Understanding the wettability and natural floatability of PbS with different types of vacancy defects: A perspective from spin-polarized DFT-D and MD

Abstract

Natural galena (PbS) usually contains some defects and impurities, which will greatly affect its wettability and natural floatability. In this paper, the wettability and wetting mechanisms of the perfect PbS (1 0 0) surface (PG) and defective surfaces with sulfur vacancy (SV), lead vacancy (PbV), and double neighboring vacancies (DV) were innovatively investigated using spin-polarized Density Functional Theory-Dispersion included (DFT-D) calculations and Molecular Dynamics (MD) simulations. We found the active sites for H2O adsorption on the perfect and defective PbS surfaces were the S atoms, and the reactivity of S at the defect on SV surface decreased, on PbV surface slightly increased while on DV surface greatly increased. Furthermore, we found H-bond between H and S atoms was the main driving force for H2O adsorption, and the single sulfur vacancy increased the hydrophobicity, lead vacancy decreased the hydrophobicity while double neighboring vacancies more decreased the hydrophobicity. Thus, the natural floatability of different PbS was in the order of SV > PG > PbV > DV. Moreover, the primary factor to determine the differences in the wettability and natural floatability of different types of PbS was found to be the reactivity of S at the defects but not the steric hindrance effect and the density of the active sites.