Synergistic Enhancement of the Extraction and Separation Efficiencies of Lanthanoid(III) Ions by the Formation of Charged Adducts in an Ionic Liquid

Assessment of the Equilibrium Constants of Mixed Complexes of Rare Earth Elements with Acidic (Chelating) and Organophosphorus Ligands

A survey of the experimental equilibrium constants in solution for the mixed complexes of 4f ions with acidic (chelating) and O-donor organophosphorus ligands published in the period between 1954 and 2022 is presented. These data are widely used in both analytical and solvent extraction chemistry. Important data evaluation criteria involved the specification of the essential reactions, process conditions and the correctness of techniques and calculations used, as well as appropriate equilibrium analysis of experimental data. Higher-quality data have been evaluated, compiled and presented herein, providing a synoptic view of the unifying theme in this area of research, i.e., synergism.

Thenoyltrifluoroacetone: Preferable Molecule for Solvent Extraction of Metals—Ancient Twists to New Approaches

A review of the investigations devoted to the solvent extraction processes of metal ions with a chelating ligand thenoyltrifluoroacetone (HTTA) is presented herein. It seems that this molecule has been preferred in the field for more than half a century, and that it is used very often as an extractant for almost all metals. The main objective of the present review is also to provide an overview of the synergistic solvent extraction of lanthanoids, particularly with the use of a β-diketone−neutral mixture. Based on the previous published results in the open literature, the extraction efficiency has been examined in detail and discussed further mainly in terms of the corresponding equilibrium constants among other outlined, so-important parameters. Major conclusions on the role of ligating groups of extractants towards the mechanism, an improved extraction enhancement, and selectivity are additionally provided. The fact that ionic liquids (ILs) appear to be replacing volatile diluents in the field of the liquid–liquid extraction of metals, again with the participation of this β-diketone, is not surprising. As is well known, a very efficient and simple way to determine the stoichiometry of the extracted species in the organic phase is by the simple use of the slope analysis method; however, it is sometimes difficult to perform, either because it somehow requests good solubility of the ligand or because obtained slopes are quite often far from integer values in ILs.

Solvent extraction of rare earths elements from nitrate media in DMDOHEMA/ionic liquid systems: performance and mechanism studies

Extraction of La(iii), Eu(iii) and Fe(iii) was compared in n-dodecane and two ionic liquids (ILs) (1-ethyl-1-butylpiperidinium bis (trifluoromethylsulfonyl)imide [EBPip⁺] [NTf₂⁻] and 1-ethyl-1-octylpiperidinium bis (trifluoromethylsulfonyl)imide [EOPip⁺] [NTf₂⁻]). Using the extractant N,N′-dimethyl-N,N′-dioctylhexylethoxymalonamide (DMDOHEMA), the effect of pH was investigated in detail to recover extraction mechanisms. The use of ILs as the organic solvent instead of n-dodecane, greatly enhances extraction efficiency, and an ionic liquid with a shorter alkyl chain [EBPip⁺] [NTf₂⁻] provides higher extraction than [EOPip⁺] [NTf₂⁻]. The mechanistic study points out that for low nitric acid concentrations ([HNO₃] ≤ 0.01 M), metal is extracted via a cation of the ionic liquids, while for higher nitric acid concentrations ([HNO₃] ≥ 1.0 M), extraction occurs through pure solvation mechanism of DMDOHEMA as in conventional diluents. This latter case is of high interest for applications, as higher extraction can be obtained without any loss of ILs by ion exchange mechanisms.

Extraction of La(iii), Eu(iii) and Fe(iii) was compared in n-dodecane and in two ionic liquids (ILs) [EBPip⁺] [NTf₂⁻] and [EOPip⁺] [NTf₂⁻]. Extraction mechanisms have been investigated as a function of pH.

Recovery of Rare Earth Elements (REEs) Using Ionic Solvents

Rare earth elements (REEs) are becoming more and more significant as they play crucial roles in many advanced technologies. Therefore, the development of optimized processes for their recovery, whether from primary resources or from secondary sources, has become necessary, including recovery from mine tailings, recycling of end-of-life products and urban and industrial waste. Ionic solvents, including ionic liquids (ILs) and deep-eutectic solvents (DESs), have attracted much attention since they represent an alternative to conventional processes for metal recovery. These systems are used as reactive agents in leaching and extraction processes. The most significant studies reported in the last decade regarding the recovery of REEs are presented in this review.

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.