Effects of surface spatial structures and electronic properties of chalcopyrite and pyrite on Z-200 selectivity

Chalcopyrite (CuFeS2) is one of the main copper minerals, and is always found associated with pyrite (FeS2). To obtain a satisfactory Cu concentration, the undesirable pyrite component must be discharged into tailings. O-isopropyl-N-ethyl thionocarbamate (Z-200) has been proven to be a collector with good selectivity for chalcopyrite flotation. However, the fundamental mechanism for the much greater selectivity of Z-200 for chalcopyrite than for pyrite is still not clear. In the present study, density functional theory (DFT) calculations have been performed to investigate the interaction mechanism of Z-200 with chalcopyrite (1 1 2) and pyrite (1 0 0) surfaces, and to understand the better selectivity of Z-200 for chalcopyrite during Cu–S flotation separation. Calculated parameter tests suggest that, for the calculation of chalcopyrite, using antiferromagnetism and the Hubbard U correction is very important to obtain its reasonable structural and electronic properties. Moreover, antiferromagnetism determines the activity of copper ions on the chalcopyrite surface. The Z-200 adsorption results suggest that the structures of the mineral surfaces and Z-200 molecules as well as the electronic structures of the Cu and Fe ions are critical for the selectivity of Z-200. The (1 1 2) surface of chalcopyrite obviously relaxes after cleavage, leaving iron, copper, and sulphur ions almost on the same plane. The adsorption of Z-200 on the chalcopyrite (1 1 2) surface has an energy barrier of 78.7 kJ/mol and is exoenergetic by 101.5 kJ/mol, whereas the adsorption of Z-200 on the pyrite surface is very weak, with an adsorption energy of –32.0 kJ/mol. Copper atoms can be pulled up from the surface by the adsorption of Z-200 to restore the tetrahedral structure of Cu, but the pyrite surface Fe atoms cannot be pulled up. Considering these results, the surface structure of pyrite is determined to be non-conducive to the adsorption of Z-200, and the possible influences of the electronic structure of Cu and Fe ions on the adsorption of Z-200 are discussed.