Oxidation of galena (PbS) is of crucial importance in environmental and geochemical processes. Hydrophobic nature of galena surface hinders the adsorption of water, which involves and determines the finally oxidative product of galena. In this work, DFT simulations of the adsorption of O-2 and H2O on the hydrophobic galena surface have been performed. Results show that the isolated O-2 molecule is dissociated and adsorbed on the S atoms of galena surface, and the isolated H2O molecule hardly interacts with the hydrophobic galena surface. However, the dissociation of both H2O and O-2 molecules occur after coadsorption, and water molecule dissociates into O-w and H radicals, which then react with surface S atom and adsorbed O-2 molecule to form S=O-w radical and hydrogen peroxide, respectively. Further adsorption of hydrogen peroxide on surface Pb atoms produces lead hydroxyl radicals. This work could provide microscopic insight into the mechanism of galena oxidation. (C) 2017 Published by Elsevier B.V.