Extraction Of Lanthanides Research Articles

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

Research on the extraction of rare earth elements from ash-slag waste

The research investigates the patterns of rare earth elements (REE) extraction from ash-slag waste of thermal power plants using sintering processes. The aim of the study was to determine the optimal parameters for the process: the composition of the flux, the ratio of the sintering flux to the waste, and the sintering temperature. It has been shown that the change in the type of sintering reagent, its ratio to the waste, and the process temperature significantly affect the degree of REE extraction from the insoluble form in ash-slag to the soluble form in sinter. The optimal sintering temperatures (300–4500C) for the extraction of REE from ash-slag waste have been determined. The influence of various sintering reagents on the process of REE extraction from ash-slag waste has been investigated. It has been shown that the use of sodium hydroxide as a sintering reagent allows increasing the degree of REE extraction from waste up to 100%. Based on the analysis of the obtained experimental data, the main technological parameters of REE extraction in sinter have been determined.

Extraction properties of diglycolamide for rare earth: Contribution of N-substituents

A successful extraction process relies heavily on an excellent extractant structure. The theory of extractant structure and extraction performance is still insufficient to guide the design of new extractants, despite extensive research into extractants. However, diglycolamide extractants have demonstrated certain advantages in nuclear fuel reprocessing and rare earth extraction and separation. This paper focuses on the synthesis of 13 structurally serially changed extractants. There is a good connection between the extraction performance and the energy consumption of the carbonyl conformation torsion of the extractant with symmetrical straight-chain alkyl substituents. The extraction capacity of extractant decreases with the increase of alkyl chain length. The methyl substituent extractant shows higher extractability than the other. The steric effect of the alkyl chain with more than two carbons is not significantly different. The relationship between the structure and performance of extractants was systematically studied by the combination of theoretical calculations and experimental data to investigate the effects of symmetric, asymmetric and branched N-substituents on extraction performance.

Thermal decomposition behavior of Mountain Pass rare earth concentrate in air/CO2 atmosphere

The Mountain Pass mine is recognized as one of the world’s primary sources of rare earth minerals. These rare earth minerals mainly consist of bastnaesite and a small amount of monazite phosphate, which cannot be decomposed and recovered through conventional oxidative roasting and hydrochloric acid leaching process. An efficient, clean, and economical process called the "combined method" was proposed for the utilization of the Mountain Pass mine to extract rare earths from Mountain Pass rare earth concentrate (MPREC). The main steps of this process include weak oxidation atmosphere roasting, step leaching of hydrochloric acid, solid-liquid separation, the monazite slag with sulfuric acid roasting water leaching, etc. In this paper, the roasting process of MPREC under a weak oxidation atmosphere was investigated. The study examines the thermal decomposition kinetics, phase transition process, and leaching behavior of MPREC in air/CO2 atmosphere. Results show that, the activation energy (Ea) for MPREC thermal decomposition in air and CO2 atmosphere are 146 and 320 kJ/mol, respectively. At temperature above 500 °C in air or above 700 °C in CO2 atmosphere, REOF are generated from bastnaesite through an in-situ reaction with CaO, which is decomposed from CaCO3, to form CaF2 and rare earth oxide (REO). Thus, F is regulated into solid phase. In an oxidizing atmosphere, the thermal decomposition of bastnaesite is accompanied by the rapid oxidation of Ce(Ⅲ). In contrast, the oxidation of Ce(Ⅲ) in a CO2 atmosphere is significantly inhibited. At 700 °C, the oxidation rate of Ce in air is 74.09%, while in a CO2 atmosphere, it is only 33.83%. The hydrochloric acid leaching experiment shows that, the leaching rate of rare earth after roasting at 600 °C under an air atmosphere reaches to 82.9%, and it reaches 87% after roasting at 800 °C under a CO2 atmosphere. The reduction of Ce oxidation in a weak oxidizing atmosphere significantly improves the leaching rate of Ce.

Recovery of Rare Earth Elements from Coal Fly and Bottom Ashes by Ultrasonic Roasting Followed by Microwave Leaching

Considering the rising demand for rare earth elements (REEs), researchers are looking for new sources for their extraction, thereby fostering economic and environmentally justified processing solutions. Among potential industrial sources, coal fly ash emerges as one of the most promising. The recovery of REEs from coal fly and bottom ashes derived from different thermal power plants was the main focus of this study. A dual-step methodology was conducted on ash samples, which involved an ultrasonic roasting process to disintegrate the silica matrix, followed by a microwave-assisted acid leaching step to extract REEs. The roasting procedure was studied using the Plackett–Burman design, and the Box–Behnken design was subsequently implemented to optimize the leaching procedure. The optimized ultrasonic roasting procedure was set up at 95 °C for 10 min with an ash-to-roasting agent (3M NaOH) ratio of 0.5:1 (m/V). For acid leaching, the optimal conditions were obtained at 174 °C for 30 min with an HCl ÷ HNO3 mixture (1:1 V/V). The standard reference material (NIST 1633c) was used in the conclusive experiments to estimate the average recovery (80%) of REEs. The green aspects of this methodology were evaluated using several metrics (atom economy, E-factor, and energy consumption). The proposed process outperforms high-temperature roasting procedures in terms of greenness; however, the REE recovery rate is lower.

Recovery of rare earths and lithium from rare earth molten salt electrolytic slag by lime transformation, co-leaching and stepwise precipitation

The rare earth molten salt electrolytic slag (REMSES) has recently attracted significant attention due to its potential environmental hazards and high content of rare earths and lithium, leading to a surge in recycling efforts. In this study, we propose and demonstrate a novel and straightforward process for the simultaneous extraction of rare earths and lithium from REMSES through lime transformation and sulfuric acid leaching at low temperatures. Firstly, during the lime transformation process, REMSES is converted into hydroxides that can be easily dissolved in acids. Secondly, REEs and Li present in the slag are co-extracted using a conditional sulfuric acid leaching method, resulting in 95.72% REEs leaching efficiency and 99.41% Li leaching efficiency under optimal conditions. Finally, REEs and Li in the solution are precipitated using oxalic acid and trisodium phosphate with precipitation efficiencies of 99.02% for REEs and 94.85% for Li respectively. This innovative process enables the conversion of REEs and lithium from REMSES into high-purity products (a mixture of REOs with 99.31% purity; Li<sub>3</sub>PO<sub>4</sub> with 98.93% purity), thereby facilitating their valuable utilization.

The impact of apatite on sulfuric acid baking of a monazite concentrate and the benefit of goethite addition on rare earth leaching

Sulfuric acid baking of monazite ((Ce,La,Th)PO4) bearing ores is one of the major processes used in commercial production of rare earth elements. In hydrothermal vein type rare earth deposits, apatite is often found together with monazite. Rare earth enriched fluorapatite ores may also contain significant amounts of rare earths hosted in monazite. An understanding of the effect of apatite on the sulfuric acid baking of monazite is therefore important for the development of effective sulfuric acid based treatment methods for such ores. In this work, the addition of a natural hydroxyapatite (Ca5(PO4)3(OH)) sample to a monazite acid bake followed by acid leach was investigated using a combination of chemical analyses, SEM-EDS, XRD and TG-DSC. Hydroxyapatite addition significantly decreased the dissolution of rare earth elements from monazite in the leach after baking at temperatures above 300 °C. For a bake temperature of 500 °C, the rare earth dissolution in the leach dropped from 80% for monazite alone, to 30% for a 1:1 (w/w) addition of hydroxyapatite. This decrease in rare earth leaching was attributed to the formation of an insoluble thorium and rare earth bearing polyphosphate. The rare earth elements were incorporated into this polyphosphate phase in preference to calcium. At 800 °C, monazite was re-formed, causing a further reduction in rare earth extraction, while simultaneous formation of calcium pyrophosphate (Ca2P2O7) led to an increase in calcium and phosphorus dissolution. The detrimental effect of apatite could be partially overcome by the addition of goethite. Addition of goethite to the acid bake of a monazite/apatite mixture at 500 °C improved the total rare earth dissolution from 29% to 85% in the subsequent leach. Results also demonstrated that the order of reactivity, in terms of formation of polyphosphates is Fe > REE > Ca.

Rare Earth Extraction from Phosphogypsum by Aspergillus niger Culture Broth.

The extraction of rare earth elements (REEs) from phosphogypsum (PG) is of great significance for the effective utilization of rare earth resources and enhancing the resource value of PG waste residues. This study used Aspergillus niger (A. niger) fungal culture filtrate as a leaching agent to investigate the behavior of extracting REEs from PG through direct and indirect contact methods. According to the ICP-MS results, direct leaching at a temperature of 30 °C, shaking speed of 150 rpm, and a solid-liquid ratio of 2:1, achieved an extraction rate of 74% for REEs, with the main elements being yttrium (Y), lanthanum (La), cerium (Ce), and neodymium (Nd). Under the same conditions, the extraction rate of REEs from phosphogypsum using an A. niger culture filtrate was 63.3% higher than that using the simulated organic acid-mixed solution prepared with the main organic acid components in the A. niger leachate. Moreover, the morphological changes observed in A. niger before and after leaching further suggest the direct involvement of A. niger's metabolic process in the extraction of REEs. When compared to using organic acids, A. niger culture filtrate exhibits higher leaching efficiency for extracting REEs from PG. Additionally, using A. niger culture filtrate is a more environmentally friendly method with the potential for industrial-scale applications than using inorganic acids for the leaching of REEs from PG.

Selective separation and recovery of boron from spent Nd-Fe-B magnets leaching solution

The accumulation of boron during the recovery of rare earth elements (REEs) from spent Neodymium-Iron-Boron (Nd-Fe-B) magnets affects the extraction of REEs and causes environmental pollution through the boron-containing wastewater. Given that boron is a globally scarce strategic resource, this study proposes a method for the selective separation and recovery of boron from spent Nd-Fe-B magnets leaching solution. The synergistic extraction of boron adopting 2-ethylhexanol (EHA) and 2-ethyl-1,3-hexanediol (EHD), and the extraction mechanism were investigated. Under optimized conditions (30 % EHA-20 % EHD-50 % sulfonated kerosene, 1:1O/A phase ratio, pH 3.3, 10 min), the two-stage countercurrent extraction achieved a remarkable 99.9 % extraction efficiency with minimal loss of REEs. Slope analysis, Raman, FT-IR, and NMR combined with DFT were used to elucidate the extraction mechanism. Specifically, some of the boric acid molecules complexed with the OH groups of EHD to form stable six-membered ring complexes, while another part bound with both EHA and EHD to form linear complexes containing six-membered rings. Employing 0.4 mol/L NaOH as the stripping agent, the two-stage countercurrent stripping process achieved a stripping efficiency of 99.8 %. Subsequently, borax pentahydrate products exceeding 99 % purity were obtained via evaporative crystallization from the stripping solution. Notably, the raffinate contained only ∼ 5 mg/L of boron, which could be further reduced below the discharge standard via the REEs recovery process, allowing for safe emission. This work offers a novel approach for the selective separation and recovery of boron from spent Nd-Fe-B magnets, eliminating its adverse effects on REEs extraction and the environment, while simultaneously recovering a valuable resource.

The Beneficial Effect of Iron in Aluminum-Cerium-Based Cast Alloys

Iron (Fe) has been considered a major impurity since it is detrimental to the mechanical properties of many cast aluminum alloys due to the formation of Fe-containing brittle intermetallic phases. Fe is found naturally as an impurity in bauxite ore, resulting in Fe contamination of aluminum alloys with increasing contamination from current recycling practices. The Al–Ce–Fe system was investigated using CALPHAD (CALculation of PHAse Diagrams) modeling and experimental casting techniques. It was found that additions of Fe to the Al–Ce system are beneficial to the strength (slightly) and ductility (significantly) of the ternary alloys, which is attributed to the formation of fine metastable Al8CeFe2 phase with aggregate morphology and equilibrium Al10CeFe2 phase, suppressing coarse proeutectic Al11Ce3 phase in near-eutectic Al–Ce alloys. Heat treatment study showed that the metastable Al8CeFe2 phase transforms to predicted equilibrium Al10CeFe2 phase at 500 °C, with essentially no intermetallic or grain coarsening; thus, the alloy displayed excellent property retention. The Al–Ce–Fe alloy system offers opportunities for sustainable, recyclable alloy development using low-cost Fe and low-cost cerium (a byproduct of rare-earth extraction).

Rare Earth Element Recovery and Hydrochar Evaluation from Hyperaccumulator by Acid Leaching and Microwave-Assisted Hydrothermal Carbonization

Phytomining is a sustainable approach that uses hyperaccumulators for critical element extraction from various substrates, such as contaminated soils, mine tailings, and aqueous solutions. In this study, grass seeds were fed with a solution containing Y, La, Ce, and Dy, resulting in around 510 mg/kg (dry basis) of total rare earth elements (TREEs) accumulated in grass leaves. Electron probe microanalyzer (EPMA) analysis showed that rare earth elements (REEs) in the grass leaves (GL) predominantly complexed with phosphorous (P). Around 95% of Y, 93% of La, 92% of Ce, and 93% of Dy were extracted from the GL using 0.5 mol/L H2SO4 at a solid concentration of 5 wt.%. Subsequently, microwave-assisted hydrothermal carbonization (MHTC) was used to convert the leaching residue into hydrochar to achieve a comprehensive utilization of GL biomass. The effect of temperature on the structural properties and chemical composition of the resulting hydrochar was evaluated. Scanning electron microscopy (SEM) analysis revealed that the original structure of GL was destroyed at 180 °C during MHTC, producing numerous microspheres and pores. As the reaction temperature increased, there was a concurrent increase in carbon content, a higher heating value (HHV), and energy densification, coupled with a decrease in the hydrogen and oxygen contents of hydrochar. The evolution of H/C and O/C ratios indicated that dehydration and decarboxylation occurred during MHTC. The results showed that the waste biomass of the GL after REE extraction can be effectively converted into energy-rich solid fuel and low-cost adsorbents via MHTC.

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.

Establishing forward mixing model to mass transfer overview in multi-impeller agitated column for rare Earth extraction process

The current study develops comprehensive mass transfer models to optimize the rare earth extraction. A plug flow, axial dispersion, backflow, forward mixing-based mass transfer model was created and solved numerically using the fitting technique. The investigated process is a multi-impeller agitated column designed to provide proper contact between organic and aqueous phases to extract rare-earth ions. Taking Sm(III)–Gd(III) separation as an application case, extraction efficiency in the agitation speed of 200 rpm was obtained equal to 95.14%, 76.67% by this column for Gd(III), and Sm(III) ions, respectively. The model's findings were compared with experimental data, and a significant agreement was achieved with the forward mixing model. The results indicated that the high agitation speed is beneficial to increasing the interfacial area while reducing the mass-transfer coefficient. On the contrary, the circulation within the larger droplet improves the transfer of mass, albeit at the expense of reducing the interfacial area. The results showed that the drop size distribution is a crucial factor as the droplet sizes significantly affect the droplet mass transfer. The mathematical models’ values of Ec for mass transfer parameters showed that the operational variables significantly affect the mass transfer rate and can cause deviations from the ideal flow path. A reasonable and appropriate estimation of the organic-side volumetric overall mass transfer coefficient was provided, which can be applied to this contactor’s design and scale-up.

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.

Rapid and efficient extraction of cerium by forming Al-Ce alloys in LiCl-KCl molten salts

The extraction of lanthanides in spent fuel reprocessing plays a key role in the development of nuclear energy. In this work, the extraction of the typical fissionable cerium elements has been studied by electrolytic co-reduction of Al(III) and Ce(III) in LiCl-KCl-CeCl3 molten salts assisted by KAlCl4. The electrochemical behavior of the reduction of Al(III) and Ce(III) on a molybdenum electrode was studied by cyclic voltammetry (CV), square wave voltammetry (SWV), and open circuit chronopotentiometry (OCP), and specific peaks of five Al-Ce intermetallic compounds were detected. After 2.7 h of galvanostatic electrolysis at a current density of 0.064 A cm-2, the extraction efficiency and current efficiency of Ce(III) reached 99.9 % and 91.3 % respectively. Potentiostatic electrolysis is slightly more efficient, with 99.9 % Ce(III) extraction in 3.5 h at a current efficiency of 97.8 %. The products of electrolysis are rod-shaped alloys (Al11Ce3, Al3Ce, Al2Ce), and the molten salts purified by electrolytic separation are free of impurity signals and can be reused for electrolytic refining.

Rationally designed nanotrap structures for efficient separation of rare earth elements over a single step

Extracting rare earth elements (REEs) from wastewater is essential for the growth and an eco-friendly sustainable economy. However, it is a daunting challenge to separate individual rare earth elements by their subtle differences. To overcome this difficulty, we report a unique REE nanotrap that features dense uncoordinated carboxyl groups and triazole N atoms in a two-fold interpenetrated metal-organic framework (named NCU-1). Notably, the synergistic effect of suitable pore sizes and REE nanotraps in NCU-1 is highly responsive to the size variation of rare-earth ions and shows high selectivity toward light REE. As a proof of concept, Pr/Lu and Nd/Er are used as binary models, which give a high separation factor of SFPr/Lu = 796 and SFNd/Er = 273, demonstrating highly efficient separation over a single step. This ability achieves efficient and selective extraction and separation of REEs from mine tailings, establishing this platform as an important advance for sustainable obtaining high-purity REEs.

Adsorption using Selective Adsorbents as An Effective Method for Rare Earth Elements Recovery–a Review

Rare Earth Elements (REEs) are strategically important for the industry, especially in the manufacture of high-technology products and components, such as electric batteries for energy storage, energy conversion, defense and security industry, electric vehicles, components on smartphones, laptops, liquid crystal display, and others. Generally, REEs are processed by liquid-liquid extraction. However, this process is very costly due to the use of chemicals and high operational costs, so the waste has the potential to pollute the environment. Currently, innovative separation/recovery techniques are continuously being developed for effective and environmentally friendly extraction of rare earths. The adsorption method using the optimal adsorbent is one of the most efficient methods for recovering REEs at low concentrations. This method offers several advantages, including high release effectiveness, ease of installation and operation, low maintenance costs, and reduced chemical consumption. This study reviews the mechanism, characterization, and several adsorbents from natural to synthetic materials, especially nanocomposite-based adsorbents for the recovery of rare earths. In addition, the discussion of several parameters that affect the adsorbent. However, the results of several methodological breakthroughs that have been carried out show how much further research is needed

A novel bifunctional ionic liquid [N1888][OOB] for the separation of rare earth and transition metal in NdFeB magnet

In this paper, a series of novel bifunctional ionic liquids with methyltrioctylammonium as the cation and o-alkoxybenzoic acetate as the anion were synthesized. Their extraction properties were investigated for the separation of rare earth and transition metal for NdFeB waste recycling. It was found that [methyltrioctyl ammonium][o-octyloxybenzoic acetate] ([N1888][OOB]) could preferentially extract rare earth while the extraction abilities of Fe and Co were weak. The extraction mechanism of rare earth with [N1888][OOB] was indicated to be ion association in a molar ratio of 2:1. The rare earth loaded by [N1888][OOB] could be selectively stripped with water. Based on the above research results, a novel separation process was developed to separate rare earth, Fe and Co with [N1888][OOB]. This study intensified the separation process of rare earth and transition metals. The novel separation strategy based on [N1888][OOB] has revealed the advantages of efficiency and sustainability for rare earth recovery.

Prospecting for rare earth element (hyper)accumulators in the Paris Herbarium using X-ray fluorescence spectroscopy reveals new distributional and taxon discoveries.

Rare earth elements (REEs) are increasingly crucial for modern technologies. Plants could be used as a biogeochemical pathfinder and a tool to extract REEs from deposits. However, a paucity of information on suitable plants for these tasks exists. We aimed to discover new REE-(hyper)accumulating plant species by performing an X-ray fluorescence (XRF) survey at the Herbarium of the Muséum national d'Histoire naturelle (MNHN, Paris, France). We selected specific families based on the likelihood of containing REE-hyperaccumulating species, using known taxa that accumulate REEs. A total of 4425 specimens, taken in the two main evolutionary lineages of extant vascular plants, were analysed, including the two fern families Blechnaceae (n = 561) and Gleicheniaceae (n = 1310), and the two flowering plant families Phytolaccaceae (n = 1137) and Juglandaceae (n = 1417). Yttrium (Y) was used as a proxy for REEs for methodological reasons, and a total of 268 specimens belonging to the genera Blechnopsis (n = 149), Dicranopteris (n = 75), Gleichenella (n = 32), Phytolacca (n = 6), Carya (n = 4), Juglans (n = 1) and Sticherus (n = 1) were identified with Y concentrations ranging from the limit of detection (LOD) >49 µg g-1 up to 1424 µg g-1. Subsequently, analysis of fragments of selected specimens by inductively coupled plasma atomic emission spectroscopy (ICP-AES) revealed that this translated to up to 6423 µg total REEs g-1 in Dicranopteris linearis and up to 4278 µg total REEs g-1 in Blechnopsis orientalis which are among the highest values ever recorded for REE hyperaccumulation in plants. It also proved the validity of Y as an indicator for REEs in XRF analysis of herbarium specimens. The presence of manganese (Mn) and zinc (Zn) was also studied by XRF in the selected specimens. Mn was detected in 1440 specimens ranging from the detection limit at 116 µg g-1 up to 3807 µg g-1 whilst Zn was detected in 345 specimens ranging from the detection limit at 77 µg g-1 up to 938 µg g-1. This study led to the discovery of REE accumulation in a range of plant species, substantially higher concentrations in species known to be REE hyperaccumulators, and records of REE hyperaccumulators outside of the well-studied populations in China.

Understanding the Complexation Behavior of Carbamoylphosphine Oxide Ligands with Representative f-Block Elements.

The complexation behavior of carbamoylmethylphosphine oxide ligands (CMPO), a bifunctional phosphine oxide, and their substituted derivatives with Ce(III), Eu(III), Th(IV), U(VI), and Am(III) was probed at the density functional theory (DFT) level. The enhanced extraction of trivalent rare earth elements by the 2-diphenylphosphinylethyl derivative over the conventional CMPO ligand is identified due to the availability of an additional P═O donor group in the former. In addition, the orbital and dispersive interactions play a vital role in the preference of Th(IV) over U(VI) during extraction using CMPO ligands. The better complexing ability of ligands having long alkyl chain substituents at the P atom is justified due to the observed enhanced dispersion interactions in these systems.