On the kinetics of bisulfite autoxidation catalyzed by manganese(II) ions

Manganese(II)-catalyzed oxidation of bisulfite aqueous solutions by dissolved oxygen is considered with a stress on the kinetics of the reaction. The review includes an experimental study of the radiation-induced oxidation as well as a steady state analysis of its kinetics coupled with experimental data. The oxidation is shown to be a chain reaction involving Mn(II)/Mn(III) redox cycling induced by reactions of oxysulphur radicals SOx-(x = 3 - 5). The MnHSO3+ complex is found to be the reactive bivalent state of manganese(II). These results, together with those present in the literature, make it possible to extend the so-called general free radical mechanism by adding reactions involving Mn(III), in particular those responsible for chain termination: Mn(III) + Mn(III), Mn(III) + SO5-, Mn(III) + HO2 (in oxygenated solutions). A critical analysis of available rate constants of the elementary steps involved in the oxidation, as well as empirical rate laws for the catalytic reaction as a whole, are given. Estimations of the rate constants of a number of elementary steps of the oxidation are reported. This kinetic analysis is found also to describe the kinetics of the ''dark'' initiated reaction due to unavoidable traces of Fe(II)/Fe(III) present in the system. An analysis is given of the effect of atmospheric fluxes of OH/HO2 radicals on the kinetics of S(IV) oxidation.