Radiation oxidation of tetravalent uranium solutions

Abstract

Treatment of a sulfuric acid solution of tetravalent uranium. containing 0.8 N H₂SO₄, in the absence of O₂ and at a concentration of U⁺⁴ ∼100 mg-equiv/liter, with Co⁶⁰ γ-radiation gave an oxidation yield of U⁺⁴ close to 5.0. U⁺⁴ was not oxidized by the molecular ion H ⁺₂ even with greatly increased acidity of the solution and a decreased U⁺⁴ concentration. A decrease in U⁺⁴ concentration resulted in a lower yield mainly due to recombination of the H and OH radicals. An equation for the relation of G to [U⁺⁴] is put forward which agrees with experimental data, and a ratio involving the rate constants of the three reactions H + OH, H + H and U⁺⁴ + OH was found. A decrease in the yield G was observed on increasing the U⁺⁴ concentration above 110 mg-equiv/liter. This phenomenon is apparently explained by the reduction of U⁺⁴ radicals by H. We considered, some mechanism by which uranyl ions may retard U⁺⁴ oxidation. As a result of this consideration we were able to calculate the ratio of the rate constants of the reactions UO ⁺²₂ + H and H + H and a ratio involving the rate constants of the reactions UO ⁺²₂ + OH, H + OH and H + H.

An equation based on the mechanism suggested for the oxidation of tetravalent uranium in dilute solution in the presence of uranyl ion has been deduced for the relation of G to [U⁺⁴] and [UO ⁺²₂ ] and this agrees with the experimental data for a wide range of concentrations.