The kinetics and mechanism of the photo-induced reductive dissolution of hematite (α-Fe2O3) by S(IV) oxyanions, in aqueous suspensions of hematite, have been investigated. Experimental quantum yields for Fe(II)aq production are reported for deoxygenated hematite suspensions containing S(IV). Quantum yield studies together with spectroscopic information indicate that ≡Fe(III)-S(IV) surface complexes undergo a photo-induced ligand to metal charge transfer reaction resulting in the reductive dissolution of hematite and production of Fe(II)aq.
The autoxidation of S(IV) in oxygenated hematite suspensions exhibits autocatalytic behavior. This behavior is interpreted in terms of three general processes: i) production of Fe(II)aq from photo-induced ligand to metal charge transfer reactions of ≡Fe(III)-S(IV) surface complexes, ii) oxidation of Fe(II)aq to Fe(III)aq and, iii) the Fe(III)aq catalyzed autoxidation of S(IV).A numerical model, based on these processes, is developed to predict the disappearance of S(IV) in oxygenated hematite suspensions under illumination.
