Separation Of Lanthanides Research Articles

Separation and Complexation of Lanthanides with an Acidic Phenanthroline Carboxamide Ligand: Extraction, Spectroscopy, and Crystallography

Separation and Complexation of Lanthanides with an Acidic Phenanthroline Carboxamide Ligand: Extraction, Spectroscopy, and Crystallography

Efficient separation and comprehensive recovery of rare earth, bismuth and iron by one-step extraction and two-step stripping

A route was proposed to separate bismuth, iron, and rare earth elements from a solution containing nickel and magnesium through one-step extraction and two-step stripping. Firstly, saponified di-(2-ethylhexyl) phosphoric acid (D2EHPA) was used as the extractant to separate target elements. RE(III), Bi(III), and Fe(III) could be separated from Ni(II) and Mg(II), with extraction efficiencies of more than 99 %. Secondly, RE(III), Bi(III), and Fe(III) were stripped selectively by nitric acid and oxalic acid, respectively. Subsequently, the iron present in the oxalic acid stripping solution was treated under UV irradiation for 15 min to recover oxalic acid and obtain the ferrous oxalate product. The stripping efficiencies of RE(III), Bi(III), and Fe(III) were up to 100 % for four-stage countercurrent stripping, and the recovery rates of RE(III) and Bi(III) were 97.3 % and 99.2 %. The purities of nitrate rare earth enrichment solution, bismuth oxalate and ferrous oxalate were 99.7 %, 98.4 % and 99.5 %, respectively. In addition, the extraction dynamic demonstrated that the double salt precipitation was not observed during the extraction when the extraction time exceeded 7 min and the extraction mechanism was analyzed using the slope method. This process shortens steps, and is more efficient to separate RE(III), Bi(III), and Fe(III) from the mixed solution containing Ni(II) and Mg(II), which has a prospective industrial application.

Rare earth elements in biology: From biochemical curiosity to solutions for extractive industries.

Rare earth elements (REEs) are critical for our modern lifestyles and the transition to a low-carbon economy. Recent advances in our understanding of the role of REEs in biology, particularly methylotrophy, have provided opportunities to explore biotechnological innovations to improve REE mining and recycling. In addition to bacterial accumulation and concentration of REEs, biological REE binders, including proteins (lanmodulin, lanpepsy) and small molecules (metallophores and cofactors) have been identified that enable REE concentration and separation. REE-binding proteins have also been used in several mechanistically distinct REE biosensors, which have potential application in mining and medicine. Notably, the role of REEs in biology has only been known for a decade, suggesting their considerable scope for developing new understanding and novel applications.

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.

Mathematical modeling of rare earth element separation in electrodialysis with adjacent anion exchange membranes and ethylenediaminetetraacetic acid as chelating agent

This research delves into the effective use of electrodialysis for the separation of rare earth elements (REEs), specifically separating dysprosium (Dy) from praseodymium (Pr) and neodymium (Nd). A robust mathematical model based on the extended Nernst-Planck equation is introduced, simulating the process within a configuration that includes two adjacent anion exchange membranes. The model integrates aspects such as feed equilibrium, ion exchange within the membrane, and overall ion flux. Validation of the model's predictability was conducted through Chi-squared tests and root mean square error (RMSE) calculations, affirming its capability to accurately predict ion concentrations across different compartments. The study examines essential parameters such as applied voltage, rinse solution concentration, and feed concentration, assessing their impacts on separation performance and energy efficiency. Results indicate that higher voltages above 8 V, while speeding up separation, detrimentally impact energy use. It also highlights a critical balance in rinse solution concentration; lower concentrations below 0.05 mol/L enhance energy efficiency but may undercut separation efficacy due to early depletion. A linear correlation between the necessary rinse concentration and feed concentration was established, with higher feed concentrations demonstrating reduced specific energy consumption, thus enhancing overall efficiency. However, challenges remain in current efficiency due to the independent migration of SO42− ions in this specific setup. The findings advocate exploring alternative configurations, like alternating cation and anion exchange membranes, to optimize both environmental and economic aspects of REE separation. This study provides valuable insights and recommendations for refining electrodialysis systems in REE processing, contributing to sustainable and cost-effective electrodialysis systems.

Green approach for separating iron and rare earths from complex polymetallic solid residues via hydrogen-based mineral phase transformation: A pilot-scale study

The Bayan Obo low-grade polymetallic ore (BOLPO) has been abandoned for many years owing to its difficult beneficiation and remains as a solid residue. This is causing significant ecological damage to the surrounding environment. In this pilot-scale study, hydrogen-based mineral phase transformation (HMPT) technology and associated equipment were used to successfully separate iron and rare earths from BOLPO, demonstrating stable operation for 48 h. Optimal HMPT conditions included a feed rate of 120 kg/h, HMPT temperature of 500 °C, gas flow rate of 3.5 m3/h and gas concentration of 22.5 vol%. After grinding and flotation defluorination, the obtained iron concentrate had a TFe grade of 65.26 wt%, a recovery of 85.29 wt%, and a low F grade of 0.28 wt%. Product analysis revealed phase transformations of iron and rare earths during the HMPT process, which increased the magnetic difference between the magnetic and non-magnetic products. The formation of pores and cracks during this process also facilitates the subsequent separation of iron and rare-earths. This study paves the way for clean and efficient iron and rare earth separation with regional mineral recovery potential.

Insights into coordination and ligand trends of lanthanide complexes from the Cambridge Structural Database

Understanding lanthanide coordination chemistry can help develop new ligands for more efficient separation of lanthanides for critical materials needs. The Cambridge Structural Database (CSD) contains tens of thousands of single crystal structures of lanthanide complexes that can serve as a training ground for both fundamental chemical insights and future machine learning and generative artificial intelligence models. This work aims to understand the currently available structures of lanthanide complexes in CSD by analyzing the coordination shell, donor types, and ligand types, from the perspective of rare-earth element (REE) separations. We obtain four sets of lanthanide complexes from CSD: Subset 1, all Ln-containing complexes (49472 structures); Subset 2, mononuclear Ln complexes (27858 structures); Subset 3, mononuclear Ln complexes without cyclopentadienyl ligands (Cp) (26156 structures); Subset 4, Ln complexes with at least one 1,10-phenanthroline (phen) or its derivative as a coordinating ligand (2226 structures). The subsequent analysis of lanthanide complexes in these subsets examines the trends in coordination numbers and first shell distances as well as identifies and characterizes the ligands and donor groups. In addition, examples of Ln-complexes with commercially available complexants and phen-based ligands are interrogated in detail. This systematic investigation lays the groundwork for future data-driven ligand designs for REE separations based on the structural insights into the lanthanide coordination chemistry.

Exploring the bonding and extraction separation effects of N donor ligands with different skeletons on Am(III) and Eu(III)

Designing ligands for effective separation of actinide(III)/lanthanide(III) is one of the key issues in the treatment of spent nuclear fuel. However, due to the chemical similarity of trivalent actinides and lanthanides, their separation faces a great challenge in the reprocessing of spent nuclear fuel. Nitrogen donor extractants are considered as promising reagents for separation of trivalent actinides and lanthanides. To the best of our knowledge, the pre-organized structure of the ligand has a strong influence on the extraction separation capacity. In this work, we designed four N-donor ligands (L1 and L2 with pyridine and bipyridine skeletons, respectively, and L3 and L4 both with phenanthroline skeletons) with different pre-organized structures and investigated their selective extraction for Am(III) and Eu(III) by using scalar relativistic density functional theory (DFT). The absolute minimum ESP values of these ligands and the higher HOMO level suggest that the ligand L2 may have a stronger affinity for Am(III)/Eu(III) ions than other ligands. The three average bond lengths of each complex indicate that the Am(III) and Eu(III) ions have larger bond lengths with N2 atoms than with N1 atoms. Various theoretical approaches have been used to evaluate the properties of the four ligands as well as the coordination structures, bonding properties and thermodynamic properties of the complexes of the four ligands with Am(III) and Eu(III). The WBIs, QTAIM, NBO, DOS and EDA analysis indicate that the metal–ligand bonds are mainly ionic in character, the Am-N bond has more covalency than the Eu-N bond because the Am 5f orbitals are more involved in bonding with ligand than Eu 4f orbitals. According to the extended transition state and natural orbital chemical valence theory (ETS-NOCV) analysis, electrons are obviously transferred from the lone pair of the ligand N atom to the hybrid s, d and f orbitals of the metal ion. The thermodynamic results show that the four ligands can coordinate well with the Am and Eu ions, and also have suitable separation capacity for Am and Eu. Among the four ligands, the L2 and L3 ligands have the strongest coordination ability for metals and the best extraction separation effect for Am and Eu. It can be seen that the bridging skeleton of the ligand and the number of N atoms on the five-membered ring and also different organic solvents have obvious effects on the extraction and separation capacity of the ligand. This study provides a theoretical basis for the efficient separation of Am(III)/Eu(III) by adjusting the preorganization level of ligands, and provides a theoretical basis for the design and screening of ligands by preorganization.

Aluminum Removal from Rare Earth Chloride Solution through Regulated Hydrolysis via Electrochemical Method

Due to the coexistence of Al3+ and RE3+ and their similar properties, the separation of aluminum from rare earths is difficult. In this study, selective precipitation was used to separate aluminum from rare earth chloride solution via electrochemical regulated hydrolysis. By controlling the current density and electrolytic time, the rate of hydroxyl ion production was regulated, and the selective separation of rare earth and aluminum was realized according to the different precipitation sequences. By altering the temperature, current density, pH value, and other parameters, the separation performance of aluminum from rare earth in mixed rare earth chloride systems was systematically investigated. The removal rate of aluminum reached 88.35%, and the loss rate of rare earth was only 5.99% under optimized conditions. Compared with traditional neutralization hydrolysis, the new process showed higher efficiency and lower rare earth loss rate. Furthermore, a kinetic analysis of aluminum precipitation revealed that the reaction adhered to pseudo-first order kinetics. Additionally, the precipitate obtained via separation and filtration was amorphous alumina hydroxide with a small amount of rare earth attached. No reagent was consumed for the new process, which was more efficient and cleaner, providing a new idea for removing aluminum impurities from rare earth solutions.

Selective separation of rare earths and aluminum from low-concentration rare earth solution via centrifugal extraction

The separation of rare earths (REs) and aluminum (Al) has always been a practical challenge in the rare earth industry. In this paper, the effects of contact time, the concentrations of Al3+ and RE3+ on the extraction and separation of REs and Al during the solvent extraction of low-concentration rare earth sulfate solution using P507 were investigated. Significant differences in the extraction kinetics between REs and Al can be observed at the same contact time. For instance, when the contact time is 10 s, the extraction efficiency of Y reaches up to 97.5 %, whereas that of Al is only 9.1 %. Under the conditions of initial pH of the rare earth solution 4.0, Al3+ concentration 0–20.0 mmol/L, and RE3+ concentration 1.5–12.0 mmol/L, both the separation factors of Gd/Al (βGd/Al) and Y/Al (βY/Al) are higher than 100 at the contact time of 10–300 s, indicating that M−HREs can be easily separated from Al through solvent extraction using P507. The separation factors of La/Al (βLa/Al) and Nd/Al (βNd/Al) are 10.8–12.3 and 40.5–58.7, respectively, at the contact time of 15–30 s, which are much lower than those of M−HRE (such as Gd and Y), but are much higher than those at the contact time of 300 s (βLa/Al = 2.8, βNd/Al = 31.5). It means that the separation of LRE and Al serves as the key for the separation of REs and Al in the low-concentration rare earth solution, and controlling the contact time in the range of 15–30 s is conducive to the separation of LREs from the Al. The increase in the Al3+ concentration in the rare earth solution has no significant impact on the separation of REs and Al at the contact time of 10–60 s, but the increase in the RE3+ concentration induces the separation of REs and Al. In conclusion, REs in the low-concentration rare earth solution can be selectively separated from the Al via centrifugal extraction technology.

Biocompatible nanoparticles for metals removal from fresh water with potential for rare earth extraction applications

Freshwater contamination by metals can come from a variety of sources and be damaging to wildlife, alter landscapes, and impact human health. Metals removal is desirable not only for improving water quality and preventing adverse effects but also for metals collection and recycling. Nanoadsorption of metals is economically feasible and nanoscale materials exhibit a high surface-area-to-volume ratio that is promising for high adsorption and reactivity. However, the extraordinarily small dimensions of these materials allow them to maneuver biological systems, and combined with high reactivity, this translocation can result in toxicity. In this work, nanoparticles (NPs) composed of a magnetite core coated in hydroxyapatite (HA) and functionalized for adsorption with titanium dioxide (TiHAMNPs) were synthesized. The magnetic core enabled NP retrieval, while HA enhanced adsorption and minimized toxicity. Here, synthesis and characterization are presented, revealing a stable NP structure exhibiting a near neutral surface charge. Results of adsorption studies showed that as compared to silica-coated magnetite nanoparticles (SiMNPs), traditionally used for this application, TiHAMNPs exhibited significantly higher adsorption (43.28% more Cu removal) after 24 h. The equilibrium rate constant for the adsorption of Cu by TiHAMNPs was 0.0003 g/(min*mg) and TiHAMNP adsorption data indicated that TiHAMNPs adsorb metals in a monolayer at the particle surface with a maximum capacity of 2.8 mmol/g. Metabolic and toxicity assays showed TiHAMNPs were highly biocompatible as compared to SiMNPs. This work also explores rare earth element (REE) separation applications of TiHAMNPs, finding that TiHAMNPs may provide a promising alternative for REE retrieval and/or separation.

Scaling high-speed counter-current chromatography for preparative neodymium purification: Insights and challenges

Efficient rare earth element (REE) separations are becoming increasingly important to technologies ranging from renewable energy and high-performance magnets to applied radioisotope separations. These separations are made challenging by the extremely similar chemical and physical characteristics of the individual elements, which almost always occupy the 3+ oxidation state under ambient conditions. Herein, we discuss the development of a novel REE separation aimed at obtaining purified samples of neodymium (Nd) on a multi-milligram scale using high-speed counter-current chromatography (HSCCC). The method takes advantage of the subtle differences in ionic radii between neighboring REEs to tune elution rates in dilute acid through implementation of the di-(2-ethylhexyl)phosphoric acid (HDEHP)-infused stationary phase (SP) of the column. A La/Ce/Nd/Sm separation was demonstrated at a significantly higher metal loading than previously accomplished by HSCCC (15 mg, RNd/REE > 0.85), while the Pr/Nd separation was achieved at lower metal loadings (0.3 mg, RNd/Pr = 0.75 – 0.83). The challenges associated with scaling REE separations via HSCCC are presented and discussed within.

Studies for Extraction and Separation of Rare Earth Elements by Adsorption from Wastewater: A Review

Studies for Extraction and Separation of Rare Earth Elements by Adsorption from Wastewater: A Review

New hematite method: efficient and enhanced separation of rare earth and iron by alkaline regulation of pH in rare earth chloride solutions

Iron in RECl3 solutions is a detrimental impurity, adversely impacting both the purification efficiency of RECl3 and purity of rare earth compounds. RECl3 solutions employs the neutralization precipitation method for iron removal, leading to iron slag rich in valuable rare earth elements and radioactive thorium. This practice not only results in rare earth resource wastage but also poses significant ecological challenges. This study introduces an innovative hematite method for efficient and enhanced separation of rare earth and iron from RECl3 solutions. This method involves adjusting the solution's pH using alkali in a high-pressure reactor. Results indicate optimal conditions: a OH− to Fe3+ ratio of 1.5:1, temperature at 180°C, duration of 3 hours, and a Fe3+ (as Fe2O3) to Fe2O3 crystal seed molar ratio of 1:1. Under these conditions, the iron slag contains 1.3% REO and 63.69% TFe, with a rare earth loss rate of 0.35% and a TFe removal rate of 90.36%. Thermodynamic analysis reveals that at 25°C, ammonia water adjusts the pH of RECl3 solutions to 2-3, with the presence of Fe(OH)2+ and Fe(OH)2+ in the solution. The potential pH diagram of Ce-Fe-H2O at 180°C indicates that a pH range of -1.87 to 2.99 is crucial for Fe2O3 and Ce3+ formation. SEM analysis shows that the iron slag phase is a densely packed elliptical hematite sphere of approximately 1 micron and contains 0.36% thorium. This new hematite method using alkali-regulated high-temperature and high-pressure conditions for iron removal from RECl3 solutions not only minimizes rare earth loss but also mitigates iron slag's environmental impact. Furthermore, it offers a novel iron removal technique for the smelting industry.

Multistep pH-peak-focusing liquid chromatography with a hydrophilic polymer gel column for separation of rare earth elements

Multistep pH-peak-focusing liquid chromatography with a column packed with a hydrophilic polymer gel (a cross-linked hydroxylated methacrylic polymer gel) was developed for separation of rare earth metal ions. Metal ions in a sample solution introduced to the column are chromatographically extracted into the stationary gel phase at the top of the column equilibrated with a basic solution used as the first mobile phase containing acetylacetone and 1,10-phenanthroline by synergistic extraction effect. After the sample solution is introduced, the mobile phases are delivered into the column by stepwise gradient elution in order of decreasing pH. Each metal ion is concentrated at a pH border formed between the zones of different pH in the column and moves toward the outlet of the column with the pH border. Mutual separation of La(III), Ce(III), Nd(III), Eu(III), Y(III), Tb(III), and Yb(III) was achieved by the present method for an 1-mL sample injection with the column of which the inner volume is 11.8 mL. The multistep pH-peak-focusing liquid chromatography with a hydrophilic polymer gel column developed in this study has great potential as a useful method for the separation of rare earth metal ions on a preparatory scale.

Lanthanide transport in angstrom-scale MoS2-based two-dimensional channels.

Rare earth elements (REEs), critical to modern industry, are difficult to separate and purify, given their similar physicochemical properties originating from the lanthanide contraction. Here, we systematically study the transport of lanthanide ions (Ln3+) in artificially confined angstrom-scale two-dimensional channels using MoS2-based building blocks in an aqueous environment. The results show that the uptake and permeability of Ln3+ assume a well-defined volcano shape peaked at Sm3+. This transport behavior is rooted from the tradeoff between the barrier for dehydration and the strength of interactions of lanthanide ions in the confinement channels, reminiscent of the Sabatier principle. Molecular dynamics simulations reveal that Sm3+, with moderate hydration free energy and intermediate affinity for channel interaction, exhibit the smallest dehydration degree, consequently resulting in the highest permeability. Our work not only highlights the distinct mass transport properties under extreme confinement but also demonstrates the potential of dialing confinement dimension and chemistry for greener REEs separation.

High performance flow-focusing droplet microreactor. Extractive separation of rare earths as case of study

This work advances the knowledge of the design and manufacture of microdroplet reactors for reactive liquid–liquid systems assisted by advanced simulation techniques (CFD). The mathematical model is based on the integrated analysis of the fluid dynamics for multiphase systems, passive mixing of reactants inside and outside the microdroplet and interfacial reaction rate. To validate the results obtained with the predictive model a spiral microdevice with droplet generation using flow-focusing geometry has been designed and fabricated by additive manufacturing. First, the influence of fluid flowrate, hold-up and viscosity on the droplets frequency and size has been evaluated with the model and assessed experimentally. Next, the performance in the separation of a binary Dysprosium-Lanthanum system has been tested, working with a dispersed aqueous phase containing the rare earth elements (REEs) solution and a continuous organic phase constituted of a solution of the extractant Cyanex® 572 in Shellsol® D70. The extraction experiments have been conducted at residence times between 3 and 60 s to generate aqueous phase monodispersed droplets with high interfacial area that varies between 61.4 and 49.2 cm2·cm−3 depending on the operating conditions. At pH 1, 90 % of dysprosium has been extracted, and almost complete separation of both REEs has been achieved. Very good agreement between simulated and experimental results has been reached with an error lower than 12 %. Therefore, here we provide the tools to design and predict the microdroplet enhanced performance of extractive liquid–liquid microreactors.

Shape-persistent COF-derived functional carbon microspheres for No-carrier added 177Lu separation

Porous carbon materials stemming from covalent organic frameworks (COFs) have emerged as pivotal candidates in various fields. However, no COF or relevant derivative has stepped into the recovery of no-carrier added (NCA) 177Lu, one of the most important radionuclides in modern medicine, from irradiated target. In this work, shape-persistent COF-derived carbon microsphere (COF-CMS) was successfully synthesized via self-templated carbonization and subsequently functionalized with active component 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (P507). The prepared functional COF-CMS@P507 has shown high selectivity and fast adsorption kinetics for Yb3+/Lu3+ in static batch adsorption and great potential in dynamic column separation of Lu3+ from Yb3+. More importantly, based on plenty of tracer experiments and practical investigations, a separation process flow was established to realize the isolation of 177Lu from an irradiated 176Yb target. Consequently, 177Lu product can be effectively obtained in preferable recovery (86%) with high radinuclidic and chemical purity (≥99.99%). The present study provides a new idea for NCA 177Lu production, which is also valuable for the development of lanthanide separation and functional COFs.

Application of diglycolamide extractant in rare-earth extraction

Diglycolamide (DGA) extractant is a kind of rare-earth extractant with promising applications that has the advantages of high extraction capacity, ease of synthesis, good thermal stability and good radiation stability. It is a green extractant that contains only four elements, C, H, O and N, and produces no residue after incineration. The properties of DGAs containing branched N,N′-alkyl substituents have been much studied in recent years, and it has been shown that branched side chains lead to better separation. The introduction of structurally rigid elements in DGA provides new possibilities for separation of rare earth elements (REEs). Owing to the tiny differences in the chemical properties of adjacent REES, the simple use of DGA extractant cannot meet all separation requirements, and a masking agent is added to the aqueous phase to improve the separation by coextraction to meet the requirements of different processes. This review presents the structural analysis of the complexes and crystals of diglycolamide extractants with rare-earth ions through different characterization means, and the effects of different structural extractants, solvents, nitric acid and phase modifiers on extraction behavior are reviewed. This review pays special attention to the effect of the side chain structure of diglycolamide on extraction behavior, which provides a theoretical basis and guiding direction for the field of separation of the REEs by diglycolamide extractants.

Highly efficient separation of Sc3+ and Y3+ in acid solution by a graphene oxide membrane with interlayer sieving

Sc and Y are key rare earth elements and are widely used in lamp phosphors, lasers and high-performance alloys. However, highly efficient extraction and separation of Sc3+ and Y3+ is laborious, harmful, slow, and costly, strongly necessitating more efficient extraction and separation techniques. Here, we produced hydrated Sc3+- and hydrated Y3+-controlled graphene oxide (GO) membranes and find that both hydrated cations were completely self-rejected by the membrane. By combining this self-rejection effect of the larger hydrated Y3+-controlled GO membrane and the rapid passage of the membrane through the smaller hydrated Sc3+, we proposed a strategy to separate Sc3+ and Y3+ by using a hydrated Y3+-controlled GO membrane. The experimental results show that the permeation rate of Sc3+ exceeds that of Y3+ when the separation factor reaches 4.02, which can be attributed to the interlayer sieving effects of the GO membrane. Our finding illustrates the use of a forward osmosis process with a GO membrane for the efficient separation of Sc3+ and Y3+ by interlayer sieving, which provides a new effective and eco-friendly method for the separation of rare earth elements.