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

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.