New insights into the surface relaxation and oxidation of chalcopyrite exposed to O2 and H2O: A first-principles DFT study

In order to unravel the oxidation mechanism(s) of chalcopyrite (CuFeS₂) surfaces, the surface anisotropy of CuFeS₂ was investigated under both dry and aqueous atmospheres through a fundamental density functional theory (DFT) study. Results showed that the CuFeS₂ (112) surface was the preferred cleavage surface, rather than the commonly-assumed (001) surface. Iron oxides were formed when contacting with either molecular O₂ or dissociated O atoms, but sulfoxy species were only formed in the presence of dissociated O atoms, exposing Cu atoms on the S-terminated (001) and (112) surfaces. This indicates that strong oxidation conditions are beneficial to CuFeS₂ oxidation and the release of metals into solution. In addition, CuFeS₂ was preferentially oxidized by O₂ prior to the adsorption of H₂O under an aqueous condition with both H₂O and O₂. The H₂O adsorbed on the O-oxidized surface further promoted CuFeS₂ oxidation, resulting in the formation of a hydrophilic surface, rather than the naturally hydrophobic surface. This study has unveiled, for the first time, the mechanisms of the oxidation of the most stable and reactive CuFeS₂ (112) and (001) surfaces under both dry and aqueous environments at an atomic level, with potential applications in CuFeS₂ flotation and leaching processes.