Development of complex technology for pyrite-cobalt concentrate processing by sodium carbonate-carbon reductive...

An integrated pyro-hydrometallurgical technology for the processing of pyrite-cobalt concentrates has been developed based on sodium carbonate-carbon reductive smelting followed by aqueous treatment of the slag-matte melt. Thermodynamic modeling of the Fe-Ni-Co-Cu-O-S system demonstrated that at 1450-1500 °C the Na₂CO₃-C system forms a strongly reducing environment due to CO generation and sulfur fixation as Na₂S. It was established that this mechanism simultaneously decreases oxygen and sulfur potentials, shifting sulfide systems into the metallic stability region of Me-O-S diagrams. New experimental data were obtained on the distribution of Ni, Co, Fe, Cu, and Zn between metallic alloy, slag-matte melt, and volatilized phases during soda-reductive smelting of synthetic and industrial sulfide materials. The optimal smelting parameters were determined as 7-8 wt% carbon and 130-140% Na₂CO₃ of the theoretical requirement for Fe, Ni, and Co (180% for Cu). Under these conditions, recoveries reached up to 96.5% Fe, 94-96% Ni, 97.5-99% Co, and 93.2% Cu. For Zn-bearing sulfide cakes, selective separation was observed: Ni, Co, and Fe were concentrated in a metallic alloy, whereas Zn was transferred predominantly to dust (up to 82.3%). The resulting alloy (Ni ≈ 26%, Co ≈ 42%, Fe ≈ 30%, S ≈ 0.074%) forms a homogeneous γ-(Ni, Co, Fe) solid solution suitable as an intermediate material for alloyed steels and functional alloys.