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

Abstract

The structural and electronic properties of Cu_1.96S 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 Cu_1.96S > 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.