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Rational design of novel carboxylic acid functionalized phosphonium based ionic liquids as high-performance extractants for rare earths

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Abstract

Developing the novel ionic liquids as the potential substitutes for conventional organic solvents in extraction of the rare-earth metals is highly desirable but remains facing challenges. In this study, the well-designed carboxylic acid functionalized phosphonium based ionic liquids, (4-carboxyl)butyl-trioctyl-phosphonium chloride/nitrate, are synthesized and characterized. The as-prepared samples are tested as the undiluted hydrophobic acidic extractant for rare-earth metal ions, affording the maximal loading of 3 mol/mol towards Nd(III) in aqueous solution and the remarkable stripping performance. The results also reveal their excellent extractability and selectivity for Sc(III) in the mixtures of six rare-earth ions, as well as the outstanding separation properties between rare-earth and first row transition-metal ions (i.e., La/Ni, Sm/Co). Moreover, the extraction mechanism indicates that the extracted rare-earth complex via a proton exchange in the ionic liquid phase is structurally similar to the complexes obtained with neutral extractants. This work presents a prototype for the fabrication of the hydrophobic cation-functionalized ionic liquids for highly efficient rare-earth extraction and provides the future application in recycling of rare-earth metals from the spent magnets.

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... Where 1 and 2 are different REEs The Stripping efficiency can be calculated using the following equation (4) [77] ...
... It was observed that the distribution ratio of neodymium was directly proportional to the concentration of ILs. Furthermore, these carboxylicbased phosphonium ILs can recycle REEs from magnets and batteries [77]. for the recycling of REE from neodymium-iron-boron-magnets [NIBM]. ...
... A) cations used to separate ree., b) Anions used for REE separation[39,56,77]. ...
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This work dives deep into the emerging role of ionic liquids as green solvents for separating precious Rare Earth Elements (REEs)—a critical area for advancing sustainable technologies. From their environmental benefits to innovative applications, this review provides a comprehensive overview and bibliometric analysis of the field, highlighting key trends and future directions. These innovative solvents pave the path for a sustainable future in REE extraction while promoting reusability and recyclability by addressing toxicity, biodegradability, and waste problems.
... According to the literature, acid-base-coupled ionic liquids are one other type of interesting ionic liquids for REE separations. Although most ionic liquids utilize an anionic-based exchange mechanism as part of the separation, this type of approach helps to combine the coordination ability and hydrophobic nature in a single ionic liquid [77]. On the whole, the ionic liquid application for solvent extraction enhances selectivity, and the type of ionic liquid application varies by the target metal required as a part of the extraction. ...
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Facilitating the demands of modern society, namely, smartphones, televisions, electric vehicles, and high-stability aircraft structures, requires low-cost and high-performance materials and a corresponding change in the approach needed to design them. Rare earth elements (REEs) play a significant role in achieving these objectives by adding small amounts of these elements to alloys, thereby enhancing material properties. Despite being more abundant than precious metals, the 17 REEs exhibit subtle variations in their chemical and physical characteristics. Thus, their separation is still crucial for industrial applications. There is a corresponding need to develop more effective and efficient separation methods. Adding to the separation challenge is the complexity of the sources of REEs and related materials. Thus, large-scale production of REE materials is difficult. Current REE processing techniques can be categorized into pre-treatment, beneficiation, separation, and refining. Researchers have developed various technologies encompassing chemical, physical, and biological methods, focusing on economic and environmental considerations. However, not all these approaches can be scaled up for mass production. This article focuses on feasible strategies such as precipitation and crystallization, oxidation and reduction, ion exchange, adsorption, solvent extraction, and membrane separation. Further research into these traditional and modern methods can potentially revolutionize the separation dynamics of REEs.
... For rare earth elements extraction and separation, diverse extractants, including D2EHPA [7][8][9][10], Cyanex 272 [11][12][13][14], Cyanex 921 [15][16], PC88A [17][18][19][20], TBP [21][22][23][24], EHEHPA [25][26][27][28], and various ionic liquids [29][30][31][32], have been utilized in operational conditions and different aqueous sulfate, chloride, and nitrate mediums. All trivalent lanthanide ions have extremely similar properties owing to the coverage of 4f electrons. ...
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Emission pollutants in rare earths hydrometallurgy industry have been the main constraint restricting its development. Membrane technology, as a sustainable green strategy with easy operation, is receiving great attentions in metal separation and wastewater treatment. Numerous membrane strategies for rare earths separation have been designed but few reviews could be found. The present article makes a state-of-the-art summary on current membrane techniques in rare earths separation including both liquid and non-liquid membranes. Further understandings of the crucial scientific and technical issues, such as REEs transport features, extraction performances, separation efficiency, transport models and mechanisms, membrane stability, operation modes and transport apparatus were discussed in details. Evaluations of each strategy and critical perspectives for future researches were suggested. Novel developments in non-liquid membrane techniques, such as polymer inclusion membranes, imprinted membranes, nanocomposite membranes and metal-organic framework membranes, were recommended and highlighted as potential strategies for rare earths separation in the near future. We hope that this overview would be a stimulator providing more opportunities for reference in membrane techniques for rare earths separation.
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Generally, phosphate rock contains about 0.05 wt% rare earth elements (REEs) on average. And the world commercial phosphate rock production is estimated to be 250 million tons per year, that makes phosphate rock a potential new REEs resource. However, low content of REEs in phosphate rock leads to the technical challenges and cost overages, that hindered the commercial recovery of REEs. In this paper, an overview of achievements aiming at solving the challenges is given. Based on the decomposition processes of phosphate rock by H2SO4, HNO3, HCl, H3PO4, various REEs recovery processes via crystallization, precipitation, solvent extraction and ion exchange methods are systematically reviewed. In H2SO4 processes, REEs are recovered based on the removal of impurities from phosphoric acid and phosphogypsum since the main challenge is the diluted content of REEs in these products. In the case of HCl, HNO3 and H3PO4 processes, REEs entirely transfers into leaching solution and the recovery research are mainly focused on REEs extraction from leaching solutions. For REE extraction from high phosphorus content leaching solutions, crystallization, precipitation, and ion exchange methods are currently inconsiderable due to the high energy consumption, impurity involvement and low efficiency, respectively. Solvent extraction seems to be the potential promising method in terms of its good overall performance. Finally, recommendations to promote the development of REEs recovery technologies from phosphate rock are provided.
Article
A novel ionic liquid type saponification processing based on quaternary phosphonium type bifunctional IL was developed for yttrium separation from ion-adsorbed rare earth deposit. The extractabilities of ([trihexyl(tetradecyl)phosphonium][sec-octylphenoxy acetate] ([P6,6,6,14][SOPAA]) were pronouncedly higher than those of sec-octylphenoxy acetic acid (HSOPAA), a mixture of HSOPAA and [P6,6,6,14]Cl for rare earth elements (REEs). The ion association extraction mechanism contributed to avoiding the numerous saponification procedures using alkali and resulting in saponification wastewater. After 13 stages of extraction and 6 stages of scrubbing sections, the Y(III) was successfully separated from industrial heavy RREs feed, the purity of Y(III) in raffinate was approximately to be 98.9%. Stripping by distilled water was effectively achieved for REEs, which contributed to the decreased consumption of acid to a considerable extent.
Article
An effective and sustainable strategy of regeneration is important for the industrial application of functionalized ionic liquid in hydrometallurgy. The transformations of [tri-n-octylmethylammonium][bis-sec-octylphenoxyl acetate] ([N1888][SOPAA]) and [trihexyl (tetradecyl) phosphonium][sec-octylphenoxy acetate] ([P6,6,6,14][SOPAA]) under acidic and alkaline conditions were investigated. This paper developed a novel approach for sustainable stripping and efficient regeneration of acid-base coupling bifunctional ionic liquid (ABC-BIL) for rare earth element (REE) separation. After the stripping using deionized water, both of NaOH and Na2C2O4 were indicated to be effective for the regeneration of organic phase containing [N1888][SOPAA]. In order to recycle REE, the precipitates of REE(OH)3 and REE2(C2O4)3 were analysed, and sedimentation-calcination strategy was proposed. The investigation of sedimentation-calcination also offered a promising method for the preparation of REE nanomaterial.
Article
This paper reviewed various systems such as neutral phosphorus and acid phosphorus, carboxylic acid and amine extractant for solvent extraction chemistry of yttrium, including thermodynamics, kinetics and yttrium extracting separation process containing the development course and new separation process.
Article
It is always difficult to separate scandium from yttrium and lanthanides due to their similar physicochemical properties. In this work, a selective separation strategy for Sc (III) from yttrium and lanthanides in aqueous solution was developed by using ionic liquids 1-alkylcarboxylic acid-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([(CH2)nCOOHmin][Tf2N]) (n=3, 5, 7) as extractants and 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Cnmim][Tf2N]) (n=4, 6, 8, 10) ionic liquids as diluents. The extraction parameters such as phase valume ratio, equilibrium time, pH value of the aqueous phase, alkyl chain length of the extractants and diluents, and system temperature were investigated systematically. It was shown that the extraction efficiency of Sc (III) increased with the increase of aqueous phase pH value, and was as high as 99.5% at pH 4.2. Sc (III) could be extracted selectively from yttrium and lanthanides by simple tuning of pH value of the aqueous phase, and the separation factor was 10³. After the extraction, stripping of Sc (III) from the ionic liquids was attempted by using dilute aqueous HNO3. In addition, an ion exchange mechanism of the proton of extractants and the cation of the diluents was proposed from a series of control experiments. Since both the proton of the extractants and cation of the diluents participated in the extraction process, amount of the ionic liquids transferred to water phase can be greatly reduced compared with the cation exchange based metal extraction using only ionic liquid extractants.
Article
Bauxite residue (red mud) is a waste product of the alumina refining in the Bayer process and contains significant concentrations of critical metals, including scandium. Greek bauxite residue contains exploitable levels of scandium and is thus considered a suitable source for its production. A process was developed to recover scandium from Greek bauxite residue using a combination of sulfation-roasting-leaching and solvent extraction with the hydrophobic ionic liquid betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N]. Sulfation-roasting-leaching was the preferred leaching technique to dissolve scandium from bauxite residue because of the low acid consumption, good selectivity towards scandium and low co-dissolution of the major elements. The scandium concentration in the leachate was increased by applying multistage leaching, during which the obtained leachate is contacted multiple times with freshly roasted material. In a next step, scandium was selectively extracted from the obtained leachate with [Hbet][Tf2N]. To improve the separation between scandium and iron, Fe(III) was reduced to Fe(II) by addition of ascorbic acid to the sulfate leachate prior to extraction. The phase ratio and pH of the extraction were optimized to achieve high extraction and the concentration of scandium in the ionic liquid phase. Co-extracted metal ions were scrubbed from the loaded ionic liquid phase by HCl and the purified scandium was removed by stripping with H2SO4. Scandium was recovered from the strip solution by precipitation together with sodium. Finally, the entire process was performed on lab scale as a proof-of-principle.
Article
Extraction and separation of yttrium in chloride medium using tri-n-octylmethylammonium (2-sec-octylphenoxy) acetate ([N1888][SOPAA]) as an extractant were studied in this article. Tri-n-butyl phosphate (TBP) was used as a phase modifier to accelerate phase separation and improve the stability of organic phase. The addition of TBP contributed to shortening phase separation time, increasing extraction capacity of rare earth elements (REEs) and decreasing viscosity of organic phase. The slope analysis method and infrared spectroscopy were conducted to investigate the ion-association extraction mechanisms. Extraction and stripping performances of the different systems were also compared. The article showed that the extraction performance of mixed [N1888][SOPAA] and TBP is superior to that of [N1888][SOPAA] for heavy rare earth element (HREE).
Article
Rare earth metals are essential ingredients for the development of modern industry as well as designing and developing high technology products used in our daily lives. Consequently, the worldwide demand of rare earth metals is rising quickly and predicted to surpass the supply by 40,000 tons annually. However, their availability is declining, mainly due to the export quotas imposed by the Chinese government and actions taken against illegal mining operations. This has laid emphasis to exploit and expand technologies to meet the future necessities of rare earth metals. Bastnasite, monazite, and xenotime are their chief mercantile sources, which are generally beneficiated by flotation, gravity or magnetic separation processes to get concentrates that are processed using pyro/hydrometallurgical routes. To develop feasible and eco-friendly processes, R&D studies are being conducted for the extraction of rare earth metals from leached solutions (chloride, nitrate, sulfate, thiocyanate, etc.) using different cationic, anionic and solvating solvents or ions depending on material and media. Commercial extraction of rare earth metals has been carried out using different extractants viz. D2EHPA, Cyanex 272, PC 88A, Versatic 10, TBP, Aliquat 336, etc. The present paper reviews the methods used for the recovery of rare earth metals from primary as well as secondary resources, with special attention to the hydrometallurgical techniques, consisting of leaching with acids and alkalis followed by solvent extraction, ion exchange or precipitation. The piece of comparative and summarized review will be useful for the researchers to develop processes for rare earth recovery under various conditions.
Article
Separation and recovery of some rare earth elements, including cerium (Ce (IV)), ytterbium (Yb(III)) and yttrium (Y(III)) from nitric acid solution using CYANEX 923 in kerosene at 25 °C was studied. The parameters which influence the extraction process were separately investigated. On the basis of the slope analysis method on the obtained data, the composition of the extracted species was found to be [Ce (NO3)3(OH)·2CY], [Yb (NO3)2(OH)·2CY·H2O], and [Y (NO3)2(OH)·2CY·H2O], for Ce (IV), Yb (III) and Y (III), respectively, where CY denotes CYANEX 923. The structures of the extracted metal species showed by FT-IR investigations indicated the presence of OH– and NO3− groups. Moreover, the thermodynamic parameters associated with the extraction process were evaluated. Based on the obtained results, as well as those obtained in a previous publication for the extraction of Pr (III), Sm (III) and Nd (III) with CYANEX 923 under similar conditions, a process for the recovery of REE from the Egyptian monazite was proposed and evaluated.
Article
The synergistic effect produced by functionalized ionic liquids in silica hybrid material for rare earth adsorption is presented for the first time in this article. Interestingly, distribution coefficient and synergistic enhancement coefficient of Lu(III) adsorbed by mixed [P66614][EHEHP] and [N1888][BTMPP] in silica hybrid material (SHM) are pronounced higher than their individual contributions. The doped functionalized ionic liquids act as porogens and adsorbents in the SHM. Moreover, the structural difference of functionalized ionic liquids offers the possibility for their quantitative determinations, which is crucial for the investigation of synergistic effect from doped functionalized ionic liquids in the SHM. The synergistic interplay of functionalized ionic liquids is the key to the higher absorptivity of SHM for rare earth. Moreover, the synergistic effect of doped ILs in SHM is indicated to be stable for rare earth adsorption in five recycling. The elimination of third phase from ionic liquid is another remarkable advantage of the SHM over common extraction. Overall, the prepared SHM reveals efficient and sustainable potentials for rare earth adsorption from a new perspective.
Article
To develop sustainable and efficient separation technology for heavy rare earth elements (HREEs), the extraction of Lu(III) and neighboring HREEs using EHEHP type acid-base coupling bifunctional ionic liquid (ABC-BIL) was studied for the first time. Selectivity and stripping performances of the ABC-BIL based system were investigated. Primary mechanism of the ABC-BIL based system was indicated to be ion-association. The EHEHP type ABC-BIL contributes to avoid the saponification wastewater from HEH[EHP]. Higher extractabilities of the ABC-BIL for HREEs, i.e., Ho(III), Y(III), Er(III), Tm(III), Yb(III), and Lu(III), are pronounced advantages of the IL based extracting system than traditional HEH[EHP] system.
Article
The continuous miniaturization of electric motors, hard disks and wind turbines is causing an increasing demand for high-performance neodymium-iron-boron magnets (NdFeB). The supply risk for the rare-earth elements (REEs) used in these magnets is a growing concern and has sparked the development of recycling schemes for these end-of-life products. In this paper a new recycling process for (microwave) roasted NdFeB magnets is proposed, based on the carboxyl-functionalized ionic liquid: betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N]. Using the thermomorphic properties of the [Hbet][Tf2N]-H2O system, a combined leaching/extraction step was designed. The change from a homogeneous system during leaching (80 [degree]C) to a biphasic system at room temperature causes the dissolved metal ions to distribute themselves amongst the two phases. The valuable elements (Nd, Dy, Co) are thus separated from the iron with high separation factors. The stripping was done very efficiently using oxalic acid to pr
Article
The ionic liquid betainium bis(trifluoromethylsulfonyl)imide [Hbet][Tf2N] was used for the extraction of scandium from aqueous solutions. The influence of several extraction parameters on the extraction efficiency was investigated, including the initial metal concentration, phase ratio, and pH. The extraction kinetics was examined, and a comparison was made between conventional liquid-liquid extraction and homogeneous liquid-liquid extraction (HLLE). The stoichiometry of the extracted scandium complex was determined with slope analysis. Scandium(III) is extracted as a complex with zwitterionic betaine in a 1:3 stoichiometry, with three bis(trifluoromethylsulfonyl)imide counterions. Upon extraction of scandium(III), proton exchange occurs and three protons are transferred to the aqueous phase. Scandium is an important minor element present in bauxite residue (red mud), the waste product that results from the industrial production of alumina by the Bayer process. To evaluate the suitability of [Hbet][Tf2N] for the selective recovery of scandium(III) from red mud leachates, the extraction of other metals present in the leachates (La(III), Ce(III), Nd(III), Dy(III), Y(III), Fe(III), Al(III), Ti(IV), Ca(II), Na(I)) was considered. It was shown that the trivalent lanthanide ions, yttrium(III) and the major elements aluminum(III), titanium(IV), calcium(II), and sodium(I), are all poorly extracted, which is advantageous for the selective recovery of scandium(III) from red mud. Iron(III) showed an extraction behavior similar to that of scandium(III). Scandium recovery was examined from a multielement rare-earth solution. Scandium could be separated from the other rare-earth elements by extraction with [Hbet][Tf2N] and subsequent scrubbing of the loaded ionic liquid phase to remove coextracted metal ions. The extracted scandium was recovered from the ionic liquid phase by using back-extraction with hydrochloric acid or precipitation stripping with oxalic acid.
Article
Given the fact that the basicity of imidazolate was higher than that of acetate, imidazolate-based ionic liquids (ILs) were developed to be studied. By combining six different cations, including traditional cation, functionalized cation, and dication, together with imidazolate, a series of ILs were prepared and found to be effective for CO2 capture. The mechanism of the studied ILs was proposed as the formation of the carboxylation reactions on C2 position of the imidazolium rings. A strong interaction between the newly formed carboxylate portion of the zwitterion and the C2–H proton of another cation was also formed, leading to a 0.5 molar ratios of CO2 to IL. In addition, the CO2 absorption capacity of dicationic IL was 1.0 molar ratio, twice that of the monocationic analogue. Significantly, an improvement on absorption result was exhibited by the amino-functionalized IL, but similar performance was not observed in the hydroxyl-functionalized one. The effects of operating pressure and temperature on CO2 absorption were also discussed.
Article
In this Article, bifunctional ionic liquid extractants (Bif-ILEs) tricaprylmethylammonium sec-octylphenoxy acetic acid ([A366][CA-12]) and tricaprylmethylammonium sec-nonylphenoxy acetic acid ([A336][CA-100]) used for the rare earths (REs) extraction from the chloride medium have been investigated. The effects of extractants concentration, equilibrium pH of aqueous phase, salt concentration, temperature, etc., were discussed. The results show that the extraction ability of [A336][CA-12] and [A336][CA-100] is higher than that of the conventional extractants sec-octylphenoxy acetic acid (CA-12), sec-nonylphenoxy acetic acid (CA-100), tri-n-butyl phosphate (TBP), and di-(1-metylheptyl)methyl phosphate (P350) under the same conditions. Furthermore, in the [A336][CA-12] system, the separation factors (β) between La(III) and other REs(III) are higher than 6.0, which indicates that [A336][CA-12] would be suitable for the La(III) extraction and separation. The extraction mechanism is also proposed, and there is a similar extraction tendency in both the [A336][CA-12] and the [A336][CA-100] systems. The loaded organic phase is easy to strip; more than 95% La(III) could be stripped from the loaded organic phase when the stripping acidity is higher than 0.03 M. The recycling experiments also indicate that the two extraction systems could be recycled without loss of the extraction efficiency.
Article
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.
Article
Six dicationic ionic liquids (DILs) were synthesized, including four amino acid-functionalized DILs (AA-DILs) and two traditional DILs (T-DILs), and were found to be effective for CO2 capture as reversible absorbents. Their physical properties were measured, containing density, conductivity, thermal decomposition temperature, glass transition temperature and viscosity. Their CO2 absorption behaviors under different pressures and temperatures with various water contents were also investigated. The results showed that the CO2 absorption capacities of pure AA-DILs were enhanced heavily compared to other monocationic ionic liquids. Mixing AA-DIL and water could be combined in a more rapid and efficient manner for CO2 gas capture, superior to the use of pure DIL only, due to their visible decrease in viscosity. The effect of temperature on CO2 absorption by aqueous AA-DIL mixtures at ambient pressure was extremely obvious: when temperature rose from 30 to 50 °C, the capacity of the 60 wt% [Bis(mim)C4][Pro]2 solution decreased from 1.52 to 0.78 mol/mol; as the pressure rose up to 10.0 bar, the total maximal capacity also dropped by more than a half. On the other hand, the two traditional DILs also exhibited an excellent physical absorption compared to varieties of monocationic ionic liquids.
Article
The extraction behaviour of trivalent rare earths namely La, Ce, Pr, Nd, Sm, Gd, Dy and Ho including Y (M(III), where M represents rare earths and yttrium ) from chloride medium has been studied with the solutions of high molecular weight carboxylic acids such as cekanoic, naphthenic, neo-heptanoic and Versatic 10 in dodecane. The effects of equilibrium pH, extractant concentration, metal ion concentration etc have been investigated. Using slope analysis technique it has been inferred that the metal ions form monomeric complex of the type [M(HA2)3] with carboxylic acids (H2A2, the dimer form). The stoichiometry of the species has also been confirmed using non-linear least square regression method. The carboxylic acids show different behaviour for Y extraction, it resembles to that of heavy rare earth (Ho), for sterically hindered acids (neo-heptanoic and Versatic 10) and to that with lighter rare earths (Ce, Pr) for the less sterically hindered acids (cekanoic and napthenic). The extraction order for the rare earths has been found to be the same with the four acids, i.e., La
Article
The solvent extraction of the trivalent lanthanides and yttrium from nitrate media by 0.5M solutions of four different 2-bromoalkanoic acids (HA) in xylene was studied. The extraction of these metals was found to take place in a pH range about one pH unit more acidic than with the parent alkanoic acids. The order of selectivity towards the individual lanthanides and yttrium was found to depend markedly on the structure of the 2-bromoalkanoic acid. Thus, for the most sterically hindered compound used (2-bromo-2-ethylhexanoic acid) the pH0 5 values decrease more or less continuously from lanthanum to lutetium, although the overall difference is quite small (pH0 5 pH0 5 = 0,30 pH unit). With this extractant the behaviour of yttrium most closely resembles that of the light lanthanide, neodymium. For the least sterically hindered extractant used (2-bromodecanoic acid) the pH0 5 values decreased only in the interval from lanthanum to praseodymium, following which the values increase more or less continuously through to lutetium, with the overall change representing a small selectivity towards lanthanum (pH0 5 pH0 5 = -0.12 pH unit). With 2-bromodecanoic acid and analogous compounds of low steric hindrance (2-bromo-3-cyclohexylpropanoic and 2-bromo-3,5,5-trimethylhexanoic acids), the extraction of yttrium was found to be less than that of any of the lanthanides.Slope analysis studies showed that 2-bromo-2-ethylhexanoic acid extracts monomeric complexes (such as EuA3(HA) 2 or EuA3(HA) 3) throughout the series of lanthanides (and yttrium), whereas with the less sterically hindered bromo-acids dimeric complexes are formed with the lighter lanthanides (such as (LaA3(HA) 3) 2) and monomeric species are formed with yttrium and the heavier lanthanides (such as LuA3(HA)3).
Article
The structure and stoichiometry of the lanthanide(III) (Ln) complexes with the ligand 2-thenoyltrifluoroacetone (Htta) formed in a biphasic aqueous room-temperature ionic liquid system have been studied by complementary physicochemical methods. Equilibrium thermodynamics, optical absorption and luminescence spectroscopies, high-energy X-ray scattering, EXAFS, and molecular dynamics simulations all support the formation of anionic Nd(tta)4(-) or Eu(tta)4(-) complexes with no water coordinated to the metal center in 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide (C4mim+Tf2N(-)), rather than the hydrated, neutral complexes, M(tta)(3)(H2O)n)(n = 2 or 3), that form in nonpolar molecular solvents, such as xylene or chloroform. The presence of anionic lanthanide complexes in C4mim+Tf2N(-) is made possible by the exchange of the ionic liquid anions into the aqueous phase for the lanthanide complex. The resulting complexes in the ionic liquid phase should be thought of as weak C4mim+Ln(tta)4(-) ion pairs which exert little influence on the structure of the ionic liquid phase.
Development course of separating rare earths with acid phosphorus extractants: a critical review
  • Li
Insights into the coordination and extraction of Yttrium(III) ions with a phenoxyacetic acid ionic-liquid extractant
  • Guo