Effect of Ag substitution in galena lattice on the adsorption mechanism of flotation reagents: A DFT study

In this study, density functional theory (DFT) calculations were employed to investigate the effects of Ag substitution in the galena lattice on the electronic structure and adsorption mechanisms of flotation reagents. The results show that substitution of Pb by Ag in the galena lattice shifts the valence band toward the conduction band and causes it to cross the Fermi level (E _f ), thereby enhancing the electrochemical activity of the Ag-bearing galena surface. Compared with surface Pb sites, surface Ag sites are more favourable for the adsorption of the collector potassium butyl xanthate (KBX), with an adsorption energy of -0.3061 eV. This behaviour can be attributed to the smaller energy gap ΔE (E _HOMO - E _LUMO ) between the collector and the surface Ag site. Both OH ^- and CaOH ⁺ adsorb more strongly on the Ag-bearing galena surface than on the pure galena surface. This enhanced adsorption is mainly associated with the more covalent character of the Ag-O bond relative to the Pb-O bond, as confirmed by the markedly higher Mulliken population of the Ag-O bond. In addition, Ca ²⁺ in CaOH ⁺ can interact with a surface S site through the formation of a Ca-S bond, resulting in a stronger depressing effect of CaOH ⁺ than OH ^- . These results explain why Ag-bearing galena exhibits better floatability than pure galena but is also more susceptible to depression by OH ^- or CaOH ⁺ . The findings provide a theoretical basis for optimising flotation conditions to improve silver recovery from lead-zinc ores.