Electronic Structure and Oxidation Mechanism of Nickel–Copper Converter Matte from First-Principles Calculations

The structural and electronic properties of Cu 1.96 S and Ni 3 S 2 present in nickel-copper converter matte and sulfides such as CuS, Ni 7 S 6 , NiS, Ni 3 S 4 , and NiS 2 , 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 Cu 1.96 S > Ni 3 S 2 > Ni 7 S 6 > NiS > Ni 3 S 4 > NiS 2 > CuS. This oxidation sequence leads to thermodynamically favorable substitution reactions between the nickel sulfides and Cu 2+ for obtaining more stable CuS, which is the theoretical basis of Sherritt Gordon's selective leaching process.