Recovery Of Rare Earth Elements Research Articles

Highly selective recovery of rare earth elements from mining wastewater using phyto-synthesized biochar dispersed iron nanoparticles

Recovery of rare earth elements (REEs) from secondary sources such as mining wastewater has attracted much recent attention due to the rising global demand for REEs and the need to environmentally protect potentially contaminated mine sites. One significant issue it that most adsorbents proposed for removal and/or recovery of REEs are not generally selective for REEs. In this study, biochar dispersed iron nanoparticles synthesized using a plant extract (BC-FeNPs) were successfully used for the selective recovery of REEs from mining wastewater, where the Kd values were Nd(III) (918 mL∙g−1), Eu(III) (1253 mL∙g−1), Tb(III) (1119 mL∙g−1), Dy(III) (1032 mL∙g−1), Lu(III) (1898 mL∙g−1), compared to only 23.9 mL∙g−1 for Zn(II). The maximum adsorption efficiency of REEs for the composite was higher than the constituent parts being 88.4 % for BC-FeNPs, but only 8.72 % for biochar and 82.4 % for FeNPs, respectively. FTIR, XPS and Zeta potential analysis suggested that the observed selective adsorption of REEs, involved interactions of REEs with O and N, as well as ion-exchange with H+ from the biochar and capping layer, as well as electrostatic interactions. The desorption efficiency of bound REEs from BC-FeNPs was > 85 % when using acetic acid, and was attributed to efficient competitive ion exchange. Pearson correlation analysis further demonstrated that the adsorption mechanism included ion complexation, ion exchange and electrostatic adsorption, while the desorption mechanism was mainly via ion exchange. Overall, BC-FeNPs has significant potential to practically recover REEs from mining wastewater having demonstrated excellent reusability after five adsorption–desorption cycles.

Review of Methods for Obtaining Rare Earth Elements from Recycling and Their Impact on the Environment and Human Health

Rare earth elements (REEs) are at the forefront of discussions, given their crucial role in cutting-edge and eco-friendly innovations that propel the industrial revolution towards a green economy. These elements have become indispensable to various modern technologies, such as smartphones, electronic devices, and renewable energy sources. Many different concepts and analyses have been introduced, such as the chemical similarities among REEs, health risks and ecological damages, the negative environmental impacts of current recovery processes, and strategies for advancing REE recovery towards a circular economy. Although these elements have been widely used in various applications over the last 20 years, the literature on these aspects is fragmented and spread across different research areas, shared by multiple branches and application fields. These fields include safety concerns, economic challenges, and technology. Summarizing and classifying this literature is challenging due to its fragmented nature, the variety of topics, and the different approaches used. The quest for cleaner recycling strategies necessitates a comprehensive assessment covering economic, technological, and environmental aspects. The primary goal of this review is to provide a holistic perspective on REEs, with a central focus on their economic, technological, and environmental dimensions, particularly emphasizing reuse, recycling, and occupational safety. The review begins by addressing complexities of REEs, highlighting the associated technologies, environmental concerns, and economic considerations. It further explores the aspects of reuse and recycling of REEs, shedding light on the advantages, drawbacks, hazards, and costs associated with recycling technologies for REE recovery. Additionally, the review summarizes occupational exposure and safety considerations related to REEs.

Utilization of Eggshell Waste Calcite as a Sorbent for Rare Earth Element Recovery.

The green energy transition requires rare earth elements (REE) for the permanent magnets used in electric cars and wind turbines. REE extraction and beneficiation are chemically intensive and highly damaging to the environment. We investigated the use of eggshell waste as a sustainable alternative sorbent for the capture and separation of REE from aqueous solutions. Hen eggshell calcite was placed in multi-REE (La, Nd, Dy) solutions at 25 to 205 °C for up to 3 months. A pervasive diffusion of the REE inside the eggshell calcite was observed along pathways formed by the intracrystalline organic matrix and calcite crystal boundaries. At 90 °C, kozoite (REECO3OH, orthorhombic) spherulites precipitate on the surface of the dissolving calcite. At 165 and 205 °C, an interface-coupled dissolution-precipitation mechanism is observed, resulting in the complete dissolution of the calcite shell and its pseudomorphic replacement by polycrystalline kozoite. At 205 °C, kozoite is slowly replaced by hydroxylbastnäsite (REECO3OH, hexagonal), the stable form of the rare earth hydroxycarbonate polymorphs. Our results demonstrate two potential applications of eggshell waste for the uptake of rare earth elements in solution: at low temperatures, as a mixed organic-inorganic adsorbent and absorbent, given sufficient sorption time; and at higher temperatures, as an efficient sacrificial template for the precipitation of rare earth hydroxycarbonates.

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.

Recovery of rare earth elements from weathering crust soils using electrokinetic mining technology☆

Ion-absorption deposits (IADs) of rare earth elements (REEs) constitute the main economic resources of the essential heavy rare earth elements (HREE). Nonetheless, the existing leaching methods for extracting REEs from IADs face limitations stemming from significant environmental consequences and a poor REE recovery rate. In a recent development, electrokinetic mining (EKM) has emerged as a novel technology for extracting REEs from ion-adsorption deposits, demonstrating the potential for environmentally friendly and efficient recovery of REEs from weathering crusts. However, the transport mechanism of REE in weathering crust soil in an applied electric field remains poorly understood, and the influence of the EKM process has yet to be studied. In this study, we systematically investigated the transport characteristics of REE in weathering crust soil under the influence of an electric field. We demonstrate that the transport of REE is simultaneous with the transport of water, H+, and OH– in the applied electric field, where the EKM process is influenced by the voltage gradient, initial soil water content, electrode numbers, and power-on time. Under the optimal EKM conditions, 78.8% of REE is recovered from a 45 kg-scale weathering crust soil. Additionally, we identify the transport diversity between light REE (LREE) and HREE, which assists in the separation and pre-enrichment of LREE and HREE. Furthermore, we demonstrate that the mechanism for REE transport under an electric field involves a combination of electromigration, electroosmosis, and electrolysis working synergistically. This study provides new perspectives on the transport behavior and mechanism of REEs in weathering crust soil under an electric field. These findings pave the way for the practical implementation of EKM technology.

Recovery of neodymium and iron from NdFeB waste by combined electrochemical–hydrometallurgical process

The recovery of rare-earth elements and Fe from NdFeB waste has significant potential. However, conventional hydrometallurgical and pyrometallurgical processes are energy intensive, chemical consuming, and accompanied by waste emissions, resulting in low-value iron products. This study introduced a combined electrochemical–hydrometallurgical process for NdFeB waste recovery. Electrochemical analysis revealed the active dissolution of NdFeB waste under 370 mA/cm2, enabling Fe2+ reduction to Fe even in the presence of Nd3+. Electrolysis at 60 °C using Nd2(SO4)3 and FeSO4 as electrolytes, along with H3BO3 as a pH buffer, resulted in the uniform dissolution of waste, releasing Nd3+ and Fe2+ into the electrolyte, whereas Fe2+ underwent electrodeposition onto Fe at the cathode. Investigation of FeSO4 concentration revealed its influence on current efficiency, cathode-product properties, and energy consumption. When the concentration of FeSO4 was 0.5 M, a cathode product with 87.94 wt% Fe and 0.03 wt% Nd was obtained. Finally, Nd was recovered by hydrometallurgical high-temperature crystallization at 90 °C under N2 atmosphere, yielding Nd2(SO4)3·nH2O mixed crystals with 0.1 wt% Fe. The process formed a closed loop, consuming only FeSO4 and a minimal amount of H2SO4, with an energy consumption of 0.73–1.53 kW·h/kg NdFeB.

Extraction of rare earth Eu from waste blue phosphor strengthened by microwave alkali roasting

Spent phosphor is an important secondary resource for extracting rare earth elements. Microwave absorption properties and enhanced extraction of Eu from blue phosphor by microwave alkali roasting were studied. Dielectric properties of alkali roasting system were measured by resonator perturbation method. Dielectric constant increases linearly from 250 °C until it reaches a peak at 400 °C. The dielectric loss reaches a higher value at 400–550 °C, due to the strong microwave absorption properties of molten alkali and roasted products. Effects of roasting temperature, roasting time and alkali addition amount on Eu leaching were investigated. The phosphor was completely decomposed into Eu2O3, BaCO3 and MgO at 400 °C. The alkaline decomposition process of phosphor is more consistent with diffusion control model with Eα being 28.9 kJ/mol. Effects of the main leaching conditions on Eu leaching were investigated. The leaching kinetic of Eu was in line with diffusion control model with Eα being 5.74 kJ/mol. The leaching rules of rare earths in the mixed phosphor were studied. The results showed that the presence of red and green phosphor affected the recovery of blue phosphor. The optimum process parameters of rare earth recovery in single blue phosphor and mixed phosphor were obtained, and the recovery of Eu were 97.81% and 94.80%, respectively. Microwave alkali roasting promoted the dissociation of phosphor and leaching of rare earths. The results can provide reference for the efficient and selective recovery of rare earths in phosphors.

In Situ Modification of Activated Carbon Made from Camellia oleifera Shell with Na2EDTA for Enhanced La3+ Recovery

It is important to recover La3+ from metallurgical solutions or wastewater. However, the recovery rate of La3+ is usually less than 1% and the recovery methods are not environmentally friendly or user-friendly. Therefore, a straightforward, efficient, clean, and economically friendly method is needed. In this investigation, a modified adsorbent, COSAC-Na2EDTA-15, which was made from the Camellia oleifera shell (COS) and disodium ethylenediaminetetraacetic acid (Na2EDTA), was invented. In addition, characterization of the COSAC-Na2EDTA-15 adsorbent was conducted using SEM and XPS, and the principle of adsorption was revealed. The adsorption kinetics followed P-S-O KM, while the isotherm of COS-activated carbon (COSAC) aligned more closely with the Langmuir model. Compared to COSAC, the maximum La3+ adsorption capacity of COSAC-Na2EDTA-15 increased from 50 to 162.43 mg/g, and the content of O and N changed from 7.31% and 1.48% to 12.64% and 4.15%, respectively. The surface of the COSAC-Na2EDTA-15 exhibited abundant C, N, and O elements, and La3+ was detected on the sample surface after adsorption. The test and analysis results fully indicate that La3+ can be successfully adsorbed on the surface of COSAC-Na2EDTA-15. Because of its easy preparation, low cost, and superior performance, activated carbon made from COS finds extensive applications in the adsorption and recovery of rare earth elements.

Recovery of Rare Earths from Rare-Earth Melt Electrolysis Slag by Mineral Phase Reconstruction

Recovery of Rare Earths from Rare-Earth Melt Electrolysis Slag by Mineral Phase Reconstruction

Greening the supply chain: Sustainable approaches for rare earth element recovery from neodymium iron boron magnet waste

The increasing demand for modern technologies has led to a growing reliance on rare earth elements (REEs). To address this issue, recycling used products such as permanent magnet waste containing REEs. However, this approach necessitates the development of advanced extraction and separation techniques to ensure high yields and purity of the REEs extracted. This review provides an overview of the latest extraction and separation technologies, with a particular focus on the hydrometallurgical approach for extracting REEs from secondary sources, notably permanent magnets. Hydrometallurgy, which involves leaching followed by solvent extraction for purification, has gained widespread use for obtaining REEs from secondary sources, as evidenced by its reported high recovery efficiencies. We found that the recovery of REEs using chemical leaching varied between 80% and 99%, influenced by factors such as type of source material, leaching solvent, leaching conditions, impurities, reaction kinetics and solid-liquid ratio. However, effectively employing this process on a larger scale still faces certain challenges due to the excessive use of corrosive solvents for leaching magnet waste and the generation of toxic chemicals as end products in the form of leachate. Additionally, the current process exhibits deficiencies in the targeted recovery of REEs from magnet waste, specifically in achieving purity and selectivity by eliminating iron impurities. This article concludes that the future prospects for the selective recovery of REEs from neodymium iron boron magnet waste lie in green and environment-friendly solvents. One such approach revolves around the utilization of biodegradable organic acids and salt aqua regia for leaching. These solvents are less corrosive and have high dissolution efficiency, which results in less chemical consumption and an overall environment-friendly and cost-effective recovery process.

Sustainable recovery of rare earth elements from Ni-MH batteries: Flux-free thermal isolation and Subsequent hydrometallurgical refinement

This study details a sustainable approach for efficient recovery of highly pure rare earth elements oxides (REOs) from Ni-MH batteries. REOs (i.e., La, Ce, Sm, Nd, and Pr oxides) were thermally isolated from spent Ni-MH batteries into an oxide phase with the REO concentration of 67.4 wt%. Subsequently, separate leaching processes were conducted using sulfuric acid and hydrochloric acid solutions, and the results were compared in terms of efficiency and feasibility. Sodium REEs sulfate hydrate (NaRE(SO4)2.xH2O) was precipitated from the sulfuric acid leachate by adjusting the pH to 1.5 using sodium hydroxide, while the addition of oxalic acid to the hydrochloric acid leachate enabled the recovery of REEs as oxalate hydrate (RE2(C2O4)3.xH2O). The resulting sulfate salt was mixed with a sodium hydroxide solution, leading to the formation of REEs hydroxide. The REEs hydroxide and oxalate were calcined at 1000 °C, resulting in the production of REOs with a purity exceeding 99.7%. This research demonstrates the feasibility of developing an efficient, environmentally friendly, and sustainable approach for the recovery of highly pure REOs from Ni-MH batteries which potentially can minimize the environmental impact associated with the extraction of REOs from virgin sources, while addressing the challenge of effective recycling of end-of-life Ni-MH batteries.

ZIF-8 Used for the Selective Recovery of Heavy Rare Earth Elements from Mining Wastewater.

In this study, a sample of 2-methylimidazole zinc salt (ZIF-8) demonstrated high selectivity for the recovery of heavy rare earth elements (REEs) from real rare earth mining wastewater. Results show that the distribution coefficient values of Y3+ (4.02 × 104 mL·g-1), Gd3+ (7.8 × 104 mL·g-1), and Dy3+ (6.8 × 104 mL·g-1) are orders of magnitude higher than those of K+ (359.51 mL·g-1), Mn2+ (266.67 mL·g-1), Ca2+ (396.42 mL·g-1), and Mg2+ (239.48 mL·g-1). Moreover, the desorption efficiency of heavy REEs exceeded 40%. Advanced characterizations and density functional theory (DFT) calculations were utilized to elucidate that the heavy REEs were more likely to bind to the nitrogen atoms of imidazole groups on ZIF-8 compared to non-REEs. Furthermore, the adsorption and desorption of heavy REEs primarily depend on the chemical interaction confirmed by adsorption kinetics, isotherm model, and thermodynamic analysis, which involves the dissociation of water and the formation of REE-O bonds. Finally, the ZIF-8 exhibits a remarkable recovery efficiency of over 40% for heavy REEs in column tests conducted over 7h. The findings reported here provide new insights into the selective recovery of heavy REEs from real mining wastewater.

The fractional extraction for sustainable recovery of rare earth and thorium in radioactive waste with oxoacetate functionalized ionic liquid

Rare earth (RE) are critical elements in many technologies, their clean production has attracted widespread attentions. To develop clean separation technology for RE, a novel oxoacetate ionic liquid (IL) extractant was developed to recovery RE elements and Thorium (Th) in the radioactive waste residue from ion-absorbed RE separation industry. The IL [N-methyl-N,N-dioctyloctan-1-aminium][2-(bis(2-ethylhexyl)amino)-2-oxoacetate] ([N1888][DEAO]) had good selectivity to RE and Th, which helps to remove radioactive Th and recover RE from waste residue leachate. RE and Th could be effectively separated with 0.02 mol/L [N1888][DEAO]. Maximum extraction capacity of Th reached 1.02 g/L, which could meet the needs of Th removal in the waste residue. A combination of saturated NaC2O4 solution and NaOH solution was used for the stripping of Th. After five cycles, the extraction efficiency of Th remained above 90 %. After four-stage extraction with [N1888][DEAO] and three-stage scrubbing, a RE solution with Th content less than 0.6 mg/L was obtained. It is fully achieved that there is no excess wastewater and waste salt in the fractional process. The RE elements in the waste residue can be effectively recycled, also the collection of the radioactive element Th can be realized.

Adsorption of the rare earth elements cerium, lanthanum, and neodymium onto ZSM-5 zeolite: A statistical physics approach

The recovery of rare earth elements (REE) is essential to meet the growing demand for these resources and promote the reuse of available resources. This study investigated the potential of ZSM-5 zeolite in the recovery of trivalent ions of cerium, lanthanum and neodymium under conditions of pH 6 and temperatures between 298 and 328 K. REE equilibrium isotherms were analyzed using five statistical physics models. The results indicate that removing all REE occurs predominantly in monolayers, as these models showed better prediction performance (coefficient of determination > 0.97 and mean squared error < 18.0). The best model determined that lanthanum and neodymium have one adsorption energy, while cerium has two adsorption energies involved in the process. The predominant functional groups are those containing silicon. Increasing temperature causes an increase in the number of REE ions captured per functional group, which reduces the adsorption space available on the surface. The model parameters indicate that the adsorption of these ions implies a multi-ionic mechanism (number of ions adsorbed per site greater than 1) and is an exothermic process. Based on the calculated adsorption capacities at saturation, the order of preference in adsorption can be established: neodymium > cerium > lanthanum. The adsorption energies indicate that the process occurred mainly due to physical forces since all energy values are below 40 kJ mol−1. The study’s results led to the proposal of a mechanism for the adsorption of REE on ZSM-5 zeolite, which highlights the predominance of electrostatic interactions and complex formation, which result in the formation of a monolayer on the adsorbent’s surface.

Recovery of rare earth elements from low-grade coal fly ash using a recyclable protein biosorbent.

Rare earth elements (REEs), including those in the lanthanide series, are crucial components essential for clean energy transitions, but they originate from geographically limited regions. Exploiting new and diverse supply sources is vital to facilitating a clean energy future. Hence, we explored the recovery of REEs from coal fly ash (FA), a complex, low-grade industrial feedstock that is currently underutilized (leachate concentrations of REEs in FA are < 0.003mol%). Herein, we demonstrated the thermo-responsive genetically encoded REE-selective elastin-like polypeptides (RELPs) as a recyclable bioengineered protein adsorbent for the selective retrieval of REEs from coal fly ash over multiple cycles. The results showed that RELPs could be efficiently separated using temperature cycling and reused with high stability, as they retained ∼95% of their initial REE binding capacity even after four cycles. Moreover, RELPs selectively recovered high-purity REEs from the simulated solution containing one representative REE in the range of 0.0001-0.005mol%, resulting in up to a 100,000-fold increase in REE purity. This study offers a sustainable approach to diversifying REE supplies by recovering REEs from low-grade coal fly ash in industrial wastes and provides a scientific basis for the extraction of high-purity REEs for industrial purposes.

High-efficiency stepwise recovery of gallium and rare earths from NdFeB waste by a hydrometallurgical process

NdFeB waste serves not only as a crucial resource for the recovery of rare earth elements (REEs) but also as an underutilized source of gallium (Ga). In this work, to simultaneously extract REEs and Ga from NdFeB waste, an efficient and novel method was developed, which involved the process of leaching, reduction, solvent extraction, precipitation, and calcination. Initially, the Pr, Nd, and Ga were co-leached with 5 mol/L HCl and liquid-solid ratio (mL/g) of 5:1 at 90 °C for 150 min, resulting in the leaching rate of Pr, Nd, and Ga were 98 %, 99 %, and 98 %, respectively. Secondly, to mitigate the interference of Fe (III) on the extraction process, Fe (III) was reduced to Fe (II) completely using Fe powder for 10 min, given that the excess iron powder factor was 1.2. Then, the tributyl phosphate (TBP) was chosen as the extractant for Ga due to its high selectivity. Under the optimal conditions, three-stage counter-current extraction achieved an extraction efficiency of 99 % for Ga, with the addition of 10 % isodecanol to eliminate the third phase. The gallium was completely stripped by water at a phase ratio (O/A) of 2:1. Subsequently, di-2-ethylhexylphosphoric acid was selected as the Pr and Nd extractant because of its high separation ability between REEs and Fe (II). The extraction efficiency of Pr and Nd achieved more than 99 % through three-stage counter-current extraction and the entire stripping of Pr and Nd was realized by 1.8 mol/L HCl. Additionally, a significant amount of Fe (II) in the raffinate was treated via adding oxalic acid to obtain FeC2O4 ⋅ 2H2O. Finally, the Ga2O3 and Nd2O3 (PrO2) were prepared from the stripping solution. According to the whole process, the yield of Ga, Pr, and Nd was 93.4 %, 97 %, and 98 %, with the purity of Ga2O3 and Nd2O3 (PrO2) being 98.6 % and 98.4 %, respectively. The results suggested that the stepwise recovery of REEs and Ga from NdFeB waste can be achieved.

Recovery of Rare Earth Elements from Ion-Adsorption Deposits Using Electrokinetic Technology: The Soil Conductivity Mechanism Study

Rare earth elements (REEs) are essential raw materials for modern industries but mining them has caused severe environmental issues, particularly the recovery of heavy REEs (HREEs) from ion-adsorption deposits (IADs). Very recently, an emerging technology, electrokinetic mining (EKM), has been proposed for the green and efficient recovery of REEs from IADs. However, the conduction mechanism of the weathering crust soil, which is also a prerequisite for EKM, remains unclear, making the EKM process unpredictable. Here, we systematically investigated the conductivity of weathering crust soil in the presence of light REEs (LREEs, i.e., La3+ and Sm3+) and HREEs (Er3+ and Y3+), respectively. Results suggested that the voltage was dynamically and spatially redistributed by the movement of REEs and water during EKM, and the conventional assumption of the linear distribution of voltage leads to an inaccurate description of soil voltage. We proposed an improved Archie’s equation by coupling the mechanisms of liquid phase and solid-liquid interface conduction, which can predict soil conductivity more precisely. Moreover, the extended Archie’s equation is able to recalculate the voltage distribution at distinct times and spaces well during EKM. More importantly, the water content in field-scale weathered-crust soils can be retrieved by the newly proposed Archie’s equation, which helps optimize the leaching wells and improve the recovery rate of REE. This study focuses on the conduction mechanism of weathering crust soil, which provides a theoretical basis for better use of the EKM technology and promotes mining efficiency fundamentally.

Electro-assisted sorption behavior and mechanism of low-concentration rare earth elements on carbon based materials

With increasing demands for rare earth elements (REEs) in high-tech and futuristic applications, developing efficient methods for recovering low-concentration REEs is necessary. Here, electro-assisted sorption of low-concentration REEs, La(III), Gd(III) and Y(III) (as symbol of light, medium, and heavy REEs) on carbon-based materials, activated carbon (AC), graphene, and graphite by a facile method was reported. Recovery of La(III), Gd(III) and Y(III) could reach ∼100 % under low-concentration condition where the maximum adsorption capacity was up to 342.38 mg/(g·dm2). Variants including applied voltage, electrodes-distance, pH, impurities, and concentration were considered to study the effects on REEs recovery. Interestingly, adsorption capacity and recovery under low voltage were respectively almost 20 and 14 folds than that without voltage, because voltage promoted REEs transfer and strengthened electrostatic interaction between electrodes and REEs. The mechanism for enhancing REEs recovery on carbon-based electrodes was resulted from high electric double layer (EDL) capacitance and low charge transfer resistance. Total desorption of REEs from electrodes could be quickly realized using NH4Cl or HCl solution. Overall, the study gave a new insight of low-concentration REEs recovery using carbon-based materials, and provided an efficient route using electric method with porous materials for REEs recovery.

Maximizing the Processing of Polymetallic Concentrates via Actinide Separation and Rare Earth Retrieval

During the last decades, the growing demand for rare earth elements (REEs) has led to numerous recent studies to recover these elements from various bearing ores and wastes. Therefore, the recovery of REEs from Ras Baroud polymetallic concentrate has been investigated in the current study. Physical beneficiation for the Ras Baroud pegmatite sample was carried out, yielding a concentrate for euxenite (Y), fergusonite (Y), xenotime (Y), monazite (Ce), allanite, thorite, uranothorite, and Hf-zircon, which resulted in raising the concentrations of rare earth elements, Th, Zr, U, and Ti in the sample. Fusion digestion processes with sodium hydroxide were studied using the Conceived Predictive Diagonal (CPD) technique. The three experimental digestion groups proved the dissolution of 99.9, 95.6, 99.9, 52.5, and 0.47% for REEs, Th, U, Ti, and Zr, respectively, under fusion conditions of 723 K, 120 min, 1/1.5 ore/alkali ratio, and − 100-μm particle sizes. Fusion kinetics, isotherms, and thermodynamics were investigated using several suggested models, namely, pseudo reversible first order, uptake general model, and shrinking core model which matched well with the experimental digestion results. Selective recovery of actinide content from REE content of the digested concentrate chloride solutions was accomplished using solvent extraction with di-2-ethyl hexyl phosphoric acid. About 99.9, 99.9, and 4.2% extraction efficiencies for Th, U, and REEs were performed, respectively, using 0.3 mol/L solvent concentration in kerosene as a diluent, 1/2 organic to aqueous ratio, an aqueous pH of 0.2, and 15-min contact time. Thorium and uranium ions were stripped with sulfuric acid solution 2.5 mol/L with 94 and 98% stripping efficiency, respectively. A highly purified REE precipitate was obtained from the raffinate solutions. Zircon mineralization tailings were obtained as a by-product through the alkaline digestion process.

Comprehensive recycling of slag from the smelting of spent automotive catalysts

Spent automotive catalyst is a valuable source of platinum group metals (PGMs), making them crucial secondary resources. Currently, the main process for recovering PGMs from these catalysts is metal capture method. The smelting process would produce a significant amount of residual slags containing various components like SiO2, Al2O3, CaO, Fe2O3, Na2O, as well as high levels of heavy metals including Cr, Pb, and Ni. These slags are considered either solid waste or hazardous waste and usually disposed of in landfills, which can have detrimental effects on the environment. Furthermore, the smelting slags also contain approximately 2–5 % rare earth elements and trace amounts of precious metal elements. In this study, vacuum carbothermal reduction is employed to pretreat the smelting slags. This method not only successfully removes the heavy metal element lead, but also efficiently achieves the recovery of rare earths, and the enrichment of platinum group metals by mineral phase transformation of cerium-zirconium solid solution and in-situ iron capture. The lead removal rate exceeded 99 %, and the grade of precious metals in the enrichment process was approximately 12 times higher than the original material, with a recovery rate more than 90 %. The leaching rate of rare earths also increased from less than 50 % to more than 95 % after vacuum carbothermal reduction. The effect of vacuum carbothermal reduction pretreatment on the smelting slag phase was systematically studied, and the mechanism behind the increasing rare earth leaching rate due to this pretreatment was further analyzed.