Gibbs Energy Modeling of High-Temperature Bornite: Application on Calculation of Phase Equilibria of the Cu-Fe-S System

Gibbs energy modeling of high temperature bornite is carried out from liquidus to mediate temperatures at a total pressure of one bar. A three sublattice approach using the compound energy formalism is developed which is consistent with a recently reported critical assessment and optimization of the Cu-S sulfide digenite. The first comprehensive comparison with experimental phase diagram data can be carried out on the basis of an adequate reproduction of the homogeneity range of high-temperature bornite which emanates from digenite into the Cu-Fe-S phase space with a substantial iron solubility. Ternary heat capacity data at the composition of Cu5FeS4, considered for the first time for Gibbs energy modeling, provides the basis for a reliable extrapolation to lower temperatures. A recently presented two-sublattice model for high-temperature pyrrhotite is adapted for accordance with its limited but relevant copper solubility. Eleven phase diagram sections of the Cu-Fe-S system – five isopleth and six isothermal sections – are calculated over the total ternary composition range for comparison with experimental data available in the literature. Together with further development of the Cu-Fe-S liquid phase model agreement between calculation and experimental data is achieved in a fair to a very satisfactory manner.