Reduction of oxyiron(V) by sulfite and thiosulfate in aqueous solution

The reduction of oxyiron(V), Fe(V)O(4)(3-) by inorganic oxysulfur species (SO(3)(2-) and S2O(3)(2-)) has been studied anaerobically in alkaline medium by using a premix pulse radiolysis technique. Studies on the reactions of Fe(VI)O(4)(2-) with the two sulfur radicals were also carried out. The spectroscopic results demonstrated that sulfur radicals reduced Fe(VI)O(4)(2-) to Fe(V)O(4)(3-) which is subsequently reduced by oxysulfur species by a two-electron reduction step to Fe(III). The rate constants for reduction of Fe(VI)O(4)(2-) to Fe(V)O(4)(3-) by sulfite and thiosulfate radicals (*SO3- and S4O(6)(*3-)) were found to be (1.9 +/- 0.3) x 10(8) and (7.5 +/- 0.8) x 10(7) M(-1) s(-1), respectively. However, the reactions of Fe(V)O(4)(3-) with the SO(3)(2-) and S2O(3)(2-) ions were separated by an order of magnitude, with SO(3)(2-) reacting at (3.9 +/- 0.3) x 10(4) M(-1) s(-1) while S2O(3)(2-) reacted with Fe(V) at (2.1 +/- 0.1) x 10(3) M(-1) s(-1) at pH 11.4.