Effect of sulphuric acid on the cobalt-60 γ-ray induced oxidation of ferrous sulphate solutions

Abstract

The effects of variations in sulphuric acid and oxygen concentrations on the yields of ferric ion from cobalt-60 gamma irradiated solutions of ferrous sulphate have been studied. Various kinetic models, some derived from reaction mechanisms suggested in the literature and some derived from new mechanisms, were used to compare calculated G(Fe³⁺) values with experimental values from over 600 irradiations of solutions ranging in sulphuric acid concentration from 0.04 mol dm^–3 acid/0.1 mol dm^–3 sodium sulphate to 1.0 mol dm^–3 acid. The reaction stoichiometry over the entire range of acid and solute concentration was well described by an equation which incorporated terms for inhibition of charge pair recombination by the acid and solute. The calculated values of G(H + e^–_aq) are significantly lower than those usually quoted and show little variation with acid concentration; 3.07 ± 0.05 to 3.18 ± 0.05 for the acid range used. G(charge pair) from the model was found to be 0.7 ± 0.05 and G(total ion pair) 4.7 ± 0.15. The ratio of rate constants k_H,Fe²⁺/k_H,O2 was found to be (1.14 ± 0.03)× 10^–3 and independent of pH.