Hydroperoxo [Fe(III)-OOH] and ferryl-oxo [Fe(IV) = O] oxidative species involved in As(III) oxidation catalyzed by pyrite under alkaline conditions

Pyrite is an extensively-distributed mineral that catalyzes oxidation of As(III) to As(V) by dissolved oxygen (DO) in natural environments; however, the catalytic mechanism of pyrite under alkaline conditions is still not clear. In this study, we observed increased oxidation rates of soluble As(III) with increasing pHs under alkaline conditions (7.5-11.0). ESP analysis and quenching experiments rule out contributions of center dot OH, O-2(center dot-) and (1)O(2 )to As(III) oxidation, and indicate that Fe(III)-OOH and/or H2O2 are indeed the primary oxidative species at pHs 9.0 and 11.0, and Fe(IV) = O also contributes at pH 11.0. Selective oxidation of a series of organic substrates to the corresponding oxidation products confirms the presence of Fe(III)-OOH and/or Fe(IV) = O in the pyrite system in alkaline solutions or organic solvents. Although the addition of glucose apparently increases the production of H2O2 at pHs 9.0 and 11.0, such an increase does not apparently accelerate the oxidation rate of As(III), implying that H2O2 is not the predominant species in the oxidation of As(III). This study provides new insight into the oxidative species in the pyrite-DO system under alkaline conditions.