A thermodynamic database for copper smelting and converting
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I. INTRODUCTION
THE present study is concerned with the development of thermodynamic models and a thermodynamic database of model parameters for the matte, slag, and blister copper phases in the Cu-Ca-Fe-Si-O-S system. When used with the Gibbs energy minimization software and other databases of the FACT thermodynamic computing system, these databases will permit the calculation of matte-slag-copper-gas phase equilibria that take place during copper smelting and converting. In particular, the copper, sulfur, and magnetite contents of the slag can be accurately calculated over wide ranges of temperature, iron to silica ratio, percentage of lime, and oxygen potential. The solubility of iron in the matte as well as that of sulfur, iron, and oxygen in blister copper can also be computed. Furthermore, one can calculate liquidus temperatures and conditions for precipitation of solid phases from the slag. All these calculations can be readily used to develop a better understanding of modern smelting and converting processes and to optimize the operating conditions. It should be noted that direct experimental study of the gas-matte-slag-copper equilibria is subject to experimental errors because of the complexity of the system and because of problems with sampling, quenching, and analysis of the phases. Entrainment of matte in the slag can also affect the accuracy of measurements.[1] Taking into account the fact that operating conditions of most smelters and converters are not far from equilibrium,[2] one can expect calculations SERGEI A. DEGTEROV, Senior Research Associate, and ARTHUR D. PELTON, Professor of Metallurgy, are with the Centre de Recherche en ´ ´ ´ Calcul Thermochimique, Ecole Polytechnique de Montreal, Montreal, PQ, Canada H3C 3A7. Manuscript submitted August 10, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS B
to be as accurate as or, in certain cases, even more accurate than direct experiments because they are based on experimental data of good quality obtained for less complex subsystems, which are much easier to study. For example, the difference between the measured losses of copper in the slag and the calculated copper solubility will represent the amount of entrained copper. Under conditions of interest for copper smelting and converting, the concentrations of Ca and Si in the matte and liquid copper alloy are very small. Hence, the presence of these components was neglected. The oxygen content in the matte is reported[3,4,5] to decrease with increasing matte grade (wt pct Cu in the matte). For example, the oxygen concentration is about 1.1 6 0.2, 0.8 6 0.2, and 0.2 6 0. 1 wt pct for 50, 60, and 78 wt pct Cu in the matte, respectively. The matte grade is normally higher than 50 wt pct Cu in present day plant practice. Therefore, the presence of oxygen will have only a small effect on the matte-slag-copper-gas equilibria considered in the present study. Consequently, oxygen was not taken into account in the matte model. Oxygen impurity in blister copper after converting may be of some importance, and so
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