Equilibrium Distributions of Pb, Bi, and Ag between Fayalite Slag and Copper-Rich Metal, Calcium Ferrite Slag and Copper-Rich Metal. Thermodynamic Assessment and Experimental Study at 1250 °C

Abstract

Rising concentrations of impurities are expected at copper fire-refining stage due to lower availability of high-quality copper concentrates and due to increasing recycling of electronics and other secondary materials in primary copper smelting. Extra steps involving the removal of impurities from copper into the slag phase may provide a solution, but better understanding of thermochemistry is needed to evaluate the feasibility of changes in the process. In the present study, the distribution coefficients of Pb, Bi, and Ag between the fayalite or calcium ferrite slags and copper-based metal at 1250 °C were measured experimentally, using high-temperature equilibration, rapid quenching, and electron probe X-ray microanalysis (EPMA). The experiments were undertaken in a closed system using a modified substrate support technique, at relatively high oxidizing conditions typical for copper refining. The improved substrate technique enables the measurement of distributions coefficients for slags in equilibrium with solid spinel (Fe3O4) or dicalcium ferrite (Ca2Fe2O5). Experimental results of the present study and the literature data were analyzed together using thermodynamic modeling. As a result, thermodynamic database has been developed and used to predict the effects of oxygen partial pressure, wt% Cu in slag, temperature, and Fe/SiO2 and Fe/CaO in slags on the distribution coefficients of Pb, Bi, and Ag for the fayalite and calcium ferrite slag systems.