γ-Radiation and H2O2 induced oxidative dissolution of uranium(iv) oxide in aqueous solution containing phthalic acid

Abstract

This study aims to reveal possible involvements of organic acids in the oxidative dissolution of UO₂. Using phthalic acid as a model compound, we have measured adsorption on UO₂ and investigated effects on the reaction between H₂O₂ and UO₂ and on oxidative dissolution induced by γ-irradiation. Significant adsorption of phthalic acid was observed even at neutral pH. However, the reaction between H₂O₂ and UO₂ in phthalic acid solution induced oxidative dissolution of U(VI) similar to in aqueous bicarbonate solution. Moreover, degradation products of phthalic acid were not detected after the reaction of H₂O₂. These results indicate that even though phthalic acid adsorbs on the UO₂ surface, it is not involved in the interfacial reaction of H₂O₂. In contrast, the dissolution of U by irradiation was inhibited in aqueous phthalic acid solution, whereas H₂O₂ generated by radiolysis was consumed by UO₂. Based on these contrasting results, possible roles of radical species generated by water radiolysis were discussed.