Leaching Of Rare Earth Elements Research Articles

Selective leaching of rare earths, base metals and precious metals from used smartphones

ABSTRACT Discarded smartphones represent a valuable source of rare earths (REE), base metals and precious metals. This study focussed on the optimisation of three-stage selective leaching conditions for REE, copper and precious metals (Au and Ag), respectively, contained in printed circuit boards (PCBs) found in end-of-life smartphones. The effects of several leaching conditions, such as sulphuric acid and thiourea concentrations, were investigated using a statistical approach based on a design of experiments using Box–Behnken methodology. Optimum leaching efficiencies were achieved when PCB powder was contacted (solid concentration of 100 g/L) with (1) a 0.2 M H2SO4 solution for 30 min at a temperature of 20°C for REEs; (2) a 1 M H2SO4 solution with 67 g H2O2/L for 180 min at 80°C for Cu and (3) a solution of 42 g thiourea/L in 0.1 M H2SO4 and 9 g Fe2(SO4)3/L for 120 min at 20°C for Au and Ag. Using these optimal conditions, a complete leaching procedure included an REE solubilisation step and a base metal leaching step, both repeated twice, and a precious metal leaching step. This procedure solubilised 91% of the REE, 100% of the copper, 98% of the gold and 87% of the silver contained in the PCB powder during their respective leaching stages.

Efficient Leaching of Rare Earth Elements from Coal Gangue: A Mild Acid Process with Reduced Impurity Extraction

Efficient Leaching of Rare Earth Elements from Coal Gangue: A Mild Acid Process with Reduced Impurity Extraction

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.

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.

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.

Sulfuric Acid Leaching Recovery of Rare Earth Elements from Wizów’s Phosphogypsum in Poland

Rare earth elements (REEs) are considered vital raw materials for the economy and are on the European Union’s list of critical raw materials (CRMs). Europe is mainly dependent on REE imports. This dependence could be reduced if locally available primary or secondary resources would be processed. In Poland, there are, for instance, over 5 million metric tons of phosphogypsum (PG), a fine powdery byproduct from the fertilizer industry, available near the former Wizów Chemical Plant near Bolesławiec. This material that is considered a waste in Poland contains significant amounts of REEs that could theoretically be recovered and contribute to Europe’s economy. This work is the first systematic analysis of REE leaching studies with sulfuric acid and PG from Wizów. Process parameters such as temperature, particle size, concentration of the leaching solution, and the addition of oxidant and reductant agents were tested to determine the most efficient process. Ultimately, a leaching efficiency of 99% was obtained. Lanthanum exhibited the highest leaching efficiency at almost 100%, followed by Yttrium, Neodymium, Terbium, and Dysprosium. The results of the laboratory experiments are promising and suggest that larger pilot or commercial experiments can be performed next.

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.

Extraction of Rare Earth and CaF2 from Rare Earth Calcium Thermal Reduction Slag by Using CaO Roasting–Acid Leaching Method

The rare earth calcium thermal reduction slag (RCS) generated during the production of heavy rare earth metal contains large amounts of rare earth and fluoride compounds. In this study, rare earth elements (REEs) and fluorine in the RCS were recovered by the CaO roasting–hydrochloric acid leaching method. Firstly, the thermodynamic feasibility of converting rare earth fluoride to rare earth oxides through CaO roasting was demonstrated. The influence of roasting conditions and leaching conditions on the leaching rate of the REEs was investigated. Optimal results, a 95.48% leaching rate of the REEs, were obtained under the following conditions: a CaO dosage of 15%, a roasting temperature of 1000 °C, and a roasting duration of 90 min. XRD, SEM, and EDS results revealed that during the calcination process, the REEs present in fluorite (CaF2) in isomorphic form were transformed into acid-soluble rare earth oxides; furthermore, the rare earth metallic in the RCS remained unchanged even after roasting. In the leaching process, rare earth metals and rare earth oxides are efficiently extracted, while CaF2 rarely dissolves. The leaching slag contained 97.31% CaF2 with a F recovery of 96.92%. The kinetics of the rare earth leaching process was analyzed, and the results show that the three-dimensional diffusion control at the phase interface of the kinetic model best fits the process. The calculated apparent activation energy for the leaching rate of REEs is 20.869 kJ/mol. Therefore, efficient comprehensive recovery of rare earth and fluorite from RCS can be achieved by using the CaO roasting–hydrochloric acid leaching method.

Enhanced enrichment of rare earth elements during pedogenesis under subtropical climate

Rare earth elements (REE) are crucial strategic resources, and weathering-crust rare earth deposits are one of the primary sources. To systematically understand the geochemical behavior (e.g., enrichment and leaching) of REE in soils (or weathering crusts) formed from diverse parent rocks under varying climatic conditions, 171 soil profiles (weathering crusts) developed from three main types of parent rocks (granite, basalt, and carbonate rock) worldwide were studied. Granite shows the highest concentration of rare earth elements at 264 (interquartile range (IQR): 278) ppm, 171 (IQR: 151) ppm and 11.9 (IQR: 36.4) ppm in basalt and carbonate rock, respectively (median test: p < 0.05). The median REE values within the soil profiles were significantly different (median test: p < 0.05), with the concentration of 318 (IQR: 441) ppm, 267 (IQR: 217) ppm and 207 (IQR: 417) ppm in soils derived from granite, carbonate rock, and basalt, respectively. Principal component analysis (PCA) and Linear mixed-effects models (LME) revealed that soils developed from granite and basalt inherit the mineral characteristics of their parent rocks, with REE concentrations primarily influenced by the REE content of the parent rock and climate. In contrast, the REE concentrations in soils developed from carbonate rocks are predominantly controlled by climate. LME and correlation analysis indicates that the enrichment of REE (Q REE ) shows a trend of initially increasing and then decreasing with rising temperature and precipitation, due to variations host clay minerals. The greatest enrichment occurs in the subtropical region (mean annual temperature (MAT) = 15 ̶ 23 °C; mean annual precipitation (MAP) = 1000 ̶ 2000 mm); weathering-crust type REE deposits are primarily found in the subtropics.

Effect of Fine Particle Content on Solution Flow and Mass Transfer of Ion-Adsorption-Type Rare Earth Ores

Fine particle content significantly affects the in situ leaching of ion-adsorption-type rare earth ores. This study investigated the effect of fine particle content on solution flow and mass transfer in leaching. The results showed that with the increase in fine particle content, the peak concentration and peak time of rare earth increased. When the fine particle content exceeded 20%, all ion-exchangeable-phase rare earth ions could be replaced with a low dosage of the leaching solution. The leachate flow rate exhibited multi-stage variation, influenced by solution permeation, ion exchange, and fluctuations in accumulated liquid height. A mass transfer analysis showed that a higher fine particle content corresponded to a smaller plate height and a larger plate number of theoretical plates. As fine particle content increased, the final rising height of capillary water decreased, with rising rates varying across different stages for the samples. Moreover, an increase in fine particle content from 5% to 20% resulted in a 94% decrease in the samples’ permeability coefficients. A mechanism analysis showed that when the fine particle content was higher, the fine particles were embedded in the gaps between coarse particles, and the ore particles in the sample were arranged continuously, resulting in a lower permeability coefficient. Then, the leaching solution could penetrate uniformly, which was beneficial for reducing leaching blind spots and improving leaching efficiency. However, excessive fine particle content might have detrimental effects. Based on these results and considering actual mining conditions, the optimal fine particle content for rare earth leaching is 20%.

Efficient extraction of rare earth elements from coal-series kaolin by combining alkali fusion and sulfamic acid leaching

As a solid waste produced by coal mining, the comprehensive utilization of coal-series kaolin is the focus of attention. In this paper, the extraction of rare earth elements (REEs) from coal-series kaolin was carried out by alkali fusion and sulfamic acid leaching. The occurrence modes of REEs in coal-series kaolin was analyzed by means of inductively coupled plasma-mass spectrometry analyse and sequential chemical extraction. The influence of alkali fusion conditions on the leaching of REEs was investigated, and the activation mechanism of alkali fusion was revealed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and field emission scanning electron microscope (FESEM) analysis. In addition, the effect of key operating parameters on the leaching efficiency of REEs from coal-series kaolin was further investigated. The results show that REEs mainly existed in silicate & aluminosilicate state of coal-series kaolin. The mineral structure was destroyed by alkali fusion, and the leaching efficiency of REEs was increased by 59.08 %. At the sulfamic acid concentration of 0.5 mol/L, H2O2 concentration of 0.2 mol/L, solid to liquid ratio of 1/50, the leaching efficiencies of total rare earth elements, light rare earth elements and heavy rare earth elements were 84.91 %, 88.43 % and 71.03 %, respectively.

Leaching process assisted by cetyltrimethylammonium chloride for weathered crust elution-deposited rare earth ores: Leaching behavior, kinetic analysis and interfacial regulation

Magnesium salts are commonly employed as ammonium-free leaching agents in the extraction of weathered crust elution-deposited rare earth ores (WCE-REO). Nonetheless, these salts frequently face technical challenges, including relatively low leaching rates and inadequate permeability in the in-situ leaching process. In this study, cetyltrimethylammonium chloride (CTAC) was used as a novel leaching aid agent to improve the rare earth leaching process. The effects of CTAC and pH on the rare earth leaching behavior and permeability was investigated. The leaching kinetic model was established and the regulation mechanism by which CTAC interacts with clay mineral surfaces was revealed for rare earth leaching process enhanced by CTAC. The results indicate that the appropriate amount of CTAC can increase the permeation velocity by 1.16×10−4 cm·s−1. Moreover, the rare earth leaching rate increased from 83.75 % to 95.65 %, accompanied by a reduction in leaching equilibrium time under optimal conditions. However, a higher concentration of CTAC results in a lower permeation velocity due to the increasing viscosity and the hydrophilicity. The relatively low pH will affect permeability of composite leaching agent in the ore pillar, diminishing its beneficial impact on rare earth leaching. The kinetic equation, fitted by the shrinking core model, suggests that the leaching adheres to an internal diffusion control mechanism, underscoring mass transfer as the pivotal limiting factor in rare earth leaching. CTAC reduces surface tension and viscosity, facilitating the permeation of the leaching solution into the rare earth ore. Furthermore, CTAC can be adsorbed on the surface of rare earth mineral particles, increasing the contact angle of clay minerals, elevating the Zeta potential, and diminishing the thickness of the diffusion layer, thus promoting mass transfer during leaching. The results of atomic force microscopy (AFM) analysis shows that the appropriate amount of CTAC adsorbed on rare earth ores can decreases the thickness of the hydration film on the particles’ surface, further improving the mass transfer efficiency during the leaching process. The findings of this study offer new insights into the green and efficient extraction of rare earth resources from both theoretical and technical perspectives.

Hydrochloric acid leaching of rare earth elements from a novel source of deep-sea sediments and advantage of reduction with H2O2

In this study, the mineralogy of a novel resource of deep-sea sediments containing rare earth elements (REEs) was investigated, along with the leaching of REEs using hydrochloric acid. The results revealed that, apart from 62.0% of the Ce found in the Mn oxides, the other REEs in the deep-sea sediments mostly existed in hydroxyapatite mineral which can be easily decomposed via a hydrochloric acid leaching. An optimized REEs leaching percentage of 89.5% was achieved using 2.0 mol/L hydrochloric acid as the leaching agent, with a liquid-solid ratio of 4:1, at 60 °C for 30 min. However, Mn oxides remained stable during the leaching process, resulting in a low Ce leaching percentage of 30.7%. Under the optimized conditions, Mn oxides could be decomposed by adding 30% H2O2 as a reducing agent, leading to improved leaching percentages of Ce and REEs to 86.6% and 93.2%, respectively. The high leaching efficiency of REEs may further increase the utilization potential of this novel resource.

Study on the role of microbial metabolites in in-situ noncontact bioleaching of ion-adsorption rare earth ore

Ion adsorption rare earth ore nearly satisfy global market demand for heavy rare earth elements (HREEs). Bio-leaching has important potential for the clean and efficient extraction of ion-adsorption rare earth ore. However, the complexities of in-situ mining restrict the use of contact/direct bio-leaching, and non-contact/indirect bio-leaching would be the best choice. This study explore the potential of fermentation broths prepared by Yarrowia lipolytica (ATCC 30162) for the bio-leaching of ion-adsorption rare earth ore, and three typical metabolites (potassium citrate (K3Cit), sodium citrate (Na3Cit) and ammonium citrate ((NH4)3Cit) of Yarrowia lipolytica were further evaluated in simulated bioleaching (non-contact bioleaching) of ion-adsorption rare earth ore, including leaching behavior, seepage rule and rare earth elements (REEs) morphological transformation. The column leaching experiments shown that direct leaching of REEs using fermentation broths results in incomplete leaching of REEs due to the influence of impurities. Using the purified and prepared metabolites as lixiviant, REEs can be effectively extracted (leaching efficiency >90%) at cation concentration was only 10 % of the commonly used ammonium sulfate concentration (45 mM). Cation type had less effect on leaching efficiency. During the ion-adsorption rare earth ore leaching process, rare earth ions form a variety of complex chelates with citrate, thus transferring rare earth elements from the mineral surface to the leachate. Experimental results showed that pH and concentration together determined the type and form of rare earth chelates, which in turn affect the leaching behavior of REEs and solution seepage rule. This study helps to provide a theoretical basis for the regulation and enhancement of ion-adsorption rare earth ore non-contact bioleaching process.

Highly efficient preparation of crystalline yttrium carbonate in sodium carbonate system: Formation and growth mechanism

The recovery of rare earths from industrial rare earth leaching solution is typically achieved through the ammonium carbonate precipitation method, which presents challenges in terms of prolonged production cycle and ammonia nitrogen pollution. The present study explored the synthesis of crystalline yttrium carbonate in a sodium carbonate system, employing a conventional mother liquor derived from yttrium chloride. The growth of yttrium carbonate was explored through the lens of density functional theory (DFT) calculations, unveiling a novel perspective on its formation mechanism. The synthesized yttrium carbonate demonstrates enhanced crystallinity, with a D50 value of 19.75 μm achieved under reaction conditions comprising a temperature of 60 °C, stirring rate of 200 r/min, feeding rate of 4 mL/min, and aging time of 30 h. The molar ratio for precipitation is set at 1.6:1. The morphology of yttrium carbonate undergoes a transition from needle-like structures to sheet-like formations, ultimately culminating in the formation of spherical aggregates. The variation in surface energy among distinct crystal planes and CO32– configurations within crystal cells accounts for this phenomenon. The DFT calculations unveil a progression of growth and transformation in yttrium carbonate, commencing from a one-dimensional configuration and culminating in a multidimensional morphology.

Mass balance and economic study of a treatment chain for rare earths, base metals and precious metals recovery from used smartphones

In the present study, a comprehensive hydrometallurgical process was developed for the recovery of several types of metals from used cell phone printed circuit board assemblies. The overall process is divided into four stages of selective leaching of rare earth elements (REE), copper, nickel, silver and finally gold. After solubilization, the metals were purified using precipitation, solvent extraction, electrodeposition, and cementation techniques. Laboratory pilot-scale tests of the complete smart phone printed circuit board processing line showed REE, copper, nickel, silver, and gold recovery efficiencies of 78.0 %, 98.8 %, 81.8 %, 100 % and 96.1 %, respectively. The purity of the products obtained is evaluated at 94.8 % for rare earth oxides (70.0 % Nd2O3, 18.5 % Pr2O3, 2.8 % Dy2O3 and 2.4 % Sm2O3), 99.8 % for elemental copper, 94.3 % for nickel oxide, 93.8 % for silver and 89.3 % for gold. A scenario involving the installation of a plant processing 1 t/h of waste was evaluated using SuperPro Designer software. For a total investment of $53.22 million and an operating cost of $18.23 million per year, the main revenue is $65.77 million per year, with a return on investment of 91.6 % and a payback period of 1.1 years.

Comparison of Microwave and Conventional Roasting in the Leaching of Rare Earth Elements, V, Ni, and Li from Polymetallic Black Shale

Comparison of Microwave and Conventional Roasting in the Leaching of Rare Earth Elements, V, Ni, and Li from Polymetallic Black Shale

Selective leaching and recovery of rare earth from NdFeB waste through a superior selective and stable deep eutectic solvent

The recovery of rare earth elements (REEs) from NdFeB waste is crucial for advanced industrial development. The green and superior selective recovery methods can effectively avoid the problem of generating large amounts of wastewater and high pollution in the NdFeB waste recycling process. In this work, a novel deep eutectic solvent (DES) synthesized by tetraethylammonium chloride (TEAC) and levulinic acid (LA) was designed and achieved selective leaching of REEs from NdFeB waste without wastewater produced. The leaching ratio of Nd can reach up to 97.63 %, while Fe is less than 0.435 %, the separation factor can exceed 9000, and the purity of the obtained product Nd2O3 is 99.649 %. In addition, the solubility of Nd2O3 in TEAC-LA is over 75.6 g/L, the thermal stability temperature reaches 132.4 °C much higher than the working temperature, and the viscosity is 12.8 cP at the working temperature which is close to prevalent organic solvents. After three cycles, TEAC-LA still maintains its original selective leaching ability and shows excellent thermal stability. This study provides a superior selective and stable method for green and efficient recycling of NdFeB waste.

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.

Study on the adsorption/desorption characteristics and dynamic diffusion mechanism of rare earth hydrated ions on the kaolinite (001) surface

Coal gangue (CG) contains abundant rare earth elements (REEs), which is a potential REE resource. REEs are mainly present in clay minerals as hydrates. The adsorption, desorption, and diffusion of REEs-hydrates on the surface of clay minerals are the key to regulating the leaching effect of REEs. The paper focuses on the typical clay minerals kaolinite and REEs-hydrates and combines quantum mechanics and molecular dynamics methods to systematically study the adsorption, desorption, and dynamic diffusion behavior of REEs-hydrates in acid solution. The research results indicate that stable REEs-hydrates La(H2O)9 and Y(H2O)7 are formed, with ion bonds between REEs and water molecules. La(H2O)9 and Y(H2O)7 mainly interact with the kaolinite (001) surface through hydrogen bonding. Competitive adsorption is formed between water molecules, hydrated hydrogen ions, and REEs-hydrates. Water molecules and hydrated hydrogen ions occupy the adsorption active sites of REEs-hydrates and form a dense water molecular layer on the surface. The distance between H3O+ and REEs-hydrates and the number of H3O+ in the solvent layer affect the desorption and diffusion behavior of hydrates. The bonding law, dynamic desorption, and diffusion mechanism of REEs-hydrates can provide meaningful references for selective leaching of REEs from CG.