Adjacent Lanthanides Research Articles

Development and optimization of high-performance extraction chromatography method for separation of rare earth elements

The effectiveness of commonly used extractants for chromatographic separation of rare earth elements (REEs) was compared. Columns loaded with similar molar concentrations of tributyl phosphate (TBP), di-(2-ethylhexyl) phosphoric acid (HDEHP), and N-Methyl-N, N, N-tri-octyl-ammonium chloride (Aliquat-336), with mineral acid as eluent were evaluated. Retention factors were determined, and separation efficiency was assessed based on the resolution data of the REEs acquired under the same elution conditions for each column. HDEHP demonstrated the best separation efficiency for the entire REE series (mean Rs = 2.76), followed by TBP (mean Rs = 1.52), while Aliquat-336 exhibited the lowest performance (mean Rs = 1.42). The HDEHP-coated column was then used to optimize the extraction chromatographic separation of the REEs. The primary challenge was to completely elute the heavy REEs (Tb – Lu) while maintaining adequate separation of the light REEs (La – Gd) within a reasonably short time. The stepwise gradient elution procedure improved the resolution between adjacent REEs, allowing the complete separation of the entire REE series within 25 minutes. Better separation efficiency for light REEs was achieved at higher column temperatures and a mobile phase flow rate of 1.5 mL/min in the tested domain of 20–60 °C, and 0.5–2.0 mL/min, respectively, resulting in plate heights (H) ranging from 0.011 to 0.027 mm.

Separation of Adjacent Light Rare Earth Elements Using Silica Gel Modified with Diglycolamic Acid.

The separation of adjacent rare earth elements (REEs) is a challenging issue due to their chemical similarity. We have investigated the separation of adjacent REEs using four types of adsorbents consisting of silica gel modified with diglycolamic acid with different functional groups at the amide position. For all the adsorbents, the adsorption ratio of REEs increased with the increase in atomic number from La to Sm and then became constant for heavy REEs. Among them, EDASiDGA, an adsorbent containing secondary and tertiary amides, showed a high separation factor for Nd/Pr of 2.8. The EDASiDGA-packed column was tested for individual recovery of Pr, Nd, and Sm. After the adsorption of these REEs from 0.10 M HCl, desorption tests were performed with 0.32 and 1.0 M HCl. As a result, Pr and Nd were eluted separately with 0.32 M HCl, and Sm was recovered with 1.0 M HCl. Since the EDASiDGA-packed column showed excellent separation of Pr/Nd/Sm without any chelating agent, it is promising for practical use.

Extraction of Rare Earth Elements from Chloride Solutions Using Mixtures of P507 and Cyanex 272

In this study, the extraction of rare earth elements (REEs) from chloride solutions after leaching REE carbonate concentrate with solutions of the mixtures of P507 (2-ethylhexylphosphonic acid mono-2-ethylhexyl ester) and Cyanex 272 (bis(2,4,4-trimethylpentyl)phosphinic acid) (1:1) at various concentrations was experimentally studied. It was shown that the distribution ratios of all REEs decrease with the increasing concentration of these metals in the initial solution, which is associated with the loading of the organic phase. The most significant improvement in the extraction is observed for the heavy group of rare earth elements. The extractability of REEs increases with the increasing atomic number of the element, as is typical for the extraction of these metals with acidic organophosphorus extractants. The data obtained show that the separation factors of adjacent rare earth elements decrease slightly with the increasing concentration of metals in the initial aqueous solution. Increasing the concentration of the extractant mixture does not have a significant effect on the values of the adjacent REE separation factors. The data obtained on the distribution ratios and separation factors made it possible to propose a flow sheet for the separation of rare earth elements with the production of Y, Ho, Tb and Dy.

Elemental composition x-ray fluorescence analysis with a TES-based high-resolution x-ray spectrometer

The accurate analysis of the elemental composition plays a crucial role in the research of functional materials. The emitting characteristic x-ray fluorescence (XRF) photons can be used for precisely discriminating the specified element. The detection accuracy of conventional XRF methodology using semiconductor detector is limited by the energy resolution, thus posing a challenge in accurately scaling the actual energy of each XRF photon. We adopt a novel high-resolution x-ray spectrometer based on the superconducting transition-edge sensor (TES) for the XRF spectroscopy measurement of different elements. Properties including high energy resolution, high detection efficiency and precise linearity of the new spectrometer will bring significant benefits in analyzing elemental composition via XRF. In this paper, we study the L-edge emission line profiles of three adjacent rare earth elements with the evenly mixed sample of their oxide components: terbium, dysprosium and holmium. Two orders of magnitude better energy resolution are obtained compared to a commercial silicon drift detector. With this TES-based spectrometer, the spectral lines overlapped or interfered by background can be clearly distinguished, thus making the chemical component analysis more accurate and quantitative. A database of coefficient values for the line strength of the spectrum can then be constructed thereafter. Equipped with the novel XRF spectrometer and an established coefficient database, a direct analysis of the composition proportion of a certain element in an unknown sample can be achieved with high accuracy.

Electrochemical separation of Gadolinium from variable valence europium in molten LiCl-KCl via liquid LBE alloy electrode

The highly effective separation of two adjacent rare earth is significant to the rare earth and nuclear industries. This paper investigates the highly effective separation of Gd over Eu using liquid lead–bismuth eutectic (LBE) alloy cathode in molten LiCl-KCl-EuCl3-GdCl3 by pulse potential electrolysis (PPE). Underpotential deposition of Eu and Gd is observed on the LBE alloy, with a depolarization value far greater than that of the liquid Pb electrode. Furthermore, the higher exchange current density and the lower activation energy of the electrode reaction indicate that the LBE alloy cathode has higher kinetic performance than the liquid Pb. Then, the practical electro-separation in LiCl-KCl-EuCl3-GdCl3 systems is carried out by applying different electrolysis technology. The effects of varying electrolysis methods and parameters on separation factor (SF), extraction efficiency, cathode product morphology, and crystal size are studied and compared. The results show that both the extraction efficiency and the separation factor obtained by the PPE are the largest. The calculated extraction efficiency of Gd and the actual separation factor SFGd/Eu of Gd/Eu could be up to 99.1 % and 759, respectively.

Kinetic enhanced separation of praseodymium and neodymium induced by specific ion effect

The precise and controllable separation of Pr/Nd is the key to restricting the recovery of rare earths from neodymium magnets. However, it is difficult to realize the efficient separation by difference in thermodynamic properties of Pr3+ and Nd3+. In present work, the enhanced separation was achieved by a kinetic extraction strategy in systems with different salting-out agents. The comprehensive effect of multiple ions including salt anions and cations on enhanced separation of Pr3+/Nd3+ were investigated. Experimental results revealed that the separation coefficient can be higher than 8. The enhancing effect on separation of Pr3+/Nd3+ from different salting-out agents followed the order of NaCl < NaNO3 < NaSCN < LiNO3. It had a relationship with the salting-out effect, which could be influenced by the type and concentration of salting-out agents. In details, the salting-out effect was closely related with hydration of salt anions and cations. There are differences in the binding ability of rare earth ions to the above anions. The behaviors of rare earth ions arriving at the interface were different under specific ion effect of Li+ and Na+. By molecular dynamics simulations, it verified that the separation behaviors were related with diffusion mass transfer rate to the interface and the adsorption behaviors of rare earth ions at the interface. At the end, the recycling and recovery of lithium was suggested. This work provides a basis for developing a new method for efficient and green separation of adjacent rare earths.

Nonlinearity in regulating the metal to insulator transition of ReNiO3 towards low temperature range

Among the existing material family of the correlated oxides, the rare earth nickelates (ReNiO3) exhibit broadly adjustable metal to insulator transition (MIT) properties that enables correlated electronic applications, such as thermistors, thermochromics, and logical devices. Nevertheless, how to accurately control the critical temperature (TMIT) of ReNiO3 via the co-occupation of the rare-earth elements is yet worthy to be further explored. Herein, we demonstrate the non-linearity in adjusting the TMIT of ReNiO3 towards lower temperatures via introducing Pr co-occupation within ReNiO3 (e.g., PrxNd1-xNiO3 and PrxSm1-xNiO3) as synthesized by KCl molten-salt assisted high oxygen pressure reaction approach. Although the TMIT is effectively reduced via Pr substitution, it does not strictly follow a linear relationship, in particular, when there is large difference in the ionic radius of the co-occupation rare-earth elements. Furthermore, the most significant deviation in TMIT from the expected linear relationship appears at an equal co-occupation ratio of the two different rare-earth elements, while the abruption in the variation of resistivity across TMIT is also reduced. The present work highlights the importance to use adjacent rare-earth elements with co-occupation ratio away from 1:1 for achieving more linear adjustment in designing the metal to insulator transition properties for ReNiO3.

Electrochemical Oxidation and Speciation of Lanthanides in Potassium Carbonate Solution

Increasing lanthanide demand to support clean energy goals drives the need to develop more efficient approaches to separate adjacent lanthanides. Most approaches for lanthanide separations are not very selective and are based on small differences in lanthanide ionic radii. Concentrated potassium carbonate media has shown some potential to enable oxidation of praseodymium (Pr) and terbium (Tb) to their tetravalent states, which could ultimately enable a separation based on differences in oxidation states, but very little is known regarding the system’s chemistry. This work completes a detailed examination of cerium (Ce) redox chemistry in concentrated carbonate media to support the development of Pr and Tb oxidation studies. The half-wave potential (E1/2) of the Ce(III)/(IV) redox couple is evaluated under various solution conditions and computational modeling of carbonate coordination environments is discussed. Cyclic voltammetry shows higher carbonate concentrations and temperatures can lower the potential required to oxidize Ce(III) by 54 mV (3.5 to 5.5 M) and 39 mV (from 10 °C to 70 °C). Chronoabsorptometry shows Ce(III) and Ce(IV) carbonate complexes are chemically stable and reversible. Computational modelling suggests the most likely coordination environment for the Ce(IV) complex is Ce(CO3)4(OH)5− which is less entropically favorable than the lowest energy Ce(III) complex, Ce(CO3)4 5−.

Efficient and sustainable separation of yttrium from heavy rare earth using functionalized ionic liquid [N1888][NDA

The separation of adjacent rare earth (RE) is one of the most difficult separation tasks, especially the separation and purification of yttrium (Y) from heavy rare earth (HREE). In the traditional Y separation process, the organic phase composed of acidic extractants such as naphthenic acid (HA) and neodecanoic acid (NDA) need to be saponified with sodium hydroxide or ammonia in each cycle. The resulting alkali consumption and saponification wastewater have negative impacts on the environment. In this article, a bifunctional ionic liquid [methyltrioctyl ammonium][neodecanoate] ([N1888][NDA]) was synthesized. The extraction capacity, stripping property and recycling stability of [N1888][NDA] were systematically studied. On this basis, the separation process of Y was developed. The separation factors (β) of Ho/Y and Er/Y were 2.64 and 4.32, especially the Lu/Y reached 16.27. A higher separation factor is of significance for the separation of Y from HREEs. The extraction sequence of rare earth elements (REEs) with [N1888][NDA] follows the positive sequence extraction, which is the same as that in neodecanoic acid system. In addition, the separation process of industrial HREE feed liquid containing 0.20 mol L−1 REEs (Y, 88.87 mol.%) was studied. By adjusting the extraction conditions, salting-out reagent such as NaCl did not need to be used in the aqueous phase, which helps to avoid high salt components in RE products. Through the fractional extraction experiment of 11-stage extraction and 4-stage scrubbing, the Y product with a purity of 99.03 mol.% was obtained. The organic phase composed of [N1888][NDA] was stable after being regenerated with NaOH for recycling extraction.

Poly (vinyl alcohol-co-ethylene) (EVOH) modified polymer inclusion membrane in heavy rare earths separation with advanced hydrophilicity and separation property

Efficient separation of adjacent rare earths is an interesting and challenging job for membrane separation scientists. In this article, a novel polymer inclusion membrane (PIM) incorporating the hydrophilic additive random copolymer poly (vinyl alcohol-co-ethylene) (EVOH) was synthesized. Due to the polarity of P = O and P-OH groups in Cyanex272 and hydrophilicity of –OH groups in EVOH, the membranes exhibited much smaller water contact angles than pure PVDF membranes. And FT-IR results indicated that the addition of EVOH made no difference on the coordination between P = O, P-OH in Cyanex272 and Lu3+. SEM and AFM results indicated that the addition of appropriate amount of EVOH could generate more and larger surface pores and internal channels. Optimum membrane compositions and permeation conditions were fixed via static adsorption and dynamics permeation experiments. Separation factor was calculated as high as 3.78, which was much higher than previous studies no matter in solvent extraction or membrane separation. It is worth noting that it’s the first time an obvious carrier’s leakage was observed via characterizations which implied Cyanex272 may be not a perfect carrier in terms of PIM’s stability. All these results proved that this novel PIM with EVOH serving as hydrophilic additive could be further testified in heavy rare earths separation and purification process.

Effect of Dy dopant on the ferromagnetic characteristics of indium nitride nanosheets

Herein, Dy3+ doped indium nitride nanosheets with ferromagnetism at room-temperature were synthesized via a vapor - solid phase nitriding reaction. The as-synthesized samples exhibit clear ferromagnetism at room-temperature. The ferromagnetic properties of the samples could be changed by doped Dy3+. The saturation magnetization value of various Dy3+ doped indium nitride nanosheet samples display a parabolic-like change with the Dy3+ doped content increase and reaches the top value of 0.1455 emu g−1 corresponding to the Dy3+ doped content of 1.06 at. % at room temperature. The magnetic properties were originated from the d-f interaction between localized carriers and adjacent rare earth Dy3+ ions in the carrier orbits based on the first-principles calculation. The as-synthesized Dy doped indium nitride nanosheets can be widely used in spintronic devices due to the room temperature ferromagnetism.

Structure Activity Relationship Approach toward the Improved Separation of Rare-Earth Elements Using Diglycolamides.

The separation of adjacent lanthanides continues to be a challenge worldwide because of the similar physical and chemical properties of these elements and a necessity to advance the use of clean-energy applications. Herein, a systematic structure-performance relationship approach toward understanding the effect of N-alkyl group characteristics in diglycolamides (DGAs) on the separation of lanthanides(III) from a hydrochloric acid medium is presented. In addition to the three most extensively studied DGA complexants [N,N,N',N'-tetra(n-octyl)diglycolamide, TODGA; N,N,N',N'-tetra(2-ethylhexyl)diglycolamide, TEHDGA; N,N'-dimethyl-N,N'-di(n-octyl)diglycolamide, DMDODGA], 12 new extracting agents with varying substitution patterns were designed to study the interplay of steric and electronic effects that control rare-earth element extraction. Subtle changes in the structure around diglycolamide carbonyl oxygen atoms result in dramatic shifts in the lanthanide extraction strength and selectivity. The effects of the chain length and branching position of N-alkyl substituents in DGAs are elaborated on with the use of experimental, computational, and solution-structure characterization techniques.

Tuning the Separation of Light Lanthanides Using a Reverse-Size Selective Aqueous Complexant.

Efficiently separating the chemically similar lanthanide ions into elementally pure compositions is one of the greatest scientific challenges of the 21st century. Although extensive research efforts have focused on the development of organic extractants for this purpose, the implementation of aqueous complexants possessing distinct coordination chemistries has scarcely been explored as an approach to enhancing intralanthanide separations. In this study, we investigate the lanthanide coordination chemistry of macrophosphi, a novel analogue of the reverse-size selective expanded macrocycle macropa. Our studies reveal that substitution of the pyridyl-2-carboxylic acid pendent arms of macropa with pyridyl-2-phosphinic acid arms of macrophosphi gives rise to a dramatic enhancement in the ability to discriminate between light lanthanides, reflected by a binding affinity of macrophosphi for La3+ that is over 5 orders of magnitude higher than that for Gd3+. Furthermore, upon implementation of macrophosphi as an aqueous complexant in a biphasic extraction system containing the industrial extractant bis(2-ethylhexyl)phosphoric acid, separation factors of up to 45 were achieved for the Ce/La pair. These results represent a remarkable separation of adjacent lanthanides, demonstrating the significant potential of reverse-size selective aqueous complexants in lanthanide separation schemes.

Extraction and complexation of trivalent rare earth elements with tetraalkyl diglycolamides

The extraction and complexation behaviors of four tetraalkyl diglycolamide (TRDGA, where R represents n-butyl, n-hexyl, n-octyl and 2-ethylhexyl) ligands with linear chain or branched chain structure were described with respect to La3+, Pr3+, Nd3+; Eu3+, Gd3+; Y3+, Er3+ and Yb3+ as the representatives of light, middle and heavy rare-earth group ions in HNO3 solution. Effects of acidity, ligand concentration and temperature on the distribution ratio of these ions were examined. High acidity was good for the extraction. For same metal ion, the extractability of DGA ligands followed the order of T2EHDGA < THDGA < TODGA < TBDGA at the same acidity, which was also supported by nuclear magnetic resonance (NMR) analyses. Meanwhile, for different metal ions, their extracted efficiencies by the same DGA ligand increased in the sequence of lanthanide contraction. The average separation factors of adjacent lanthanides within light, middle and heavy rare-earth groups could attain about 2.4, 1.7 and 2.1, respectively. Slope analysis indicated that the formation of predominant 1:3 and 1:2 metal/ligand extracted species for linear chain and branched DGA, respectively. In methanol solution, 1:1, 1:2 and 1:3 Eu3+/DGA species were also observed using fluorescence spectroscopy titration. Fourier transform infrared spectroscopy (FT-IR) analyses suggested that the carbonyl oxygens compared with ether oxygen play a dominant role in coordination. Moreover, the stability constants (log β) and the thermodynamic parameters (ΔH, ΔS and ΔG) for the complexation of Eu3+ with DGAs were also presented.

Separation of adjacent heavy rare earth Lutetium (III) and Ytterbium (III) by task-specific ionic liquid Cyphos IL 104 embedded polymer inclusion membrane

Adjacent rare earth separation has always been one of the hardest separation tasks around world. In this article, a task-specific ionic liquid Cyphos IL 104 embedded polymer inclusion membrane (PIM) was fabricated to realize the adsorption and separation of adjacent heavy rare earth elements Lutetium (III) and Ytterbium (III). Chemical composition of the PIM was verified by attenuated total reflectance Fourier transformed infrared spectroscopy and X-ray photoelectron spectroscopy. And results confirmed only PO and P–O groups participated in the formation of Rare Earth (III)-Cyphos IL 104 complex. A typical thumb-like asymmetric structure was observed by scanning electron microscopy. And the addition of Cyphos IL 104 promoted the hydrophilicity of the PIM as the water contact angle became smaller. Static adsorption and dynamic transport performances were studied in details to get the optimum separation condition. The permeability coefficients of Yb(III) and Lu(III) were 156 μm s−1 and 114.82 μm s−1, respectively; And the initial membrane fluxes were 90.17 μm m−2 s−1 and 65.61 μm m−2 s−1, respectively. The separation factor between Yb(III) and Lu(III) was calculated as 1.37 under the optimized transport condition. All these would provide promising developments of adjacent heavy rare earth separation with an efficient and practical membrane strategy.

Synergistic solvent extraction of heavy rare earths from chloride media using mixture of HEHHAP and Cyanex272

The synergistic extraction of heavy rare earths from chloride medium was investigated using the mixture of heptylaminomethylphosphonic acid mono-(2-ethyl-hexyl) ester (HEHHAP, HA) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex272, HB) in heptane. The extraction efficiency of heavy rare earths and the separation factors between adjacent lanthanides with the HEHHAP-Cyanex272 mixture are both better than those for the sole HEHHAP or Cyanex272 system. The separation factors between adjacent heavy rare earths are also higher than those for other synergistic systems. The rare earth extraction is a cation exchange process deduced by both slope analysis method and constant molar method. The extracted complexes are determined to be LnH2Cl2A2B (Ln = Yb, Lu). The loaded metal ions can be easily stripped by HCl or H2SO4. The stripping efficiency is over 90% when the concentration of HCl was more than 1 mol/L. The synergistic extraction of heavy rare earths with the mixed HEHHAP-Cyanex272 system is an endothermic reaction. The negative values of ΔG indicates that the extraction reaction of Ln(III) is spontaneous and favorable.

A novel method for synthesis of styryl phosphonate monoester and its application in La(III) extraction

Herein, styryl phosphonate monoester (SPE) was synthesized and first introduced as rare earth extractant. The solvent extraction of lanthanum (III) from nitrate solution using styryl phosphonate mono-iso-octyl ester (SPE108), di-2-ethylhexyl phosphoric acid (D2EHPA) and 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (EHEHPA) as extractants was investigated. The effects of experimental parameters including equilibrium time, extractant concentration, aqueous pH, phase ratio and salt concentration on the extraction process were studied. The results indicate that the extraction ability and capacity of the extractants follow the order: SPE108 > D2EHPA > EHEHPA. What's more, the extraction process is less affected by ammonium sulfate in the aqueous phase with SPE108. The results of the separation between lanthanum and adjacent lanthanides (Ce, Pr, Nd, Sm) show that SPE108 can separate lanthanides efficiently at low pH. The extraction mechanism of SPE108 is proved to be similar to D2EHPA, and the density functional theory (DFT) calculation results infer that SPE108 exhibits superior extraction ability due to its strong electron-accepting ability.

Separation of adjacent rare earth elements enhanced by “external push-pull” extraction system: An example for the separation of Pr and Nd

Separation of adjacent rare-earth elements, such as Pr and Nd, is extremely difficult due to the similarity in their physicochemical properties. Enhanced separation of adjacent rare-earth elements based on the “push-pull effect” by addition of water-soluble complexing agents was an effective strategy in traditional organic-aqueous two-phase extraction. However, environmental pollution is serious due to the residual of complexing agent in the extraction raffinates. In present work, a novel “external push-pull” extraction system, composed of three coexisting liquid phases, P507 organic phase, ionic liquid (tributyl-methyl ammonium nitrate, N4441NO3)-rich phase and NaNO3 aqueous solutions, is suggested to improve the separation between Pr and Nd. It is revealed that Nd and Pr can be enriched respectively into the P507 organic top phase and N4441NO3-rich ionic liquid middle phase in the external push-pull extraction system, owing to a so-called “external push-pull effect” from a reversed extraction selectivity of P507 organic phase and N4441NO3 ionic liquid-rich phase towards Nd and Pr, respectively. Compared to traditional organic-water two-phase systems, the separation factor of Pr to Nd in the suggested external push-pull extraction system could increase obviously to 3.5 or even more. Various effects from the aqueous pH, NaNO3 concentration, the initial concentration ratios of Pr to Nd in feed aqueous solutions, and the addition amount of N4441NO3, the volume of P507 organic phase on the separation between Pr and Nd are discussed. In addition, reversal extraction of rare earth ions in the ionic liquid-rich phase is found to be closely related to the complexation behavior of rare earth ions with NO3− ions by using molecular dynamic simulations. Based on this work, a possibility for extraction and separation of 14 rare-earth element ions from their coexisting aqueous solutions using the suggested external push-pull extraction system is also explored. The present work highlights a novel green strategy for improving the separation of adjacent rare-earth elements.

Microcolumn lanthanide separation using bis-(2-ethylhexyl) phosphoric acid functionalized ordered mesoporous carbon materials

Adjacent lanthanides are among the most challenging elements to separate, to the extent that current separations materials would benefit from transformative improvement. Ordered mesoporous carbon (OMC) materials are excellent candidates, owing to their small mesh size and uniform morphology. Herein, OMC materials were physisorbed with bis-(2-ethylhexyl) phosphoric acid (HDEHP) and sorption of Eu3+ was investigated under static and dynamic conditions. The HDEHP-OMC materials displayed higher distribution coefficients and loading capacities than current state-of-the-art materials. Using a small, unpressurized column, a separation between Eu3+ and Nd3+ was achieved. Based on these experimental results, HDEHP-OMC have shown potential as a solid phase sorbent for chromatographic, intragroup, lanthanide separations.

A triple tandem columns extraction chromatography method for isolation of highly purified neodymium prior to 143Nd/144Nd and 142Nd/144Nd isotope ratios determinations

A new separation scheme is presented for the isolation of Nd fractions highly purified from adjacent lanthanides, especially Ce and Pr, in preparation to demanding isotope ratios applications, e.g. determination of 142Nd/144Nd, or measurement of 143Nd/144Nd on very small samples by using NdO+ ion beams.