Extraction Of Lanthanide Ions Research Articles

Structure-Function Insights into Thermoresponsive Copolymers as Lanthanide Precipitants.

The synthetic toolbox for stimuli-responsive polymers has broadened to include many tunable variables, making these materials applicable in diverse technologies. However, unraveling the key composition-structure-function relationships to facilitate ground-up design remains a challenge due to the inherent dispersity in sequence and conformations for synthetic polymers. We here present a systematic study of these relationships using a model system of copolymers with a thermoresponsive (N-isopropylacrylamide) backbone in addition to metal-chelating (acrylic acid) and hydrophobic structural comonomers and evaluate their efficiency at isolating technologically critical lanthanide ions. The efficiency of lanthanide ion extraction by precipitation was quantitated with a metallochromic dye to reveal trends relating copolymer hydrophobicity to improved separations. Further, we examined the role of different hydrophobic comonomers in dictating the solution-phase conformation of the polymer in the presence and absence of lanthanide ions, and we correlated key features of the hydrophobic comonomer to extraction efficiency. Finally, we identified how the local proximity of thermoresponsive, chelating, and hydrophobic subunits facilitates metal extraction by manipulating the copolymer sequence with multiblock polymerization. Through mechanistic analysis, we propose a binding-then-assembly process through which metal ions are coprecipitated with macromolecular chelators.

Electrochemical Extraction of Rare Earth Ions from Solution: A Hands-on Experiment for Undergraduates

Electrochemical Extraction of Rare Earth Ions from Solution: A Hands-on Experiment for Undergraduates

Extraction of rare earth ions using thermomorphic ionic liquid: In situ spatial and temporal distribution combined with thermodynamic description

Homogeneous Liquid–Liquid Extraction (HLLE) provides a valuable opportunity for recycling Rare Earth Elements (REE) by circumventing the liquid–liquid interface and avoiding the problems linked to the high viscosity of ionic liquids (IL). For optimizing these processes with the ultimate goal of implementing them at the industrial scale, it is crucial to understand the mechanisms at play at various scales. In this study, we focused on the extraction of two REE elements, La(III) and Ce(III) with an HLLE system composed of the IL [Chol][TFSI], water and betaine as the extractant. We first established the phase diagram of [Chol][TFSI]/betaine/water using 1H nuclear magnetic resonance (NMR) spectroscopy. We then determined the efficiency E and distribution ratio D of the HLLE for different betaine concentrations. HLLE was modeled thermodynamically to access the most likely number of betaine molecules involved in the extraction process, which appears to be 2. Finally, we monitored in situ the extraction using X-ray Absorption Spectroscopy (XAS) at the K-edge of both lanthanum and cerium. It allowed us on one hand, to get some insight into the local environment around the REE, and on the other hand to measure the local concentration of REE at each position within the extraction system. In this latter process, we could evidence an accumulation of REE accumulates close to the liquid–liquid interface, a feature that was suggested by some recent simulations.

Enhanced solvent extraction of rare earth elements in ultra-high phase ratio with pore-throat microchannels

To enrich and recover low-concentration (101–102 ppm) rare earth elements from ores and industrial wastes, high phase-ratio solvent extraction is favored. However, high phase-ratio solvent extraction is limited by low mass transfer efficiency in the continuous phase due to the insufficient contact between large volume continuous phase and sparse droplets. To realize efficient solvent extraction of rare earth ions from low concentrations (100 ppm) aqueous phase to oil phase with high phase ratio, we introduce a type of microchannel with sequential pore-throat geometry. This sequential pore-throat geometry creates capillary barriers and effectively retains dispersed droplets, leading to a reduction of apparent water–oil volume ratio and thereby major mass transfer enhancement in the continuous phase. We experimentally highlight its advantage over classic uniform microchannel for solvent extraction of rare earth ions under high phase ratios: in a double pore-throat microchannel, extraction equilibrium can be reached within 30 s under high phase ratios of 50–250; for an extreme phase ratio of 500:1, extraction efficiency can achieve 77 % within a quadruple pore-throat channel, while that within a uniform microchannel is only below 40 %. The superiority of sequential pore-throat microchannel for extraction at a high phase ratio is reproduced using different types of rare earth ions. We thus conclude that sequential pore-throat geometry can drastically promote the performance of microfluidic-based solvent extraction at extreme phase ratios, for rare earth enrichment and potentially for other relevant applications.

Recovery of rare earth elements from sedimentary rare earth ore via sulfuric acid roasting and water leaching

Rare earth elements were extracted using a sulfuric acid roasting-water leaching process. The effect of acid roasting on a new type of low-grade sedimentary rare earth ore found in Guizhou Province, China was analyzed using X-ray diffraction and scanning electron microscopy. A systematic study was conducted on process parameters such as amount of acid, roasting temperature, roasting time, water leaching temperature, and leaching time. The results reveal that the total recovery of rare earth elements reaches 81.37%, which is 3.1 times higher than that achieved through direct acid leaching, under the optimal conditions. In addition, the leaching rate of heavy rare earth elements reaches 72.53%. Rare earth elements and some other valuable metals are transformed into soluble sulfate through the local decomposition of clay minerals under the action of the sulfuric acid attack. The dissolution rates of aluminum, iron, and titanium ions are 34.94%, 17.05%, and 62.77%, respectively. The precipitation rate of Ti reaches 99%, and the loss of rare earth ions in the solution is less than 1%. Meanwhile, the results of a leaching kinetics analysis indicate that the leaching process of rare ions is controlled by diffusion. Precious metal ions such as iron and aluminum in the leaching solution can reduce the adsorption of rare earth ions by kaolinite. This study efficiently recovered rare earth ions under conditions of low calcination temperature and direct water leaching, resulting in reduced energy consumption of the extraction process and acidity of the leaching solution. These findings provide a solid foundation for the further separation and extraction of rare earth ions.

Preparation of magnetic oil-based gel microspheres containing di(2-ethylhexyl)phosphoric acid for extraction of scandium ions at low concentrations in aqueous solutions

Extraction of low-concentration rare earths is one of the important paths for the sustainability of the rare earth industry. The research and development of materials suitable for the extraction of rare earth ions at low concentrations is of great significance. Currently, the application of solvent extraction in the rare earth production industry is highly mature. However, it is not economical to use it for the extraction of low concentration rare earths with problems of phase separation and organic phase loss. This work innovatively proposes to encapsulate the extractant and diluent in magnetic oleogel microspheres, which are obtained by solubilizing magnetic poly (phenyl divinylbenzene)(PS-DVB) microspheres with the extractant and diluent.. The magnetic PS-DVB microspheres of 3 ∼ 16 μm were prepared by suspension polymerisation, followed by encapsulation of di(2-ethylhexyl)phosphoric acid (D2EHPA) and dichloroethane in magnetic PS-DVB microspheres using emulsion swelling, and then magnetic oil-based gel microspheres containing D2EHPA with a particle size of 10 ∼ 32 μm were obtained. The magnetic oil-based gel microspheres containing D2EHPA consist of about 96 wt% liquid phase and about 4 wt% solid phase, with D2EHPA accounting for more than 4.19 wt%. The magnetic oil-based gel microspheres are very close to small oil droplets and are superparamagnetic. The magnetic oil-based gel microspheres containing D2EHPA could completely extract 60 ppm of scandium ions(Sc3+) under the conditions of O:A = 1:50,1:60,1:70, and the extraction equilibrium times were 6, 9 and 12 min, respectively. This extractant encapsulation scheme inherits the selectivity of traditional extractants while simultaneously preserving the advantages of rapid extraction by solvent extraction.

Covalent organic framework for highly efficient extraction of rare earth ions

Covalent organic framework for highly efficient extraction of rare earth ions

Selective transport of trivalent lanthanide in electrodialysis: Limitations due to concentration polarization

Extraction of rare-earth ions from mixtures with other cations is an important part of recovering rare-earth ions from recycling or other streams. This study examines whether highly selective Donnan partitioning into a cation-exchange membrane can lead to effective electrodialysis (ED) extraction of La3+ from solutions containing monovalent or divalent ions. In Nafion membranes, trivalent La3+ sorbs selectively over Na+ and Mg2+, and the La3+/Na+ partitioning selectivity increases to values > 100 with decreasing ionic strength and/or higher ratios of Na+ to La3+ in solution. However, the experimental La3+/Na+ and La3+/Mg2+ ED selectivities are <10. The low La3+ mobility in the membrane accounts for some of the difference between partitioning and transport selectivities. Equally important, concentration polarization due to different ion transport numbers in the solution and the membrane likely leads to significant diffusion of monovalent ions through the membrane. For example, although simulated La3+/Na+ electromigration selectivities reach 35 in dilute solutions, diffusion of Na+ across the membrane reduces the overall ED transport selectivity to <10. This work shows the importance of accounting for concentration polarization when considering applications of ED for ion separations.

Advancing Rare-Earth Separation by Machine Learning.

Constituting the bulk of rare-earth elements, lanthanides need to be separated to fully realize their potential as critical materials in many important technologies. The discovery of new ligands for improving rare-earth separations by solvent extraction, the most practical rare-earth separation process, is still largely based on trial and error, a low-throughput and inefficient approach. A predictive model that allows high-throughput screening of ligands is needed to identify suitable ligands to achieve enhanced separation performance. Here, we show that deep neural networks, trained on the available experimental data, can be used to predict accurate distribution coefficients for solvent extraction of lanthanide ions, thereby opening the door to high-throughput screening of ligands for rare-earth separations. One innovative approach that we employed is a combined representation of ligands with both molecular physicochemical descriptors and atomic extended-connectivity fingerprints, which greatly boosts the accuracy of the trained model. More importantly, we synthesized four new ligands and found that the predicted distribution coefficients from our trained machine-learning model match well with the measured values. Therefore, our machine-learning approach paves the way for accelerating the discovery of new ligands for rare-earth separations.

Analysis of the kinetics ions Ho(III), Pr(III), Gd(III) transport at the liquid-liquid interface in the presence of a magnetic field gradient

In the present work, the kinetics of transport of selected rare earth ions at the liquid-liquid interface in the presence of a magnetic field gradient was investigated. A uniform magnetic field was applied to the classic liquid-liquid solvent extraction system. The influence of temperature, initial concentration of selected ions and magnetic field gradient on the extraction rate was determined. It was shown that the uniform magnetic field could affect the kinetics of the extraction of rare earth ions in the liquid-liquid system. The observed differences constitute a promising prospect worthy of further research. Figs 6, Refs 10.

Synergistic solvent extraction of lanthanide ions with mixtures of D2EHPA and MIDPA in phosphonium-based ionic liquids

In this study, the synergistic solvent extraction of lanthanide(III) with mixtures of di-(2-ethylhexyl)phosphoric acid (D2EHPA, H2A2) and monoisodecyl phosphoric acid (MIDPA, H2B2) in phosphonium-based ionic liquid was investigated from amide acid medium. The method of slope analysis was used for the determination of the extraction reaction. In the case of D2EHPA or MIDPA single extractant system, Ln(III) (Ln = Pr and Nd) was extracted as [LnA3HA] or [LnB3HB], respectively. Tb(III) or Dy(III) were extracted as [TbH2A2B2(NTf2)] or [DyH2A2B2(NTf2)] instead of [TbA3HA(NTf2)] or [DyA3HA(NTf2)] for D2EHPA and MIDPA synergistic system. According to the equilibrium constants (KA, KB and KAB) and the formation constants (β1, β1 and β3), it was found that the extracted complex [TbHA2B2] or [DyHA2B2] was more stable than [LnA3HA] or [LnB3HB] due to the synergistic effect of D2EHPA and MIDPA. The thermodynamic functions (ΔH, ΔG, and ΔS) were estimated from the temperature dependence of the synergistic extraction system. The result indicated that the synergistic extraction reaction was endothermically driven for this extraction system. Furthermore, the synergistic extraction effects were investigated to study the possibility of separating Dy(III) from Pr(III) and Nd(III) according to their separation factors.

Efficient recovery of neodymium and praseodymium from NdFeB magnet-leaching phase with and without ionic liquid as a carrier in the supported liquid membrane

In this study, the presence and absence of ionic liquids as a carrier in the SLM system was investigated for the extraction of praseodymium and neodymium ions from the NdFeB magnet-leaching solution. The rate of permeability coefficient in the ion transport process inside the supported liquid membrane was studied by utilizing the variation in the acidity of the source and stripping phases and the role of different carriers in the transport. The highest permeability coefficients were obtained with the synergistic system containing [C6MIM][NTf2], TOPO, and TPB extractants. The higher efficiency is related to the particular ionic property in the extraction of rare earth ions compared with TOPO, and TBP extractants diluted in kerosene. The experimental data of the acidity of the source and stripping phases showed that the neutral pH ~ 6 in the feed phase and the average acidity of 1.8 M nitric acid in the stripping phase were suitable for the transport of ions between both phases. The kinetics of ion transport inside the ionic liquid membrane based on logarithmic variations showed that the process of ion transfer inside the membrane follows the first-order kinetics. The investigation of stability with ionic liquids indicated that a more stable system was provided with ionic liquid as a green solvent in the carrier phase.

Synthetic saponite clays as promising solids for lanthanide ion recovery

The extraction of lanthanide ions (Ln3+) from aqueous solutions was accomplished with layered materials based on synthetic saponite clays, showing interesting uptake performance and good selectivity.

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.

The nature of salt effect in enhancing the extraction of rare earths by non-functional ionic liquids: Synergism of salt anion complexation and Hofmeister bias

Separation and recycling of rare-earths using ionic liquids as extractant are becoming a promising approach to replace traditional volatile organic solvents in recent years. Generally, the addition of some special salts could improve the extraction efficiency of rare-earths by numerous non-functional ionic liquids. However, knowledge behind the nature of the salt effect is limited. Here, we found that the enhancement in the extraction of rare-earth ions, Pr3+ ions, using non-functional ionic liquid, [A336][NO3] (Tricaprylmethylammonium nitrate) was driven by the synergism of Hofmeister bias and complexation behaviors of salt anions with Pr3+ ions. Molecular dynamic simulations offered a new insight into the interaction mechanism of the ionic liquid with Pr3+ ions at liquid/liquid interface. It was revealed that salt anions could perform as a bridge to connect Pr3+ ions and the ionic liquid, so that promoted the extraction of Pr3+ ions. Therefore, the strong complexation ability of salt anions with Pr3+ ions and poor hydration of salt anions faciliated the transport of Pr3+ ions across liquid/liquid interface.

Specific Salt Effect on the Interaction between Rare Earth Ions and Trioctylphosphine Oxide Molecules at the Organic–Aqueous Two-Phase Interface: Experiments and Molecular Dynamics Simulations

Understanding the essence of the specific salt effect on the enhancement of the transport of metal ions across the liquid/liquid interface during the process of solvent extraction is of crucial importance for the development of a new approach to extract and selectively separate various valuable metals from complex aqueous solutions. However, some abnormal experimental phenomena involved in the salt effect on the liquid/liquid solvent extraction could not be understood only from the conventional interpretation based on the salting-out ability of salt ions. The knowledge into the microscopic mechanism behind the specific salt effect was urgent. Herein, as an example, the effect of adding various salts on the extraction performance of rare earth ion Pr3+ using trioctylphosphine oxide (TOPO) as the organic extractant was investigated. It was revealed that the difference in the interface propensity of different salt anions enriched at the organic-aqueous two-phase interface played a crucial role in promoting the interaction of TOPO molecules with Pr3+ions, despite the occurrence of the salting-out effect of those salt anions with the increase of their concentrations in aqueous solutions. The interfacial interaction mechanism obtained by molecular dynamics simulations revealed that both the interface propensity and the salting-out ability of the coexisting salt anions contributed to the enhancement in the extraction of Pr3+ into the TOPO organic phase. However, when the concentrations of coexisting salts in aqueous solutions were low enough, the extraction of Pr3+ was mainly dominated by the interface propensity of those added salt anions but not their salting-out ability. With the increase in the concentration of salts, the salting-out effect gradually became significant and, therefore, began to join with the interface propensity of salt anions to co-dominate the transport of Pr3+ ions across the liquid/liquid interface. The present study highlights the microscopic nature of the salt effect on promoting the extraction of rare earth ions and suggests that the interaction of organic extractant molecules with rare earth ions at liquid/liquid interface was dependent not only upon the salting-out ability of the coexisting salt ions but also their interface propensity.

Recovery of rare earths from nitric acid leach solutions of phosphate ores using solvent extraction with a new amide extractant (TODGA)

The rare earths in phosphate ores are not effectively utilized and they cannot be directly extracted from leach liquor with the traditional extractants, such as organic phosphoric acid. This paper presents a new solvent extraction method for rare earths from nitric acid leaching of phosphate rock using N,N,N′,N′-tetraoctyl diglycol amide (TODGA) without interfering with the normal route for fertilizer production. When the concentration of extractant increased to 0.1 mol/L, the extraction rate of lanthanum, cerium, praseodymium, and neodymium have been found to be 98.1%, 99.1%, 98.8% and 98.6%, respectively. The recovery rate reached to 99.9% when a three-stage countercurrent extraction was carried out on the simulated leach solution. There was almost no extraction of other impurity ions and the rare earths could be separated with TODGA from Ca2+, PO43−, Fe3+, and Mg2+. The presence of phosphoric acid in solution enhanced the extraction of rare earth ions. The stripping of the loaded rare earth in the organic phase was readily carried out with water under room temperature with high efficiency. The mixed rare earth oxides (REO) with an assay of >95% could be recovered as a final product.

Extraction of rare earth ions from phosphate leach solution using emulsion liquid membrane in concentrated nitric acid medium

It is very significant to recover rare earths (REs) from wet-process phosphoric acid, in terms of extraction rate and selectivity, the current carrier di(2-ethlhexly) phosphate (D2EHPA) out there is still inferior. Based on this question, our team modified D2EHPA to synthesize new extractants. This paper presents a comprehensive study on the extraction of rare earth ions (RE3+) from phosphate leach solution using emulsion liquid membrane (ELM) in concentrated nitric acid medium. The ELM system is made up of (RO)2P(O)OPh-COOH as carrier, polyisocrotyl succinimide (T154) as surfactant, sulfonated kerosene as diluent, phosphoric acid (H3PO4) as stripping solution. Different chemical parameters such as type and concentration of carrier, surfactant, stripping solution, volume ratio of oil phase to internal phase, and volume ratio of emulsion ratio to external phase were analyzed. The extraction of RE3+ was evaluated by the yield of extraction. In addition, the demulsification process was also investigated. The proposed method of ELM using (RO)2P(O)OPh-COOH as carrier can be expected to provide an efficient, simplify operation, and facilitated method for extracting RE3+.

Frontispiece: Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions

Frontispiece: Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions

Frontispiz: Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions

Frontispiz: Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions