Basic Study on Solvent Extraction Characteristics of [Hbet][Tf₂N] for Advanced Removing Process of Mo(VI) and Zr(IV) from High Level Liquid Waste

Abstract

Molybdenum and zirconium in high-level liquid waste (HLLW) are known to disturb the vitrification process of the nuclear wastes, losing the chemical stability of the vitrified wastes. Therefore, these elements should be removed from HLLW in advance. In this study, we examined the separation behavior of Zr(IV) and Mo(VI) in a biphasic system consisting of HNO 3 (aq) and betainium bis(trifluoromethanesulfonyl)imide ([Hbet][Tf 2 N]) ionic liquid. As a result, the extraction of Zr(IV) was highly efficient (>98.2％) at [HNO 3 ] ＝ 0.01-0.3 mol dm-3. In contrast, precipitation of Mo(VI) was observed in relatively high yield (>86.0％) at [HNO 3 ] ＝ 0.01-0.1 mol dm-3. Based on these results, it was suggested that [Hbet][Tf 2 N] can be employed to separate Zr(IV) and Mo(VI) from HLLW. In addition, we have clarified that the carboxy group of Hbet + is involved in the extraction and the precipitation of Zr(IV) and Mo(VI), respectively, as nothing has happened in use of trimethylpropylammonium bis(trifluoromethanesulfonyl)imide ([TMPA][Tf 2 N]) bearing no carboxy groups. Furthermore, we have also demonstrated that the extracted Zr(IV) can be recovered in high efficiency by back-extraction from [Hbet][Tf 2 N] upon contact with an H 2 C 2 O 4 aq.