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

Dissolution tests of Th(1-x)Ln(x)O(2-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 R-L,R-0 values. Also, by studying the effects of temperature and acidity, this work allowed determining the partial order related to H3O+ (n approximate to 0.7) as well as the activation energy of the dissolution reaction (E-A approximate to 95 kJ mol(-1)) which both account for a surface-controlled reaction mechanism. (C) 2012 Elsevier B.V. All rights reserved.