Mechanism for Solvent Extraction of Lanthanides from Chloride Media by Basic Extractants

Hoogerstraete, Tom Vander; Souza, Ernesto Rezende; Onghena, Bieke; Banerjee, Dipanjan; Binnemans, Koen

doi:10.1007/s10953-018-0782-4

Cited by 19 publications

(20 citation statements)

References 45 publications

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“…Although LiCl only acts as a chloride source to promote extraction of Co(II) and Sm(III) (according to eqs and , respectively), TEAC plays different roles for the extraction of Sm(III) and Co(II): (1) It acts only as a chloride source for Sm(III) extraction (according to eq ), but the ammonium cation does not bind with Sm(III) because Sm(III) cannot form an anionic chlorometallate complex in ethylene glycol as a result of the low stability of the Sm–Cl complex. , (2) It functions both as a chloride source (when TEAC < 1.2 mol·L –1 , according to eq ) and as a complexing agent in the case of Co(II) extraction (when TEAC > 1.2 mol·L –1 , according to eq ).…”

Section: Resultsmentioning

confidence: 99%

Enhancing Metal Separations Using Hydrophilic Ionic Liquids and Analogues as Complexing Agents in the More Polar Phase of Liquid–Liquid Extraction Systems

Onghena

et al. 2019

Ind. Eng. Chem. Res.

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The separation of metals by liquid–liquid extraction largely relies on the affinity of metals to the extractants, which normally reside in the organic (less polar) phase because of their high hydrophobicity. Following a different route, using aminopoly(carboxylic acid)s (e.g., EDTA) as complexing agents in the aqueous (more polar) phase was found to enhance metal separations by selectively complexing metal cations. In this study, we demonstrate that, hydrophilic ionic liquids and analogues in the more polar phase could also selectively complex with metal cations and hence enhance metal separations. As an example, Cyanex 923 (a mixture of trialkyl phosphine oxides) dissolved in p-cymene extracts CoCl2 more efficiently than SmCl3 from a chloride ethylene glycol (EG) solution. However, when tetraethylammonium chloride is added into the EG solution, CoCl2 is selectively held back (only 1.2% extraction at 3.0 M tetraethylammonium chloride), whereas the extraction of SmCl3 is unaffected (89.9% extraction), leading to reversed metal separation with a separation factor of Sm(III)/Co(II) > 700. The same principle is applicable to a range of hydrophilic ionic liquids, which can be used as complexing agents in the more polar phase to enhance the separations of various metal mixtures by liquid–liquid extraction.

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Section: Resultsmentioning

confidence: 99%

Enhancing Metal Separations Using Hydrophilic Ionic Liquids and Analogues as Complexing Agents in the More Polar Phase of Liquid–Liquid Extraction Systems

Onghena

et al. 2019

Ind. Eng. Chem. Res.

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“…Dissociation energies ( D e ) were calculated by determining the difference in the electronic energy between the diatomic at its optimized geometry and the energy of the two infinitely separated substituent atoms. The ground-state electronic configurations of the lanthanide ions were taken from ref (assuming the Ln + charge state for the fluorides and Ln 2+ for the oxides). In addition, frequency calculations were performed on optimized geometries to acquire harmonic zero-point vibrational energies (ZPVEs) so that experimental dissociation energies ( D 0 ) could be converted to values directly comparable to the theoretical values.…”

Section: Computational Detailsmentioning

confidence: 99%

“…The size of this market and the criticality of some of the lanthanides in modern technology demand efficient separation. However, because lanthanide cations have similar physicochemical properties, their separation becomes a very challenging task. , Solvent extraction is the most often used separation process; in this process, the slight differences in the properties along the lanthanide series are exploited to allow preferential extraction of specific lanthanides from a mixture using organic-based ligand extractants. − …”

Section: Introductionmentioning

confidence: 99%

Selecting Quantum-Chemical Methods for Lanthanide-Containing Molecules: A Balance between Accuracy and Efficiency

2020

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An analysis of how different density functionals, basis sets, and relativistic approximations affect the computed properties of lanthanide-containing molecules allows one to determine which method provides the highest accuracy. Historically, many different density functional methods have been employed to perform calculations on lanthanide complexes and so herein is a detailed analysis of how different methodological combinations change the computed properties of three different families of lanthanide-bearing species: lanthanide diatomic molecules (fluorides and oxides) and their dissociation energies; larger, molecular complexes and their geometries; and lanthanide bis(2-ethylhexyl)phosphate structures and their separation free energies among the lanthanide series. The B3LYP/Sapporo/Douglas−Kroll−Hess (DKH) method was shown to most accurately reproduce dissociation energies calculated at the CCSDT(Q) level of theory with a mean absolute deviation of 1.3 kcal/mol. For the calculations of larger, molecular complexes, the TPSSh/Sapporo/DKH method led to the smallest deviation from experimentally refined crystal structures. Finally, this same method led to calculated separation factors for lanthanide bis(2ethylhexyl)phosphate structures that matched very closely with experimental values.

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“…They concluded that an anion exchange mechanism for adsorption on resins was correct, although significant adsorption was already found when only very low concentrations of anionic species were present. , Also, no explanation for the decreasing adsorption efficiency at high HCl concentrations could be given. Onghena et al and Vander Hoogerstraete et al investigated the speciation of trivalent lanthanide ions in solvent extraction systems and concluded that the speciations in the aqueous and organic phase are different. Deferm et al studied the solvent extraction and speciation of In(III) and related the aqueous In(III) species to the extraction efficiency of In(III) .…”

Section: Introductionmentioning

confidence: 99%

Model for Metal Extraction from Chloride Media with Basic Extractants: A Coordination Chemistry Approach

et al. 2019

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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.

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Mechanism for Solvent Extraction of Lanthanides from Chloride Media by Basic Extractants

Cited by 19 publications

References 45 publications

Enhancing Metal Separations Using Hydrophilic Ionic Liquids and Analogues as Complexing Agents in the More Polar Phase of Liquid–Liquid Extraction Systems

Enhancing Metal Separations Using Hydrophilic Ionic Liquids and Analogues as Complexing Agents in the More Polar Phase of Liquid–Liquid Extraction Systems

Selecting Quantum-Chemical Methods for Lanthanide-Containing Molecules: A Balance between Accuracy and Efficiency

Model for Metal Extraction from Chloride Media with Basic Extractants: A Coordination Chemistry Approach

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