Dependency of extraction behavior of inert platinum group metals (PGMs) like Ru­(III) and Rh­(III) on temperature has been investigated in a biphasic system consisting of HNO3(aq) and betainium bis­(trifluoromethylsulfonyl)­amide ([Hbet]­[Tf2N]) ionic liquid. The extraction reactions of Ru­(III) and Rh­(III) took 3.5 days and 113 days, respectively, at 298 K, while equilibrated within 1 and 3 h to reach 99.2% and 96.5% extraction at 353 K. Further mechanistic studies clarified that the complexation of these PGMs and [Hbet]+ is rate-determining in their extraction and that it is successfully accelerated and enhanced by elevating the temperature.

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We propose an extraction-electrodeposition process involving the solvent extraction of platinum group metals (PGMs) to an ionic liquid phase followed by the direct electrodeposition of a selected metal from the ionic liquid phase to separate and recover PGMs efficiently. To examine the compatibility of betainium bis (trifluoromethanesulfonyl) imide ionic liquid ( ［Hbet］ ［ Tf 2 N］ ) in this process, we investigated the electrochemical behavior of Ru (III) , Rh (III) , and Pd (II) actually extracted from HNO 3(aq) to the ［Hbet］ ［ Tf 2 N］ phase. Through the potentiostatic electrolysis of Pd (II) in ［Hbet］ ［Tf 2 N］ , fine particles of Pd metal were deposited over time at applied potentials at -500, -600, and -750 mV vs Fc/Fc ＋ . In contrast, no electrodeposition of Ru (III) and Rh (III) from ［Hbet］ ［ Tf 2 N］ solutions was observed. We also examined the potentiostatic electrolysis of a mixture of Pd (II) , Ru (III) , and Rh (III) in ［Hbet］ ［ Tf 2 N］ at -600 mV vs Fc/Fc ＋ . As a result, Pd (II) was selectively electrodeposited in a nearly quantitative yield (＞99％) with high purity (＞97％) , while little Ru and Rh were included in the deposit.

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.