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NdFeB magnets are used in wind turbines and hybrid electric vehicles and are instrumental in progression toward a low-carbon economy. Recycling rare-earth elements (REEs) from NdFeB magnet waste is an important step toward building a sustainable REE supply chain. In this study, we describe an electrochemical process to selectively extract REEs from NdFeB magnet waste at room temperature. First, an electrolysis pretreatment step was performed to convert the elements present in the magnet waste into the respective hydroxides. A dual anode system was used where NdFeB magnet waste was taken as an anode along with an inert anode in an electrochemical reactor. The inert anode was used to ensure that iron in the magnet waste was converted into the Fe(III) form in the mixed hydroxides precipitate. Subsequently, the mixed hydroxides were leached with HCl. More than 97% of REEs and cobalt leached into the solution leaving iron in the residue. REEs were then selectively precipitated as rare-earth oxalates using oxal...

Ionic liquids are largely used to leach metals from primary (ores) and secondary sources (end-of-life products). However, dry ionic liquids with a carboxylic function on the cation have not yet been used to leach metals at temperature above 100 °C and under atmospheric pressure. The ionic liquid betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N], was used in the dry state to recover neodymium, dysprosium and cobalt from NdFeB magnets and NdFeB production scrap. The magnets and the scrap were crushed, milled and roasted before being leached above 100 °C. Recovery efficiencies below 10% and a lack of selectivity for all the parameters tested pointed to the importance of water in the dissolution process. The influence of the viscosity of the ionic liquid and the composition of the metal oxides after roasting was investigated as well. Although the dissolution of pure metal oxides was faster than the dissolution of the magnets, the low leaching efficiencies could not be attributed to the composition and crystal structure of the samples, since magnets roasted with the same protocol have already been successfully leached in the past, albeit in the presence of water. The role of water on the mass transfer and on the coordination of the metals was studied by viscometry and by spectroscopic methods, respectively. It is shown that for leaching of rare earths with [Hbet][Tf2N], the presence of ligands such as water is mandatory to saturate the first coordination sphere of the dissolved rare-earth ions. This paper provides new insights in the dissolution mechanism of metal oxides by [Hbet][Tf2N] at leaching temperatures higher than those typically used in hydrometallurgical leaching processes. ispartof: RSC Advances vol:8 issue:17 pages:9299-9310 ispartof: location:England status: published

NdFeB magnet waste is one of the important secondary resources from which rare-earth elements (REEs) can be recovered. Herein we present an electrochemical route to selectively extract REEs from the magnet waste at room temperature. First, the magnet waste was partially leached with HCl. The partial leachate along with undissolved magnet waste was taken in the anolyte side of a two compartment reactor separated by an anion exchange membrane whereas the catholyte consisted of sodium chloride solution. The Fe(II) present in the leachate was oxidized and precipitated as Fe(OH)3 while more than 95% of REEs were extracted into the solution. Subsequently, oxalic acid was used to selectively precipitate REEs as rare-earth oxalates. Hydrochloric acid liberated during the oxalic acid precipitation process could be directly reused in the partial leaching step. Sodium chloride was the only chemical consumed during the electrolysis. The effect of the NaCl concentration in the anolyte and catholyte on the extraction of metals was investigated. From magnet waste to rare-earth oxides, the developed recycling process is environmentally friendly and consumes only electricity, NaCl and oxalic acid. ispartof: Green Chemistry vol:20 issue:5 pages:1065-1073 status: published

Most metal extraction studies focus on the kinetics, the maximum loading and the extraction equilibrium, while structural information on the extracted complexes has been limited. This paper concerns the nature of the indium(III) chloride complexes, present in the organic and aqueous phase during the solvent extraction of indium(III) from an aqueous HCl solution by undiluted ionic liquids Cyphos® IL 101 and Aliquat® 336. In an aqueous HCl solution (0–12 M), indium(III) exists as octahedral mixed complexes, [In(H2O)6−nCln]3−n (0 ≤ n ≤ 6). EXAFS and 115In NMR were used to characterize these species. The stoichiometric composition of the extracted complexes, which is estimated from viscosity and maximum loading studies and confirmed by EXAFS, is unaffected by the HCl concentration in the aqueous phase. Indium(III) is present in the ionic liquid phase as the tetrahedral [InCl4]− complex. Based on the speciation results an extraction mechanism is proposed. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: Koen Binnemans (ORCID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal history: Received 19 February 2017; Accepted 8 March 2017; Accepted Manuscript published 8 March 2017; Advance Article published 15 March 2017; Version of Record published 27 March 2017 ispartof: Dalton Transactions vol:46 issue:17 pages:4412-4421 ispartof: location:England status: published

Leaching of cobalt and nickel from ores, urban waste and industrial residues is in general performed by sulfuric acid rather than hydrochloric acid, because sulfuric acid is cheaper and much less corrosive than hydrochloric acid. The choice of the acidic lixiviant has a large influence on the down-stream separation of Co and Ni, since the anion in the leachate determines the choice of solvent extraction system that can be applied. Co/Ni separations from sulfate media are traditionally performed by acidic extractants. In this paper, the extraction of Co(II) from sulfate media and its separation from Ni(II) is investigated using the quaternary phosphonium ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101, [C101][Cl]). Several extraction parameters have been optimized: acid concentration, salt concentration, time, temperature and the initial metal concentration in the aqueous feed solution. Furthermore, the extraction mechanism was investigated. The separation factors of Co(II)/Ni(II) are very high, in the order of 105. Stripping of the extracted Co(II) ions from the loaded ionic liquid phase was achieved by mixing with water. The ionic liquid phase was afterwards regenerated by washing with a CaCl2 solution. The extraction of Co(II) and Ni(II) with [C101][Cl] was compared to the extraction with the thiocyanate form of Cyphos IL 101, [C101][SCN]. It was found that extraction of Co(II) with [C101][SCN] occurred according to a split-anion mechanism, whereas a regular anion-exchange mechanism was observed for [C101][Cl]. ispartof: RSC Advances vol:7 issue:57 pages:35992-35999 status: published

In the lanthanide series, Eu3+ is most easily reduced to its divalent state. Reduction of Eu3+ has been studied extensively in aqueous media that are insensitive to reducing conditions. Recently, it has been reported that reduction of Eu3+ is also feasible in aqueous nitrate solutions and that Eu2+ remained sufficiently stable in these media to conduct separation experiments. However, additional fundamental research on the reduction efficiency of Eu3+ and stability of Eu2+ in these media has not been reported yet. In this paper, cyclic voltammetry, magnetic susceptibility measurements, UV-vis absorption spectroscopy and X-ray absorption near edge structure (XANES) spectroscopy were used to gain more insights into the reduction of Eu3+ in aqueous nitrate media. Within the parameters used in this work, near-quantitative reduction of Eu3+ could be achieved within 120 min in highly concentrated nitrate salt solutions, using both chemical and electrochemical reduction techniques. Moreover, Eu2+ was remarkably stable in these solutions, showing just a small percentage of back-oxidation after 5 h in a sealed measurement cell. ispartof: DALTON TRANSACTIONS vol:48 issue:39 pages:14758-14768 ispartof: location:England status: published

The metal extraction mechanism of basic extractants is typically described as an anion exchange process, but this mechanism does not correctly explain all observations. This paper introduces a novel model for the extraction of metals by basic extractants from chloride media supported by experimental data on methyltrioctylammonium chloride and Aliquat 336 chloride systems. This model relies on the hypothesis that the metal species least stabilized in the aqueous phase by hydration (i.e., the metal species with the lowest charge density) is extracted more efficiently than the more water stabilized species (i.e., species with higher charge densities). Once it is transferred to the organic phase, the extracted species can undergo further Lewis acid-base adduct formation reactions with the chloride anions available in the organic phase to form negatively charged chloro complexes, which than associate with the organic cations. Salting-out agents influence the extraction, most likely by decreasing the concentration of free water molecules, which destabilizes the metal complex in the aqueous phase. The evidence provided includes (1) the link between extraction and transition-metal speciation, (2) the trend in extraction efficiency as a function of the concentration of different salting-out agents, and (3) the behavior of HCl in the extraction system. The proposed extraction model better explains the experimental observations in comparison to the anion exchange model and allows the prediction of optimal conditions for metal extractions and separations a priori, by selecting the most suitable salting-out agent and its concentration. ispartof: INORGANIC CHEMISTRY vol:58 issue:18 pages:12289-12301 ispartof: location:United States status: published

Leaching of semiconductors (GaN, GaAs, and InAs) and light-emitting diodes (LEDs) in a nonvolatile tribromide ionic liquid, and the selective recovery of gallium, indium, and arsenic from this ioni...

Aqueous waste streams of the metallurgical industry often contain considerable concentrations of metal salts. Previous research showed that the metal chloride salts of zinc(ii), manganese(ii) and iron(iii) can be recovered by solvent extraction using a sustainable and renewable fatty acid based ionic liquid as the extractant. In this paper, the extraction mechanism of Zn(ii), Co(ii) and Ni(ii) from chloride media has been studied systematically. The metal extraction performances of the precursors, sodium oleate and tetraoctylammonium chloride, were compared to the extraction performance of the ionic liquid tetraoctylammonium oleate. Slope analysis experiments were performed to determine the number of ionic liquid molecules involved in the extraction. The experimental data showed that Co(ii) and Ni(ii) were extracted in the pH range from 6 to 8 by the formation of negatively charged metal carboxylate complexes with tetraalkylammonium counter ions. In contrast, Zn(ii) gets extracted as a mixed metal chloride carboxylate anionic complex with tetraalkylammonium counter ions. This extraction mechanism was supported by EXAFS measurements.

Correction for ‘Split-anion solvent extraction of light rare earths from concentrated chloride aqueous solutions to nitrate organic ionic liquids’ by Mercedes Regadío et al., RSC Adv., 2018, 8, 34754–34763, DOI: 10.1039/c8ra06055j.

The solvent extraction of lanthanides from chloride media to an organic phase containing an anion exchanger in the chloride form is known to show low extraction percentages and small separation factors. The coordination chemistry of the lanthanides in combination with this kind of extractant is poorly understood. Previous work has mainly used solvent extraction based techniques (slope analysis, fittings of the extraction curves) to derive the extraction mechanism of lanthanides from chloride media. In this paper, EXAFS spectra, luminescence lifetimes, excitation and emission spectra, and organic phase loadings of lanthanides in dry, water-saturated and diluted Aliquat 336 chloride or Cyphos IL 101 have been measured. The data show the formation of the hydrated lanthanide ion [Ln(H2O)8–9]3+in undiluted and diluted Aliquat 336 and the complex [LnCl6]3−in dry Aliquat 336. The presence of the same species [Ln(H2O)8–9]3+in the aqueous and in the organic phase explains the small separation factors and the poor selectivities for the separation of mixtures of lanthanides. Changes in separation factors with increasing chloride concentrations can be explained by changes in stability of the lanthanide chloro complexes in the aqueous phase, in combination with the extraction of the hydrated lanthanide ion to the organic phase. Finally, it is shown that the organic phase can be loaded with 107 g·L−1of Nd(III) under the optimal conditions. ispartof: Journal of Solution Chemistry vol:47 issue:8 pages:1351-372 status: published

Cobalt(II)-containing ionic liquids were synthesized using N,N-dimethylformamide, N-methylpyrrolidone (NMP), dimethylsulfoxide (DMSO), N,N-dimethylacetamide (DMAc), pyridine-N-oxide (py-O), 1,10-phenanthroline (phen), ethylenediamine (en) and dimethylimidazolidinone (DMI) as ligands. The weakly coordinating bis(trifluoromethylsulfonyl)imide (Tf2N−) was used as a counter anion. Several compounds had a melting temperature below 100 °C, and the compound [Co(DMAc)6][Tf2N]2 was liquid at room temperature, with a viscosity of only 18 mPa s at 80 °C. Several compounds were recrystallized to give high quality single crystals and their crystal structures were determined. EXAFS measurements were performed on [Co(DMAc)6][Tf2N]2 at different temperatures and it was observed that the [Co(DMAc)6]2+ ion partially dissociated at higher temperatures, which explains the temperature-dependent color change (thermochromism). The electrochemical properties of the compounds with the lowest melting points were also investigated. Adherent, crack-free metallic cobalt layers could be electrodeposited from [Co(DMAc)6][Tf2N]2, [Co(DMI)6][Tf2N]2 and [Co(NMP)6][Tf2N]2. From the first two, black deposits consisting of micrometer-sized needles were obtained, whereas the latter resulted in a dull grey cobalt layer consisting of micrometer-sized cobalt spheres. The Co(III)/Co(II) redox couple was not found to occur in any compound with an O-donor ligand, but the Co(III)/Co(II) redox couple was found to be quasi-reversible for [Co(phen)3][Tf2N]2 dissolved in [BMP][Tf2N]. ispartof: Dalton Transactions vol:47 issue:14 pages:4975-4986 ispartof: location:England status: published

Ionic liquids (ILs) with trichloride anions ([Cl3]−) combined with different cations were synthesised by bringing chlorine gas into contact with the corresponding chloride (Cl−) ILs at room temperature. These trichloride ILs safely store chlorine and are useful as oxidising agents for dissolution of various metals and alloys under mild conditions. ispartof: Chemical Communications vol:54 issue:5 pages:475-478 ispartof: location:England status: published

© 2017 American Chemical Society. Several ionic liquids (ILs) were tested for their suitability to synthesize the aramid polymer poly-p-phenylene terephthalamide (PPTA) in an attempt to diminish the dependence on the toxic N-methylpyrrolidone (NMP) that is currently used in industry. The room-temperature IL 3-methyl-1-octylimidazolium chloride ([C8MIM][Cl]) showed the highest promise as, with this medium, the polycondensation reaction proceeds with a mechanism similar to how it occurs in the solvent mixture of NMP with CaCl2. With this IL, PPTA polymer with an inherent viscosity of 1.95 dL/g was obtained in a low-temperature polycondensation reaction. This is the highest reported molecular mass of PPTA to date that was obtained by polymerization in an ionic liquid. An extended X-ray absorption fine structure (EXAFS) and solid-state NMR spectroscopic study showed that [C8MIM][Cl] and the current industrial solvent of NMP and CaCl2 show similar characteristics when it comes to the synthesis of PPTA. ispartof: ACS SUSTAINABLE CHEMISTRY & ENGINEERING vol:6 issue:1 pages:1362-1369 status: published

International audience; Despite its benefits, the extraction of rare earths (REEs) from chloride solutions with neutral or basic extractants is not efficient, so that separation is currently carried out by using acidic extractants. This work aims to improve this process by replacing the conventional molecular diluents in the organic phase by ionic liquids (ILs) which contain coordinating anions. The extraction of La(m), Ce(iii) and Pr(iii) from concentrated chloride solutions was tested with a quaternary ammonium and a phosphonium nitrate IL extractant. Dissolution of a trialkylphosphine oxide neutral extractant (Cyanex 923) in the nitrate ILs changed the preference of the organic phase from lighter to heavier REE and increased the overall extraction efficiency and the loading capacity of the organic phase. An increase of the CaCl2 concentration in the feed solution resulted in higher extraction efficiencies, due to a lower activity of water and hence to a poorer hydration of the REE ions. In that respect, chloride ions were not coordinating to the REE ion after extraction from concentrated chloride solutions. To achieve selectivity, one should fine-tune the loading by varying the CaCl2 and/or Cyanex 923 concentrations. Adjustment of the CaCl2 concentration in the feed and stripping solutions is essential for the separation of mixtures of REE. However, and unlike in the case of acidic extractants, no control of equilibrium pH is required. The split-anion extraction offers the possibility to separate mixtures of REEs in different groups without having to change the chloride feed solution. It leads to safer and environmentally friendlier extraction processes by (1) using solvents that are not volatile, not flammable and do no accumulate static electricity, (2) consuming no acids or alkali, (3) easy stripping with water and (4) avoidance to create nitrate-containing effluents.

Lanthanides are extracted to basic nitrate-based extractants, like trihexyl(tetradecyl)phosphonium nitrate, as pentanitrato lanthanide complexes., A speciation study was carried out for lanthanide complexes formed in the organic phase after solvent extraction with quaternary ammonium and phosphonium nitrate extractants. These extractants are liquid at room temperature and were applied in their undiluted form. A comparison was made between the quaternary compound trihexyl(tetradecyl)phosphonium nitrate, the nitrate form of the commercial extractant Cyphos IL 101, and Aliquat 336 nitrate, the nitrate form of the commercial trialkylmethylammonium chloride extractant Aliquat 336 (alkyl = mixture of C8 and C10 chains). The structures of the lanthanide complexes across the entire lanthanide series (with the exception of promethium) were determined by a combination of solvent extraction techniques, FTIR, NMR, high-resolution steady-state luminescence spectroscopy, luminescence life time measurements, elemental analysis and EXAFS spectroscopy. The results suggest that the lanthanide ions form an anionic nitrate complex in the organic phase by coordinating with five bidentate nitrate ligands. Charge neutralization is provided by two counter cations of the extractant present in the outer coordination sphere of the complex. Furthermore, it is suggested that the pentanitrato complex is the sole lanthanide species that is formed in significant concentrations in the organic phase.

A combination of X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy have been used to provide an experimental measure of nitrogen atomic charge in nine ionic liquids (ILs). These experimental results are used to validate charges calculated with three computational methods: charges from electrostatic potentials using a grid-based method (ChelpG), natural bond orbital (NBO) population analysis and the atoms in molecules (AIM) approach. By combining these results with those from a previous study on sulfur, we find that ChelpG charges provide the best description of charge distribution in ILs. However, we find that ChelpG charges can lead to significant conformational dependence and therefore advise that small differences in ChelpG charges (

In a conventional solvent extraction system, metal ions are distributed between two immiscible phases, typically an aqueous and an organic phase. In this paper, the proof-of-principle is given for the distribution of metal ions between three immiscible phases, two ionic liquid phases with an aqueous phase in between them. Three-liquid-phase solvent extraction allows separation of a mixture of three metal ions in a single step, whereas at least two steps are required to separate three metals in the case of two-liquid phase solvent extraction. In the triphasic system, the lower organic phase is comprised of the ionic liquid betainium- or choline bis(trifluoromethylsulfonyl)imide, whereas the upper organic phase is comprised of the ionic liquid trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide. The triphasic system was used for the separation of a mixture of tin(II), yttrium(III), and scandium(III) ions. ispartof: Chemistry - a European Journal vol:21 issue:33 pages:11757-11766 ispartof: location:Germany status: published

Crystals of hydrated bisIJtrifluoromethylsulfonyl)imide (Tf2N) salts of the naturally occurring trivalent rareearth ions were grown from aqueous solution and analysed by X-ray diffraction. Their structures can be classified into three main groups. The lighter lanthanides La–Gd (except Sm) have a cubic crystal structure with the formula Ln(H2O)3(Tf2N)3, which has Tf2N anions coordinating in a bidentate fashion. The middle and heavy lanthanides (Sm, Tb, Dy, Er, Yb) have a monoclinic crystal structure with formula Ln(H2O)5(Tf2N)3, where the Tf2N anions are coordinating in a monodentate fashion. The heavy lanthanides Gd–Lu (except Tb, Tm) crystallise with very large unit cells making structural identification difficult. Partial structure solution of one of these compounds indicates that the structures contain fully hydrated Ln3+ ions and very disorderd Tf2N anions. Y was found to behave as the heavy lanthanides and Sc was found in a crystal structure of formula [Sc(H2O)7][Tf2N]3·H2O. In addition, La was found in a hexagonal crystal structure of formula La(H2O)3(Tf2N)3·2.5H2O, when a small amount of residual HTf2N was present during crystallisation. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information related_data: Crystal Structure Data copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 1 July 2015; Accepted 13 August 2015; Accepted Manuscript published 13 August 2015; Advance Article published 20 August 2015; Version of Record published 16 September 2015 ispartof: CrystEngComm vol:17 issue:37 pages:7142-7149 status: published

The solvent extraction behavior of a series of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, In3+, La3+, Nd3+, Sm3+, Dy3+, Er3+, Yb3+) from an aqueous chloride feed solution by the nonfluorinated fatty acid-based ionic liquid (IL) tetraoctylphosphonium oleate [P8888][oleate] has been investigated as a function of the pH. The possibility to extract metal chlorides from an aqueous stream via the anion or cation of the hydrophobic, low-viscous water-saturated [P8888][oleate] IL has been exploited. [P8888][oleate] can be considered as a bifunctional or binary IL. At high pH values (pH > 5), all metals are extracted via the oleate anion, whereas some transition metals are extracted at high HCl concentrations and thus low pH values as anionic chloro complexes in combination with [P8888] cations. A difference of one pH unit is observed between the extraction curves (%E as a function of the pH) of the transition metals and those of the rare earth metals. Rare earths are not extracted at low pH values, whereas some transition metals (Fe, Mn, Co, Zn, Cu, In) are extracted. This makes [P8888][oleate] a promising extractant for the separation of transition metals from rare earths. It is also shown that this bulky and long-chained IL has a very low viscosity due to the uptake of water.

Total reflection X-ray fluorescence (TXRF) is becoming more and more popular for elemental analysis in academia and industry. However, simplification of the procedures for analyzing samples with complex compositions and residual matrix effects is still needed. In this work, the effect of an inorganic (CaCl2) and an organic (tetraalkylphosphonium chloride) matrix on metals quantification by TXRF was investigated for liquid samples. The samples were spiked with up to 20 metals at concentrations ranging from 3 to 50 mg L–1 per element, including elements with spectral peaks near the peaks of the matrix elements or near the Raleigh and Compton scattering peaks of the X-ray source (molybdenum anode). The recovery rate (RR) and the relative standard deviation (RSD) were calculated to express the accuracy and the precision of the measured element concentrations. In samples with no matrix effects, good RRs are obtained regardless of the internal standard selected. However, in samples with moderate matrix content, the use of an optimum internal standard (OIS) at a concentration close to that of the analyte significantly improved the quantitative analysis. In samples with high concentrations of inorganic ions, using a Triton X-100 aqueous solution to dilute the sample during the internal standardization resulted in better RRs and lower RSDs compared to using only water. In samples with a high concentration of organic material, pure ethanol gave slightly better results than when a Triton X-100–ethanol solution was used for dilution. Compared to previous methods reported in the literature, the new sample-preparation method gave better accuracy, precision, and sensitivity for the elements tested. Sample dilution with an OIS and the surfactant Triton X-100 (inorganic media) or ethanol (organic media) is recommended for fast routine elemental determination in matrix containing samples, as it does not require special equipment, experimentally derived case-dependent mathematical corrections, or physicochemical removal of interfering elements. ispartof: Analytical Chemistry vol:89 issue:8 pages:4595-4603 ispartof: location:United States status: published

Deep-eutectic solvents (DESs) are used as a promising alternative to aqueous solutions for the recovery of valuable metals from NdFeB magnets. A deep-eutectic solvent based on choline chloride and lactic acid (molar ratio 1 : 2) was used for the leaching of rare earths and other metals from NdFeB magnets. A process for the separation of Fe, B and Co from Nd and Dy in the deep-eutectic solvent was developed by using the ionic liquid tricaprylmethylammonium thiocyanate (Aliquat 336 SCN, [A336][SCN]) diluted in toluene (0.9 M). The extraction parameters were optimized and stripping of B was efficiently carried out by HCl, while EDTA was employed for the recovery of Fe and Co. The separation of Nd and Dy was assessed by using two different types of extractants, a mixture of trialkylphosphine oxides (Cyanex 923) and bis(2-ethylhexyl)phosphoric acid (D2EHPA). Based on the distribution ratios, separation factors and the ease of subsequent stripping, Cyanex 923 was chosen as the most effective extractant. The purified Dy present in the less polar phase was easily recovered by stripping with water, while the Nd present in the deep-eutectic solvent was recovered by precipitation stripping with a stoichiometric amount of oxalic acid. Nd2O3 and Dy2O3 were recovered with a purity of 99.87% and 99.94%, respectively. The feasibility to scale up this separation process was corroborated by a setup of mixer-settlers and highlighted by the possibility to fully recover and reuse the deep-eutectic solvent and the less polar phases employed in the extractions. The new proposed system based on a deep-eutectic solvent combined with traditional organic extraction phases presented higher selectivities and efficiencies than the analogous aqueous system. Extended X-ray absorption fine structure (EXAFS) was employed to elucidate the different mechanisms for extraction of Co and Fe from the deep-eutectic solvent and from an aqueous solution. ispartof: RSC Advances vol:7 issue:51 pages:32100-32113 status: published

A solvent extraction process comprising two immiscible organic phases has been developed for the extraction of rare earths. The more polar organic phase was ethylene glycol with dissolved rare-earth nitrate salts and lithium nitrate, while the less polar phase was a solution of the neutral extractant Cyanex® 923 dissolved in n-dodecane. The solvent extraction mechanism was determined by slope analysis and the main species in the organic phase was identified by Extended X-ray Absorption Fine Structure (EXAFS) studies. The extraction from the ethylene glycol solution was compared with extraction from an aqueous feed solution. When compared to aqueous feed solutions, the light rare-earth elements (LREEs) are less efficiently extracted and the heavy rare-earth elements (HREEs) more efficiently extracted from an ethylene glycol feed solution, resulting into the easy separation of HREEs from LREEs. The separation factors between neighboring elements are higher for this non-aqueous solvent extraction process than for extraction from an aqueous feed solution. ispartof: Separation and Purification Technology vol:174 pages:544-553 status: published

Cobalt(II)-containing liquid metal salts (LMS) with N-alkylimidazole ligands and bis(trifluoromethanesulfonyl)imide (bistriflimide, Tf2N−) or methanesulfonate (mesylate, OMs−) anions were synthesized and characterized. The chain length of the alkyl side chain on the imidazole ligand was varied. All compounds were characterized using CHN analysis, DSC and FTIR measurements. Single-crystal X-ray diffraction measurements were performed on six of the compounds for which single crystals of good quality could be obtained. All cobalt(II) centers are six-coordinate with the N-alkylimidazole ligands in an octahedral configuration and the anions are non-coordinating. The same coordination environment was observed by EXAFS measurements on cobalt(II) liquid metal salts in the liquid state. The electrochemical properties of the compounds with the lowest melting temperatures were investigated using cyclic voltammetry. It was found that part of the current was consumed in the electrodeposition of cobalt, whereas the other part of the current was consumed in the electrochemical formation of cobalt(0) nanoparticles. ispartof: Dalton Transactions vol:46 issue:38 pages:12845-12855 ispartof: location:England status: published

Novel 1,2,3-triazolium ionic liquids with a high base stability were synthesized for use in solvent extraction of first-row transition elements and rare earths from chloride media. The synthesis of these ionic liquids makes use of a recently reported, metal-free multicomponent reaction that allows full substitution of the 1,2,3-triazolium skeleton. The physical and chemical properties of these ionic liquids are compared with those of a trisubstituted analog. Peralkylation of the 1,2,3-triazolium skeleton leads to ionic liquids with superior properties, such as low viscosity, low solubility in water and higher thermal and base stability. Iodide and thiocyanate ionic liquids with peralkylated cations were applied to the solvent extraction of metal ions, and their stability in alkaline media was exploited in the selective stripping of the metals from the loaded ionic liquid phase by alkaline solutions. EXAFS and Raman spectroscopy were performed to gain insight into the extraction mechanism. The applicability of these extraction systems was demonstrated in separations relevant for the recovery of metals from ores and end-of-life products: Fe(III)/Cu(II)/Zn(II) (copper ores, brass scraps) and Fe(III)/Nd(III) (rare earth magnets) crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: Wim Dehaen (ORCID) identifier: Koen Binnemans (ORCID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal history: Received 19 February 2017; Accepted 21 March 2017; Accepted Manuscript published 22 March 2017; Advance Article published 5 April 2017; Version of Record published 19 April 2017 ispartof: Dalton Transactions vol:46 issue:16 pages:5113-5460 ispartof: location:England status: published

The determination and quantification of halide impurities in ionic liquids is highly important because halide ions can significantly influence the chemical and physical properties of ionic liquids. The use of impure ionic liquids in fundamental studies on solvent extraction or catalytic reactions can lead to incorrect experimental data. The detection of halide ions in solution by total reflection X-ray fluorescence (TXRF) has been problematic because volatile hydrogen halide (HX) compounds are formed when the sample is mixed with the acidic metal standard solution. The loss of HX during the drying step of the sample preparation procedure gives imprecise and inaccurate results. A new method based on an alkaline copper standard Cu(NH3)4(NO3)2 is presented for the determination of chloride, bromide, and iodide impurities in ionic liquids. The 1-butyl-3-methylimidazolium ([C4mim]) ionic liquids with the anions acetate ([C4mim][OAc]), nitrate ([C4mim][NO3]), trifluoromethanesulfonate ([C4mim][OTf]), and bis(trifluoromethylsulfonyl)imide ([C4mim][Tf2N]) were synthesized via a halide-free route and contaminated on purpose with known amounts of [C4mim]Cl, [C4mim]Br, [C4mim]I, or potassium halide salts in order to validate the new method and standard. ispartof: Analytical Chemistry vol:86 issue:8 pages:3931-3938 ispartof: location:United States status: published

An accurate quantitative determination of halide ions X (X = Cl, Br, I) in aqueous solution by total reflection X-ray fluorescence (TXRF) is not possible using the traditional acidic internal standards. In general, the standard solutions are highly acidic (e.g., Ga(NO3)3 in HNO3) to avoid precipitation of hydroxides of the standard element and to obtain a stable and reliable standard. In acidic solutions, dissolved halide salts can exchange their cation for a proton. The resulting volatile HX compounds can vaporate during the drying procedure of the TXRF sample preparation. In this technical note, we show that an alkaline Cu(NH3)4(NO3)2 standard can be used for the determination of chlorine, bromine and iodine without facing problems of HX evaporation. ispartof: Analytical Chemistry vol:86 issue:3 pages:1391-1394 ispartof: location:United States status: published

A solvent extraction process with the ionic liquid trihexyl(tetradecyl)phosphonium nitrate has been developed to extract rare earths and separate them from nickel or cobalt. The process is environmentally friendlier than traditional solvent extraction processes, since no volatile and flammable diluents have to be used. Compared to conventional ionic liquid metal extraction systems, the advantage of using the new ionic liquid is that expensive and persistent fluorinated ionic liquids can be avoided. The ionic liquid can be prepared by a simple metathesis reaction from the commercially available ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101). The extraction is facilitated by an inner salting-out effect of a highly concentrated metal nitrate aqueous phase. Feed solutions containing 164 g L−1 cobalt(II) and 84 g L−1 samarium(III), or 251 g L−1 nickel(II) and 61 g L−1 lanthanum(III) were tested. Percentage extractions of more than 99% were obtained for the rare earths and after a subsequent scrubbing step, the purity of the rare earth in the loaded ionic liquid phase was 99.9%. Complete stripping and regeneration of the ionic liquid could be performed using no chemicals other than pure water. Special attention was paid to the viscosity of the loaded ionic liquid phase and the kinetics of the extraction process, because the high viscosity and the slow mass transfer are the reasons why non-fluorinated ionic liquids have always been diluted in the past with conventional hydrophobic organic solvents such as kerosene, toluene or chloroform. The extraction mechanism of the rare earths samarium and lanthanum was studied and it was shown that different anionic complexes are formed. Lanthanum(III) is extracted at maximal loading via the hexakis anionic complex [La(NO3)6]3−, whereas samarium(III) is extracted at maximal loading via the pentakis anionic complex [Sm(NO3)5]2−. The difference in electrical charge of the anions has a pronounced effect on the viscosity of the ionic liquid phases. The separation of lanthanum and samarium from nickel or cobalt, out of highly concentrated metal salt solutions by solvent extraction, is of importance for the recycling samarium–cobalt permanent magnets or nickel metal hydride (NiMH) batteries. crosscheck: This document is CrossCheck deposited copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 2 August 2013; Accepted 6 January 2014; Accepted Manuscript published 7 January 2014; Advance Article published 15 January 2014; Version of Record published 24 February 2014 ispartof: Green Chemistry vol:16 issue:3 pages:1594-1606 status: published

A chemical process which consumes a minimum amount of chemicals to recover rare-earth metals from NdFeB magnets was developed. The recovery of rare-earth elements from end-of-life consumer products has gained increasing interest during the last few years. Examples of valuable rare earths are neodymium and dysprosium because they are important constituents of strong permanent magnets used in several large or growing application fields (e.g. hard disk drives, wind turbines, electric vehicles, magnetic separators, etc.). In this paper, the rare-earth elements were selectively dissolved from a crushed and roasted NdFeB magnet with a minimum amount of acid, further purified with solvent extraction and precipitated as pure oxalate salts. The whole procedure includes seven steps: (1) crushing and milling of the magnet into coarse powder, (2) roasting to transform the metals into the corresponding oxides, (3) the selective leaching of the rare-earth elements with acids (HCl, HNO3) to leave iron behind in the precipitate, (4) extracting remaining transition metals (Co, Cu, Mn) into the ionic liquid trihexyl(tetradecyl) phosphonium chloride, (5) precipitating the rare earths by the addition of oxalic acid, (6) removing the precipitate by filtration and (7) calcining the rare-earth oxalates to rare-earth oxides which can be used as part of the feedstock for the production process of new magnets. The magnet dissolution process from the oxides utilized four molar equivalents less acid to dissolve all rare earths in comparison with a dissolution process from the non-roasted magnet. Moreover, the less valuable element iron is already removed from the magnet during the dissolution process. The remaining transition metals are extracted into the ionic liquid which can be reused after a stripping process. Hydrochloric acid, the side product of the rare-earth oxalate precipitation process, can be reused in the next selective leaching process. In this way, a recycling process consuming only air, water, oxalic acid and electricity is developed to recover the rare earths from NdFeB magnets in very high purity. crosscheck: This document is CrossCheck deposited copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 13 October 2014; Accepted 14 November 2014; Accepted Manuscript published 14 November 2014; Version of Record published 27 November 2014 ispartof: RSC Advances vol:4 issue:109 pages:64099-64111 status: published

Several fundamental extraction parameters such as the kinetics and loading were studied for a new type of metal solvent extraction system with ionic liquids. The binary mixture of the ionic liquid betainium bis(trifluoromethylsulfonyl)imide and water shows thermomorphic behavior with an upper critical solution temperature (UCST), which can be used to avoid the slower mass transfer due to the generally higher viscosity of ionic liquids. A less viscous homogeneous phase and mixing on a molecular scale are obtained when the mixture is heated up above 55 °C. The influence of the temperature, the heating and cooling times, were studied for the extraction of neodymium(III) with betaine. A plausible and equal extraction mechanism is proposed in bis(trifluoromethylsulfonyl)imide, nitrate, and chloride media. After stripping of the metals from the ionic liquid phase, a higher recovery of the ionic liquid was obtained by salting-out of the ionic liquid fraction lost by dissolution in the aqueous phase. The change of the upper critical solution temperature by the addition of HCl or betaine was investigated. In addition, the viscosity was measured below and above the UCST as a function of the temperature. ispartof: INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES vol:14 issue:11 pages:21353-21377 ispartof: location:Switzerland status: published

Binary mixtures of the ionic liquid betainium bis(trifluoromethylsulfonyl)imide and water show an upper critical solution temperature. This solvent system has been used to extract metal ions by phase-transition extraction, using zwitterionic betaine as extractant. The system is efficient for the extraction of trivalent rare-earth, indium and gallium ions. This new type of metal extraction system avoids problems associated with the use of viscous ionic liquids, namely, the difficulty of intense mixing of the aqueous and ionic liquid phases by stirring. ispartof: Journal of Physical Chemistry Letters vol:4 issue:10 pages:1659-1663 ispartof: location:United States status: published

Despite the fact that Total Reflection X-ray Fluorescence (TXRF) is becoming more and more popular as a quantification technique in analytical chemistry due to its simplicity and robustness, there are still some key aspects related to the sample preparation that need to be improved. In this work, the effect of different parameters is investigated: measurement time, carrier position, sample volume and sample drying time. The measurement time and the sample volume on the carriers mainly affect the recovery rate and relative standard deviation of the quantified metal from aqueous solutions. The most important parameters that play a fundamental role in the calibration of a TXRF machine such as choice of the standard element and concentration ratio between the analyte and the standard are discussed. Practical and easy guidelines for the correct preparation of aqueous samples are presented. These can be used by both less and more experienced TXRF users, interested in measuring metal ion concentrations in aqueous samples. publisher: Elsevier articletitle: Practical guidelines for best practice on Total Reflection X-ray Fluorescence spectroscopy: Analysis of aqueous solutions journaltitle: Spectrochimica Acta Part B: Atomic Spectroscopy articlelink: http://dx.doi.org/10.1016/j.sab.2016.09.001 content_type: article copyright: © 2016 Elsevier B.V. All rights reserved. ispartof: Spectrochimica Acta B, Atomic Spectroscopy vol:124 pages:109-115 status: published

The dissolution of metal oxides in an acid-saturated ionic liquid, followed by selective stripping of the dissolved metal ions to an aqueous phase is proposed as a new ionometallurgical approach for the processing of metals in ionic liquids. The hydrophobic ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) saturated with a concentrated aqueous hydrochloric acid solution was used to dissolve CaO, NiO, MnO, CoO, CuO, ZnO and Fe2O3. It was found that nickel(II) and calcium(II) could be separated from all other transition metals present in the ionic liquid phase by stripping at high chloride concentrations. By scrubbing the ionic liquid solutions phase with water, manganese(II) and cobalt(II) could be stripped together with a fraction of iron(III) and copper(II), leaving zinc(II) and the remainder of copper(II) and iron(III) in the ionic liquid phase. These metal ions could be removed from the ionic liquid using ammonia. Copper(II) and zinc(II) formed ammine complexes and were back-extracted, while iron(III) precipitated as iron(III) hydroxide. After removal of all the metals present in the ionic liquid phase, the ionic liquid was prepared for reuse. Unfortunately, the mutual separations nickel–calcium, cobalt–manganese, or zinc–copper could not be achieved. This system would be useful when nickel is the metal of interest, since separation of nickel from all other transition metals present in the solution is achieved by one stripping step. ispartof: Hydrometallurgy vol:144 pages:27-33 status: published

An environmentally friendly process for the separation of the transition metals copper, cobalt, iron, manganese and zinc from rare earths by solvent extraction with the ionic liquid trihexyl(tetradecyl)phosphonium chloride has been developed. The solvent extraction process is carried out without the use of organic diluents or extra extraction agents and it can be applied as a sustainable hydrometallurgical method for removing transition metals from neodymium–iron–boron or samarium–cobalt permanent magnets. The recycling of rare earths is of high importance because of the possible supply risk of these elements in the near future. The method was tested for the removal of cobalt and iron from samarium and neodymium, respectively. The highest distribution ratios for cobalt and iron were found with 8.5 and 9 M HCl. At the tested conditions, the concentrations of neodymium and samarium in the ionic liquid were below 0.5 mg L−1 (0.5 ppm), even for feed concentrations of 45 g L−1. The separation factors of Nd/Fe and Sm/Co are 5.0 × 10^6 and 8.0 × 10^5, respectively. The percentage extraction of iron is still higher than 99.98% at loadings of the ionic liquids with 70 g L−1 of iron. The viscosity of the ionic liquid containing the tetrachloroferrate(III) complex [FeCl4]− is lower, and less depending on the feed concentration, than in the case with a tetrachlorocobaltate(II) anion [CoCl4]2−. After extraction, cobalt can be stripped very easily from the ionic liquid phase with water. However, due to the very high distribution ratio, iron could only be stripped by forming a water-soluble iron complex with ethylenediaminetetraacetic acid (EDTA). Also the possibility to extract chromium, nickel, aluminium, calcium and magnesium with trihexyl(tetradecyl)phosphonium chloride has been investigated, but the distribution ratios of these elements are very low in the tested conditions. ispartof: Green Chemistry vol:15 issue:4 pages:919-927 status: published

A series of ionic liquids with copper(ii), nickel(ii) or cobalt(ii)-containing cations have been synthesised and characterised, where possible with single crystal X-ray diffraction. A number of N-methylimidazole (MeIm), N-ethylimidazole (EtIm), N-butylimidazole (BuIm) or N-hexylimidazole (HeIm) ligands are coordinated to the metal centres and bis(trifluoromethyl) sulfonyl imide (Tf 2N) anions provide the charge balance. Two types of metal complexes have been analysed. One has the general formula [Cu(AlkIm) 4][Tf 2N] 2 (AlkIm = MeIm, EtIm, BuIm and HeIm) and contains square planar copper(ii) centres with longer interactions to oxygen atoms of bis(trifluoromethylsulfonyl)imide anions. The other type of metal complex has a metal:ligand ratio of 1:6, with composition [M(MeIm) 6][Tf 2N] 2 (M = Cu, Ni, Co) and contains octahedral metal centres. The ionic liquids have low melting points and the change in melting points is discussed as a function of alkyl chain length on the imidazole ligand and as a function of the metal centre. The metal-ligand interactions and intermolecular interactions in the crystal structures are analysed and related to the properties of the metal complexes.

© 2018 Elsevier B.V. SmCo permanent magnets are used in the automotive and aircraft industries. They are preferable over NdFeB magnets for applications above 150 °C. End-of-life SmCo magnets are a valuable secondary source of cobalt and samarium. This study presents solvent extraction systems without addition of molecular diluents. Undiluted quaternary ammonium ionic liquids with chloride, thiocyanate and nitrate anions were used to extract metals from aqueous feed solutions with high chloride concentrations in order to separate the main metals (Sm/Co/Cu) present in SmCo magnets. A chloride/chloride extraction was compared with two split-anion extraction systems (i.e. chloride in the aqueous phase and either nitrate or thiocyanate in the organic phase). The advantage of split–anion extraction is that it can be done from a chloride solution, but with the extraction behavior of nitrate or thiocyanate solutions. Split-anion extraction was in this work applied to the separation of rare earth elements/transition metals instead of previous applications to the mixtures of rare earths. For all the systems, the selectivity of extraction, scrubbing and stripping from a multi-element solution were investigated. High separation factors (>7500) were found for Co/Sm separations. Co(II) and Cu(II) extracted in the chloride/chloride and chloride/nitrate systems could be stripped simply by water. However, stripping of the loaded ionic liquid in the chloride/thiocyanate system with water was not feasible. The extraction mechanism for the different ionic liquids was studied by extended X–ray absorption fine structure (EXAFS). A possible explanation on the extraction behavior of samarium ions in the presence of transition metal ions (cobalt and copper) is given. ispartof: SEPARATION AND PURIFICATION TECHNOLOGY vol:210 pages:209-218 status: published

The separation of a mixture of rare earths by non-aqueous solvent extraction with two immiscible organic phases has been studied. The more polar organic phase was ethylene glycol with dissolved lithium chloride and the less polar organic phase was the extractant diluted in n-dodecane. Cyanex 923 was found to be the most performant extractant amongst the investigated acidic, basic and solvating extractants: Cyanex 272, Cyphos IL 101, Aliquat 336, bis(2-ethylhexyl)amine, trioctylphosphine oxide (TOPO) and Cyanex 923. The replacement of the aqueous chloride feed solutions by non-aqueous ethylene glycol feed solutions had a profound effect on the distribution ratios and separation factors. The separation factors for extraction of pairs of rare earths from aqueous chloride solutions by Cyanex 923 are too low to be of practical use. On the contrary, a mixture of rare earths can be separated conveniently in four different groups by extraction with Cyanex 923 from ethylene glycol (+LiCl) solutions. The influence of several parameters such as the chloride concentration, the type of chloride salt, the addition of other polar solvents to the ethylene glycol phase, the addition of second extractant to the less polar organic phase, and the addition of complexing agents to the ethylene glycol phase has been studied. The extraction mechanism for extraction of ytterbium(III) was studied by slope analysis experiments. The ytterbium(III) species in the ethylene glycol phase and the extracted species in the n-dodecane phase were determined by EXAFS. Furthermore, a conceptual flow sheet for the fractionation of rare earths from an ethylene glycol (+LiCl) feed solution into different groups by extraction with Cyanex 923 has been proposed. The new extraction system is useful for extraction of scandium and for separation of scandium from the other REEs. ispartof: RSC Advances vol:7 issue:72 pages:45351-45362 status: published

Experimental near edge X–ray absorption fine structure (NEXAFS) spectra are reported for 12 ionic liquids (ILs) encompassing a range of chemical structures for both the sulfur 1s and nitrogen 1s edges and compared with time–dependent density functional theory (TD–DFT) calculations. The energy scales for the experimental data were carefully calibrated against literature data. Gas phase calculations were performed on lone ions, ion pairs and ion pair dimers, with a wide range of ion pair conformers considered. For the first time, it is demonstrated that TD–DFT is a suitable method for simulating NEXAFS spectra of ILs, although the number of ions included in the calculations and their conformations are important considerations. For most of the ILs studied, calculations on lone ions in the gas phase were sufficient to successfully reproduce the experimental NEXAFS spectra. However, for certain ILs – for example, those containing a protic ammonium cation – calculations on ion pairs were required to obtain a good agreement with experimental spectra. Furthermore, significant conformational dependence was observed for the protic ammonium ILs, providing insight into the predominant liquid phase cation–anion interactions. Among the 12 investigated ILs, we find that four have an excited state that is delocalised across both the cation and the anion, which has implications for any process that depends upon the excited state, for example, radiolysis. Considering the collective experimental and theoretical data, we recommend that ion pairs should be the minimum number of ions used for the calculations of NEXAFS spectra of ILs.