Measurements of the free charge carrier (FCC) absorption of infrared (IR) radiation during oxidation of lead sulfide surfaces both in air and in aqueous solutions, either by dissolved oxygen or by anodic polarization, shows that oxidation of PbS is always accompanied by the formation of a metal-depleted layer at the surface. However the attained degree of non-stoichiometry is limited and the sulfur-enriched layer at the surface relaxes spontaneously with the formation of stoichiometric PbS and sulfur species. Oxidized PbS surfaces adsorb xanthate from deoxidized solutions easily and fast, even if the oxidized lead species have been removed from the surface. The electrosorption of xanthate radicals driven by the oxidation of xanthate ions by the sulfur species present at the surface seems to be the most probable explanation of that behavior.
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