Solvent Extraction Of Lanthanides Research Articles

Triflimide Effect in Solvent Extraction of Rare-Earth Elements from Nitric Acid Solutions by TODGA

ABSTRACT Outer-sphere interactions play an important role in the liquid-liquid extraction and separation of metal ions and they could be used to tune the efficiency and selectivity of recovery. Here, we report the extraction behaviour and separation of trivalent rare-earth elements from aqueous nitric acid solutions with N,N,N’,N’-tetra-n-octyl diglycolamide (TODGA), which was preliminarily contacted with an aqueous solution of N-H acid bis[(trifluoromethyl)sulfonyl]imide (triflimide, HTf2N; Tf = CF3SO2) resulting in an adduct TODGA⋅HTf2N. We examined in detail the extraction system composed of TODGA acidified with HTf2N and 1,2-dichloroethane as diluent. The effect of various experimental conditions such as the nature of diluent, aqueous nitric acid concentration, and TODGA⋅HTf2N concentration in the organic phase was studied. It has been found that the distribution coefficient values for metal ions are much greater, especially at low aqueous acidity in the extraction systems with the acidified organic solvent phase. Furthermore, the heavier lanthanides were effectively extracted and the intergroup lanthanide selectivity was greatly improved (separation factors for the Lu/La pair increased by 40 and 2 times for the two systems under study, respectively).

Solvent Extraction and Complexation Studies of Pyridine-di-Phosphonates with Lanthanides(III) in Solutions

ABSTRACT In this work, we studied the complex formation (1H, 31P NMR-titration, UV–vis titration, luminescent titration) and solvent extraction of lanthanides with pyridine diphosphonates. The stoichiometry of the complexes was determined: ML and ML2 forms are present. This is confirmed by all of the above methods. It was found that the pyridine ring and P=O groups are involved in the coordination of the metal cation. The coordination environment of the Eu(III) cation was studied more thoroughly using the EXAFS method in solution. Coordination numbers and distances were determined for the complex in solution. The influence of the lanthanide radius on the value of the stability constant was shown. The change in extraction efficiency in the series of lanthanide is described. A new pattern, unusual for other phosphorus-containing ligands, was obtained. To explain the change in the parameters of complexation depending on the system, DFT calculations were carried out. The effect of various initial states of the extracted cations was shown. The initial state with a large amount of nitrates corresponds to a two-phase system during extraction, and with a smaller amount, to a single-phase system with acetonitrile. Additionally, the luminescent properties of the complexes were described in detail as one more applied aspect of the work. .

Effect of polar molecular organic solvents on non-aqueous solvent extraction of rare-earth elements

The extraction and separation of five different rare-earth elements, La, Nd, Eu, Dy and Yb, from an aqueous chloride solution and from different chloride non-aqueous solutions using the solvating extractant Cyanex 923 was investigated. As previous studies had demonstrated the potential of non-aqueous solvent extraction (NASX) to refine rare earths from ethylene glycol, structural analogues of ethylene glycol (1,2-propanediol and 1,3-propanediol) and to other polar organic solvents (triethylene glycol, dimethylsulfoxide, methanol, N,N-dimethylformamide and N,N-dimethylacetamide) were studied. The extraction data were interpreted in terms of different solvent properties: dielectric constant, Gutmann donor number, molecular structure and hydrogen-bonding capabilities. Remarkable differences were observed between the extraction behaviour from ethylene glycol, 1,2-propanediol and 1,3-propanediol. Therefore, these solvent systems were further studied to elucidate the speciation of the rare-earth elements by optical absorption and luminescence spectroscopy. Based on these studies, both contact-ion-pair formation and solvation strength are assumed to play an important role in the extraction of rare earths by Cyanex 923 from different polar organic solvents. The differences in extraction behaviour can be exploited to fine-tune the separation of rare earths.

Solvent Extraction of Lanthanides(III) in the Presence of the Acetate Ion Acting as a Complexing Agent Using Mixtures of Cyanex 272 and Caprylic Acid in Hexane

A new extraction system containing a mixture of Cyanex 272 and caprylic acid is proposed for the extraction and separation of lanthanides(III). It was shown that this system possesses a high level of extraction ability and capacity. The extraction of lanthanides(III) from chloride-acetate and nitrate-acetate media was investigated on an example of La(III). The composition of the extracted species was confirmed, based on the analysis of lanthanum(III) extraction isotherms. In the case of acetic-acetate aqueous solutions, a decrease in lanthanum(III) extraction efficiency was observed, due to the decreasing equilibrium pH of the aqueous phase in accordance with the cation-exchange mechanism. The composition of the synergistic mixture of Cyanex 272-caprylic acid established demonstrates highly efficient separation of rare-earth metal ions.

Solvent extraction of lanthanides(iii) with mixtures of 1,3,5-tris(2-diphenylphosphoryl-4-ethylphenoxymethyl)benzene and 4-benzoyl-5-methyl-2-phenyl-3-pyrazolone

Solvent extraction of lanthanides(iii) with mixtures of 1,3,5-tris(2-diphenylphosphoryl-4-ethylphenoxymethyl)benzene and 4-benzoyl-5-methyl-2-phenyl-3-pyrazolone

Stoichiometry of Lanthanide-Phosphate Complexes at the Water Surface Studied Using Vibrational Sum Frequency Generation Spectroscopy and DFT Calculations.

In the solvent extraction of metal ions, the transport mechanism of metal ions through the liquid-liquid organic/aqueous interface remains unclear. In this study, the adsorption process of trivalent lanthanide ions from the aqueous phase to the interface in the solvent extraction of lanthanides with di(2-ethylhexyl)phosphoric acid (HDEHP) extractant is investigated by using a model interface-water surface covered with HDEHP (air/HDEHP/aqueous interface). As a result, symmetric POO- stretch signals of HDEHP observed by vibrational sum frequency generation spectroscopy and density functional theory calculations show that the stoichiometric ratio of lanthanide-HDEHP complexes formed at the air/HDEHP/aqueous interface is 1:1. The formation of the interfacial 1:1 lanthanide-HDEHP complex could be an elementary chemical process occurring just before the transfer of lanthanide ions to the side of the organic phase.

How acidity rules synergism and antagonism in liquid–liquid extraction by lipophilic extractants—Part II: application of the ienaic modelling

ABSTRACT In this article Part II, we consider the application of ienaic modeling for solvent extraction of rare earths in the case of the mixed DMDOHEMA/HDEHP extractant system. The system exhibits a synergistic extraction effect depending on the acid concentration and the extractant mole fraction, as demonstrated in the experimental article Part I. In this work, we directly compare experimental findings with theoretical predictions of the droplet model. The model considers the effective free energy of transfer as a combination of competing molecular forces, but contrary to previous micelle models that focus only on the dominant stoichiometry, it allows calculations of free energies of every possible spherical aggregate. The resulting image of the extraction process is that different behaviors can be obtained depending on the acidity and mole fraction of extractants, which are associated with different aggregation regimes in a complex free energy landscape of the system. Nevertheless, self-assembly is tuned by the extraction of all solutes, and not only the target metal cations.

Solvent Extraction of Lanthanides(III) from Nitric Acid Solutions with Novel Functionalized Ionic Liquids Based on the Carbamoyl(methyl)phosphine Oxide Pattern in Molecular Diluents

ABSTRACT The extraction of lanthanides(III) from nitric acid solutions in the systems involving novel functionalized ionic liquids based on cationic carbamoyl(methyl)phosphine oxide (CMPO) derivatives and dinonylnaphthalenesulfonate anions in molecular diluents was studied. The stoichiometry of the Ln(III) extracted species was determined using slope analysis. The influence of the concentration of HNO3 in the aqueous phase and the nature of organic diluents on the metal ion extraction efficiency into the organic phase was considered. Functionalized ionic liquids 1-[3-[[(diphenylphosphinyl)acetyl]amino]propyl]-1H-imidazol-1-ium dinonylnaphthalenesulfonate (L1HA) and 1-[2-[[(diphenylphosphinyl)acetyl]amino]ethyl]-pyridin-2-ium dinonylnaphthalenesulfonate (L2HA) demonstrate higher extraction ability towards Ln(III) than their neutral CMPO analog, diphenylphosphorylacetic acid N-nonylamide (L).

Solvent extraction of lanthanides(III) from chloride and nitrate media with di(2-ethylhexyl) phosphoric acid and ionic liquids in three-component biphasic solvent systems

In this paper, as an alternative to the traditional extraction systems, multicomponent biphasic solvent systems used in liquid-liquid chromatography are suggested for application in hydrometallurgy. Three-component biphasic solvent system (1:1:1) consisting of water, hexane, and isopropyl alcohol was tested for the extraction of lanthanides(III) from chloride and nitrate media by adding different extractants to the system. Di(2-ethylhexyl)phosphoric acid (D2EHPA) and mixtures of ionic liquids (IL) dissolved in hexane were investigated as extractants. Results showed that the extraction efficiency of Ln(III) with D2EHPA increases with the addition of sodium acetate or a mixture of CH3COONa and CH3COOН. Extraction of lanthanides(III) with mixtures of various IL from 0.5 M solutions of NaCl or NaNO3 was examined. Effective separation of Ln(III) was observed by using a mixture of trioctylammonium di(2-ethylhexyl)phosphate and dicyclohexylammonium caprylate (2:1), whereas by using a mixture of trioctylammonium caprylate and dicyclohexylammonium di(2-ethylhexyl)phosphate (2:1) the Ln(III) separation did not occur.

Structural effects of neutral organophosphorus extractants on solvent extraction of rare-earth elements from aqueous and non-aqueous nitrate solutions

A series of neutral organophosphorus extractants, comprising phosphine oxides, phosphinates, phosphonates and phosphates with linear and branched alkyl chains have been synthesized. Together with some similar commercial extractants, the performance of these new compounds in the extraction of Nd(III) and Dy(III) from both aqueous nitrate and non-aqueous ethylene glycol nitrate solutions was investigated. It was observed that: (1) the order of extraction efficiency of the rare-earth elements is the same as the basicity (electronegativity) of the extractant molecules: phosphine oxide > phosphinate > phosphonate > phosphate; (2) the same type of extractants with longer alkyl chains show higher metal extraction efficiencies, and branched chains hamper the extraction; (3) extraction from ethylene glycol solutions give higher separation factors for all types of neutral organophosphorus extractants than the corresponding aqueous solutions; and finally (4) phosphinates and phosphonates are more promising extractants than phosphine oxides and phosphates for separation of Nd(III) and Dy(III) by solvent extraction from ethylene glycol solutions. These results are useful for the development of more efficient and more selective new extractants and separation processes.

Interfacial structure in the liquid-liquid extraction of rare earth elements by phosphoric acid ligands: a molecular dynamics study.

Solvent extraction (SX), wherein two immiscible liquids, one containing the extractant molecules and the other containing the solute to be extracted are brought in contact to effect the phase transfer of the solute, underpins metal extraction and recovery processes. The interfacial region is of utmost importance in the SX process, since besides thermodynamics, the physical and chemical heterogeneity at the interface governs the kinetics of the process. Yet, a fundamental understanding of this heterogeneity and its implications for the extraction mechanism are currently lacking. We use molecular dynamics (MD) simulations to study the liquid-liquid interface under conditions relevant to the SX of Rare Earth Elements (REEs) by a phosphoric acid ligand. Simulations revealed that the extractant molecules and varying amounts of acid and metal ions partitioned to the interface. The presence of these species had a significant effect on the interfacial thickness, hydrogen bond life times and orientations of the water molecules at the interface. Deprotonation of the ligands was essential for the adsorption of the metal ions at the interface, with these ions forming a number of different complexes at the interface involving one to three extractant molecules and four to eight water molecules. Although the interface itself was rough, no obvious 'finger-like' water protrusions penetrating the organic phase were seen in our simulations. While the results of our work help us gain fundamental insights into the sequence of events leading to the formation of a variety of interfacial complexes, they also emphasize the need to carry out a more detailed atomic level study to understand the full mechanism of extraction of REEs from the aqueous to organic phases by phosphoric acid ligands.

Recovery of critical materials from mine tailings: A comparative study of the solvent extraction of rare earths using acidic, solvating and mixed extractant systems

Our society heavily depends on the availability of raw materials. Technology metals such as rare earth elements (REEs) are vital in many applications. Because their virgin mining and production is constrained by a multitude of factors, future exploitation of secondary sources is strongly considered. Tailings from past and present mining activities are important sources of REEs and other critical raw materials, e.g., tungsten and phosphate. The possibility of processing such tailings was thoroughly investigated in the ENVIREE European Project (2015–2018). In this paper, we assess the use of solvent extraction to recover REEs from tailings originating from New Kankberg (Sweden) and Covas (Portugal). Extraction of REEs from common mineral acid solutions was carried out using solvating (Cyanex 923 and TODGA) and acidic extractants (DEHPA and Cyanex 572). Extraction was studied in the presence of high amounts of phosphate, iron and copper in solution. This was to identify bottlenecks in the separation process and ways to mitigate them. While copper and phosphate didn't pose significant issues, iron was co-extracted with the REEs in several systems, e.g., DEHPA – sulfuric acid. Co-extraction was reduced by using a blended DEHPA – Cyanex 923 organic phase. At the same time, the extraction efficiency of REEs improved. Control of the contact time between the aqueous and organic phase, and selective stripping were also used to effectively mitigate the extraction of iron.

Tripodal organophosphorus ligands as synergistic agents in the solvent extraction of lanthanides(III). Structure of mixed complexes and effect of diluents

The solvent extraction of lanthanides (III) (except for Pm) from chloride medium (at μ = 0.1) into an organic phase containing 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone (HPy) and neutral tripodal ligands on the triphenylphosphine oxide platform with anchored carbamoyl side arms (2-R2NC(O)CH2OC6H4)3PO, where R = Bu (L1) and cyclo-Hex (L2) has been studied. A considerable synergistic effect (up to 107) has been observed in the presence of neutral ligands L1 or L2 in the organic phase containing HPy. The stoichiometry of the Ln(III) extracted species has been determined by slope analysis and the equilibrium constants have been calculated. It has been found that the lanthanides(III) ions are extracted with mixtures of HPy and neutral ligands L1 or L2 in toluene as LnPy3L species. The [LaPy3(H2O)2], and new [LaPy3(L1)] and [LaPy3(L2)] complexes have been synthesized and characterized via elemental analysis and IR spectroscopy. Solution structure of the above complexes has been examined by IR and multinuclear (1H, 13C, and 31P) NMR spectroscopy in toluene-d8 and CDCl3. The effect of diluents on synergistic extraction and the solution structure of mixed complexes are discussed.

Understanding the Recovery of Rare-Earth Elements by Ammonium Salts

While the recovery of rare earth elements (REEs) from aqueous solution by ionic liquids (ILs) has been well documented, the metal compounds that are formed in the organic phase remain poorly characterized. Using spectroscopic, analytical, and computational techniques, we provide detailed chemical analysis of the compounds formed in the organic phase during the solvent extraction of REEs by [(n-octyl)3NMe][NO3] (IL). These experiments show that REE recovery using IL is a rapid process and that IL is highly durable. Karl-Fischer measurements signify that the mode of action is unlikely to be micellar, while ions of the general formula REE(NO3)4(IL)2− are seen by negative ion electrospray ionization mass spectrometry. Additionally, variable temperature 139La nuclear magnetic resonance spectroscopy suggests the presence of multiple, low symmetry nitrato species. Classical molecular dynamics simulations show aggregation of multiple ILs around a microhydrated La3+ cation with four nitrates completing the inner coordination sphere. This increased understanding is now being exploited to develop stronger and more selective, functionalized ILs for REE recovery.

Synergistic Solvent Extraction of Lanthanides (III) with Mixtures of Tetraphenylmethylenediphosphine Dioxide and Picrolonic Acid from HCl Solutions

ABSTRACTThe solvent extraction of lanthanides(III) from hydrochloric acid solutions into the organic phase containing neutral bidentate extractant tetraphenylmethylenediphosphine dioxide (L) and picrolonic acid (HP) has been studied. A considerable synergistic effect was observed in the presence of HP in the organic phase containing neutral bidentate organophosphorus ligand. The extraction equilibrium was investigated and the equilibrium constants were calculated. It was found that the lanthanide(III) ions are extracted from weak acidic solutions as LnP3L and LnP3L2 complexes. The mixture L–HP offers higher extraction efficiency toward Ln(III) than mixtures of L with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 or picric acid.

Solvent extraction of rare earths using a bifunctional ionic liquid. Part 1: Interaction with acidic solutions

Bifunctional ionic liquid extractants have been examined in recent years for the separation of rare earth elements by solvent extraction. One such extractant is the quaternary ammonium phosphonate ionic liquid ‘R4N+EHEHP−’ formed from Aliquat 336 (trioctyl/decylmethylammonium chloride) and EHEHPA (2-ethylhexyl phosphonic acid 2-ethylhexyl ester, also known as P507 or PC88A).In this work, the uptake of hydrochloric acid by R4N+EHEHP− is investigated, by studying the effect of pH, chloride, diluent and extractant concentration and composition on the extraction of acid. A fundamental understanding of the interactions between R4N+EHEHP− and acid is considered crucial in order to describe the distribution of rare earths in such a system.The results show that when dissolved in low concentration in a polar phase, the acid uptake by the ionic liquid as a function of pH is indistinguishable from EHEHPA. However, when dissolved in toluene at process relevant concentrations (up to 0.5M), the protonation reaction occurs over a broader pH range and shifts to lower pH when compared with EHEHPA alone. Increasing the chloride concentration shifts the reaction to higher pH. The reaction stoichiometry, 31P{1H} NMR spectra and observed trends are consistent with protonation of the phosphonate ion and simultaneous formation of R4N+Cl−. It is suggested that ion-pairing between the quaternary ammonium and phosphonate ions is responsible for the observed change in the protonation behaviour compared with EHEHPA alone. Our results indicate that the combination of Aliquat 336 and EHEHPA behaves as a mixture of R4N+EHEHP− and R4N+Cl−+EHEHPA, with the protonation dependent on the pH, and not as a different chemical form. Hence, regardless of how the ionic liquid has been prepared, once it is exposed to acid containing solutions, the acid-base behaviour of the ionic liquid is indistinguishable from a mixture of the two reagents.

Progress towards a process for the recycling of nickel metal hydride electric cells using a deep eutectic solvent

Solvent extraction experiments relating to the recycling of the transition metals and lanthanides in nickel metal hydride cells are presented. The metal extraction is occurring from a deep eutectic solvent which is formed from chemicals suitable for use in food and related products. While it has been shown that the water content of the DES has a large effect on the extraction of transition metals by a mixture of chloride ionic liquid (Aliquat 336) and an aromatic solvent, the water content has a smaller effect on the solvent extraction of lanthanides with a solution of di(2-ethylhexyl) hydrogen phosphate (DEHPA) in a saturated aliphatic hydrocarbon. This study suggests that an industrial scale solvent extraction process for the recycling of metals from nickel hydride electrical cells will be feasible.

Liquid-liquid solvent extraction of rare earths: a crystallographic analysis.

Liquid-liquid solvent extraction has become the primary research topic for separating mixtures of rare-earths. [1] Current research on this topic focuses on extraction processes involving ionic liquids as basic extracting agents. In the aqueous phase, the rare-earth is coordinated by the anionic entities of the ionic liquid, forming an anionic complex. The large organic cation of the ionic liquid neutralizes the complex (ion-pair complex) and migrates the entity to an organic phase. The choice of these agents is solely based on the calculation of thermodynamical extraction parameters, whilst structural information about these compounds is rare or even non-existent. Our research focuses on obtaining structural information via crystallography on the above-mentioned molecules and relating the interactions between anion and cation to the stability of the complexes. A difference in stability between the anionic complex and cation can give a different extractability. Different rare-earth chloride salts were dissolved in an aqueous phase, containing ionic liquids with β-diketonate anions and 1-alkyl-3-methylimidazolium cations. After the extraction, crystals of the formed compounds are grown from the organic phase and measured. Current results show us that an intermolecular non-classical C-H ... O hydrogen bond is persistent across the different molecules, whilst small interactions between the cation side chain and halogens on the β-diketonate add extra stability to the crystal structure. Structures formed with 2-thenolytrifluoroactylacetonate anions have no intention to form side chain interactions, leaving the alkyl chain of the 1-alkyl-3-methylimidazolium in a void, whilst structures formed with hexafluoroacetylactonate have strong side chain interactions, which leads to a better packing. The different solubility of both compounds can be related to the different interactions and stability in the crystal structure.

Synergistic Solvent Extraction of Lanthanides(III) with Mixtures of 4-benzoyl-3-methyl-1-phenylpyrazol-5-one and Some Novel Carbamoyl- and Phosphorylmethoxymethylphosphine Oxides

The solvent extraction of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y from weak acidic hydrochloric acid solutions into an organic phase containing 4-benzoyl-3-methyl-1-phenylpyrazol-5-one (HP) and neutral tridentate organophosphorus ligands R2P(O)CH2OCH2C(O)NBu2 R = Bu (I), R = Ph (II) and R2P(O)CH2OCH2P(O)R12 R = R1 = Bu (III); R = Bu, R1 = Ph (IV); R = R1 = Ph(V) has been studied. A considerable synergistic effect was observed in the presence of HP in the organic phase containing tetraoctyldiglycolamide (TODGA) and neutral organophosphorus ligands I - V. A successive replacement of C(O)NAlk2 groups in the diglycolamide extractant molecule by P(O)Ph2 groups leads to an increase in the extraction efficiency of Ln(III) ions when toluene was used as diluent. Phosphoryl-containing podand I possess a higher extraction efficiency towards Ln(III) ions than TODGA. The extraction equilibrium was investigated and the equilibrium constants were calculated. It was found that the lanthanide(III) ions are extracted as LnLP3 and LnL2P3 complexes with mixtures of HP and I in toluene from weak acidic solutions.

Solvent extraction of lanthanides and yttrium from aqueous solution with methylimidazole in an ionic liquid

1-Methylimidazole (1-MIM) and 2-methylimidazole (2-MIM) are miscible in water and imidazolium based ionic liquids (ILs), and can coordinate with soft metal ions. This paper reports a novel solvent extraction process for trivalent lanthanides and yttrium from aqueous solutions into ILs, which was promoted by a hydrophilic 1-MIM or 2-MIM. Slope analysis confirmed that MIM in ILs formed a 1 : 1 complex with La(3+) and Y(3+) and a 1 : 4 complex with Eu(3+) and Lu(3+), depending on the atomic number of the metal and the metal-ligand interactions that have been characterized by FTIR spectroscopy and ESI-MS. The effect of nitrate concentration on the extraction of lanthanides with 1-MIM in ILs was analysed. It indicated that nitrate anions were involved in the extraction process. Under the same conditions, the extraction of lanthanides with MIM into n-pentanol was carried out. The extractability was by far lower than that obtained in ILs. Both cationic exchange and neutral solvation mechanisms occurred in ILs and only the neutral solvation mechanism occurred in n-pentanol, which were demonstrated by the extraction tests and the structure of extracted species determined by ESI-MS. The competitive extraction in ILs showed good selectivity for lanthanides compared to alkali metals and alkaline earth cations. After extraction, lanthanides could be stripped very easily from the ionic liquid phase with dilute nitric acid. From the temperature dependence data, the thermodynamic parameter values (ΔH, ΔS and ΔG) were calculated. The results indicated that the extraction reactions were spontaneous and went through an endothermic process.