Dissolution of Cerium(IV)–Lanthanide(III) Oxides: Comparative Effect of Chemical Composition, Temperature, and Acidity

The dissolution of Ce_1–<i>x</i>Ln_<i>x</i>O_{2–<i>x</i>/2} solid solutions was undertaken in various acid media in order to evaluate the effects of several physicochemical parameters such as chemical composition, temperature, and acidity on the reaction kinetics. The normalized dissolution rates (<i>R</i>_L,0) were found to be strongly modified by the trivalent lanthanide incorporation rate, due to the presence of oxygen vacancies decreasing the samples cohesion. Conversely, the nature of the trivalent cation considered only weakly impacted the <i>R</i>_L,0 values. The dependence of the normalized dissolution rates on the temperature then appeared to be of the same order of magnitude than that of chemical composition. Moreover, it allowed determining the corresponding activation energy (<i>E</i>_A ≈ 60–85 kJ·mol^–1) which accounts for a dissolution driven by surface-controlled reactions. A similar conclusion was made regarding the acidity of the solution: the partial order related to (H₃O⁺) reaching about 0.7. Finally, the prevailing effect of the incorporation of aliovalent cations in the fluorite-type CeO₂ matrix on the dissolution kinetics precluded the observation of slight effects such as those linked to the complexing agents or to the crystal structure of the samples