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

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.