Rare Earth Resources Research Articles

Fabrication of core-shell structured Fe3O4@amide humic acid magnetic nanoparticles and their highly efficient adsorption for La (III)

ABSTRACT The enhancement and removal of rare earth ions from wastewater resources have emerged as a crucial study to ensure the superior quality of rare earth resources application. In this work, amide humic acid-coated Fe3O4 magnetic nanoparticles (Fe3O4@AHA MNPs) were fabricated by chemical coprecipitation hydrothermal technique. The fabricated nanoparticles showed excellent stability in aqueous solutions. They could be easily collected from solutions using a magnetic separation strategy. Adsorption studies were used to investigate the adsorption performance of Fe3O4@AHA MNPs for La (III) under a variety of circumstances. Furthermore, isothermal adsorption lines and kinetic and thermodynamic modeling were used to examine the adsorption mechanism of La (III). Results revealed that Fe3O4@AHA MNPs had a high adsorption capacity of 148.83 mg g−1 and adsorption equilibrium was attained after 45 min when the adsorbent dose was 20 mg at pH 6. Fe3O4@AHA MNPs demonstrated high reusability for La (III), retaining 78.5% of initial adsorption capability after five cycles. Finally, the fabricated Fe3O4@AHA MNPs was successfully employed and applied to remove La (III) from industrial wastewater samples. According to these results, the Fe3O4@AHA MNPs have potential to be a useful material for enrichment and preconcentration of La (III) or other trivalent lanthanides from wastewater.

Leaching of rare earth elements from phosphogypsum via citric acid medium: optimization through central composite design and kinetics studies.

Due to limited resources of rare earth elements (REEs) and their high demand, these are subjected to supply constraints. So it is important to recover REEs from potential secondary resources. Phosphogypsum is the waste generated on an enormous scale (300 million metric tons per year) from the fertilizer industry. It contains valuable REEs and its disposal has become a major environmental issue. The aim of this research work is to optimize the leaching parameters and determine the kinetics of leaching of REEs from phosphogypsum waste using citric acid. Response surface methodology (RSM) through central composite design (CCD) has been used to assess the influence of three key input variables, i.e., leachant concentration, temperature, and leaching time on the dissolution efficiency of REEs. The results of regression analysis and response surface plots revealed that with the increase in citric acid concentration as well as leaching time, the dissolution ratio of REEs would increase significantly. Under the optimum leaching conditions of 2mol/L citric acid, 343K temperature, and leaching duration of 180min, 90.11% dissolution efficiency was achieved. The kinetics of the leaching was elucidated with the use of shrinking sphere model and was found to be diffusion-controlled. This shows that the high leaching of REEs under moderate conditions is attainable, offering eco-friendly citric acid as a substitute to recover these critical elements from PG waste. The present work tends to develop efficient leaching protocols for the recovery of REEs, which are indispensable raw materials in numerous technological applications.

Coal as a non-conventional resource of Rare Earth Elements (REEs) and Trace Elements: Benefits and Impacts on Environment and Human Health - A Review

Coal as a non-conventional resource of Rare Earth Elements (REEs) and Trace Elements: Benefits and Impacts on Environment and Human Health - A Review

Geochemical exploration of rare earth element resources in highland karstic bauxite deposits in the Sierra de Bahoruco, Pedernales Province, Southwestern Dominican Republic.

This study investigates the geochemical characteristics of rare earth elements (REEs) in highland karstic bauxite deposits located in the Sierra de Bahoruco, Pedernales Province, Dominican Republic. These deposits, formed through intense weathering of volcanic material, represent a potentially valuable REE resource for the nation. Surface and subsurface soil samples were analyzed using portable X-ray fluorescence (pXRF) and a NixPro 2 color sensor validated with inductively coupled plasma optical emission spectrometry (ICP-OES). We employed compositional data analysis (CoDA) and machine learning models to estimate total REE concentrations, demonstrating that pXRF and the color sensor, when properly calibrated, are effective tools for remote geochemical exploration. The results reveal that REE concentrations increase with depth and elevation, with light REEs (LREEs) dominating the profiles. The correlation of REE concentrations with morphological soil development suggests that higher-altitude areas are enriched in REEs due to progressive weathering processes. The study also shows a strong relationship between REE concentrations and environmental factors such as latitude and elevation. While pXRF provided reliable estimates of total REE concentrations, to our surprise, the NixPro2 color sensor proved similarly accurate. The research emphasizes the practical value of the x-ray and color sensors for remote exploration, provided that a well-explored, robust calibration is performed to account for site-specific variability. These findings contribute to understanding the geochemical distribution of REEs in karstic bauxite deposits and highlight the potential for further exploration in remote, high-altitude regions. Future research should explore using these and other portable sensors, singly or combined, to predict REE speciation, for expediting information related to the environmentally sustainable extractability and potential economic feasibility of resources in expeditionary locations.

A stable method for ionic rare earth element extraction and quantitative analysis of total quantity and composition of batch samples.

The development of a stable, high-precision and batch ion-adsorption rare earth element detection method is highly anticipated in the delineation and evaluation of the mining value of rare earth element mines. In this study, a novel mixed extractant of ammonium sulfate + ammonium citrate + aceto-sodium acetate buffer was used to significantly improve the extraction efficiency of rare earth elements. Following a series of parameter optimizations, an off-line internal standard addition method and the collision mode of the inductively coupled plasma-mass spectrometer were used to improve the detection efficiency for batch samples, effectively eliminating oxide interference between the rare earth elements and improving the detection accuracy. The detection limit for ion-adsorption rare earth elements was 3.4 μg g-1 and the detection range was 12-8000 μg g-1. More importantly, the spiked and recovery experiments carried out in multiple laboratories with internal quality control samples show that the relative deviation was -5.61 to 3.79%, which indicates that the method has sufficient stability. Establishment of this method will help to improve the comprehensive utilization efficiency of rare earth resources and provide important support for rare earth element mining.

Electrochemical reduction method for leaching terbium and cerium from waste phosphors.

Rare earth elements are commonly used in various fields due to their unique physical and chemical properties. Waste phosphors represent an important secondary source of rare earth elements, and their recovery is a crucial means of improving the utilization of these resources. When using FeCl2 as a reducing agent to reduce Tb4+ and Ce4+ from washed phosphors, a large amount of reducing agent is required, and the Fe2+ cycle becomes complicated. In this study, the electrochemical reduction process was employed to treat washed phosphors. Under optimum conditions of FeCl2 concentration of 0.10 mol L-1, current density of 100 A m-2, HCl concentration of 3 mol L-1, temperature of 80 °C, L/S ratio of 30 mL g-1, and time of 60 min, the leaching efficiencies of Tb and Ce reached 99.2% and 98.5%, respectively. The apparent activation energies of Tb and Ce were calculated as 17.71 and 18.46 kJ mol-1, respectively, illustrating that the leaching processes of Tb and Ce depend on the diffusion. By applying an external electric field, Fe2+ can be recycled in the system, thereby reducing the amount of reducing agent needed and achieving a higher leaching efficiency for Tb and Ce. These results are beneficial for the resource utilization of waste phosphors and have significant implications for the sustainable development of rare earth resources.

Rare earth element (REE) speciation in municipal solid waste incineration ash

A robust and sustainable supply of rare earth elements (REE) is critically needed for clean-energy technologies, which has stimulated substantial interests in REE recovery from waste streams. Municipal solid waste incineration ash (MSWIA) was recently recognized as a potentially important REE resource, yet REE speciation in MSWIA remains poorly understood. This study employed synchrotron X-ray spectroscopy and microscopy techniques to elucidate the speciation of representative REE (Y, Ce, and Nd) in different MSWIA samples. Linear combination fitting of bulk X-ray absorption near edge structure (XANES) data indicated that Y-bearing Al/Fe oxides and phosphates are the primary Y-hosting phases. Micro-XANES of individual Y-containing particles identified by micro X-ray fluorescence (μXRF) mapping revealed notably different Y speciation at micro-scale from the bulk, consistent with the highly heterogeneous nature of MSWIA samples. The main REE-bearing phases in different size-fractionated MSWIA are similar: Y and Nd as oxides and xenotime/monazite, and Ce as apatite and monazite. Our results provide important insights for designing pre-screening processes (e.g., density separation) and optimizing extraction methods (e.g., pH, use of ligands) for cost-effective REE recovery from MSWIA.

A 35-Year Analysis of Vegetation Cover in Rare-Earth Mining Areas Using Landsat Data

Fractional vegetation cover (FVC) plays a significant role in assessing ecological quality and protection, as well as soil and water conservation. As a typical rare-earth resource county in China, Dingnan County has experienced rapid development due to rare-earth mining, resulting in significant alterations to vegetation cover. To elucidate the spatio-temporal changes in vegetation within Dingnan County over the past 35 years and the effects of natural and human factors on these changes, the spatial and temporal variations in FVC were analyzed using Landsat-TM/OLI multispectral images taken in 1988, 1995, 1997, 2002, 2006, 2013, 2017, and 2023. The findings indicate that (1) vegetation coverage in Dingnan County decreased from 1988 to 2002, followed by a gradual increase; (2) high vegetation cover is predominantly found in forested areas that maintain their natural state, while the central town and mining areas exhibit generally low coverage; (3) there are regional differences in the relationship between vegetation cover and environmental factors in Dingnan County. This research facilitates the alignment of ion-type rare-earth mining with ecological protection, thereby promoting the sustainable development of the mining area and providing scientific guidance for local governments to formulate more effective management and protection strategies for the mining ecosystem. Additionally, this research offers a scientific foundation for mining areas globally to develop sustainable policies and informed decision-making regarding environmental protection and sustainable development.

High-abundant rare earth La/Ce substituted Nd2Fe14C based permanent magnet materials prepared by mechanochemical method

To balance the utilization of rare-earth resources and reduce the preparation cost, the La and Ce substituted Nd2Fe14C hard magnetic alloys were prepared by a facile mechanochemical method for the first time. A two-step process is typically employed: 1) Decomposition of hydrocarbon and disproportionation of (Nd1-xREx)2.5Fe14B0.08 (RE=La or Ce, x=0–0.3) alloys during high-energy ball milling, Nd+Nd2Fe17+n-hexane→NdH2+δ+α-Fe+Fe7C3; 2) (Nd, RE)2Fe14C hard magnetic powders were obtained via the vacuum annealing at 800 °C for 2 min. The phase relation, magnetic properties and microstructural evolution of (Nd, RE)2Fe14B0.08C0.92 (named Nd-RE-Fe-C-based) alloys were systematically investigated. Substitution of La for x=0.1 Nd in the Nd-RE-Fe-C-based alloy increase the coercivity from 15.6 kOe to 18.6 kOe without reducing the remanence. First-principles calculation was performed to study the mechanism of magnetic properties La and Ce substituted samples. The results showed that La tends to be expelled from 2:14:1 phase to form more minor phases which act as the domain wall pinning center, increasing the coercivity. However, Ce prefers to enter the 2:14:1 phase, diminishing the permanent magnetic properties due to the poor intrinsic magnetic properties. This paper provides a novel viewpoint for the effective utilization of high abundant rare earth and the investigation of low cost Nd2Fe14C permanent magnet materials.

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).

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).

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.

Recycling impacts of renewable energy generation-related rare earth resources: A SWOT-based strategical analysis

As the global energy mix transforms and renewable energy technologies rapidly develop, there has been a significant increase in the demand for rare earth elements, which play a crucial role in renewable energy systems. By recycling rare earth resources from obsolete equipment, the reliance on newly mined rare earth resources can be reduced, thereby reducing the related environmental and energy footprints and increasing the stability of the supply chain. This study aims to systematically and strategically analyze and discuss the recycling impacts of renewable energy generation (REG)-related rare earth resources in terms of environmental, economic, social, and governance aspects. A SWOT strategical analysis framework integrating a management cycle and intelligent text data mining is built to address the above tasks from an ESG (Environment, Society, and Governance) perspective. The SWOT analysis of the rare earth recycling impacts focuses on strengths (e.g., reduced dependence on rare resources, reduced environmental and emission pressure), weaknesses (e.g., high cost, technology and management complexity), opportunities (e.g., policy support, technological innovations, diversification of the global supply chain), and threats (e.g., market volatility, the emergence of alternative materials). This analysis framework reveals textual topic changes and suggests cyclic and strategical improvement pathways to analyze the multi-dimensional recycling impacts. The text data analysis results indicate that the trend of rare earth recycling is gradually transformed from technologies, supply and demand, and secondary resources into resource and environment sustainable development. Beyond overcoming identified challenges, future pathways should focus more on the integration of advanced emerging technologies, life cycle management, and dynamic adjustment of recycling strategies. This study could provide policymakers and industry practitioners with recommendations and outlook on current development status and improvement strategies to promote REG-related rare earth recycling.

Multicolor luminescent rare-earth-free glass ceramic for thermal information indication

Temperature-dependent multicolor luminescent materials are widely used in optical temperature sensing and related applications. However, most of these materials derive their luminescence from the radiation transition of rare earth (RE) ions. Therefore, the development of RE-free luminescent materials is of great significance for RE resources and environmental protection. Here, we propose a novel RE-free multicolor luminescent glass-ceramic (GC) and offer a color regulation strategy for defect-induced luminescence. As the temperature rises, thermal expansion alters the state of the defects, causing the emission color to gradually shift from cyan-green to dark blue. This color shift is reversible, returning to the original color as the temperature decreases. Moreover, the GC retains 97.2 % of its luminescence intensity after being submerged in water for one year, highlighting its excellent physicochemical stability. A pattern label prepared by this GC, exhibits excellent luminescent color-temperature response, indicating its potential application in high-temperature information indication.

Quantitatively characterization of rare earth ore by terahertz time-domain spectroscopy

The Bayan Obo deposit is the world’s largest polymetallic associated minerals deposit of rare earths, iron and niobium, and the rarity of its physical properties restrict the knowledge and understanding of its laws. Taking the high-grade mixed rare earth concentrate of Bayan Obo as the research object, terahertz time-domain spectroscopy (THz-TDS) has been adopted for the systematic investigation of high-grade rare earth concentrate base on the traditional X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric-differential thermal analysis (TG-DTA). The absorption coefficient and refractive index of high-grade rare earth ores and their associated minerals of fluorite and dolomite, are all investigated by terahertz time-domain spectroscopy. The terahertz spectral response is affected by the type of mineral and its content. The acquired rare earth terahertz spectral data are processed by correlation analysis. Three machine learning algorithms, Partial Least Squares Regression (PLSR), Random forest (RF) and Multilayer Perceptron (MLP), are used to achieve quantitative detection of their concentrations and components with the coefficient of determination R2 of the absorption coefficient of the optical parameter reaching up to 0.975, 0.992 and 0.984, respectively. This work promotes the growing understanding of terahertz transmission spectroscopy of rare earth-bearing minerals, which can be used to help guide the search for minerals, and to detect, identify as well as quantify them in geology. Terahertz time-domain spectroscopy supplies a new method for study of rare earth resources, and the comprehensive development and utilization of resources in the Bayan Obo deposit.

Analytical Techniques for Detecting Rare Earth Elements in Geological Ores: Laser-Induced Breakdown Spectroscopy (LIBS), MFA-LIBS, Thermal LIBS, Laser Ablation Time-of-Flight Mass Spectrometry, Energy-Dispersive X-ray Spectroscopy, Energy-Dispersive X-ray Fluorescence Spectrometer, and Inductively Coupled Plasma Optical Emission Spectroscopy

Rare earth elements (REEs) hold significant industrial, scientific, and modern technological worth. This study focused on detecting and quantifying REEs in various geological ore samples. These samples were collected from different REE-bearing locations recommended by geological experts. The analysis was conducted using laser-induced breakdown spectroscopy (LIBS) and laser ablation time-of-flight mass spectrometry (LA-TOF-MS). In this work, LIBS methodology was employed using three different configurations: standard LIBS, LIBS with an applied magnetic field, and LIBS with both an applied magnetic field and target sample heating within an optimal temperature range. Elements from the REE group, specifically lanthanum (La), cerium (Ce), and neodymium (Nd), were identified and quantified. To detect, quantify, and validate the results from LIBS and LA-TOF-MS, we utilized an array of analytical techniques—Energy-Dispersive X-ray Spectroscopy (EDX), Energy-Dispersive X-ray Fluorescence Spectrometer (ED-XRF), and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Interestingly, the quantitative results for REEs (La, Ce, and Nd) in the ore samples obtained using the LIBS technique with various configurations were found to be in agreement with those from LA-TOF-MS, EDX, XRF, and ICP-OES. In addition, LIBS enables detailed microchemical imaging, allowing the map of the spatial distribution of elements within the mineral–ore matrix. The high-resolution microscale elemental mapping of REEs was accomplished using the emission lines Ce (II) at 446.0 nm, La (II) at 492.1 nm, and Nd (II) at 388.8 nm. By integrating multiple analytical techniques, our study enabled the construction of a complete elemental distribution map, providing new insights into the geochemical processes and mineral composition of rare earth ores, while advancing geochemistry and contributing valuable data for rare earth resource exploration.

Rare earth elements enrichment and extraction potential of bauxite deposits in Samar, Philippines

Abstract Rare earth elements (REE) play an integral part of modern life, from smartphones to satellites. Dubbed ‘critical metals’, the demand for REE has significantly increased, driven by the growth in global production for green technologies such as e-vehicles, solar panels, wind turbines, and other energy-economic infrastructure. Therefore, there is a need to explore alternative REE sources to ensure continued development of emerging green technologies. A possible alternative REE source is bauxite, which is soil that forms from intense weathering of aluminum oxide-rich rocks exposed to tropical climate. This paper investigates the REE enrichment and extraction potential from bauxite deposits in Paranas, Samar, Philippines. The sampling survey included collection of rock and soil on surface exposures, test pits, and drill cores from accessible portions of the bauxite mineral reservation site. The soil and parent rock samples collected were then subjected to various geochemical and mineralogical analyses. The main ore minerals of aluminum are gibbsite and boehmite; with minor goethite, hematite, and magnetite. Investigation of the geochemical composition of the bauxite reveals a total REE content of up to ~300 ppm, which is one of the highest REE and critical metal content among geological deposits in the country. These results will provide inputs in the design of a green and economical process to recover REE from bauxites. If the bauxite deposits prove to be a valuable REE resource, this study will help maximize the economic potential of the mineral resource in the Philippines and contribute to an economically efficient and environment-friendly way to produce e-tech elements for the country.

Simultaneous preparation of high-purity Si and eutectic Si-Nd alloy utilizing Nd2O3-containing waste slag and diamond-wire sawing silicon waste

Nd2O3-containing waste slag (NCWS) and diamond-wire sawing silicon waste (DSSW) are important rare earth and Si secondary resources, respectively. Currently, NCWS and DSSW are recycled respectively by at least two different routes, which is not efficient and increases the burden on the environment. The present study proposed a novel technical route for preparing high-purity bulk Si and eutectic Si-Nd alloy simultaneously using NCWS and DSSW as raw materials, depending on the concept of using waste to treat waste. The new technical route has only two steps: initially, raw Si-Nd alloys were obtained by extracting Nd from NCWS utilizing DSSW as a low-cost reductant, and the impurity, oxygen, in the DSSW was effectively removed utilizing NCWS; the highest extraction rate of Nd from NCWS reached 68.3%, and the oxygen removal rate in DSSW was 99.89%; in the subsequent step, the obtained raw Si-Nd alloys were separated and purified to produce high-purity bulk Si (＞99.98%) and eutectic Si-Nd alloy (＞99%) through a physical and clean method-electromagnetic directional crystallization. This novel route is considered effective and environmentally-friendly for the sustainability of rare earth and Si resources, because no gas and liquid wastes discharged throughout the whole route, and two high value products can be prepared simultaneously using two wastes.

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.

Recovering rare earth elements from svanbergite ores by roasting and phosphoric acid leaching

Rare earth elements (REEs) are regarded as key global strategic metals, and recovering REEs from phosphate ores might constitute an alternative method of acquiring rare earth resources. Svanbergite ores in Sichuan are particular phosphates rocks that contain abundant REEs, which are valuable resources that have not been fully developed and utilized. Consequently, the development of crucial technologies for extracting REEs from svanbergite ores hold strategic and scientific significance. This study employed roasting and phosphoric acid leaching processes to recover REEs from svanbergite ores. Response surface methodology (RSM) was applied to optimize the hydrometallurgical process parameters. This study found that the optimal conditions for REEs recovery were: a roasting temperature 600℃, a roasting time of 38.72 min, a phosphoric acid concentration of 40%, a leaching liquid/solid mass ratio of 10, a leaching temperature of 75℃ and a leaching time of 70 min, resulting in a maximum predicted REE recovery rate of 83.57%. The experimental values exhibited a high degree of proximity to the predicted values, thereby substantiating the accuracy of the model and validating the plausibility of the optimized solution. Mechanistic analysis revealed that after the roasting process, the crandallite formed new acid-soluble new phases. Following the phosphoric acid leaching process, REEs were present predominantly in the form of REE3+ in the leaching solution, consequently separating the REEs from the svanbergite ores. This study provides a valuable reference for the recovery of REEs from associated rare earth phosphate ores.