Electronic structure and oxidation mechanism of nickel-copper converter matte from first-principles calculations

Abstract

The structural and electronic properties of Cu1.96S and Ni3S2 present in nickel-copper converter matte and sulfides such as CuS, Ni7S6, NiS, Ni3S4, and NiS2, likely existing as intermediates in the oxidative leaching of the matte, were investigated using first-principles calculations. Analyses of the total and partial density of states (DOS), with electron density and differential charge density, show that Cu-S and Ni-S bonds are of covalent character, and as the ratio of Ni/Cu to S decreases for the sulfides, Cu/Ni-3d orbital energies shift downward, while S-3p orbital energies shift upward. According to the values of their Cu/Ni-3d band centers, the oxidation activity decreases in the order Cu1.96S > Ni3S2 > Ni7S6 > NiS > Ni3S4 > NiS2 > CuS. This oxidation sequence leads to thermodynamically favorable substitution reactions between the nickel sulfides and Cu2+ for obtaining more stable CuS, which is the theoretical basis of Sherritt Gordon's selective leaching process.