Extraction of uranium from aqueous solutions by using ionic liquid and supercritical carbon dioxide in conjunction.

Uranyl ions [UO(2)](2+) in aqueous nitric acid can be extracted into supercritical CO(2) (sc-CO(2)) by using an imidazolium-based ionic liquid with tri-n-butyl phosphate (TBP) as a complexing agent. The transfer of uranium from the ionic liquid to the supercritical fluid phase was monitored by UV/Vis spectroscopy using a high-pressure fiber-optic cell. The form of the uranyl complex extracted into the sc-CO(2) phase was identified to be [UO(2)(NO(3))(2)(TBP)(2)]. The extraction results were confirmed by fluorescence spectroscopy and by neutron activation analysis. This technique has potential applications in the field of nuclear waste management for extracting other actinides.