Phase equilibrium between Ni-S melt and CaO-Al2O3 based slag in Co-Co2-So2 gas mixtures at 1773 K

Abstract

To provide thermodynamic data for converting the nickel matte to liquid nickel, an experimental study was conducted in the phase equilibrium between the Ni-S alloy and the CaO-Al2O3 based slag melted in a MgO or Al2O3 crucible at 1773 K under controlled PSO2 of 10.1 kPa and PO2 in a range between 5.0 × 10-3 and 1.6 Pa by using CO-CO2-SO2 gas mixtures. The contents of nickel in these slags at PO2 of 1.6 Pa, above which solid NiO is expected to precipitate in equilibrium state, were found to be 5.6 and 7.2 mass% for the slags melted in the MgO and Al2O3 crucibles, respectively. The contents of sulfur and oxygen in the nickel melt at PO2 of 1.6 Pa were 2 and 0.4 mass%, respectively. The CaO-Al2O3 based slag with the mass% ratio (CaO/Al2O3) of about 1 melted in the MgO crucible was homogeneous in the investigated PO2 range. While, that with the ratio of about 0.5 melted in the Al2O3 crucible formed two phases composed of a liquid and an Al2O3-NiO solid solution whose nickel content was increased with increasing PO2. The dissolutions of nickel and sulfur in the slag melted in the MgO crucible were discussed on the basis of distribution ratio and sulfide capacity, respectively.