Thermodynamic Modeling of the Pb-S and Cu-Pb-S Systems with Focus on Lead Refining Conditions

Thermodynamic modeling of the Pb-S and Cu-Pb-S systems is presented. All available experimental data in these systems are collected, assessed and used to optimize the model parameters. For the liquid phase, a solution (CuI, PbII, SII) is developed using the modified quasichemical model in pair approximation. Liquid copper, liquid lead metal, as well as matte phases are described using single solution with miscibility gaps. Earlier thermodynamic assessments available in the literature did not include all the data on the solubility of Cu and S in liquid Pb at low temperatures, < 750 °C (1023 K), which is important for lead fire refining. In the present study, these additional data points are used in the optimization. For the composition of lead in equilibrium with matte at temperatures > 900 °C (1123 K), a significant discrepancy among different sets of literature data and existing thermodynamic assessments is revealed. Preliminary experiments are performed with the goal to understand the nature of the problem and to develop the methodology based on high-temperature equilibration, rapid quenching and electron probe x-ray microanalysis. The results of this study help to select accurate literature results in the optimization of model parameters. The resulting database is applicable to calculate slag/matte/metal distribution of lead in copper smelting and converting, as well as for predictions in the lead smelting and fire refining.