Extraction of Uranium from Aqueous Solutions by Using Ionic Liquid and Supercritical Carbon Dioxide in Conjunction

Uranyl ions [UO2](2+) in aqueous nitric acid can be extracted into supercritical CO2 (sc-CO2) 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-CO2 phase was identified to be [UO2(NO3)(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.