Integrated experimental and thermodynamic modeling study of phase equilibria in the ‘CuO0.5’-MgO-SiO2 system in equilibrium with liquid Cu metal for characterizing refractory-slag interactions

An integrated experimental and thermodynamic modeling study of the phase equilibria in the ‘CuO’-MgO-SiO system in equilibrium with liquid Cu metal has been undertaken to better understand the reactions between MgO-based refractories and liquid slag in copper converting and refining processes. New experimental phase equilibria data at 1250–1680 °C were obtained for this system using a high-temperature equilibration of synthetic mixtures with predetermined compositions in silica ampoules or magnesia crucibles, a rapid quenching technique, and electron probe X-ray microanalysis of the equilibrated phase compositions. The system has been shown to contain primary phase fields of cristobalite (SiO), tridymite (SiO), pyroxene/protoenstatite (MgSiO), olivine/forsterite (MgSiO), periclase (MgO), and cuprite (CuO). Three regions of 2-liquid immiscibility were found—two in the high-silica range of compositions above the cristobalite primary phase field (close to ‘CuO’-SiO and MgO–SiO binaries) and one in the low-SiO, high-‘CuO’ compositional region above the periclase and olivine phase fields. The results obtained in this study indicate that silica in high-copper refining slags likely led to olivine and pyroxene phase formation, increased solubility of MgO in liquid slag, and decline in the performance of MgO-based refractories. New experimental data were used in the development of a thermodynamic database describing this pseudo-ternary system.