Enhancement of the nickel converter slag-cleaning operation with the addition of spent potlining

The slag cleaning (or matte settling) process was experimentally investigated at 1573 K using a fayalitic nickel converter slag containing spinel and matte/alloy particles. The addition of various amounts of spent potlining (SPL) was studied in terms of its influence on matte settling and the overall metal recoveries. The slags produced were characterized by scanning electron microscopy, energy-dispersive spectroscopy, and wet chemical analysis using inductively coupled plasma optical emission spectrometry. The presence of solid spinel particles in the molten slag hindered coalescence and settling of matte/alloy droplets. Matte settling was effectively promoted with the addition of as little as 2wt% SPL because of the reduction of spinel by the carbonaceous component of the SPL. The reduced viscosity of the molten slag in the presence of SPL also contributed to the accelerated matte settling. Greater metal recoveries were achieved with larger amounts of added SPL. Fast reduction of the molten slag at 1573 K promoted the formation of highly dispersed metal particles/clusters via accelerated nucleation in the molten slag, which increased the overall slag viscosity. This increase in viscosity, when combined with rapid gas evolution from accelerated reduction reactions, led to slag foaming.