Study of the Effect of Absorbed Cu Species on the Surface of Specularite (0 0 1) by the DFT Calculations

Cu²⁺ exhibited a good activation effect on specularite. However, its microscopic activation mechanism needs further study. Additionally, Cu²⁺ was mainly present in the flotation solution as Cu²⁺, Cu(OH)⁺, and Cu(OH)₂ at pH = 7. Therefore, density functional theory (DFT) calculations were used to investigate the effect of Cu species such as Cu²⁺, Cu(OH)⁺, and Cu(OH)₂ adsorbed on the crystal structure and properties of the specularite (0 0 1) surface. The adsorption mechanism of different Cu components on the surface was also further clarified by the analyses of the adsorption model, adsorption energy, partial density of states (PDOS), charge transfer, and bond properties. In addition, the obtained results are discussed. Based on the obtained results, it can be concluded that the geometric structure and electronic properties on the surface changed after adsorbing Cu components and that the O3–Fe1–O1 structure was more susceptible to the adsorbates. The adsorption engines results show that Cu components could be spontaneously adsorbed onto the specularite (0 0 1) surface with adsorption energies of −0.76, −0.85, and −1.78 eV, corresponding to Cu²⁺, CuOH⁺, and Cu(OH)₂, respectively. Therefore, the adsorption stability of the Cu species on the specularite surface increased in the order of Cu²⁺ < Cu(OH)⁺ < Cu(OH)₂. Additionally, the adsorption sites for Cu species on the surface were different. Cu²⁺ interacted mainly with O atoms on the surface, forming Cu–O complexes, while Cu(OH)⁺ and Cu(OH)₂ acted mainly through the O atom of –OH, interacting with Fe atoms to form Cu–O–Fe complexes. The formation of Cu–O and Cu–O–Fe complexes increased the adsorption sites for sodium oleate, with more hydrophobic species being generated to improve the floatability of specularite.