Recovery Of Rare Earth Elements Research Articles

Investigating the Effect of Microwave Pretreatment on Bastnasite Grinding for Comminution Energy Reduction and Rare Earth Recovery

Investigating the Effect of Microwave Pretreatment on Bastnasite Grinding for Comminution Energy Reduction and Rare Earth Recovery

Mechanism and experimental study on the recovery of rare earth elements from neodymium iron boron waste by NaBF4 fluorination method

Pyrometallurgical recovery of rare-earth elements from NdFeB wastes is affected by the quality of the raw materials, and mixed rare-earth products add little value. Therefore, this study investigates NaBF4 fluoride roasting for the recovery of rare-earth elements and its underlying mechanisms. Reasonable roasting temperatures were determined based on thermodynamic calculations, and single-factor experiments were conducted. When roasted at 600 °C for 30 min with 65 % NaBF4, the fluorination rate of rare-earth elements reached 95.83 %. The composition of the clinker mesophase after roasting under different conditions was analyzed. At high temperatures, oxygen heteroatoms entered the crystal lattice of the rare-earth fluorides, which were subsequently removed during acid leaching, thereby reducing the recovery rate. A three-factor, three-level Box–Behnken test was conducted using the response surface methodology to analyze the effects of various factors and their interactions on the fluorination rate. Thus, an experimental basis for the recovery of rare-earth elements from NdFeB by fluoridation roasting was established. The roasting temperature had the greatest effect on the fluorination rate, followed by the roasting time and amount of NaBF4. The model predicted an optimal fluorination rate of 98.63 % when the material was roasted at 573 °C for 25 min with 59 % NaBF4. The clinker was acid-leached under optimal conditions (2.5 h at 80 °C with 9 M HCl and a liquid–solid ratio of 4 mL/g), and the fluorination rate reached 99.39 %. These results provide theoretical and experimental support for the application of pyrometallurgy in the recovery of rare-earth elements from NdFeB wastes.

Recovery of rare earth elements by adsorption on biochar of dead Posidonia oceanica leaves

Recovery of rare earth elements by adsorption on biochar of dead Posidonia oceanica leaves

Eco-friendly synthesized zeolitic imidazolate framework-8 enables one-step cerium recovery from water

The rapid pace of technology advancement has quickly depleted valuable rare earth elements (REEs), which are critical for the function and performance of electric and electronic components, and there is thus a need for REE extraction from secondary sources rather than from virgin mines. This study presents an approach involving the ball-milling-induced construction of zeolitic imidazolate framework-8 (ZIF-8) that integrates REE extraction and recovery processes. ZIF-8 demonstrates remarkable extraction capacities for various REEs, and notably promotes nanoscaled CeO2 formation. Ball-milling-prepared ZIF-8 (ZIF-8-BM) effectively concentrates cerium (III) ions (CeIII), and a purity of 99.34% is achieved by controlling the processing parameters, offering a comprehensive solution for efficient Ce retrieval from wastewater. The superior Ce extraction performance is attributed to the greater numbers of structural defects and surface hydroxyl (–OH) groups and the enhanced phase transformation efficiency. Moreover Ce extraction by ZIF-8-BM is found to be efficient in both low and high Ce concentration ranges. ZIF-8-BM nanoparticles spontaneously oxidize CeIII in solution to insoluble CeO2, thereby facilitating the efficient extraction and subsequent recovery of cerium from complex matrices. The findings of this study provide an environmentally benign approach for the safe and efficient recovery of REEs from waste streams, supported by a scientifically sound and economically feasible processing strategy.

Investigation into the purification and regeneration of rare earth polishing powder waste via continuous solid-phase conversion

The concentration of rare earth elements (lanthanum, cerium, and praseodymium) within rare earth polishing powder waste (REPPW) typically exceeds 50 %, with the majority of impurities comprised of silicon and aluminum-related compounds. Transforming REPPW into recycled rare earth polishing powders that adhere to polishing standards in an eco-friendly and economically viable way presents a significant challenge in the industry. Traditional acid or alkaline processes predominantly recover rare earth elements as oxides, which are underutilized due to their high costs. Considering the varying forms of impurities and rare earth compounds found in REPPW, this research introduces a novel physicochemical decontamination and continuous chemical transformation process aimed at producing regenerated rare earth polishing powders. Under optimal conditions, the physicochemical two-step decontamination process achieved a rare earth recovery rate surpassing 92 %, while silicon and aluminum removal rates reached 86.12 %. During the continuous chemical transformation of REPPW, the rare earth phases in an alkaline setting followed the sequence REOF (CeO2) → RE(OH)3 → RECO3OH→RECO3F→CeLa2O3F3(CeO2), which not only facilitated phase reorganization but also enhanced the particle surface structure. Notably, these chemical transformations did not disrupt the rare earth distribution; instead, they indirectly boosted product purity and uniformly dispersed within the regenerated polishing powder particles, thereby improving polishing efficiency. Consequently, the adoption of this innovative regeneration process for polishing powders holds substantial importance for the sustainable utilization of rare earth resources.

Study on selective green leaching of rare earth elements from coal gangue using mechanochemical activation

This study proposes a sustainable method for the selective leaching of rare earth elements (REEs) from coal gangue. By combining 600 °C calcination, the addition of 5 % Fe2(SO4)3, and one hour of mechanical-chemical activation, we achieved a leaching efficiency of 65 % for REEs. This method alters the surface and crystalline structure of coal gangue, facilitating the release of rare earth phosphate minerals and the formation of water-soluble compounds (rare earth sulfates). Fe2(SO4)3 transforms into insoluble iron oxide, which immobilizes impurities and promotes the selective leaching of rare earth elements. Notably, during the leaching process, the leaching rates of aluminum (Al) and iron (Fe) were only 0.37 % and 1.27 %, respectively. Kinetic analysis indicates that this process follows a mixed reaction-controlled shrinking core model. This method effectively reduces the environmental risks associated with traditional acidic reagents, providing a sustainable pathway for the recovery of rare earth elements.

Fabrication of ion imprinted graphene oxide-chitosan membrane cross linked by self polymerized polydopamine for selective adsorption of La(III)

Recovery of rare earths from secondary sources tallies with environmental remediation and sustainable exploitation of rare earth resources simultaneously. Herein, La(III) imprinted graphene oxide-chitosan membrane cross linked by self polymerized PDA (IIP-GO-CS-PDA) was constructed via using CS as functional monomer, PDA as cross linker and La(III) as template. The as constructed IIP-GO-CS-PDA was elaborately characterized in terms of crystallinity, morphology, chemical structure, porosity and thermal stability. Subsequently, adsorption efficiency and selective recovery performance of IIP-GO-CS-PDA towards La(III) were evaluated via batch adsorption. Result indicates, adsorption of La(III) by IIP-GO-CS-PDA is induced by electrostatic interaction, thereby reaching maximum adsorption efficiency at pH = 5. Functional groups C-O, C-N, −C(=O)–NH, –NH2 in IIP-GO-CS-PDA provides heterogeneous affinity for La(Ⅲ), inducing chemical adsorption. Adsorption proceeds rapidly to reach equilibrium in 30 min, manifesting impressive efficiency. The maximum adsorption capacity determined by Langmuir fitting is 275.48 mg·g−1. By virtue of its ion imprinting sites, IIP-GO-CS-PDA demonstrates selectivity coefficients 3.20, 3.34, 8.68, 9.28, 9.43, 9.58 towards La(Ⅲ) for binary solutions La/Eu, La/Dy, La/Cr, La/Cu, La/Cd, La/Pb, respectively. Owing to its membrane configuration, IIP-GO-CS-PDA can be easily recovered for cyclic adsorption, whereby retaining adsorption quantity 91.72 mg·g−1 for La(Ⅲ) in five consecutive cycles. Compared with other adsorbents, IIP-GO-CS-PDA exhibits rapid equilibrium, superior adsorption capacity and selectivity towards La(Ⅲ). This work provides a novel solution for fabricating bio adsorbent towards selective recovery of La(Ⅲ).

Investigating Physicochemical Methods to Recover Rare-Earth Elements from Appalachian Coals

The demand for rare-earth elements is expected to grow due to their use in critical technologies, including those used for clean energy generation. There is growing interest in developing unconventional rare-earth element resources, such as coal and coal byproducts, to help secure domestic supplies of these elements. Within the U.S., Appalachian Basin coals are particularly enriched in rare-earth elements, but recovery of the elements is often impeded by a resistant aluminosilicate matrix. This study explores the use of calcination and sodium carbonate roasting pre-treatments combined with dilute acid leaching to recover rare-earth elements from Appalachian Basin coals and underclay. The results suggest that rare-earth element recovery after calcination is dependent on the original mineralogy of samples and that light rare-earth minerals may be more easily decomposed than heavy rare-earth minerals. Sodium carbonate roasting can enhance the recovery of both light and heavy rare-earth elements. Maximum recovery in this study, ranging from 70% to 84% of total rare-earth elements, was achieved using a combination of calcination and sodium carbonate roasting, followed by 0.25 M citric acid leaching.

Recovery of Rare Earth Elements from Coal Fly Ash with High Calcium and Iron Contents Using Alkaline and Acid Leaching

Recovery of Rare Earth Elements from Coal Fly Ash with High Calcium and Iron Contents Using Alkaline and Acid Leaching

Characterisation and Hydrochloric Acid Leaching of Rare Earth Elements in Discard Coal and Coal Fly Ash

Rare earth elements (REEs) have been identified as valuable and critical raw materials, vital for numerous technologies and applications. With the increasing demand for and supply gap in REEs, many research studies have focused on alternative sources of REEs. This study involved an elemental and mineralogical characterisation of discarded coal from a coal plant and coal fly ash (CFA) from a power station in South Africa for REE presence. XRD results revealed that the discard coal sample consisted mainly of kaolinite, pyrite, siderite, quartz, calcite, gypsum, and muscovite, whereas CFA contained abundant glassy amorphous phases, alumina silicates, quartz, gypsum, calcite, and minute levels of muscovite and hematite. SEM-EDAX showed REE-carrying grains containing phosphorus in both discard coal and CFA samples. This was followed by investigating the leaching potential of REEs using hydrochloric acid from discard coal and CFA. This research’s potential impact is possibly providing a new and sustainable source of REEs. For that purpose, multiple batch leaching tests were performed to investigate the effects of temperature and acid concentration on the leaching efficiencies of REEs from discard coal and CFA. The experimental results indicated that temperature strongly influences REE leaching efficiency, while acid concentration has a lesser impact. This study identifies the best leaching conditions for the total REE recovery as 1 M HCl and 80 °C for discard coal and CFA.

Effect of Microgravity on Rare Earth Elements Recovery by Burkholderia cepacia and Aspergillus niger

Rare earth elements (REEs) are indispensable in modern industry and technology, driving an urgent demand for innovative, eco-friendly recovery technologies. As space exploration advances, the impact of microgravity on microorganisms has become a focal point, yet the effects on microbial growth and REEss recovery remain uncharted. This study investigates the biosorption of REEs by Burkholderia cepacia (B. cepacia) and Aspergillus niger (A. niger) from a mixed solution containing La, Ce, Pr, Nd, Sm, Er, and Y under varying initial concentrations, pH levels, and microgravity conditions. We observed that the medium’s pH rose with B. cepacia and fell with A. niger when cultured in normal gravity conditions, suggesting distinct metabolic responses. Notably, microgravity significantly altered microbial morphology and metabolite profiles, significantly enhancing REEs recovery efficiency. Specifically, the recovery of B. cepacia of Ce and Pr peaked at 100%, and A. niger achieved full recovery of all tested REEs at pH 1.5 (suboptimal growth conditions). This study pioneers the application of biosorption for the recovery of REEs in microgravity conditions, presenting a promising strategy for future resource exploitation by space biomining.

Mechanisms of roasting for improving rare earth element leaching from coal gangue

ABSTRACT Coal resources represent an important potential source for the future extraction of rare earth elements (REEs). This study, combining microscopic characterization techniques and experimental analysis, investigates the occurrence characteristics of REEs in coal gangue and the roasting activation mechanisms. The study reveals that phosphate minerals are the primary carriers of REEs, and sequential chemical extraction results further confirm the close association between REEs and phosphate minerals. Roasting at around 600°C facilitates the release of REEs from organic matter and clay minerals like kaolinite, significantly improving leaching efficiency. Under leaching conditions of 20 g/L, 50°C, 0.5 M HCl, and 1000 RPM, the leaching of REEs can reach approximately 80%. However, when the roasting temperature exceeds 1000°C, the formation of mullite leads to mineral surface sintering, reducing the recovery of REEs. This study emphasizes the importance of optimizing roasting conditions and understanding mineral phase changes to maximize REEs recovery, which is crucial for sustainable resource management and environmental remediation.

A Comparison Study on the Recovery of REEs from Red Mud by Sulfation Roasting–Water Leaching and Citric Acid Leaching

In this study, the recovery of rare earth elements (REEs) from red mud (bauxite residue) was explored through a combination of citric acid leaching and sulfation roasting–water leaching processes, introducing an innovative approach to the field. The research uniquely investigates the influence of citric acid on the leaching behavior of REEs and impurities in both untreated red mud and red mud subjected to sulfation roasting, providing a direct comparison of these methodologies. A novel aspect of this study is the evaluation of solvent extraction efficiency using DEHPA, highlighting the selective recovery of REEs over impurities from both citric acid and water-leaching solutions. Furthermore, a comprehensive phase analysis using X-ray diffraction (XRD) was conducted to track the transformations of minerals during the sulfation roasting process, an original contribution to the literature. The findings revealed that over 85% of REEs and major elements such as Fe, Al, Ca, and Ti dissolved in water after sulfation at 105 °C, while iron and titanium dissolution significantly decreased following roasting at 725 °C. Importantly, terbium, neodymium, and gadolinium extraction efficiencies were notably affected by roasting temperature. Citric acid leaching results demonstrated that the direct leaching of red mud leads to higher leaching efficiency than leaching it after the roasting process. Solvent extraction demonstrated lower terbium and neodymium recovery from citric acid solutions compared to water leaching solution. Finally, stripping experiments illustrated that 6M H2SO4 solution is capable of stripping more than 80% of rare earth elements, except terbium.

Toward a More Sustainable Future for the Rare Earths Industry

A new book explores how more sustainable methods are being applied to the recovery, processing, and purification of rare earths used in everyday technologies.

A novel extraction process for efficient recovery of rare earth elements from the leaching liquor of ion-adsorption type rare earth ore using unsaponified N, N-di(2-ethylhexyl)-diglycolamic acid

There are still challenges in the recovery of rare earth elements (REEs) from leaching liquor of ion-adsorption type rare earth ore. In this paper, unsaponified N, N-di(2-ethylhexyl)-diglycolamic acid (HDEHDGA) was used to develop a green extraction process for efficient separation and enrichment of REEs. The cation exchange mechanism of RE(III) extraction was proposed by slope analysis and FT-IR spectra. HDEHDGA exhibited excellent extraction performances, such as short equilibrium time, high selectivity towards RE(III) and easy stripping by 0.5 mol/L HCl solution. REEs was enriched from 287.5 mg/L to 63.30 g/L by five-stage counter-current extraction and three-stage counter-current stripping using unsaponified HDEHDGA. The enrichment factor reached 220, and the proportion of REEs was increased from 80.76 wt% to 98.82 %. The loss of REEs was controlled below 2.14 wt%. This extraction strategy helps to improve the REEs recovery and avoid ammonia–nitrogen wastewater, which demonstrates its application potential in the ion-adsorption type rare earth ore.

Artificial Intelligence Models for Efficiency Estimation of Adsorbents in Rare-Earth Element Recovery Based on Feature Engineering

Artificial Intelligence Models for Efficiency Estimation of Adsorbents in Rare-Earth Element Recovery Based on Feature Engineering

Selective separation of light and heavy rare earth elements from acidic mine waters by integration of chelating ion exchange and ligand impregnated resin

This study addresses the potential of sourcing Critical Raw Materials (CRMs) using Acidic Mine Waters (AMWs) as a secondary resource. AMWs, often viewed as waste, contain valuable metals like zinc and copper, as well as critical metals like magnesium and cobalt. Moreover, recent studies also reported the presence of Rare Earth Elements (REEs) at concentrations (mg/L) that make their extraction both technically and economically viable. The research focuses on a circular process to recover these metals from AMWs, specifically from the Aznalcóllar open-pit mine, which contains 216 mg/L of Al, 47 mg/L of Fe, 547 mg/L of Zn, and 18.56 mg/L of REEs. The proposed method involves pre-treating the AMW to remove Fe and Al, achieving removals of over 99.9 % and 90 %, respectively, at pH 4.5. Following this, transition metals like Zn, Cd, and Cu were removed as sulphides with a removal efficiency exceeding 99 %. This pre-treatment step reduced the concentration of competing metals in the ion-exchange process, thereby enhancing the recovery and purity of REEs. To separate heavy and light REEs, two types of resins in series were used: an impregnated resin (TP272) and a chelating resin (S930), which can be regenerated using sulphuric acid (H2SO4). The final recovery of REEs as oxalates was achieved using oxalic acid and ammonia at pH 1, with further optimization of the elution process to minimize ammonia consumption and undesired precipitation of other oxalates. Finally, REE oxalates with purities exceeding 90 % were obtained. This research demonstrates a sustainable method for efficiently recovering valuable REEs from AMWs, while also addressing environmental concerns related to hazardous sludge generation.

Moderate strategy for efficient recovery of rare earth elements from scintillation crystal waste

The lutetium has been known to be used in medical imaging materials, but its scarcity in the Earth’s crust makes it expensive. In this work, we present a process for efficient lutetium recovery from the lutetium-yttrium oxyorthosilicate crystals (LYSO) waste. The process involves preliminary mechanical activation, followed by rare earth extraction via acid leaching. The key factors for activation and leaching were studied and optimized. The mechanism of mechanical activation promoting rare earth leaching was revealed by employing the characterizations of morphology and crystal structure of LYSO. It was found that the mechanical activation process could destroy the crystal structure of LYSO waste, forming numerous amorphous phases and grain boundaries, which facilitated the breaking of existing bonds and mass transfer of acid. It was also discovered that the formation of silica gel during leaching impedes the leaching of rare earth, and low concentrations of hydrochloric acid, combined with stirring during acid leaching, could reduce the impact of silica gel. Ultimately, following a mechanical activation pretreatment at 300 rpm for 90 min, 98.7 % of lutetium could be leached after 60 min of acid leaching in 3 mol/L hydrochloric acid. This process addresses the problems associated with high energy consumption and excessive usage of acidic and alkaline reagents in conventional recycling techniques. Compared to conventional methods, the mechanical activation-acid leaching method has a minimum economic benefit improvement of 20.8 % in the process of recovery from LYSO waste. It offers an alternative and more energy-efficient and economical recycling route for waste scintillation crystals.

Fabrication of ion imprinted diethylenetriamine pentaacetic acid-polyethylenimine modified magnetic graphene oxide for selective adsorption of Ce(III)

Selective recovery of rare earth elements is essential for both sustainable exploitation of rare earth resources and environmental remediation. Herein, Ce(Ⅲ) imprinted diethylenetriamine pentaacetic acid-polyethylenimine modified magnetic graphene oxide (IIP-DTPA-PEI-MGO) was fabricated for selective adsorption of Ce(Ⅲ). Adsorption efficiency and selectivity performance of IIP-DTPA-PEI-MGO towards Ce(Ⅲ) were evaluated via batch adsorption targeted at single and mixed solution, respectively. Adsorption mechanism was elucidated based on versatile adsorption fittings (isotherms, kinetics, thermodynamics) and spectroscopic tests (XPS, FTIR). Result presents, maximum adsorption efficiency of IIP-DTPA-PEI-MGO for Ce(III) is reached at pH = 5 in 30 min, demonstrating superior efficiency. The maximum mono layer adsorption capacity determined by the Langmuir model is 281.69 mg g−1. After adsorption, 75.65 % of original Ce(Ⅲ) is transferred into Ce(Ⅳ), while 24.35 % remain as Ce(Ⅲ). Furthermore, by virtue of its paramagnetic property, IIP-DTPA-PEI-MGO can be easily recovered for cyclic adsorption, thereby keeping adsorption quantity 90.44 mg g−1 on Ce(Ⅲ) in five consecutive cycles. Owing to ion imprinting sites, IIP-DTPA-PEI-MGO exhibits selectivity coefficient 1.34, 1.69, 2.32, 2.96, 15.24, 10.51 towards Ce(III) for binary solution Ce/La, Ce/Nd, Ce/Eu, Ce/Dy, Ce/Cu, Ce/Cr, respectively. In terms of adsorption mechanism, versatile functional groups O-H, C-N, C-O in IIP-DTPA-PEI-MGO provide heterogeneous affinity for Ce(Ⅲ), inducing chemical adsorption. This work provides a novel approach towards fabricating magnetic bio adsorbent for selective recovery of Ce(Ⅲ).

Selective separation and recovery of rare-earth elements (REEs) from acidic solutions and coal fly ash leachate by novel TODGA-Impregnated organosilica media

Rare-earth elements (REEs) are essential in a wide range of applications including magnets and satellite technology, with demand driven by geopolitical factors. While multiple techniques exist for REE recovery including solvent extraction and selective precipitation, solid–liquid extraction offers key advantages in selectivity, scalability, and recyclability. N, N, N′, N′-tetraoctyl diglycolamide (TODGA) is a tridentate ligand widely used in solvent extraction, but the incorporation in a solid support to separate individual lanthanides from acid solutions remains largely unexplored. A novel TODGA-organosilica sorbent material was developed and tested to evaluate recovery of 17 elements (REEs and thorium) in terms of selectivity, kinetics, and equilibrium isotherms in 0.01 to 15.9 M nitric acid. Characterization of the new sorbent was performed before and after sorption using FTIR, XPS, and SSA techniques to help elucidate sorption mechanisms and limiting variables. REE adsorption increased from 1.26 mg g−1 to 10 mg g−1 with nitric acid concentrations of 0.01 M and 15.9 M, respectively. TODGA-organosilica exhibits high selectivity towards heavy REEs (Dy to Lu), with minimal sorption of lighter REEs (Ce to Gd). Batch adsorption experiments confirm pseudo-second-order kinetics and a Langmuir adsorption isotherm with TODGA binding to REEs in a 3:1 complex. A packed bed column study confirmed the high selectivity of TODGA-impregnated organosilica towards heavy REEs and a proof-of concept experiment with coal fly ash leachate shows high selectivity for REEs over Al, Fe, and Ca present in several orders of magnitude higher concentrations. Fractionation was observed where loading cycle effluent contained 84 % light REEs while strip cycle effluent contained 80 % heavy REEs. More than 90 % of loaded REEs were successfully stripped with water as the stripping agent.