Triflimide Effect in Solvent Extraction of Rare-Earth Elements from Nitric Acid Solutions by TODGA

Abstract

ABSTRACT Outer-sphere interactions play an important role in the liquid-liquid extraction and separation of metal ions and they could be used to tune the efficiency and selectivity of recovery. Here, we report the extraction behaviour and separation of trivalent rare-earth elements from aqueous nitric acid solutions with N,N,N’,N’-tetra-n-octyl diglycolamide (TODGA), which was preliminarily contacted with an aqueous solution of N-H acid bis[(trifluoromethyl)sulfonyl]imide (triflimide, HTf2N; Tf = CF3SO2) resulting in an adduct TODGA⋅HTf2N. We examined in detail the extraction system composed of TODGA acidified with HTf2N and 1,2-dichloroethane as diluent. The effect of various experimental conditions such as the nature of diluent, aqueous nitric acid concentration, and TODGA⋅HTf2N concentration in the organic phase was studied. It has been found that the distribution coefficient values for metal ions are much greater, especially at low aqueous acidity in the extraction systems with the acidified organic solvent phase. Furthermore, the heavier lanthanides were effectively extracted and the intergroup lanthanide selectivity was greatly improved (separation factors for the Lu/La pair increased by 40 and 2 times for the two systems under study, respectively).