Effect of Slag Basicity on Phase Equilibria and Selenium and Tellurium Distribution in Magnesia-Saturated Calcium Iron S
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INTRODUCTION
SEVERAL factors are taken into consideration when selecting a slag for a metallurgical process. In the pyrometallurgical production of copper from sulfide ore, the traditional practice is to use iron silicate slag. In recent years, calcium ferrite slag has been adopted, such as in the Mitsubishi process for the converting of matte to blister copper.[1] Calcium ferrite slag has advantages over iron silicate, such as ease of operation because of lower slag viscosity, stability of magnetite phase, and copper losses to the slag. In terms of impurities, calcium ferrite slag is basic rather than acidic in nature, so it is more useful for taking up elements such as arsenic, whereas iron silicate slag is more useful for taking up lead. Another alternative is calcium iron silicate (CFS) slag, which can result in lower associated copper losses and refractory wear problems than calcium ferrite. As high-grade ore reserves are depleted and those with higher concentrations of impurities become relied upon, the management of minor elements will become a more significant issue in the production of a high-quality final product and in the handling of waste material. M. D. JOHNSTON, formerly Ph.D. candidate, The University of Western Australia and CSIRO Minerals, Australia, currently a Post-Doctoral Fellow, is with the Department of Materials Science and Engineering, The University of Toronto, 184 College Street, Toronto, ON, Canada, M5S 3E4; S. JAHANSHAHI, Theme Leader, and L. ZHANG, Principal Research Scientist, are with CSIRO Minerals Down Under National Research Flagship, Bayview Avenue, Clayton, Victoria 3168, Australia. Contact e-mail: sharif.jahanshahi@ csiro.au F. J. LINCOLN, Honorary Research Fellow, is with the School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia. Manuscript submitted May 10, 2009. Article published online March 17, 2010. METALLURGICAL AND MATERIALS TRANSACTIONS B
Selenium and tellurium are two such minor elements that have the potential to be troublesome in the processing of low-grade ore. Both are toxic, and although they have some uses such as in electronic components, they are not in great demand. These elements have a high affinity for copper and are typically difficult to remove from the process stream until the final refining stage. Distribution coefficients of Se and Te between iron silicate-based slag, metal and matte reflect this quality.[2,3] Highly basic slags such as those based on sodium carbonate are much more effective for taking up these elements,[4] but this type of slag has inherent problems with refractory wear and environmental hazards through the formation of sodium sulfide. It is also generally preferable to retain these elements in the metal so that they can be recovered from anode slimes and do not become dispersed in the environment from discarded waste slag. The behavior of Se and Te has been characterized in calcium ferrite slag under conditions similar to those employed in co
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