Nonstoichiometry in the oxidative dissolution of pyrite in acid solutions.

The oxidative dissolution of pyrite, FeS2, by Fe(III) ions in hydrochloric acid solutions at around pH 2 was investigated by spectrophotometry, ICP-AES and X-ray photoelec-tron spectroscopy (XPS). All the experimental results showed that the preferential dissolution of iron in pyrite took place resulting in the formation of a surface layer enriched with sulfur. The preferential dissolution was enhanced by increasing the initial concentration of Fe(III) ions. Accordingly, a classical stoichiometric dissolution ([Fe]/[S] = 0.5) mechanism can not explain the present results. The dissolution rate was independent of CI ion concentration, but dependent on Fe(II) ion concentration. The oxidative dissolution of pyrite was suppressed by increasing the concentration of Fe(II) ions. The present results suggest that the kinetic equations should be formulated, considering both dissolved iron and sulfur species.