Rare Earth Resources Research Articles

Organic Ligand-Mediated Dissolution and Fractionation of Rare-Earth Elements (REEs) from Carbonate and Phosphate Minerals.

Global efforts to build a net-zero economy and the irreplaceable roles of rare-earth elements (REEs) in low-carbon technologies urge the understanding of REE occurrence in natural deposits, discovery of alternative REE resources, and development of green extraction technologies. Advancement in these directions requires comprehensive knowledge on geochemical behaviors of REEs in the presence of naturally prevalent organic ligands, yet much remains unknown about organic ligand-mediated REE mobilization/fractionation and related mechanisms. Herein, we investigated REE mobilization from representative host minerals induced by three representative organic ligands: oxalate, citrate, and the siderophore desferrioxamine B (DFOB). Reaction pH conditions were selected to isolate the ligand-complexation effect versus proton dissolution. The presence of these organic ligands displayed varied impacts, with REE dissolution remarkably enhanced by citrate, mildly promoted by DFOB, and showing divergent effects in the presence of oxalate, depending on the mineral type and reaction pH. Thermodynamic modeling indicates the dominant presence of REE-ligand complexes under studied conditions and suggests ligand-promoted REE dissolution to be the dominant mechanism, consistent with experimental data. In addition, REE dissolution mediated by these ligands exhibited a distinct fractionation toward heavy REE (HREE) enrichment in the solution phase, which can be mainly attributed to the formation of thermodynamically predicted more stable HREE-ligand complexes. The combined thermodynamic modeling and experimental approach provides a framework for the systematic investigation of REE mobilization, distribution, and fractionation in the presence of organic ligands in natural systems and for the design of green extraction technologies.

Optimized combination of room-temperature formability and high-temperature creep property in a dilute-alloyed Mg sheet via tailoring Nd solute segregation

The synergy of room-temperature formability and high-temperature creep property has been a long-term problem in the manufacturing of Mg alloy sheets. Aiming at saving rare-earth resource and providing a widely applicable approach to realize the synergy, this study focuses on the effects of preparation conditions on these two properties in Mg alloyed by dilute Nd (0.8 % in weight percent). Through comparing the mechanical behaviors of the samples prepared by different treatments, including low-temperature and long-time solution (Sample #1), high-temperature and short-time solution (Sample #2), and hot deformation for grain refinement (Sample #3), the best combination of stretch formability and creep property was successfully achieved in the Sample #1. The key reason was the conspicuous Nd solute segregation along grain boundaries after solution treated under the low-temperature and long-time condition. Such segregation behavior allowed dislocations moving freely in grain interiors but inhibited dislocations moving across grain boundaries. Finally, the stretch formability related to free dislocation slip in grain interiors and the creep property related to strong grain boundaries were synchronously enhanced. Thus, the low-temperature and long-time solution treatment is recommended for developing dilute Mg–Nd based alloy sheet used in the environment of alternating temperature changes.

Cerium oxide and neodymium oxide phytoextraction by ryegrass in bioenhanced hydroponic environments

Sustainable technologies for the recovery of rare earth elements (REE) from waste need to be developed to decrease the volume of ore mining extractions and its negative environmental consequences, while simultaneously restoring previously impacted lands. This is critical due to the extensive application of REE in everyday life from electronic devices to energy and medical technologies, and the dispersed distribution of REE resources in the world. REE recovery by plants has been previously studied but the feasibility of REE phytoextraction from a poorly soluble solid phase (i.e., nanoparticles) by different plant species has been rarely investigated. In this study, the effect of biostimulation and bioaugmentation on phytorecovery of REE nanoparticles (REE-NP) was investigated by exposing ryegrass seeds to REE-NP in hydroponic environments. This was studied in two sets of experiments: bioaugmentation (using CeO2 nanoparticles and Methylobacterium extorquens AM1 pure culture), and biostimulation (using CeO2 or Nd2O3 nanoparticles and endogenous microorganisms). Addition of M. extorquens AM1 in bioaugmentation experiment including 500 mg/L CeO2 nanoparticles could not promote the nanoparticles accumulation in both natural and surface-sterilized treatments. However, it enhanced the translocation of Ce from roots to shoots in sterile samples. Moreover, another REE-utilizing bacterium, Bacillus subtilis, was enriched more than M. extorquens in control samples (no M. extorquens AM1), and associated with 52% and 14% higher Ce extraction in both natural (165 μg/gdried-plant) and surface-sterilized samples (136 μg/gdried-plant), respectively; showing the superior effect of endogenous microorganisms’ enrichment over bioaugmentation in this experiment. In the biostimulation experiments, up to 705 μg/gdried-plant Ce and 19,641 μg/gdried-plant Nd could be extracted when 500 mg/L REE-NP were added. Furthermore, SEM-EDS analysis of the surface and longitudinal cross-sections of roots in Nd2O3 treatments confirmed surface and intracellular accumulation of Nd2O3-NP. These results demonstrate stimulation of endogenous microbial community can lead to an enhanced REE phytoaccumulation.

An experimental study on the role of F−, PO43−, Cl− and SO42− ligands in the natrocarbonatite-nephelinite system at 850 °C and 0.1 GPa

Carbonatites and their comagmatic silicate rocks related deposit provide significant resources of rare earth elements (REEs), niobium (Nb) and other elements such as U, Th, Mo, V, Ba, Sr, etc. However, the genesis of mineralization, especially for REEs and Nb, in carbonatite remains enigmatic. Previous liquid immiscibility experiments have demonstrated that both REEs and Nb are preferentially enriched in the silicate conjugate instead of carbonate melts under anhydrous conditions. Nevertheless, ligands other than carbonate ion appear to be abundant due to ubiquity of apatite, baryte, celestine, fluorite and sodalite in carbonate–silicate magmatic systems. Here, we experimentally investigate the trace element partitioning between natrocarbonate and silicate (nephelinite) melts in systems doped with varying amounts of additional F−, PO43−, Cl−, and SO42− ligands (0, 2, 4 and 6 wt%) to understand and constrain the role of ligands.The experiments were conducted at 850 °C and 0.1 GPa using rapid quench cold-seal pressure vessels (CSPVs). A comparison of experimental partition coefficients in this study reveals that the significant amounts F− and PO43− incorporated in the silicate melts can increase the D values for REE by influencing melt structure (DLaCM/SM = 0.85–7.42). In contrast, irrespective of the amount of added Cl− and SO42−, DCM/SM is not affected significantly by these species and the DREECM/SM values remain always lower than 1 (DLaCM/SM = 0.12–0.40). Notably, the DNbCM/SM values are all <1, with only one exception containing 6 wt% F. Besides, in all the investigated systems, Ba, Sr, Mo, V, Cs, Rb and Li preferentially partition into the conjugate carbonate melt. All the high field strength elements (Pb, Th, U, Zr, Hf, Nb, Ta), transition metals (Mn, Co, Cu, Zn) and common network formers (Ga, Ge) essentially partition into the silicate melt.

Geochemical characteristics of rare earth elements in late Palaeozoic coals from North China

Introduction: China is a large country of REE resources and production, supplying more than 90% of the world’s rare earth consumption market, China’s traditional REE resources, although rich, but reserves are also declining, in recent years, scholars have shown that the REEs in the specific geological conditions in the coals can be enriched, and even reach the industrial grade, the search for more REE mineral resources will be of great strategic significance.Methods: The article has selected the Zibo, Taozao, Huainan, Datong, Huozhou, Jungar, and Weibei coalfields in North China as the research objects. Based on inductively coupled plasma mass spectrometry (ICP-MS) analyses, the study provides a detailed analysis of the enrichment rules and distribution patterns of rare earth elements (REEs) in coal under different geological conditions.Results: The REE distribution patterns in Late Palaeozoic coals in North China are characterized by enrichment of LREEs, deficit of HREEs with gentle changes, and obvious negative anomalies of Eu, the enrichment of REE in coal is controlled by provenance and volcanism, and is related to distance of transport terrigenous material and the sedimentary environment. The REEs concentrations in North China indicates that Late Palaeozoic coals in the mining areas of the north, northwest, and western parts of North China are significantly enriched in REEs. In addition, REEs in Late Palaeozoic coals in the southeastern mining areas are relatively enriched, and the central and eastern regions are significantly depleted.Discussion: Large coal-type rare earth deposits are expected to be developed in North China, particularly the Datong coalfield, Jungar coal mine and the Weibei coal mine in the eastern margin of the Ordos Basin, and the Zibo coalfield.

Research on the competitive landscape of global rare earth resources demand

AbstractRare earth elements play a crucial role in modern industrial development. However, the global supply and demand dynamics of rare earth resources have encountered significant challenges due to the escalating conflict between rapidly increasing demand and limited supply in the international market. This study utilizes a gray prediction model to project the future demand of major rare earth‐consuming countries and examines the competitive landscape of global rare earth resource demand. The findings indicate that: (1) China's rare earth consumption is expected to continue its upward trend, while the consumption in the United States and Japan may decline; (2) China, the United States, and Japan are likely to maintain their positions as major consumers of rare earth elements, although the competition for rare earth resources among these countries may weaken; (3) the United States and Japan heavily rely on the import of rare earth upstream products, while China's reliance on midstream and downstream imports remains prominent. Finally, based on these research conclusions, the article presents corresponding policy recommendations.

New hematite method: efficient and enhanced separation of rare earth and iron by alkaline regulation of pH in rare earth chloride solutions

Iron in RECl3 solutions is a detrimental impurity, adversely impacting both the purification efficiency of RECl3 and purity of rare earth compounds. RECl3 solutions employs the neutralization precipitation method for iron removal, leading to iron slag rich in valuable rare earth elements and radioactive thorium. This practice not only results in rare earth resource wastage but also poses significant ecological challenges. This study introduces an innovative hematite method for efficient and enhanced separation of rare earth and iron from RECl3 solutions. This method involves adjusting the solution's pH using alkali in a high-pressure reactor. Results indicate optimal conditions: a OH− to Fe3+ ratio of 1.5:1, temperature at 180°C, duration of 3 hours, and a Fe3+ (as Fe2O3) to Fe2O3 crystal seed molar ratio of 1:1. Under these conditions, the iron slag contains 1.3% REO and 63.69% TFe, with a rare earth loss rate of 0.35% and a TFe removal rate of 90.36%. Thermodynamic analysis reveals that at 25°C, ammonia water adjusts the pH of RECl3 solutions to 2-3, with the presence of Fe(OH)2+ and Fe(OH)2+ in the solution. The potential pH diagram of Ce-Fe-H2O at 180°C indicates that a pH range of -1.87 to 2.99 is crucial for Fe2O3 and Ce3+ formation. SEM analysis shows that the iron slag phase is a densely packed elliptical hematite sphere of approximately 1 micron and contains 0.36% thorium. This new hematite method using alkali-regulated high-temperature and high-pressure conditions for iron removal from RECl3 solutions not only minimizes rare earth loss but also mitigates iron slag's environmental impact. Furthermore, it offers a novel iron removal technique for the smelting industry.

Rare Earth Extraction from Phosphogypsum by Aspergillus niger Culture Broth.

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

Sedimentary characteristics of ion-adsorption rare earth elements and assessment of their resource reuse potential due to soil and water erosion in western Fujian.

With severe soil and water erosion, the crucial ion-adsorption rare earth elements (REEs) have attracted much global attention. REEs play a vital role in tracing material sources and exploring sedimentary characteristics due to their unique and stable geochemistry properties. In the present work, three representational possible redeposition areas in western Fujian were selected as the study areas. The geochemical characteristics of REEs in the sediments of the study areas were evaluated to elucidate that REEs are the products of soil and water erosion and to assess their redeposition characteristics. In the research results, the properties of the parent rocks shown in the samples, together with the negative correlation between the content of REEs in the samples and altitude as well as the relief degree on the land surface (RDLS), fully indicate that the sediments in the study areas are the products of migration caused by soil erosion and redeposition in the downstream areas. At the same time, according to the widely applicable standard of rare earth resources exploitation, that is the boundary grade of ion-adsorption rare earth ore in southern China (∑REE = 500mg·kg-1), we found that the content of REEs in the study areas was close to or exceeded this standard, and the maximum ∑REE of Guozhai Reservoir (869.11mg·kg-1) was much larger than this standard. Therefore, the redeposited rare earth in Changting Country has high reuse potential under the current scarce resources.

RARE EARTH METALS: KEY COMPONENTS OF MODERN TECHNOLOGIES

Purpose. The aim of the article is to conduct a comprehensive analysis of the supply routes for rare earth elements and forecast the development of the market for these elements in the current conditions arising from the war and other factors. Methodology of research. The scientific research methodology was used in the process of writing the article to determine generalised synthetic indicators on strategic ways of development and diversification of rare earth elements supply, as well as statistical and graphical methods to analyse the rare earth elements market and forecast supply and demand using time series. Graphs were used to visualise this data. Findings. It has been found that lithium, cobalt, neodymium and graphite, as well as other elements, are becoming increasingly important in modern technologies and everyday life, which leads to an increase in demand for these rare earth elements. The market for rare earth elements is analysed and demand is forecasted to grow in the future due to the development of green technologies and high-tech devices. The ways of developing and diversifying the supply of rare earth elements are investigated, which made it possible to consider them critical due to possible shortages, supply restrictions and the lack of local concentrations for mining. The global REE market is dominated by Chinese production of REE oxides. That is why, in order to avoid potential risks in the supply of rare earth materials, it is important to consider alternative sources and modern processing technologies to meet demand and ensure further production of rare earth elements. Originality. The article analyses the ways of supplying rare earth elements and their important role in modern technologies. A forecast is made, with an analysis of the market for rare earth materials, which will grow in connection with the transition to a climate-neutral economy. The work is relevant because it is the first to analyse the integrated use of rare earth elements in technologies such as lithium-ion battery technology, fuel cell (FCs) technology and permanent magnet motors. Potential risks in the supply of rare earth materials were determined and ways to avoid them were proposed. Practical value. The practical significance of this research is that in the 20th century, rare earth elements became a key to the production of electronics and other technologies. China, which has significant REE resources, controls a large share of global production, which leads to geopolitical tensions in the supply sector. The results of the study can be used to analyse and forecast the ways of supplying rare earth materials, as well as to solve issues related to future challenges and the development of competition for resources. Key words: rare earth elements (REEs); critical material; lithium-ion battery technology; Fuel cells (FCs) technology; permanent magnet motors; statistical method; forecasting.

The co-movement of fossil energy, new energy, rare earth, and carbon in China: Measurement and evolution analysis

The low-carbon transition of the energy system plays a crucial role in achieving carbon neutrality. However, the development of new energy heavily relies on rare earth resources, which in turn entail substantial energy consumption and carbon emissions. This “linkage dilemma” poses constraints on the realization of carbon neutrality objectives. In this study, we employ a combination of sample entropy, cross-sample entropy, and coarse-gained network modeling methods to uncover the internal complexity and mutual synchronization of the fossil energy stock market, new energy stock market, rare earth stock market, and carbon market in China. Our findings reveal several important insights. Firstly, we observe that the co-movements among the three industry stock markets and the carbon market are dynamic and closely tied to the efficiency of each market. Secondly, the co-movement between traditional and new energy stock markets remains high, with the supply chain stock market between energy and rare earth exhibiting a similar trend. This highlights the significant impact of inherent substitution or supply chain relationships on the level of synchronization. Thirdly, the stock market crashes and the COVID-19 pandemic have resulted in heterogeneous effects with notable changes observed in carbon-related market pairs. Notably, although the carbon market exhibits relatively low co-movement with other stock markets, the patterns of co-movement and their evolution are becoming increasingly complex. Lastly, based on our findings, we present conclusions and potential implications for policymakers to address the impact of the crisis on market interconnectivity, as well as guide investors to effectively allocate their investment portfolios.

Recovery of Rare Earth Elements from Acid Mine Drainage with Supported Liquid Membranes: Impacts of Feedstock Composition for Extraction Performance.

Acid mine drainage (AMD) from inactive coal mines can be enriched in rare earth elements (REEs) and has gained much attention as an alternative source for these technology-critical metals. However, AMD is a relatively low-grade REE resource in which the abundance of impurities and the composition variability of the feedstock create major uncertainties for the performance of REE extraction technologies. This study sought to identify AMD feedstock variables that influence the extraction efficiency of REEs by supported liquid membranes (SLMs). SLM separation is a process involving a hydrophobic membrane embedded with an extracting solvent that facilitates the selective extraction of REE ions. The major aims were to (1) assess the effectiveness of SLM-based REE separation from several AMD samples representing a spectrum of aqueous composition, (2) determine the effects of AMD storage and holding time on extraction performance, and (3) assess the impact of AMD pretreatment (e.g., filtration and pH adjustment) on REE recovery. The results showed that relative extraction fluxes of REE correlated with AMD characteristics such as pH and major ions such as Fe, Ca, and Mn. The purity of the acid strippant product, expressed as the REE dry weight content, depended on the initial REE concentrations in the AMD source rather than the flux of individual REEs across the membrane. For AMD samples stored for 3 months prior to extraction, REE recovery by SLM separations was substantially decreased if oxidation of Fe(II) to Fe(III) was observed during sample storage. Pretreatment of AMD feedstocks by pH adjustment did not substantially improve the separation performance. Overall, this study establishes primary water quality parameters of AMD that influence the SLM separation flux and product purity. Such insights contribute to a mechanistic understanding of critical metals extractions by SLM for complex and nontraditional feedstocks such as AMD wastes.

Using machine learning to identify indicators of rare earth element enrichment in sedimentary strata with applications for metal prospectivity

Rare earth elements (REE), classified as critical minerals which are crucial for clean energy technologies, face soaring demand. While economic deposits are found in limited geologic environments including carbonatites and ion-adsorption clays, unconventional, secondary sources such as those from sedimentary basins could hold potential to meet this increased demand. Coal and its associated combustion by-products, phosphorites, oil sands tailings, and formation waters have all garnered interest for REE recovery, yet they remain significantly underexplored. Accordingly, new tools for data analysis and optimization such as machine learning can assist in mineral prospectivity, with these tools being subject to rapid proliferation in the Earth sciences.This work leverages compositional data analysis principles and machine learning to probe geochemical relationships and predict REE abundances in sedimentary lithologies using unsupervised (correlation, principal component, and cluster analysis) and supervised (regression, support vector machine, random forest, and boosting) machine learning models. These three unsupervised models display similar results, with REE typically being associated with incompatible elements (e.g., Th, Nb, and Hf). Gradient boosting, Adaboost, and Random Forest had the highest performance for predicting REE concentrations, with Th and P commonly being the most important predictor variables. Identifying geochemical indicators of REE enrichment that may be used to assist in discovering potentially exploitable REE resources based on existing data, as well as increasing the understanding of metal behaviour in sedimentary systems, is a step forward in understanding novel secondary and unconventional REE sources. Although REE concentrations from these sources are generally lower than primary ore deposits, the amount of available feedstock, potentially simpler, cheaper, and less environmentally taxing extraction processes, and the added benefit of remediating waste streams and contributing to the circular economy make these sources alluring.

Mycomining: perspective on fungi as scavengers of scattered metal, mineral, and rare earth element resources

Established principles and practical application of phytomining and mycoremediation bioaccumulation processes hint at a feasible and environmentally sustainable “mycomining” solution with considerable growth environment versatility.

Investigation on pretreatment method for the determination of rare earth elements in polymetallic mineral samples in Pan-Xi region by ICP-MS.

The polymetallic mineral samples in Pan-Xi region are rich in rare earth resources, and exploring an efficient and accurate analysis method is of great significance for their comprehensive utilization. In this study, the samples were decomposed by three methods, namely closed acid dissolution, open acid dissolution with five acid and alkali fusion with sodium peroxide, and the 15 REE were determined by inductively coupled plasma mass spectrometry (ICP-MS) with Rh and Re as internal standard correction elements. The comparative experiments were conducted using standard substances, and the results showed: (1) The detection limit of closed acid dissolution method was low with relative standard deviation (RSD) ranging from 2.51% to 9.56% and the accuracy of method (ΔlgC) ranging from 0.006 to 0.073, while the sample processing was long, and the results of some REE were low. (2) The RSD of open acid dissolution with five acid method ranged from 1.93% to 7.96%, and ΔlgC ranged from 0.004 to 0.045 with low results of the determination results of REE. (3) The alkali fusion with sodium peroxide method eliminated the influence of matrix effects by selecting instrument optimization, sample dilution, appropriate internal standard elements, etc. The RSD ranged from 1.24% to 6.49%, and ΔlgC ranged from 0.001 to 0.032. In conclusion, alkali fusion with sodium peroxide method has a fast analysis process, complete sample dissolution, and the accuracy and precision of test results can meet the requirements of specification (DZ/T0011-2015), which is most suitable for the analysis of REE in polymetallic mineral samples from Pan-Xi region.

Activated carbon from Camellia oleifera shells for adsorption of Y(iii): experimental and DFT studies.

Yttrium is an important rare earth element and is widely used in fields such as special glass preparation, metallurgy, and materials science. However, it is difficult to recover yttrium ion waste from dilute solutions with traditional processes, resulting in a significant waste of rare earth resources. The simple, effective, and easy-to-operate adsorption method is the most promising method for recovering yttrium, which is of great significance for sustainable development of the rare earth industry. In this study, activated carbon was prepared from Camellia oleifera fruit shells (COS) using phosphoric acid activation, and efficient recovery of Y(iii) from the Camellia oleifera fruit shell activated carbon was studied. Adsorption equilibrium data showed that this activated carbon had a Y(iii) adsorption capacity of 35.41 mg g-1, indicating significant potential for recovery of yttrium ions. The adsorption of Y(iii) by the activated carbon prepared from COS was consistent with the Langmuir model, and the adsorption data were consistent with the pseudo second-order kinetic model, indicating that the adsorption process was primarily chemical adsorption. After adsorption, the surface of the activated carbon contained large amounts of N, O, and Y, indicating that Y(iii) was stably adsorbed. The mechanisms for adsorption of Y(iii) on three types of activated carbon were studied through DFT calculations. The results showed that Y(iii) interacted with the carbon atoms on the surfaces to form new chemical bonds. The yttrium ion adsorption capacities for the three different activated carbons decreased in the order C I > C II > C.

Influence of Ho spontaneous aggregation on the coercivity and magnetic domain movement of sintered NdY-Fe-B magnets

Development of NdY-Fe-B magnets not only reduces the cost of Nd-Fe-B type magnets but also promotes the balanced utilization of rare-earth resources. However, the lower coercivity of NdY-Fe-B magnets hinders their further development. This study investigated the coercivity of NdY-Fe-B magnets via intergranular doping of Ho76Al12Ga12 powders. Although this process improved the coercivity, the remanence substantially deteriorated with the increasing content of the Ho76Al12Ga12 alloy. A coercivity of 1.37 T was achieved in a NdY-Fe-B magnet with a Ho76Al12Ga12 alloy doping of 7 wt%, showing a coercivity increment (ΔHcj) of 0.64 T compared to the original magnet. This can be attributed to the observed microstructural and elemental distributions, as well as the analysis of the magnetic domain wall movement. An abnormal Ho-biased layer is observed between the Y-rich core and the Ho-rich shell in the matrix grains, exhibiting a higher anisotropy field compared than the shell layer. Further analysis revealed that the movement of magnetic domain wall movement was obstructed by the Ho-biased layer, demonstrating a domain-wall pinning effect within the matrix grains. Additionally, the formation of a Ho-rich shell in the outer area of the 2:14:1 matrix grain and the presence of a continuous uniform grain boundary phase were found to be important for improving both coercivity and thermal stability.

Intelligent leaching rare earth elements from waste fluorescent lamps.

Rare earth elements (REEs), one of the global key strategic resources, are widely applied in electronic information and national defense, etc. The sharply increasing demand for REEs leads to their overexploitation and environmental pollution. Recycling REEs from their second resources such as waste fluorescent lamps (WFLs) is a win-win strategy for REEs resource utilization and environmental production. Pyrometallurgy pretreatment combined with acid leaching is proven as an efficient approach to recycling REEs from WFLs. Unfortunately, due to the uncontrollable components of wastes, many trials were required to obtain the optimal parameters, leading to a high cost of recovery and new environmental risks. This study applied machine learning (ML) to build models for assisting the leaching of six REEs (Tb, Y, Eu, La, and Gd) from WFLs, only needing the measurement of particle size and composition of the waste feed. The feature importance analysis of 40 input features demonstrated that the particle size, Mg, Al, Fe, Sr, Ca, Ba, and Sb content in the waste feed, the pyrometallurgical and leaching parameters have important effects on REEs leaching. Furthermore, their influence rules on different REEs leaching were revealed. Finally, some verification experiments were also conducted to demonstrate the reliability and practicality of the model. This study can quickly get the optimal parameters and leaching efficiency for REEs without extensive optimization experiments, which significantly reduces the recovery cost and environmental risks. Our work carves a path for the intelligent recycling of strategic REEs from waste.

Nanocrystalline alternative rare earth-iron-boron permanent magnets without Nd, Pr, Tb and Dy: A review

The continuous increase in the output of Nd-Fe-B permanent magnets leads to the increasing consumption of rare earth (RE) metals of Nd, Pr, Tb and Dy. As a result, a serious unbalanced utilization of RE resource occurs. To reduce the use of these critical REs, high abundance REs of Y, La, Ce and even Gd and Ho have been proposed to partly substitute Pr and Nd in sintered magnets and rapid-quenched nanocrystalline magnetic powders. Recently, the cost-effective RE-Fe-B magnets without Nd, Pr, Tb and Dy have also been developed. This type of magnet is preliminarily designed to bridge the magnetic properties gap between hard ferrites and bonded Nd-Fe-B magnets, which shows the potential applications in voice coil motor, spindle motors and magnetic resonance imaging systems. This review summarizes the progress of RE-Fe-B-type magnets containing no Nd, Pr, Dy and Tb based on the world-wide investigations and our recent findings. The fundamentals of intrinsic magnetic properties of Y, La, Ce based RE2Fe14B phases are introduced first. The relationship between magnetic properties and microstructure of rapidly quenched and bulk RE-Fe-B magnets with nanocrystalline structure is then emphatically discussed. Hard magnetic properties and performance/cost ratio of various RE-Fe-B alloy systems are summarized and compared. Furthermore, the current discoveries and the existing challenges are discussed. Some potential strategies for the future research in this field are finally proposed.

Cross-sensitivity analysis of land use transition and ecological service values in rare earth mining areas in southern China

Exploring the cross-sensitivity between land use transformation and ecological service values in rare earth mining areas is of great significance for the development of ecological protection and restoration in rare earth mining areas. To study the impact of land use changes on ecosystem service functions in rare earth mining areas, firstly, the land use change trends in the study area from 2009 to 2019 were analyzed using the land transfer matrix; then the distribution of ecosystem service values and the flow direction of ecosystem service values in the study area were measured based on the ecosystem service value equivalents; a spatial autocorrelation analysis was done on the ecosystem service values to explore their spatial distribution patterns; and finally, the cross-sensitivity coefficient was used to quantitatively assess the extent and direction of the impact of land use change on ecosystem service values. The results show that the land use types in the study area are mainly forest land and farmland, with woodland accounting for the highest proportion of the study area. The ESV changes in the study area are consistent with the trend of land use transformation, with the overall increase and decrease being comparable, and the decrease in ESV is mainly concentrated in the areas with a large increase in mining land and construction land; during the study period, the study area was significantly reduced with low—low cluster areas and the ecological environment was improved; from 2009 to 2014, the ecological sensitivity coefficient is more variable, and is more sensitive to the net conversion between water and desert, from 2014 to 2019, the ecological sensitivity coefficient is less variable, and the most sensitive is the net conversion between cultivated land and water. The study area should be reasonably developed for rare earth resources and the ecological environment around the mining area should be reasonably protected to build an ecological security pattern.