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![Normalized XANES spectra of the (a) lanthanum and (b) cerium K-edges at increasing Cy923/[C101][NO 3 ] volume ratio from 0/100 till 100/0 (grey arrow).](profile/Koen-Binnemans/publication/328195723/figure/fig8/AS:692650919329792@1542152256146/Normalized-XANES-spectra-of-the-a-lanthanum-and-b-cerium-K-edges-at-increasing.png)
Normalized XANES spectra of the (a) lanthanum and (b) cerium K-edges at increasing Cy923/[C101][NO 3 ] volume ratio from 0/100 till 100/0 (grey arrow).
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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 cont...
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... mixtures of Cy923 and [C101] [NO 3 ] in volume proportions of 0/100, 25/75, 50/50, 75/25 and 100/0 (Table S4 †). The results conrmed that different species were formed, depending on the composition of the organic phase (Section SI 6 †). The type of organic phase inu- enced the absorbance, the bandwidth and the position of the absorption maximum (Fig. 8). In general, no isosbestic points appeared in the region of 50 eV aer the edge, conrming that the REE were extracted in different predominant species, by each organic phase. Increments in Cy923/[C101] [NO 3 ] volume ratio shied the edge to higher energy denoting different species, which are summarized in . This could explain the ...
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... in the IL solutions are denoted as [La(H 2 O) x ] 3+ and [Ce(H 2 O) x ] 3+ and may have a smaller  number than in diluted aqueous solutions (without CaCl 2 ). No evidence of nitrato complexes of La(III) or Ce(III) was found by the EXAFS analyses. However, these complexes are highly stable and did appear aer extraction from nitrate aqueous media (Fig. S8 †) and aer split-anion extraction of Sm or Eu from chloride aqueous media. 58 Secondly, when Cy923 composed the whole organic phase, La(III) and Pr(III) were extracted from concentrated chloride aqueous media via neutral chloride complexes with Cy923, specically LaCl 3 $3Cy923 and PrCl 3 $3Cy923 (Section S6.2, Fig. S9, Fig. S10 and ...
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... could be determined by curve tting to a theoretical standard model with the soware. However, their main species in the lanthanum-loaded organic phase, may be the same as in the case of 0/100 and 50/50, respectively, because of the largely linear superposition of the X-ray absorption spectra 0/100 over 25/75, and especially of 50/ 50 over 75/25 (Fig. 8a). In all cases, only the chloride ions required to maintain electrical neutrality were extracted to the organic phase. Here, the EXAFS measurements did not nd chlorides coordinating to the REE ion in its rst/inner coordi- nation sphere. However, anionic REE-chloro complexes in extractants of the type of [A336][Cl], were previously ...
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... mixtures of Cy923 and [C101] [NO 3 ] in volume proportions of 0/100, 25/75, 50/50, 75/25 and 100/0 (Table S4 †). The results conrmed that different species were formed, depending on the composition of the organic phase (Section SI 6 †). The type of organic phase inu-enced the absorbance, the bandwidth and the position of the absorption maximum (Fig. 8). In general, no isosbestic points appeared in the region of 50 eV aer the edge, conrming that the REE were extracted in different predominant species, by each organic phase. Increments in Cy923/[C101] [NO 3 ] volume ratio shied the edge to higher energy denoting different species, which are summarized in . This could explain the ...
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... in the IL solutions are denoted as [La(H 2 O) x ] 3+ and [Ce(H 2 O) x ] 3+ and may have a smaller  number than in diluted aqueous solutions (without CaCl 2 ). No evidence of nitrato complexes of La(III) or Ce(III) was found by the EXAFS analyses. However, these complexes are highly stable and did appear aer extraction from nitrate aqueous media (Fig. S8 †) and aer split-anion extraction of Sm or Eu from chloride aqueous media. 58 Secondly, when Cy923 composed the whole organic phase, La(III) and Pr(III) were extracted from concentrated chloride aqueous media via neutral chloride complexes with Cy923, specically LaCl 3 $3Cy923 and PrCl 3 $3Cy923 (Section S6.2, Fig. S9, Fig. S10 and ...
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... could be determined by curve tting to a theoretical standard model with the soware. However, their main species in the lanthanum-loaded organic phase, may be the same as in the case of 0/100 and 50/50, respectively, because of the largely linear superposition of the X-ray absorption spectra 0/100 over 25/75, and especially of 50/ 50 over 75/25 (Fig. 8a). In all cases, only the chloride ions required to maintain electrical neutrality were extracted to the organic phase. Here, the EXAFS measurements did not nd chlorides coordinating to the REE ion in its rst/inner coordination sphere. However, anionic REE-chloro complexes in extractants of the type of [A336][Cl], were previously ...
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The article presents data on the solvent extraction separation of rare-earth elements (REEs), such as La(III), Ce(III), Pr(III), and Nd(III), using synergic mixtures of methyltrioctylammonium nitrate (TOMANO3) with tri-n-butyl phosphate (TBP) from weakly acidic nitrate solutions. Specifically, experimental results on separation of REEs, for the pai...
Citations
... In the system called "split anion extraction" where different anions take place in the aqueous and organic phases, the mechanism that plays a role in metal extraction is not an ion exchange, but the complexation of ions. While IL anions in the organic phase that form stable complexes with REEs prefer to migrate to the organic phase, highly hydrated anions in the aqueous phase tend to remain in the aqueous phase [18]. Larsson [SCN]) for the extraction of rare earth elements from the chloride aqueous phase. ...
A novel split anion extraction system was developed to separate thorium from cerium and lanthanum nitrate solutions. The ionic liquid Cyphos® IL 101 with chloride as the anion was used without extra extractants in the extraction process. The results showed efficient separation of thorium and the extraction mechanism is believed to be based on co-extraction with nitrate anion. The maximum loading capacity for thorium was 1395.26 mg/L and the extracted metals were stripped using EDTA solution with 0.5 M NaCl. This split anion extraction system provides a safe, green, and economical method for separating thorium from rare earth elements.
... A further increase in salt concentration eventually led to an increase in extraction efficiency and distribution ratios, with a more pronounced increase for the heavy REEs (HREEs). A positive extraction sequence is thus obtained, i.e. stronger extraction of HREEs than of light REEs (LREEs) [27,28]. These observations are in agreement with literature data [2,5,29]. ...
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.
... Cyanex 923, which is a mixture of four trialkylphosphine oxides, exhibits extraction properties similar to TOPO. Cyanex 923 has been used in ionic liquid phases for the extraction of REEs from nitric acid medium using ILs containing a bis(trifluoromethylsulfonyl) imide anion ( [130]. ...
... [C1C4im] [NTf2], [N1444] [NTf2] and [P66614] [NTf2]) [129], while nitrate ILs, such as trioctylmethylammonium nitrate ([N1888] [NO3]) and trihexyl(tetradecyl)phosphonium ([P66614] [NO3]), were employed for concentrated chloride aqueous solutions[130].Acquisition of these results led to the implementation of a process in continuous mode for the separation of Dy and Nd from chloride media using Cyanex 923 diluted in [C 1 C n im] [NTf 2 ] n = 4-10 ...
... [C1C4im] [NTf2], [N1444] [NTf2] and [P66614] [NTf2]) [129], while nitrate ILs, such as trioctylmethylammonium nitrate ([N1888] [NO3]) and trihexyl(tetradecyl)phosphonium ([P66614] [NO3]), were employed for concentrated chloride aqueous solutions[130].Acquisition of these results led to the implementation of a process in continuous mode for the separation of Dy and Nd from chloride media using Cyanex 923 diluted in ...
Rare earth elements (REEs) are becoming more and more significant as they play crucial roles in many advanced technologies. Therefore, the development of optimized processes for their recovery, whether from primary resources or from secondary sources, has become necessary, including recovery from mine tailings, recycling of end-of-life products and urban and industrial waste. Ionic solvents, including ionic liquids (ILs) and deep-eutectic solvents (DESs), have attracted much attention since they represent an alternative to conventional processes for metal recovery. These systems are used as reactive agents in leaching and extraction processes. The most significant studies reported in the last decade regarding the recovery of REEs are presented in this review.
... The closest analog of SIR 4, which is used for REEs recovery is the SIR impregnated by mixture of Cyanex 923 (a mixture of monodentate trialkylphosphine oxides) and ionic liquids [38,68,69]. We prepared SIR 12 containing 40% of mixture Cyanex 923 and [C 4 mim] + [Tf 2 N] − in molar ratio of 2:1 and compared efficiency recovery of Nd(III) with SIR 4 in identical conditions (Figure 9). ...
Novel solvent-impregnated resins (SIRs) were prepared by treatment of styrene–divinylbenzene copolymer (LPS-500) with mixtures of the promising polydentante extractant (2-diphenylphosphoryl)-4-ethylphenoxy)methyl)diphenylphosphine oxide (L) and an ionic liquid [C4mim]+[Tf2N]−for the extraction chromatography recovery of Nd(III) from nitric acid solutions. It was shown that introduction of the ionic liquid into the SIR composition results in considerable enhancement of the Nd(III) recovery efficiency compared with resin impregnated only by L in slightly acidic media. The influence of the L: ionic liquid molar ratio in the SIRs composition, their percentages, concentration of metal and HNO3 in the eluent, and acid type on the value of synergistic effect and adsorption efficiency of Nd(III) recovery was studied. The SIR containing 40% of mixture of L and [C4mim]+[Tf2N]− with molar ratio 2:1 turned out to be the most efficient. The selectivity of Nd(III) separation from light and heavy rare-earth elements was studied and the optimal conditions of Nd(III) adsorption recovery and stripping by this SIR were chosen. It was found that in recovery efficiency of Nd(III) developed SIR exceeded the SIR containing Cyanex 923 (a mixture of monodentate trialkylphosphine oxides) and [C4mim]+[Tf2N]−.
... Meanwhile, there is only a limited anion exchange of the different anions from one phase to the other to maintain electrical neutrality. [25][26][27][28] In this paper, a split-anion extraction process for the recovery of precious metals (i.e. Au(III), Pt(IV), Pd(II) and Rh(III)) from acidic chloride media using water-saturated ionic liquids is presented. ...
... According to Hofmeister series, Br − or I − anions are more hydrophobic than Cl − and stabilize in the organic phase. [25][26][27][28] Therefore, the ionic liquids play essential roles of providing the anions Br − or I − that form complexes with the precious metals ions. The extraction mechanism involves two concomitant reactions. ...
A split-anion solvent extraction process was developed for the separation of precious metal ions Au(III), Pt(IV), Pd(II) and Rh(III) from aqueous chloride media using water-saturated ionic liquids. The metal extraction and stripping behavior of the chloride form [A336][Cl], bromide form [A336][Br] and the iodide form [A336][I] of the quaternary ammonium ionic liquid Aliquat 336 were compared. The three ionic liquids extracted Au(III), Pd(II) and Pt(IV) quantitatively in most cases, whereas the co-extraction of Rh(III) was strongly dependent on the acidity and the chloride concentration. Among the studied ionic liquids, [A336][I] achieved the highest separation factors between Pd(II)/Rh(III), Pt(IV)/Rh(III), and Au(III)/Rh(III) at 6 mol L⁻¹ Cl⁻. Additionally, the selective stripping of the individual metal ions Pd(II), Au(III), and Pt(IV) was only possible from loaded [A336][I] using ammonia solution (NH4OH), sodium thiosulfate (Na2S2O3), and thiourea ((NH2)2CS), respectively. A closed-loop flow sheet was designed for the recovery of the precious metals from chloride media using split-anion extraction with [A336][I]. The integrated process was demonstrated to be suitable for the purification of Rh(III), Pt(IV) and Pd(II) from a complex metal feed such as the leachate of spent automotive catalysts. The ionic liquid-based split-anion extraction process is simple, selective and effective for the sustainable separation of the precious metals, using only one green extractant [A336][I], which can be regenerated for consecutive extraction-stripping cycles.
... Amongst these, solvent extraction (liquid-liquid extraction) appears to be a highly promising approach for wider adoption in downstream separation processess. 14,15,28 Nevertheless, the usage of numerous commercial extractants, including di-(2-ethylhexyl) phosphoric acid (D2EHPA), 29-34 2-ethyl hexyl phosphonic acid mono-2-ethyl hexyl ester (PC 88A), 33 bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272), LIX (oximes) series reagents, 31,35 tri-butyl-phosphate (TBP), 29,30,34 and amines (Alamine 336, Alamine 308), 6,36,37 has shown excellent extraction behavior in solvent extraction processes towards the uptake of tungsten/ vanadium from the corresponding aqueous phase(s), depending on the speciation of either metal ion in the aqueous media. Both tungsten and vanadium are commonly termed as strategic elements in the periodic table, as they exhibit variable oxidation states. ...
A complete extraction and stripping process to obtain enriched vanadium and tungsten concentrate from spent SCR catalyst leach liquor.
... Ionic liquids have been used in combination of di(2-ethylhexyl)2-ethylhexyl phosphonate (DEHEHP), TBP and Cyanex 925 to enhance the separation of rare-earth ions, increase the extraction capacity and decrease the viscosity of the organic phase. [51][52][53] In this paper, the effect of molecular extractants on the extraction and separation of neodymium and dysprosium using split-anion was investigated. Since hydrophobic and low viscous ionic liquids with high availability are needed for the development of these processes, phosphonium and quaternary ammonium cations with long alkyl chains combined with nitrate and thiocyanate anions were employed. ...
... 58 With the use of extended X-ray absorption ne structure (EXAFS) it has been demonstrated that when extracting to nitrate ionic liquids combined with molecular extractants, different species are formed, depending on the composition of the organic phase. 51,59 A complete study of the species formed during the extraction in the extraction system proposed here is out of the scope of this work. A combination of complementary speciation techniques and modelling should be applied to obtain an accurate and reliable description of the mechanism of extraction. ...
A solvent extraction method based on the combination of the ionic liquid trihexyl(tetradecyl)phosphonium thiocyanate or nitrate ([C101][SCN], [C101][NO3]) and the neutral extractants Cyanex 923 or tri-n-butyl phosphate (TBP) has been investigated for the separation of Nd(III) and Dy(III) from chloride media. High distribution ratios and separation factors were obtained when using Cyanex 923 diluted in [C101][SCN] 40 : 60 (wt%) and extracting from chloride media. The addition of Cyanex 923 to the ionic liquid has four advantages: (1) increase in the distribution ratios of the rare earths, (2) decrease of the viscosity of the organic phase, hence an improved mass transfer, (3) increase in the loading capacity of the ionic liquid and (4) improvement of the coalescence and phase disengagement, which is of importance when carrying out separations in continuous mode. Different extraction parameters were optimized: concentration of Cyanex 923, chloride concentration in the aqueous phase, equilibration time, pH of the aqueous phase, type of scrubbing and stripping agents. The ionic liquid combined with Cyanex 923 was recycled up to three times without losing its extraction efficiency. McCabe–Thiele diagrams were constructed to determine the number of stages needed for the separation of Nd(III) and Dy(III). Stripping of Dy(III) from the organic phase was easily achieved with water. The feasibility to run this process in continuous mode was tested in a battery of small mixer-settlers (0.12 L and 0.48 L effective volume in the mixer and the settler, respectively). As a result, this process constitutes a novel and scalable alternative for the separation of Nd(III) and Dy(III).
The recycling of nickel-metal hydride batteries (NiMHBs) has garnered significant attention in recent years due to the growing demand for critical metals and the implementation of national and international legislation aimed at achieving zero carbon emissions and reducing environmental impact. Typically, NiMHBs contain 10 wt% of rare earth elements (REEs) including La, Ce, Nd, and Pr. However, the majority of these REEs (>90%) are being discarded in landfills each year. The scarcity of these metals and the concentrated distribution of their ore deposits in only a few countries have prompted significant concern globally. One of the existing strategies to address this issue is extraction of REEs through urban mining. This study provides an in-depth fundamental and systematic review on the existing strategies and technologies for the recovery of REEs from spent NiMHBs. Further, the state-of-the-art approaches for the individual separation of La, Ce, Nd, and Pr from aqueous media are discussed, along with their corresponding challenges and shortcomings as well as the potential future directions. The research aims to provide a transformative understanding of various methods for the recovery of REEs from NiMHBs, the available techniques for the individual separation of REEs from different secondary resources, and potential improvements in the recycling process of spent NiMHBs. The outcome of this work will contribute to the development of more efficient and effective REEs recovery methods and help address the growing concern of REEs scarcity and extraction environmental impact.
Long chain quarternary alkyl phosphonium based ionic liquids have several fascinating merits over conventional imidazolium based ionic liquids. In this context, trihexyl(tetradecyl)phosphonium nitrate ([P66614][NO3]) ionic liquid (commonly known as cyphos nitrate) was chosen as the extractant in its undiluted status for the extraction and separation of trivalent Ln(III)/An(III) from the nitric acid phase. Experimental parameters such as the concentration of initial nitric acid, initial nitrate ion in the feed phase, initial feed metal concentration, equilibration time, etc. were varied precisely to furnish the extraction process. The major highlights in the study is the fascinating salting effect of the feed phase NO3⁻ ion in the efficient extraction of Eu(III)/Am(III). This methodology avoids the use of additional extractant in the ionic liquid phase for extracting the metal ion leading to an economical process. The use of [P66614][NO3] avoids the loss of any ionic liquid component to the aqueous phase during the extraction. The proposed ionic liquid was found to be radiation stable which enhances its reliability as solvent for the separation of Ln(III)/An(III) in the context of spent nuclear fuel reprocessing. The present ionic liquid was found to be superior in metal loading in comparison to other ionic liquids with similar type of structure. Another underscore of the present study is the use of only Millipore water as the stripping agent without adding any aqueous phase complexing agent which certainly offer economic and environmental benefit.
Increasing demand for low carbon technologies and renewable energy sources requires our resources and economies to be circular. Many countries agree that the responsible consumption, production, and
recycling of rare-earth-containing products is essential as a way to achieve the sustainable development goals also set out in the European Green Deal. Sustainable sourcing is targeted with carefully designed roadmap for cost efficient REE production from end-of-life products (EoLs) in addition to mining activities as providing primary sources. Hydrometallurgical methods, such as roasting, leaching, precipitation, crystallization, solvent extraction, and ion exchange includes fast developing, selective, eco-friendly, and cost-effective technologies especially for the extraction of REEs. This article provides an overview of primary and secondary resources and summarizes presents case scenario of studies carried out on the use
of some promising methods, which could serve as an economical means for recovering REEs.
