Experimental study and thermodynamic optimization of the CaO–NiO, MgO–NiO and NiO–SiO2 systems

A combination of thermodynamic modeling and experimental studies is used to characterize NiO-containing oxide systems at high temperature of interest to nickel pyrometallurgical processes. This is part of an on-going research project to develop a self-consistent multi-component thermodynamic database. A literature review and critical assessment of the previously published thermodynamic and phase equilibrium data on the NiO-containing binary systems CaO-NiO, MgO-NiO and NiO-SiO at a total pressure of 1 atm have been performed using thermodynamic modeling. Considerable discrepancies among previously available experimental data have been found for the CaO-NiO and MgO-NiO systems. To resolve the contradictions in the literature data, a new experimental investigation has been carried out using an equilibration and quenching technique followed by electron probe X-ray microanalysis (EPMA). The CaO-NiO phase diagram in air has been measured from 1200 to 1600°C. The equilibrium between the MgO-NiO solid solution, metal alloy and gas phase has been studied over the temperature range from 1000 to 1300°C, which enabled the activity of NiO to be calculated. The whole set of experimental data, including the new experimental results and previously published data, has been taken into consideration in thermodynamic modeling of oxide phases in the CaO-NiO, MgO-NiO and NiO-SiO systems at a total pressure of 1 atm. The Modified Quasichemical Model has been used for modeling of the liquid phase. A simple random mixing model with a polynomial expansion of the excess Gibbs energy has been used for the monoxide solid solution. The optimized model parameters reproduce all available thermodynamic and phase diagram data within experimental error limits.