Homogeneous liquid–liquid extraction of U(VI) from HNO3 aqueous solution to betainium bis(trifluoromethylsulfonyl)imide ionic liquid and recovery of extracted U(VI)

• Extraction of U(VI) was studied in HNO3(aq)-[Hbet][Tf2N] biphasic system.
• The extraction was readily completed by using thermomorphic behavior of [Hbet][Tf2N].
• UO2(bet)2+ is formed as an extractable species.
• The extracted U(VI) is recovered as UO2(O2) by simply adding H2O2.

In order to examine the applicability of a thermomorphic ionic liquid, betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]), for the decontamination of solid wastes contaminated with uranium, we have studied fundamental extraction behavior of U(VI) from HNO3 aqueous solutions to [Hbet][Tf2N] phases using a homogeneous liquid–liquid extraction method. As a result, it was found that the U(VI) species are extracted with relatively high distribution ratios (D > 1) in low acidic condition without any additional extractant, and proposed that the U(VI) species are extracted through the exchange reaction between [Hbet]+ and [UO2(bet)]2+. The complex formation of [UO2(bet)]2+ was found to play an important role in the extraction, because the U(VI) species were not extracted with trimethylpropylammonium bis(trifluoromethylsulfonyl)imide ([TMPA][Tf2N]) without any functional groups. We also examined the recovery method of U(VI) species from the [Hbet][Tf2N] phase. As a result, it was found that the precipitation of uranyl peroxide with the addition of H2O2 aqueous solution is the useful method for recovering U(VI) species.

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