Outer-Sphere Extraction of Uranyl(VI) from HNO3(aq) to 1-Butyl-3-methylimidazolium Nonafluorobutanesulfonate Ionic Liquid −Towards Decontamination of Uranium Wastes−

Extraction behavior of U(VI) from an HNO3 aqueous solution to 1-buty1-3-methylimidazolium nonalluorobutanesulfonate ([BMI][NfO]) ionic liquid and recovery of the extracted U(VI) by using H2O2 were investigated. With increasing [HNO3], the distribution ratio of U(VI) tends to decrease (e.g., 4.08 at [HNO3] = 0.01 M, 0.15 at [HNO3] = 1.00 M). Such extraction behavior is mainly governed by [H+], while coordination of NO3- to UO22+ also offers minor contribution to prevent partitioning of U(VI) to [BMI][NfO]. The U(VI) extraction in the current system is exclusively driven by NfO(-) to form an outer-sphere complex like {[UO2(OH2)(5)](NfO)(4)}(2-). Addition of 30 wt % H2O2 to [BMI] [NfO] containing U(VI) resulted in pale yellow precipitate of [(UO2)(O-2)(H2O)(2)]center dot 2H(2)O. The recovery efficiency increases with increasing pH of the aqueous layer, and reaches >90% at pH >1.5. This is in line with deprotonation from H2O2 through the precipitation of [(UO2)(O-2)(H2O)(2)]center dot 2H(2)O, i.e., UO22+ + H2O2 +4H(2)O = [(UO2)(O-2)(H2O)(2)]center dot 2H(2)O (s) + 2H(+) .