Experimental and thermodynamic modeling study of phase equilibria in the PbO–NiO–SiO2 system

An integrated experimental and thermodynamic modeling investigation of the phase equilibria in the PbO–NiO–SiO2 system in air and also in equilibrium with liquid metal has been undertaken to better characterize the chemical reactions taking place in the Ni‐containing Pb processing slags. New experimental phase equilibria data at 720°C–1740°C were obtained for this system using high‐temperature equilibration of synthetic mixtures with predetermined compositions in sealed silica ampoules or in Au/Pt–Ir foils, a rapid quenching technique, and electron probe x‐ray microanalysis of the equilibrated phase compositions. Phase equilibria and liquidus isotherms in the quartz/tridymite/cristobalite (SiO2), olivine (Ni2SiO4), monoxide (NiO), Ni‐barysilite (Pb8NiSi6O21), massicot (PbO), and di‐lead silicate (Pb2SiO4) primary phase fields were revealed and the extent of the high‐SiO2 two‐liquid immiscibility gap in equilibrium with cristobalite was determined. New experimental data were used in the development of a thermodynamic database describing this ternary system. Also, modeling revision of the NiO–SiO2 binary system was conducted, resulting in a smaller miscibility gap in ternary systems that was closer to the experimental results.