Multiparametric study of Th1−xLnxO2−x/2 mixed oxides dissolution in nitric acid media

Dissolution tests of Th1−xLnxO2−x/2 solid solutions were undertaken in nitric acid media in order to evaluate the effects of several physico-chemical parameters such as chemical composition, temperature and acidity on the dissolution kinetics. In these conditions, the trivalent lanthanide incorporation rate (x) was found to strongly impact the normalized dissolution rate as, the concomitant formation of oxygen vacancies weakened the crystal structure thus decreased the chemical durability. Conversely, nor the nature of the trivalent cation considered, neither that of tetravalent element, seemed to have a significant influence on the RL,0 values. Also, by studying the effects of temperature and acidity, this work allowed determining the partial order related to H3O+ (n ≈ 0.7) as well as the activation energy of the dissolution reaction (EA ≈ 95 kJ mol−1) which both account for a surface-controlled reaction mechanism.

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► Dissolution of Th1−xLnxO2−x/2 solid solutions was examined in nitric acid media.
► Preponderant role of Ln3+ loading on dissolution rate was pointed out.
► Temperature and proton activity influence were studied.
► Dissolution was found to process through surface-controlled reaction.