Dissolution and extraction of actinide oxides in supercritical carbon dioxide containing the complex of tri-n-butylphosphate with nitric acid

Dissolution of individual actinide oxides (Th, U, Pu, Np), or their mechanical mixtures, as well as of solid solutions U–Pu, U–Np, U–Am and U-Pu-Eu oxides in supercritical fluid carbon dioxide (SF-CO₂) containing the complex of tri-n-butyl phosphate (TBP) with nitric acid (TBP–HNO₃) has been investigated. The effect of the calcination temperature of solid solutions of dioxides on the separation of actinides during supercritical fluid extraction (SFE) has been studied as well. It was shown for the first time that milligram amounts of uranium dioxide could be quantitatively dissolved in (SF-CO₂) containing the TBP–HNO₃ complex and efficiently separated from Pu, Np, and Th during SFE of mechanical mixture of these oxides. On the contrary, both U and Pu are quantitatively dissolved in SF-CO₂–TBP–HNO₃ during SFE from solid solutions of U–Pu dioxide. An increase of the calcination temperature of the mixed U(IV)–Pu(IV) dioxide from 850 to 1200 °C has no influence on the relative extraction yield of these actinides during SFE. To cite this article: T. Trofimov et al., C. R. Chimie 7 (2004).

Résumé

Dissolution d’oxides d'actinides et extraction d’éléments dans le dioxide de carbone supercritique contenant le complexe tri-n-butylphosphate–acide nitrique. La dissolution d’oxydes de Th, U, Pu et Np, de leurs mélanges et de solutions solides U–Pu, U–Np, U–Am et U–Pu–Eu dans le dioxyde de carbone supercritique (CO₂-SC) contenant le complexe tri-n-butyl phosphate–acide nitrique (TBP–HNO₃) a été étudiée, et notamment l’effet de la température de calcination des solutions solides. On montre que quelques milligrammes de UO₂ peuvent être dissous dans le système CO₂-SC–TBP–HNO₃ et être séparés de Pu, Np et Th en traitant un mélange d’oxydes. En revanche, U et Pu sont dissous dans la phase CO₂-SC–TBP–HNO₃ durant le traitement des solutions solides U(IV)–Pu(IV). Une augmentation de la température de calcination de 850 à 1200 °C de ces solutions solides n’a pas d’effet sur le rendement d’extraction des actinides. Pour citer cet article : T. Trofimov et al., C. R. Chimie 7 (2004).