ON THE KINETICS OF BISULFITE AUTOXIDATION CATALYZED BY MANGANESE(II) IONS

Manganese(II)-catalyzed oxidation of bisulfite aqueous solutions by di ssolved oxygen is considered with a stress on the kinetics of the reac tion. The review includes an experimental study of the radiation-induc ed oxidation as well as a steady state analysis of its kinetics couple d with experimental data. The oxidation is shown to be a chain reactio n involving Mn(II)/Mn(III) redox cycling induced by reactions of oxysu lphur radicals SOx-(x = 3 - 5). The MnHSO3+ complex is found to be the reactive bivalent state of manganese(II). These results, together wit h those present in the literature, make it possible to extend the so-c alled 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 c ritical analysis of available rate constants of the elementary steps i nvolved in the oxidation, as well as empirical rate laws for the catal ytic reaction as a whole, are given. Estimations of the rate constants of a number of elementary steps of the oxidation are reported. This k inetic analysis is found also to describe the kinetics of the ''dark'' initiated reaction due to unavoidable traces of Fe(II)/Fe(III) presen t in the system. An analysis is given of the effect of atmospheric flu xes of OH/HO2 radicals on the kinetics of S(IV) oxidation.