupled with pressure from shareholders demanding respectable returns, opened the door to opportunities for banks to begin providing external debt by the way of project finance. However, the provision of long-term debt to the South African mining industry had generally not been common since mining companies had financed new projects with equity, or with the cash flows from existing operations. Those banks that had the appetite for exposure to the perceived high risks of the mining sector rapidly built up specialist resource banking divisions capable of addressing the increasing demands of the industry. The application of project finance, the principles of which were developed in the 1970s specifically for infrastructure projects and privatization, is now commonly applied in the financing of greenfield and brownfield mining projects. This paper outlines the approach that lending banks would typically adopt when arranging or providing mining project finance, their usual areas of concern and the way in which the finance is structured to mitigate the many inherent risks.

Jan 1, 2000

By D. Diering

Having agreed to perform this task, I naturally started to wonder what on earth I was going to talk about, and on reviewing the literature I was surprised at how little I knew and how much I?d forgotten about the origins of this industry. For example: ?I?d forgotten that the Chinese invented black powder at least 1 000 years ago, back in the 10th century (although some say this invention occurred 2 000years ago). ?I didn?t know that Roger Bacon was the first person in the Western World to give exact directions for the making of gunpowder in 1242 and to understand its potential. Pepper?s Playbook of Metals quotes:?...above all, he is named as the discoverer of gun-powder, a material which has brought more wonderful changes in the great family of man than the most potent elixir that could have been devised to prolong life?.

Jan 1, 2000