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 degrees C-1740 degrees 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.