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

[Image: see text] 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.