A thermodynamic study on cobalt containing calcium ferrite and calcium iron silicate slags at 1573 K
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NTRODUCTION
IN times of high cobalt prices, cobalt can be a significant source of income for copper and nickel smelters.[1] Nonferrous smelters therefore need to utilize strategies to maximize cobalt recovery. Knowledge of the effect of key process variables, such as slag composition and the oxidation state of the slag on the thermodynamic behavior of cobalt oxide in slag, is necessary when devising strategies to increase the recovery of cobalt during smelting and converting.[2] Calcium ferrite slag, with a composition within the system CaO-Fe2O3-FeO, is a relatively recent type of slag that is used in the Mitsubishi continuous copper-converting process, which is being installed at a smelter at Port Kembla in Australia. Recent work on continuous converting of copper concentrate into blister copper in a single step has led to the development of a slag practice, which is also based on calcium ferrite.[3] According to Yazawa et al.,[4] calcium ferrite slag is likely to be used by more nonferrous smelters in the future because it has several benefits over traditional iron silicate slag. It is little affected by magnetite precipitation at high oxygen potential conditions and so has a high “holding capacity” for iron oxides. It is much more basic than iron silicate slags so there is less loss of valuable basic metal oxides due to chemical dissolution, and it also has a high holding capacity for minor elements whose oxides are acidic, e.g., arsenic, antimony, and phosphorus. In addition the low viscosity reduces the extent of metal losses through mechanical entrainment. In smelting processes, the recovery of valuable metals such as cobalt is one of the critical success factors. As such, K.C. TEAGUE, Lecturer, formerly with the Department of Chemical and Metallurgical Engineering, Royal Melbourne Institute of Technology, is with the Division of Science and Engineering, Murdoch University, Murdoch, 6150, Australia. D.R. SWINBOURNE, Associate Professor and Discipline Leader, is with the Department of Chemical and Metallurgical Engineering, Royal Melbourne Institute of Technology, Melbourne, 3001, Australia; also Associate, G.K. Williams Cooperative Research Centre for Extractive Metallurgy, CSIRO Minerals. S. JAHANSHAHI, Chief Research Scientist and Research Program Manager, is with the G.K. Williams Cooperative Research Centre for Extractive Metallurgy, CSIRO Minerals, Clayton South, 3169, Australia. Manuscript submitted February 28, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
some effort has been directed toward the determination of thermodynamic data on the distribution of valuable metals between the phases present, including solid solutions. Takeda et al.[5] estimated the value of the activity coefficient of CoO (s) to be 1.4 in calcium ferrite at 1523 K, as part of a study into the distribution of minor elements between slag and blister copper. However, the amount of cobalt present was small so the precision of the results can be questioned. Nagamori et al.[6] developed a statistical thermodynamics model of calcium
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