Density functional theory calculation of catalytic sulfidization on the azurite (0 1 1) surface by ammonium salts and its effect on flotation

Abstract

In this study, we performed microflotation experiments and density functional theory (DFT) calculations to investigate the effect of ammonium salts on azurite sulfidization. The flotation recovery of azurite with ammonium salt and Na2S treatment was higher than that with Na2S treatment alone. The DFT calculation showed that the S atom in HS− could bond to Cu atoms on the azurite (011) surface, i.e., it chemically adsorbed on the azurite (011) surface to form copper sulfide species. In the presence of NH3, the adsorption energy decreased from −149.42 kJ/mol to −187.26 kJ/mol compared with only HS− adsorption, and the bond length of CuS increased from 2.17 Å to 2.30 Å, indicating enhanced adsorption of the S species. The Cu 3d and S 2p energy-level overlap range became wider, and the formed CuS species became complex after catalytic sulfidization by ammonium salts, enhancing the stability of the CuS species. During catalytic sulfidization, NH3 species desorbed from the azurite surface and returned to the solution, so ammonium species acted as a catalyst in azurite sulfidization. This work elucidated the role of ammonium salts in the enhanced sulfidization flotation of azurite at an atomic level and further supplemented our previous experimental statement.