Extraction of Tetra-Oxo Anions into a Hydrophobic, Ionic Liquid-Based Solvent without Concomitant Ion Exchange

Abstract

Hydrophobic ionic liquids (IL) have the potential to simplify certain separations by serving as both an extraction solvent and an electrolyte for subsequent electrochemical reductions. While IL-based solvents are known to be efficient media for metal ion extraction, separations employing these solvents are frequently complicated by the loss of constituent IL ions to the aqueous phase, resulting in deteriorating performance. In this study, we have examined the extraction of pertechnetate and related tetra-oxo anions from aqueous solutions into IL-based solvents incorporating tetraalkylphosphonium bis[(trifluoromethyl)sulfonyl]imide and a crown ether. In contrast to various previously studied IL-based cation extraction systems, facile anion extraction without significant transfer of the IL ions to the aqueous phase has been observed. In addition, the solvents exhibit high distribution ratios (100−500 for pertechnetate), significant electrical conductivity (>100 μS/cm), and a wide (∼4 V) electrochemical window. The results suggest that these solvents may provide the basis for improved approaches to the extraction and recovery of a variety of anions.

Insights into the Mechanism of Extraction of Uranium (VI) from Nitric Acid Solution into an Ionic Liquid by using Tri‐n‐butyl phosphate

“…The partitioning of actinides and fission products in nuclearfuel reprocessing is one of the potentiala pplicationso f RTILs. [22][23][24] In particular,u ranyl is recovered in industrialp lutonium and uranium refiningb ye xtraction (PUREX) process from an aqueous nitric phase into akerosene phase by using the extractant molecule tri-n-butyl phosphate (TBP). This separation is made by the formation of the neutrals olvate UO 2 (NO 3 ) 2 (TBP) 2 .Replacing the kerosene phase by an imidazolium-based or tetraalkyl-based RTIL induces ac hange in the uranium(VI)d istribution coefficient curve as af unction of the acid concentration, which exhibits a" boomerang" shape.…”

Uncertainty Principle in the Elucidation of the Extraction Mechanism of Ions from Aqueous towards Ionic Liquid Phases. PtCl62− and [C1C8IM][NTf2] as a Textbook Case

“…However, the extraction mechanism appears to be different because of the ionic nature of ILs and their limited solubility in water . Beyond a wealth of experimental works evidencing mechanistic differences (for reviews on that point, see refs), some authors have discussed the mechanisms of extraction of such metal ions towards an ionic liquid, mainly by proposing two extraction mechanisms, based on either an ion exchange or a hydrophobic ion pair formation . In some of these works, ion exchange has been opposed to ion‐pair formation, the two mechanisms being said to be antagonist and the latter being considered to be more favorable than the latter, as it would avoid undesirable loss of ILs components in the aqueous phase .…”

Supramolecular Structures in the Presence of Ionic Liquids

“…The extraction process can be easily tailored by varying the substituting groups in the imidazolium cation and the counter anions. In succession, more and more systems involved ILs and crown ethers were investigated (Chun et al, 2001;Langmaier et al, 2009;Nockemann et al, 2007;Okamura et al, 2010;Stepinski et al, 2010;Visser et al, 2000;. These results discovered that as the alkyl group in the ILs was elongated, the extraction efficiency decreased, but the extraction selectivity increased.…”