Fast selective homogeneous extraction of UO22+ with carboxyl-functionalised task-specific ionic liquids

The carboxyl-functionalised task-specific ionic liquid of 1-carboxymethyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide ([HOOCmim][NTf2]) was used as solvent and extractant for UO22+ extraction from aqueous solution. A homogeneous phase of [HOOCmim][NTf2]-H2O system could be achieved at 75 °C, and 86.8 ± 4.8% of UO22+ was separated from the aqueous solution after vibrating for only 1 min. Furthermore, nearly 97.3 ± 2.9% of UO22+ was stripped from [HOOCmim][NTf2] phase by 1 M HNO3 solution. K+, Na+, Mg2+, Dy3+, La3+, and Eu3+ have little influence on the homogeneous extraction of UO22+, and the extraction efficiency of UO22+ still remained at ca. 80%. Experimental and theoretical study on the selectivity of [HOOCmim][NTf2]-H2O system were performed for the first time. Density functional theory calculation indicates that the solvent effect plays a significant role on the selectivity of [HOOCmim][NTf2]-H2O.