INTERACTION OF GALENA WITH HYDROSULFIDE IONS UNDER CONTROLLED POTENTIALS

The surface species produced by the anodic oxidation of hydrosulphide ions at galena surfaces have been determined by X-ray photoelectron spectroscopy. Components in the S(2p) spectrum appeared at binding energies typical of sulphur atoms in an oligosulphide. The relative intensities of these components suggested that lead oligosulphides with sulphur chain lengths of up to S4 (or S8 if a chelate) had been formed on the mineral surface. No evidence was found for the deposition of elemental sulphur. The oligosulphide is associated with a dispersed layer of lead sulphide formed by interaction of oxidized lead species and HS-. Investigations were also carried out on the surface oxidation of galena on exposure to air. Previous findings that the formation of lead hydroxide becomes evident from a shifted component in the Pb(4f) spectrum without any new sulphur environment being apparent from the S(2p) spectrum were confirmed. This behaviour is ascribed to diffusion of lead atoms from the bulk to maintain only a small metal deficiency in a lead-deficient sulphide layer formed concomitantly with lead hydroxide.