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By M. P. Brungs, S. Haji Amini

Static dissolution of CaO into a CaO-SiO2-Al2O3slag and slags with additional fluxing agents (fluorspar, nepheline syenite and ilmenite) was studied. The slag was packed into dense CaO crucibles and heated to 1500ºC /1600ºC. After reaction, the crucible was air cooled and cross-sectioned. The development of the Ca2SiO4 phase and concentration profiles of various cations across the reaction zone were examined by Electron Probe Micro Analysis. At 1500ºC, a Ca2SiO4layer was found to form at the CaO/slag interface. No such layer was evident at 1600ºC. Ilmenite and nepheline syenite were found to be effective substitutes for fluorspar, increasing the rate of CaO dissolution.

Jan 1, 2004

Published experimental data on thermodynamic behaviour of cobalt-containing slags have been reviewed and used in validating a recently developed thermodynamic model. The results from the exercise show that the model provides a reasonably good description of behaviour of cobalt in multi-component slag systems. The models for cobalt containing slags, matte and oxide solid solution phases were incorporated into CSIRO?s multi-phase equilibrium (MPE) package, which was used to calculate the equilibrium distribution of cobalt between matte and slag phases under various conditions. The results agreed well with the experimental data. Furthermore, the good agreement between the calculation and the plant data indicates that the operating conditions of industrial smelting and converting processes are close to equilibrium. Two diagrams showing the effects of slag chemistry and SO2and O2partial pressures on the distribution of cobalt between phases were generated for conditions similar to smelting and converting processes. These diagrams provide some useful guidelines for developing new strategies to improve cobalt recovery.

Jan 1, 2004

By L. C. Stilwell

The paper will place into perspective the contribution that platinum makes to the South African economy. It will use statistics from official sources, namely the Department of Minerals and Energy, the Department of Customs and Excise, the South African Reserve Bank and Statistics South Africa. Surprisingly few people are aware of these statistics, especially Supply and Usage tables, published by Statistics South Africa, and trade statistics, published by the Customs and Excise division of the South African Revenue Service. The paper will therefore contain a concise explanation of input-output tables and supply usage tables, as well as the derivation of gross domestic product and an outline of the System of National Accounts, of which Input-Output Tables and supply and usage tables are components. GDP is a commonly used, but poorly understood, measure of the wealth of an economy. The paper will explain the methods used by SSA to calculate this indicator and its place in the System of National Accounts (SNA). South Africa exports almost all its platinum production (87.5% in 2002). Exports are a final demand, as opposed to intermediate demand from secondary industries, and therefore do not enter the value-adding process, which is the essence of GDP. By definition, therefore, platinum on its own is not a major contributor to GDP. The platinum industry does, however, have an impact (known as the multiplier effect) on other sectors of the economy. The paper will explain the meaning and derivation of these multipliers, using a model based on an Inverse Leontief Matrix.

Jan 1, 2004

By T. Gerritsen, R. C. Delgado, J. Janzen, E. R. Veloza

The paper describes the components of an Integrated Furnace Control system for covered-arc (shielded arc) smelting with results from the recently started 75 MW Cerro Matoso Line 2 Furnace. The paper starts with a review of the mechanisms of power and feed input and heat losses in the shielded-arc smelting process, and describes how the details of the control system are tailored to the process. The control modules of a covered-arc smelting furnace are described including measured results and screen captures. This paper focuses on Integrated Furnace Controls tailored to shielded-arc smelting, but similar approaches have been recently applied to other furnace processes including immersed-arc smelting.

Jan 1, 2004

By L. Holappa

Ferroalloys like FeCr and FeMn are mostly produced in submerged electric arc furnaces. Typical of these processes is that the amount of slag is quite high. The role of slag for the process is thus essential and specific chemical, physical and electrical properties are required. Slags in FeCr process are Al2O3-MgO-SiO2 based with minor contents of CaO and CrOx. Slags in the FeMn process are principally similar, originating from silicate minerals but can have quite large composition range depending on the manganese ore and its gangue minerals. Characteristic of the 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 MnOx in slag are not only divalent oxides but also contain some higher valent of Cr3+and Mn3+, respectively. In FeMn production conditions the slag consists mainly of Mn2+. This is a clear difference from CrOx containing slags in which both two and three valent coexist in slags in FeCr process conditions. Oxidation state of the slag depends on the ambient oxygen partial pressure and temperature in the examined process. The 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

Experimental studies on viscosity of titanium bearing slags have been reviewed and the assessed data were used in extending the capability of the structurally related viscosity model for silicate melts, developed by the present authors. Experimental data on ternary and higher order systems containing CaO, MgO, MnO, FeO, Al2O3, TiO2, Ti2O3, SiO2were assessed and used. The newly extended viscosity model represented the viscosity behaviour over broad temperature and composition ranges. The structural role played by TiO2and Ti2O3in silicate network structure is discussed with respect to their effect on viscosity of melts. Keywords: viscosity model, TiOx containing silicate melts, silicate network structure.

Jan 1, 2004

By H. Saroglou

The anisotropic behaviour of Athens Schist has been brought out through the testing of specimens with varying orientation of schistosity with respect to the major principal stress under uniaxial, triaxial and dynamic conditions. A large number of results from tests on intact rock specimens of the Athens Schist were statistically analysed and evaluated.

Jan 1, 2004

By R. M. Tyler

The importance of the heavy mineral sands to southern African economic well-being cannot be over emphasized. The value of the worldwide titanium dioxide industry is estimated at $7 billion. Six out of eight of the world?s proposed new project areas are in southern and eastern Africa, and a seventh at Tamil Nadu in India is partly owned by a South African company, Kumba Resources. The HMS industry can be highly lucrative; its return on capital is the best in the mining industry. There are, however, problems, particularly in the smelting technology. The often considerable affect of mining on environmentally sensitive coastal dunes is also becoming increasingly important. The medium-to long-term demand for Ti-dioxide pigment and ceramic grade zircon appears very healthy. If, as predicted, the costs of producing titanium metal can be reduced, then there is huge potential for the metal. In summary, the HMS industry is an attractive one to be in, with good returns and generally manageable risks. New business opportunities and their economic implications for Africa are discussed.

Jan 1, 2004

By R. G. Koelmans

In 2001 Platinum overtook gold in foreign revenue earnings for South Africa. The export sales from platinum group metals amounted to R29.3 billion as opposed to gold export sales of R28.6billion1. Organizations must undertake new ventures to replace old, worn-out and obsolete assets with new ones. These assets could be a building, a new product or process, a new mine, or anything that can help the organization to achieve its objective. These ventures are projects by their nature. When a project is pronounced a success, the judgement is usually based on some factual evidence, although not every one uses the same data. From the literature, it is obvious that there is a lack of consensus and objectivity as to what constitutes a successful project. The purpose of this paper is to address the following questions: ?What constitutes a successful project? ? How does one measure project success? ?How can one work toward project success? This paper addresses the requirements for project success of three of the primary stakeholders of a project, namely the business or client, the employees as far as the project team is concerned, and the local community. Indicators are developed into a work breakdown structure (WBS)-like chart to demonstrate success indicators. These indices take cognisance of all the constituents required for project success. The indicators are further developed to take cognisance of the requirements of the local communities. These indices are then weighted to arrive at a total score for the respective stakeholders. Using these WBS models, the success and performance of a project can be evaluated. This score is considered an objective measure of project success. Projects are evaluated more consistently across different projects and the project manager is provided with a management tool that can assist him/her in ensuring greater project success. The shortcoming of this approach is that the weights of the different indices have been estimated at this stage. Research will have to be conducted to more accurately reflect the weights assigned to the indices.

Jan 1, 2004

By S. Rupprecht, G. Rapson

Long blast hole drilling has been successfully implemented since the 1950s in caving operations, steeply dipping wide reefs and boxhole/raise developments worldwide. However, when applying long hole drilling to narrow tabular reefs, the challenges of achieving high economic drilling rates, combined with acceptable accuracy and appropriate powder factors have yet to be overcome. The focus in this paper is the selection, application and optimization of long hole drilling equipment at mining operations shallower than 2 000 meters. The drilling, blasting and cleaning operations have to be optimized as a process if maximum production at minimum per unit cost is to be achieved. For this to be possible, it is essential that the mine design and layout match the mining process being implemented. The critical parameters affecting the sustainable implementation of long hole drilling in stoping applications for platinum mines are improved safety and higher production rates compared to conventional methods. In terms of drilling, both top hammer and down-the hole hammer configurations have been considered. For economic drilling, the benefits of monitoring and optimizing performance (i.e. drill bit rotation, thrust, and percussive power) for specific rock types are discussed. While the drive is for longer, more accurate, smaller diameter holes to reduce drilling costs, the design of appropriate blast hole patterns and the corresponding charging and initiation systems is crucial for success. The effect of hole diameter and pattern on the powder factor, when comparing small diameter, shorter holes versus large diameter, longer holes, is a major factor in achieving good blasting results. Once appropriate drilling and blasting have been implemented, the cleaning process becomes a potentially critical operation to ensure the production, cost and safety goals are met. Hence, the blast hole pattern and charge have to be integrated for optimal fragmentation to suit the cleaning cycle for maximum production output. Providing that long blast hole drilling is applied as a process in a planned, committed and well-managed manner, the benefits in safety, production and cost over conventional methods should be achievable. However, if the implementation process is not planned and supported by all parties concerned, it will not be possible to succeed in the new operation. Hence, an implementation or roll-out plan of new technology is crucial for success.

Jan 1, 2004

By G. van den Berg

Anglo Platinum has initiated a project to investigate hydraulic hoisting technology for platinum mines. Hydraulic hoisting systems are categorized as pumping, fluidizing feeder or displacement feeder systems. Positive displacement piston diaphragm pumps are most suitable for pumping systems but they require that the ore be milled prior to pumping. Fluidizing feeders are unsuitable for platinum ore applications due to the large percentage of fines in the ore. The three-chamber pipe displacement feeder has been most widely used for hydraulic hoisting and is the most suitable technology for platinum mines. Eight hydraulic hoisting applications covering pumping and displacement feeder technologies are reviewed. The key factors to be assessed in selecting a hydraulic hoisting system for a platinum mine are discussed. A typical platinum mine configuration will comprise an ore preparation plant (to produce -15 mm material through screening or crushing), motive water pump on surface, high pressure water pipeline from surface to underground, ore slurrification plant, three-chamber displacement feeder, and a high pressure slurry pipeline to surface. The water and slurry pipelines are housed in a purpose drilled borehole. A hydraulic hoisting system selection chart is presented. A 150 mm diameter system with a 25 MPa pressure rating is required to hoist 60 000 t/m from a depth of 1 200 m. Generic capital and operating costs are presented . A major potential advantage of hydraulic hoisting is that the fines, which contain a high percentage of PGMs, are captured underground and transported directly to the concentrator. Hydraulic hoisting technology is ideally suited to providing supplementary hoisting capacity to existing shafts that have reached the skip hoisting capacity limit. The main advantage for new shafts is the potential to significantly simplify underground rock handling and transportation. All hydraulic hoisting system components are proven. The only risk area is the wear rates of the valves and piping. Current estimates are based on gold ore. The business cases investigated show that the financial viability of the installations are not sensitive to wear rate. Hydraulic hoisting is technically feasible and financially attractive for platinum mines. Keywords: Hydraulic hoisting, slurry

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 P. L. Duncanson, J. D. Toth

Since 1995, when "freeze lining" refractory systems were introduced to the ferroalloy industry, they have gained in popularity, due to the freeze lining?s reputation for reliability, safety, and the contribution it makes to profitability. As with many popular and effective technologies, however, the freeze lining has spawned low-cost pretenders that claim the "freeze lining" name. On the surface they appear to contain some of the components of the technology, such as thermally conductive materials, but they fail to incorporate all of the principles that define a true Freeze Lining. The term "freeze lining" refers to the refractory system?s ability to maintain a temperature profile that is low enough to freeze a layer of process material on its hot face, which insulates the refractory and prevents direct contact with molten metal and slag. In doing so, the common wear mechanisms found in the submerged arc furnace - chemical attack, erosion, and thermal stress - can be prevented. These wear mechanisms are all related to high temperature; thus, they are prevented by maintaining low temperatures. Certain refractory properties and design concepts are absolutely necessary for the lining system to function as a true Freeze Lining. The paper explains these requirements and why they are important - the Truth of freeze linings - and further explains why systems that ignore one or more of these requirements cannot claim to be freeze linings, thereby exposing the Myths.

Jan 1, 2004

By M. Sanchez, C. Morales, J. Palacios

The slag produced in the Peirce Smith converters at the Ilo smelter of Southern Peru Copper Corporation has shown a wide range of magnetite content, which introduces an additional problem in the smelting units due to materials? recirculation. However, the operation data analysis and the application of thermodynamic concepts have made it possible to produce slag with magnetite content between 18 and 20%. The results have suggested that matte grade enhances magnetite formation while silica controls its precipitation, and they are also influenced by the increasing temperature of the slag. Thus, in order to obtain the required magnetite content in the slag, matte grade is gradually enriched in equilibrium with slag containing from 25 to 32% silica.

Jan 1, 2004

By D. Ksinsik, R. Boisvert, D. Leblanc

Casting, cooling and crushing/sieving of ferroalloys has followed a well-established pattern in the whole ferroalloys industry for many years. Usually liquid metal or alloys are cast into flat open moulds of various shapes and forms, and after solidification the product is removed from such mould to further cool down to a temperature where subsequent handling steps are feasible. Common to all mechanical product fractioning is the generation of dust and fine size material with lower product value. For almost 10 years, Bécancour Silicon has investigated alternative roads to improve technology and/or reduce or solve problems related to those disadvantages. Since 1995 Bécancour Silicon operates a special silicon granulation plant targeted to product for the chemical treatment/conversion of silicon for silicones production. Prior to the development of the granulation process, various systems had been evaluated, among others the vibrating casting bed, now in operation elsewhere but judged inappropriate because of the tapping volumes to be handled at Bécancour Silicon and other disadvantages. After evaluation of all aspects of heat transfer, radiation, and conductivity in relation to transfer media and within the product, a novel system was designed and built.

Jan 1, 2004

By H. Hearnden

Whereas in the past, ladles were simply a means of transferring molten products from furnace tapholes to points of discharge be they casting pans or waste dumps, the ladle is now becoming a more integral and versatile piece of equipment in the pyrometallurgical plant. The drive behind this development is the need for continuous improvement in performance where better, faster and cheaper means remaining competitive in the global market. This paper will explore the technologies available for the rendering of a costly and otherwise cumbersome piece of pyrometallurgical equipment more efficient and versatile in adding value to the final product. Essentially it all revolves around heat and more importantly the loss of it when tapping. The common practice is to move the molten product to its point of discharge quickly with the minimum of interruption to prevent skulling and hence the cost associated with clearing it. The advances in Oxy-fuel burners, AC or DC ladle furnaces, converters, gas purging and high velocity, bath injection systems has increased the versatility of processes and enhanced the potential for adding value to intermediate products through down stream practices such as granulation and atomisation.

Jan 1, 2004

By P. R. Scheller

Reactions between metal and slag are of decisive importance for metallurgical processing. In the continuous casting process, where metal solidifies at the metal-slag interface, reaction products can cause surface defects, with quality damages of the cast products as a consequence. These investigations are focused on the contact area between casting flux and metal. The samples were taken from the mould during the casting process. The results show that layers up to approximately 300 nm from the slag/metal interface represent a specific reaction space. Sodium in this layer on the slag side plays a specific role, which is explained on the basis of experimental results. The transport of oxygen near the interface and the charge transfer is explained on the basis of the ionic character of the slag. The mass transfer rate of oxygen crossing the interface is calculated from measured data, and conclusions concerning the stability of the interfacial tension are made. Keywords: mass exchange, metal slag reaction, interface, ion transport, oxygen transfer, oxidation, casting slag, flux, sodium

Jan 1, 2004

By A. McLean, M. Iwase, K. Wakimoto, K. Katogi

For many decades control strategies have been based upon samples taken from liquid steel, molten slag and gas phase as well as from solid products. Because of recent developments in the areas of dynamic control models, artificial intelligence and expert systems, there is an increasing incentive to develop diagnostic sensors, which permit in-situ rapid determinations of concentrations of various elements in molten steel. In this paper, an overview is given on recent developments in the areas of sensors for use in ferroalloy and steel production. Particular emphasis will be given on (i) innovative application of sensors for on-line determinations of dissolved elements, Si, P, N, H and Cr in molten iron and ferroalloys, (ii) evaluation of inclusions in liquid metal and (iii) rapid determinations of slag compositions.

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 E. Milke, A. Arnold, B. Friedrich, A. Sydykov

CaF2is often used as a fluoride addition to the chloride salt flux in the melting of aluminium scrap. The solubility of CaF2in the chloride salt system is limited. Dissolved CaF2is considered to improve the properties of salt fluxes. Experimental investigations indicated that the solubility ofCaF2in 70 wt % NaCl/30 wt % KCl, German salt flux used in aluminium scrap melting, might be lower than expected according to literature data. The pseudo binary section CaF2-(70 wt % NaCl-30 wt % KCl) was investigated by differential thermal analysis (DTA). The determined solubility of CaF2appeared to be considerably lower than presented in the literature. The pseudo binary section calculated using thermodynamic data partially confirmed the results. DTA allowed us alsoto determine the crystallization temperature interval of the two phase eutectic consisting of the solid solution NaCl-KCl and CaF2. Keywords: aluminium recycling, phase system, salt flux, CaF2, NaCl, KCl, solubility

Jan 1, 2004