Pyrite dissolution in acidic media

Oxidation of pyrite in aqueous solutions in contact with air (oxygen 20%) was studied at 25°C using short-term batch experiments. Fe and SO4 2 were the only dissolved Fe and S species detected in these solutions. After a short period, R [S]tot/[Fe]tot stabilized from 1.25 at pH 1.5 to 1.6 at pH 3. These R values were found to be consistent with previously published measurements (as calculated from the raw published data). This corresponds to a nonstoichiometric dissolution (R 2) resulting from a deficit in aqueous sulfur. Thermodynamics indicate that S( I) oxidation can only produce S(s) 0 and SO4 2 under these equilibrium conditions. However, Pourbaix diagrams assuming the absence of SO4 2 indicate that S2O3 2 and S4O6 2 can appear in these conditions. Using these species the simplest expected oxidation mechanism is FeS2 s 1.5O2→ Fe 2 S2O3 2