Supercritical carbon dioxide and eutectic solvent in conjunction: Novel method for in-situ solvent preparation-dissolution and uranium extraction from solid matrices

Halide anion free hydrophilic Deep Eutectic Solvent (DES) based on choline dihydrogen citrate and urea (1:2 mol ratio) was prepared and successfully employed for dissolution of uranium compounds. Dissolution study was carried out with oxides viz. UO2, UO3 and crude yellow cakes viz. magnesium diuranate, sodium diuranate. Novel route of in-situ, single step eutectic solvent preparation and U compound dissolution was found to be promising in terms of better dissolution efficiency and process simplification. The resultant systems were probed with electrochemistry and UV–Vis spectrophotometry to get an insight about the uranium species. In all the four systems prepared by in-situ mode, stabilization of uranium in U(VI) oxidation state in the form of oxo species was indicated. This halide anion free eutectic system was amenable to be used in SC CO2 extraction set-up. SC CO2 extraction of uranium dissolved in eutectic solvent was found to be influenced by various extraction conditions viz. pressure, temperature, static and dynamic time. Uranium extraction efficiency of upto 65% for oxide system was achievable by SC CO2 modified with TTA.