In the present work, the amount of alumina pickup in sequence casting was evaluated, and the effect on mould Mould flux samples were taken from a continuous flux viscosity quantified. Changes in crystallisation were slab caster mould at various stages during casting also assessed, and will be presented in a future paper. sequences. These confirmed that the amount of alumina pickup reaches a steady state level within the first 40 min of casting (in agreement with a EXPERIMENTAL PROCEDURE simple model of alumina pickup). The steady stateMeasurement of alumina increase level was 3-4 mass-% higher than the originalThe first aim was to clarify two issues regarding alumina alumina content of the flux. Viscosity measurements increase in the mould flux during practical continuous carried out on two commercial mould fluxes, with casting: (i) the actual extent of alumina increase in modern different levels of alumina added, showed that the clean steel manufacture and (ii) the time taken to reach a viscosity increase as a result of a 4 mass-% increase steady state mould flux composition. in alumina is not likely to affect mould behaviour.Mould flux samples were obtained from two carbon steel Comparison of the measured viscosities with slab casters at the Vanderbijlpark, South Africa plant of predictions from literature models showed that no Iscor Ltd. The casters process mainly low carbon, aluminium single literature model corresponds consistently to killed steels (none of it calcium treated during the present the measured values.I&S/1504 investigation). Samples were collected from the same position in the mould (approximately halfway between the sub-The authors are in the Department of Materials Science and merged entry nozzle and the narrow face of the mould) at

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Despite lengthy operational experience, understanding of the mode and principle of Peirce-Smith converter (PSC) operation has not changed significantly. Some modifications to the typical PSC have been adopted, one notable example being the Hoboken converter, which is fitted with a siphon that permits process gas collection without atmospheric dilution (Bustos et al., 1995). Hoefele and Brimacombe (1979) allude to historical conservatism, rather than technological limitations, as the reasons for resistance to change.Small versions of copper-nickel PSCs are used in platinum group metals (PGMs) smelters for removing Fe and S chemically associated with Cu-Ni mattes rich in PGMs. Lonmin plc operates a PGM PSC approximately one-third the working volume of a typical copper-nickel PSC. Due to the bubbling regime resulting from subsonic flow conditions currently employed in these operations, common problems are encountered. These include tuyere blockages (which necessitate frequent punching operations); high refractory wear in the tuyere region; substantial splattering and splashing, which generate significant amounts of reverts (Richards et al., 1986;Wraith et al., 1994;Kapusta, 2010) and also cause operational downtime with intermittent off-stack periods for cleaning the converter mouth and aisle; and reduced oxygen efficiency, which is attributed to the punching operation as a result of substantial air losses due to leakages, limiting the converter capacity or the reprocessing of reverts and dusts. These process inefficiencies are accompanied by energy inefficiencies or 'excess' power consumption related to punching machines, leaks at the tuyere body due to punching (wasted blower air), and unreacted injected air.The conversion process occurs in a hightemperature environment in a refractory-lined steel shell vessel, which precludes visual observation and experimentation. In order to delineate critical process parameters, physical and numerical modelling techniques have been developed. Physical models with different liquids simulating matte and slag have been developed to study gas plume, splashing, mixing, phase distribution, and mass transfer phenomena (Hoefele and Brimacombe, 1979;Richards et al., 1986; Chibwe, Akdogan, and Eksteen, 2011; Chibwe, Akdogan, Aldrich, and Eric, 2011; Chibwe, Akdogan, Aldrich, and SynopsisPeirce-Smith converters (PSCs) are extensively used in the copper, nickel, and platinum group metals industries. The typical converting operation involves lateral purging of air into molten matte through a bank of tuyeres. This blowing operation occurs at low pressure from the blowers, resulting in a bubbling regime that is considered inefficient from both a process and an energy utilization perspective. Inherent drawbacks also include recurrent tuyere blockage, tuyere punching, and low oxygen efficiency.Western Platinum embarked on a full-scale industrial evaluation of generating a jetting regime by using sonic injection. Prior to industrialscale tests, a numerical assessment to ascertain the feasibil...

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The production of Platinum Group Metals (PGM) normally entails the smelting of PGM flotation concentrates, converting of the furnace matte and removal of the bulk of the Ni, Cu, Co, S and Fe t h r o u g h a t m o s p h e r i c a n d p r e s s u r e l e a c h i n g i n a b a s e m e t a l s r e f i n e r y t o p r o d u c e a P G M -r i c h concentrate. A number of impurities, mostly Se, Te, As, Bi, Os and Pb, are not removed significantly during the oxidising leach process in sulphuric acid media. In addition slag inclusions in matte leads to contamination of the PGM residues with silica, fayalite, magnetite and trevorite phases. Furthermore some Cu, Ni, Fe and S also remain. For this reason a typical Precious Metal Refinery (PMR) feed material contains less than 65% PGMs. The PMR is based on a chloride process and requires contaminants to be within narrow specification limits to prevent the formation of PGM residues that must be reprocessed or tolled, leading to poor first pass metal efficiencies and extending the duration of the production pipeline for efficient recovery.A process has been developed to significantly upgrade the BMR leach residues through pyrometallurgical processing, which include a multistep process of roasting under oxidising atmospheres, a two-step smelting process of the roasted calcine (with engineered slag chemistry and slag-refractory interactions) and subsequent atomisation of the molten alloy which can be fed as a slurry into the HCl/Cl 2 dissolution reactors in the precious metals refinery. These pyrometallurgical steps upgrade the BMR residue from a 45-50% grade up to an alloy grade of circa 90% PGMs, whilst removing the most deleterious elements with major process impacts on the PMR. This paper will focus primarily on the roasting step and it will investigate the thermochemical and mineralogical changes occurring during roasting. These changes were evaluated through a combination of thermochemical modelling and experimental investigation. The roasting step needs to be in an oxidative environment in order to achieve the vaporization of Se, Te, As, Os and S. The speciation of PGMs and their vaporization behaviour are presented, as well as the sensitivity of precious metals deportment to changes in roast conditions.