The laws governing ionic liquid extraction of cations: partition of 1-ethylpyridinium monocation and paraquat dication in ionic liquid/water biphasic systems

Recent Progress in Ionic Liquid Extraction for the Separation of Rare Earth Elements

This review summarizes recent progress in solvent extraction of rare earth elements (REEs) using an ionic liquid (IL) as the extraction solvent. These IL extraction systems are advantageous owing to the affinity of ILs for both charged and neutral hydrophobic species, in contrast to conventional organic solvent extraction systems. Herein, REE extraction studies using ILs are detailed and classified based on the type of extraction system, namely extraction using anionic ligands, extraction using neutral ligands, synergistic extraction, extraction without extractants, and a specific system using task-specific ionic liquids (TSILs). In IL extraction systems, the extracted complexes are often different from those in organic solvent systems, and the REE extraction and separation efficiencies are often significantly enhanced. Synergistic IL extraction is an effective approach to improving the extractability and separability of REEs. The development of novel TSILs suitable for IL extraction systems is also effective for REE separation.

Ionic Liquid Chelate Extraction Behavior of Trivalent Group 13 Metals into 1-Alkyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imides Using 8-Quinolinol as Chelating Extractant

Ionic liquid (IL) chelate extraction behavior of trivalent Group 13 metals including aluminum(III), gallium(III) and indium(III) with 8-quinolinol (HQ) was investigated using three 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C_nmimTf₂N, n = 2, 4 and 8) ILs. Although the three extraction systems showed similar extraction selectivity among the metals, the extractability order for the metals among the extraction systems was C₈mimTf₂N > C₄mimTf₂N > C₂mimTf₂N, which was the same as the order of hydrophobicity in the IL cation. Only the neutral 1:3 complex species was extracted in use of more-hydrophobic C₈mimTf₂N, whereas use of less-hydrophobic C₄mimTf₂N and C₂mimTf₂N resulted in competitive extraction of neutral 1:3 and cationic 1:2 complexes. For each of the metals, in addition, similar extraction constants were obtained in these three extraction systems.

Hydrophobic polymerized ionic liquids for trace metal solid phase extraction: thallium transfer from hydrochloric acid media

To our knowledge, there are a few articles on the application of polymerized ionic liquids for metal extraction from aqueous solutions.

An Ionic Liquid-based Microextraction Method for Ultra-High Preconcentration of Paraquat Traces in Water Samples Prior to HPLC Determination

An ionic liquid (IL)-based microextraction method was developed for the preconcentration of paraquat traces in water samples prior to HPLC determination. On the basis of the relationship between the aqueous solubility and the extractability of known ILs, 1-ethyl-3-methylimidazolium bis(nonafluorobutanesulfonyl)amide ([EMIm][NNf₂]) was selected as the extractant for paraquat. The distribution ratio of paraquat dication in the [EMIm][NNf₂]/water biphasic system was theoretically estimated to be nearly 10⁸ at its maximum level, indicating that [EMIm][NNf₂] was suitable for the ultra-high preconcentration (a maximum of 10⁶-fold concentration) of paraquat with a quantitative recovery (more than 99%). The extraction procedure could be performed easily and quickly following the in situ solvent formation microextraction technique, and the paraquat traces in the IL phase could be determined by hydrophilic interaction chromatography with good detection limits and linearity ranges (0.16 and 1 - 50 ng mL^-1 for paraquat, respectively). The combined method was successfully applied to four real environmental water samples spiked with paraquat and its analog, diquat at 5.0 ng mL^-1.

Thallium Transfer from Hydrochloric Acid Media into Pure Ionic Liquids

Pure hydrophobic ionic liquids are known to extract metallic species from aqueous solutions. In this work we have systematically investigated thallium (Tl) extraction from aqueous hydrochloric acid (HCl) solutions into six pure fluorinated ionic liquids, namely imidazolium- and pyrrolidinium-based ionic liquids with bis(trifluoromethanesulfonyl)imide and bis(fluorosulfonyl)-imide anions. The dependence of the Tl extraction efficiency on the structure and composition of the ionic liquid ions, metal oxidation state, and initial metal and aqueous acid concentrations have been studied. Tl concentrations were on the order of picomolar (analyzed using radioactive tracers) and millimolar (analyzed using inductively coupled plasma mass spectrometry). The extraction of the cationic thallium species Tl(+) is higher for ionic liquids with more hydrophilic cations, while for the TlX(z)(3-z) anionic species (where X = Cl(-) and/or Br(-)), the extraction efficiency is greater for ionic liquids with more hydrophobic cations. The highest distribution value of Tl(III) was approximately 2000. An improved mathematical model based on ion exchange and ion pair formation mechanisms has been developed to describe the coextraction of two different anionic species, and the relative contributions of each mechanism have been determined.

Use of dicyanamide ionic liquids for extraction of metal ions

A correlation between the extraction capacity of tetraalkylammonium dicyanamide ILs and the nature of the anion of the metal salt was investigated.