THE SURFACE OXIDATION OF PYRITE

The surface oxidation in air and air-saturated aqueous solutions of the iron sulfide mineral, pyrite, has been studied by X-ray photoelectron spectroscopy. Iron sulfate was produced on fracture surfaces within the first few minutes of exposure to air under ambient conditions. Iron oxide was also included in the oxidation products after prolonged exposure which implies that a sulfur product in addition to sulfate must be formed. It is suggested that this product is an iron-deficient sulfide. Elemental sulfur was not evident at surfaces exposed to air. Iron oxide rather than sulfate was present at abraded surfaces exposed to air for a few minutes. Oxidation of pyrite in air-saturated acid solutions resulted in the formation of a surface sulfur layer the extent and nature of which depended on solution composition and exposure time. Sulfate was the only sulfur oxidation product identified in alkaline solutions not containing soluble sulfide, and iron oxide remained at the surface after such treatment.