PNNL

Abstract

Uranium dioxide can be dissolved directly in an imidiazolium-based ionic liquid (IL) at room temperature with a tri-n-butylphosphate(TBP)-HNO3 complex. The dissolution process follows pseudo first-order kinetics initially. Raman spectroscopic studies show the dissolved uranyl ions are coordinated with TBP in the IL phase with a molar ratio of (UO2)2+: TBP = 1:2. The dissolved uranyl species can be effectively transferred to supercritical fluid carbon dioxide (sc-CO2) phase. No aqueous phase is formed in either the IL dissolution or the supercritical fluid extraction process. Absorption spectra of the extracted uranyl species in the sc-CO2 phase suggests the presence of an UO2(TBP)2(NO3)2 and HNO3 adduct probably of the form UO2(TBP)2(NO3)2·HNO3. The adduct dissociates in a water-dodecane trap solution during pressure reduction resulting in UO2(TBP)2(NO3)2 collected in the dodecane phase.