Characteristics of an oxa-diamide–HNO3 extractant in the supercritical fluid extraction of uranium

An extractant is required in the recovery process to drive the uranium to a stage that enables it to be extracted using the extraction solvent. This paper proposes the composition of a composite extractant, N , N , N′ , N′ -tetrabutyl-3-oxapentane-diamide–HNO 3 (TBODA–HNO 3 ) as an extractant, to successfully achieve the objective using supercritical carbon dioxide (sc-CO 2 ). The composite TBODA–HNO 3 extractant has a chemical composition of TBODA(HNO 3 ) 1.0 (H 2 O) 1.5 . The U(IV) in the UO 2 containing solid phase is directly oxidized to U(VI) in the form of UO 2 2 + in sc-CO 2 , which contains a CO 2 -soluble TBODA–HNO 3 extractant at 200 atm and 50 °C. The resulting UO 2 2 + /TBODA complex can be consequently extracted using acetone-modified sc-CO 2 . The chemical composition of the UO 2 2 + /TBODA complex, which can be extracted by nonpolar sc-CO 2 , is proposed in the form of an ion pair: [UO 2 (TBODA) 2 ] 2+ –2( NO 3 - ).