Experimental and thermodynamic modeling study of phase equilibria in the ZnO–SnO–SnO2–SiO2 system

Abstract

Experimental investigation and thermodynamic modeling of the phase equilibria in the ZnO–SnO–SnO₂–SiO₂ system have been undertaken to characterize Sn behavior in the high-Zn slags for recycling of waste electrical and electronic materials (WEEE) through the black copper process. Phase equilibria data at 870–1746°C were obtained through equilibration of synthetic mixtures in sealed silica ampoules or open crucibles, on Ir wires, Pt, Pt-Ir, Mo, and Re foils, followed by rapid quenching, and electron probe X-ray microanalysis. Phase equilibria and liquidus isotherms of the ZnO–“SnO”–SiO₂ system in equilibrium with Sn metal, ZnO–“SnO₂”–SiO₂ system in air, and ZnO–SnO–SnO₂–SiO₂ in equilibrium with Au–Sn metal were measured in the quartz/tridymite/cristobalite SiO₂, cassiterite SnO₂, zincite ZnO (with minor solubility of SnO₂), willemite Zn₂SiO₄, and spinel Zn₂SnO₄ phase fields.