Constructing hydroxyoxime-functionalized ionic liquid [BHIB][NTf2] for the separation of Mo(VI) from U(VI)

We describe here a hydroxyoxime-functionalized ionic liquid, 1-butyl-3-(4-hydroxy-3-((hydroxyimino)methyl)benzyl)-1H-imidazol-3-ium bis((trifluoromethyl)sulfonyl)amide ([BHIB][NTf2]), for the isolation and purification of 99Mo from 235U. This material exhibits remarkable extraction efficiency for Mo(VI) from 0.1 to 2 M HNO3 and can effectively distinguish Mo(VI) from U(VI). The attained highest separation factor (SF) of Mo(VI) over U(VI) exceeds 104, thus setting a new record for their separation. Additionally, the extracted Mo(VI) can be efficiently recovered using either NH4OH or the mixture of NH4OH and (NH4)2CO3. This excellent extraction performance is sustained even after five cycles. The extraction efficiency remains stable following exposure to 150 kGy gamma irradiation, thus providing robust experimental support for potential engineering applications. Slope analysis and EXAFS results indicate that [BHIB][NTf2] forms a 2:1 complex with Mo(VI) during the extraction process primarily driven by a cation exchange mechanism. When one equivalent of Mo(VI) migrates from the aqueous phase to the organic phase, each of two equivalents [BHIB][NTf2] remove one of H+ and migrate to the aqueous phase to maintain charge balance. This investigation introduces a highly efficient and environmentally benign method for separation, alongside providing novel insights into ligand design for the efficacious differentiation of Mo(VI) and U(VI) under HNO3 conditions, potentially streamlining current methodologies.