Thermodynamic modeling of lead distribution among matte, slag, and liquid copper
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I. INTRODUCTION
LEAD is a detrimental element that is always present in sulfide concentrates and that must be eliminated during copper smelting. Thermodynamic calculations permit a better understanding and prediction of the behavior of lead under various conditions. Calculations of the effect of process variables on the distribution of lead among the matte, slag, copper and gas phases can provide a basis for improved metallurgical control of copper quality, as well as economical and environmental factors. Thermodynamic analysis was used to assess the behavior of minor elements in copper smelting in a number of studies (e.g., References 1 through 5) and proved to be very successful. The purpose of the present work is to improve significantly the accuracy of the thermodynamic calculations by critical evaluation and optimization of all available thermodynamic data in a self-consistent and thermodynamically correct manner. We have recently critically assessed and optimized the thermodynamic properties of the slag, matte, and liquid copper phases in the Cu-Ca-Fe-Si-O-S system over the range of compositions of importance to copper smelting and converting[6] and have developed a thermodynamic database of model parameters for the three phases. With this database, it is possible to calculate accurately the copper, sulfur, and magnetite contents of the slag over wide ranges of temperature, iron to silica ratio, percentage of lime, and oxygen potential. Sulfide contents (sulfide capacities) of the slags are predicted within experimental error limits. The solubility SERGEI A. DEGTEROV, Senior Research Associate, CRCT, and ARTHUR D. PELTON, Professor, Department of Metallurgy and Materials Science, are with Ecole Polytechnique de Montreal, Montreal, PQ, Canada H3C 3A7. Manuscript submitted December 29, 1998.
METALLURGICAL AND MATERIALS TRANSACTIONS B
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. The addition of lead to this thermodynamic database is the purpose of the present article. 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.[7] Taking into account the fact that the operating conditions of most smelters and converters are not far from equilibrium,[8] one can expect the calculations to be as accurate 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. The modified quasi-chemical model[9–12] is used to describe the thermodynamic properties of the slag, matte, and liquid copper alloy. Strictly speaking, there is just one liquid phase in th
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