Heavy Rare Earth Research Articles

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

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

Strategic grain boundary diffusion process for high-performance Ce-containing sintered Nd-Fe-B magnets

Sintered Nd-Fe-B magnets are an important driver of green technology, and the grain boundary diffusion process (GBDP) has become the most economically efficient method to improve the overall magnetic properties of sintered Nd-Fe-B magnets. In the work, to further reduce the utilization cost of sintered Nd-Fe-B permanent magnets with high performance, the strategic GBDP was explored based on the demagnetization characteristics of Nd-Fe-B permanent magnet materials in motors. The peculiar fact about the process was that the diffusion source was deposited on a part of the c-plane, that is, the strategic selected area grain boundary diffusion process (S-SAGBDP). With the objective of addressing the edge demagnetization, the diffusion source was initially deposited only at the edges of the c-plane. Despite the overall magnetic properties and temperature coefficients of the diffused magnet were significantly enhanced, the serious deteriorations of squareness and surface magnetic field were particularly worrying. Consequently, the central area of the magnet was simultaneously strengthened. The squareness and demagnetization property of the magnet after S-SAGBDP were greatly improved, and the amount of heavy rare earths was reduced by 25%. The above work clearly illustrates the practical value of S-SAGBDP, which is helpful to develop the cost-effective and commercial-grade sintered Nd-Fe-B magnets.

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

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

Nature of ree accumulation in clayey interlayers and coals in Karaganda coal basin

It is the first completed complex mineralogical and geological research of REE (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in the coals of Karaganda coal basin in Central Kazakhstan. This paper presents the results of the research of REE (from lanthanum to lutetium and Y) distribution in 85 samples of coal and clayey interlayers of stratum k7 of Karaganda coal basin in the faces of Saranskaya, T.Kuzembayev, Aktasskaya mines. The ultimate composition of clayey interlayer and coal samples was analyzed by the methods of inductively coupled plasma optical emission spectroscopy and inductively coupled plasma mass spectrometry (ICP-OES and ICP-MS). Research of the lateral and vertical discontinuity of the total REE concentration has indicated the presence of mixed types of REE distribution in coals, which supposes various forms of REE migration and different mobility of heavy and light lanthanides within the hypergenesis zone. The established lanthanum-ytterbium (La/Yb) ratio in the coal, which is normalized to UCC and equals La/Yb<1, relates to the coals with Н type of REE distribution, and the one that equals La/Yb>1 and normalized to chondrite belongs to the coals with L type of REE distribution, which allows making conclusions on the presence of independent sources and different mechanisms of REE accumulation in the sediments of Karaganda coal basin. It is also established that the La/Yb ratio grows from coals to clayey interlayers, which indicates a predominantly clastogenic mechanism of REE input to the coals. The prevailing mineral form of the REE in the coal and clayey interlayer samples from the Karaganda coal basin is light lanthanide phosphates. Sparry crystals with CeLaNdPO composition were found in the coal and clayey interlayer samples. It was established that xenotime is the main deportment for Y in many coals.

Geochemical behavior of rare earth elements in agricultural soils along the Syr Darya River within the Aral Sea Basin.

The widespread use of rare earth elements (REEs) across various industries makes them a new type of pollutant. Additionally, REEs are powerful indicators of geochemical processes. As one of the two main rivers in the Aral Sea, identifying the geochemical behavior of REEs in agricultural soils of the Syr Darya River is of great significance for subsequent indicative studies. In this study, the geochemical characteristics, influencing factors, and potential application significance of REEs in agricultural soils from three sampling areas along the Syr Darya River were analyzed using soil geography and elemental geochemical analyses. The results showed that the highest total concentration of REEs in the agricultural soil was in Area I, with a mean value of 142.49μg/g, followed by Area III with a mean value of 124.56μg/g, and the lowest concentration was in Area II with a mean value of 122.48μg/g. The agricultural soils in the three regions were enriched in light rare earth elements (LREEs), with mean L/H values of 10.54, 10.13, and 10.24, respectively. The differentiation between light and heavy rare earth elements (HREEs) was also high. The concentration of REEs in agricultural soil along the Syr Darya River was primarily influenced by minerals such as monazite and zircon, rather than human activities (the pollution index of all REEs was less than 1.5). The relationship between Sm and Gd can differentiate soils impacted by agricultural activities from natural background soils. The results of this study can serve as a basis for indicative studies of REEs in Central Asia.

Machine learning models to predict rare earth elements distribution in Tethyan phosphate ore deposits: Geochemical and depositional environment implications

The global market for rare earth elements (REE) is growing rapidly, driven by rising demand and limited production sources, prompting interest in recovering REE from secondary sources such as phosphate deposits. The Tethyan belt, extending across North Africa and the Middle East contains substantial Upper Cretaceous to Eocene REE-rich phosphorite deposits but with limited geochemical data available. This study provides a novel machine-learning (ML) method to predict REE contents in these deposits and verify a useful geochemical classification based on the concentrations of nine major element oxides. Four ML models are developed to achieve this: eXtreme Gradient Boosting (XGBoost), Random Forest (RF), Support Vector Regression (SVR), and Decision Tree (DT). The datasets are divided geochemically into oxic and sub-oxic patterns and these are evaluated with the ML models separately and in combination to accurately predict light REE (LREE), heavy REE (HREE), and total REE contents (∑REE). For the oxic pattern dataset, Fe2O3 and K2O exhibit the highest feature importance consistent with a glauconite influence. For the sub-oxic pattern dataset, MnO and SiO2 exhibit the highest feature importance consistent with high terrigenous inputs (MnO), and silicification. The ML results support the importance of the local deposition environment in determining REE distributions in these deposits. Paleogeography, ocean-margin tectonics, sea-level oscillations, and marine currents exert influence on the local depositional environments. The eXtreme Gradient Boosting model generates the lowest REE prediction errors for all the datasets evaluated.

Toxicity of two heavy rare earth elements to freshwater mussels Dreissena polymorpha

Rare earth elements (REE) are essential components of many electronic devices that could end-up in solid waste disposal sites and inadvertently released in the environment. The purpose of this study was to examine the toxicity of two heavy REEs, erbium (Er) and lutetium (Lu), in freshwater mussels Dreissena polymorpha. Mussels were exposed to 14 days to increasing concentration (10, 50, 250, and 1250 µg/L) of either Er and Lu at 15 °C and analyzed for gene expression in catalase (CAT), superoxide dismutase (SOD), metallothionein (MT), cytochrome c oxidase (CO1), and cyclin D for cell cycle. In addition, lipid peroxidation (LPO), DNA damage (DNAd), and arachidonate cyclooxygenase were also determined. The data revealed that mussels accumulated Er and Lu similarly and both REEs induced changes in mitochondrial COI activity. Er increased cell division, MT, and LPO, while Lu increased DNAd and decreased cell division. Tissue levels of Er were related to changes in MT (r = 0.7), LPO (r = 0.42), CO1 (r = 0.69), and CycD (r = 0.31). Lu tissue levels were related to changes in CO1 (r = 0.73), CycD (r = − 0.61), CAT (r = 0.31), DNAd (r = 0.43), and SOD (r = 0.34). Although the lethal threshold was similar between Er and Lu, the threshold response for LPO revealed that Er produced toxicity at concentrations 25 times lower than Lu suggesting that Er was more harmful than Lu in mussels. In conclusions, the data supports that the toxicity pattern differed between Er and Lu although they are accumulated in the same fashion.

Probing the geochemical characteristics of rare earth elements in the weathering profile of yttrium-rich heavy rare earth mine

Understanding the complex geochemical characteristics of rare earth elements (REEs) in the weathering profile of ion-adsorbed rare earth ore is a crucial issue for establishing the best leaching agent dosage during in-situ leaching processes. This study focuses on soil samples collected from nine drill holes located at three hillslopes of a mining area in southwest Fujian. Analyzing the geochemical features of REEs revealed that the ore predominantly comprises Y, La, Ce, and Nd, with Y being the most abundant, constituting 20.24 %–33.64 % of total rare earth elements (TREEs) in each weathering profile. This categorizes the ore as an yttrium-rich heavy rare earth ion-adsorbed mine. Notably, REEs exhibit a concentration in the middle layer of the weathering profile, with content increasing first and then declining with deeper depth from the surface to the bottom. The ratio of light rare earth elements (LREEs) to heavy rare earth elements (HREEs) diminishes noticeably from shallow soil to middle soil, while deep soil reveals a slightly higher ratio than middle soil. These findings offer valuable insights into the scientific mining of this area and similar ion-adsorbed rare earth mines concerning their economic potential.

Advancing mechanical durability and radiation shielding properties in Silicon dioxide (SiO2) glasses through various incorporations: A comparative analysis

Silicon dioxide (SiO2) glasses, known for their high thermal stability, excellent optical transparency, and substantial mechanical strength, are crucial in numerous technological applications, including radiation shielding. This research explores the impact of compositional variations in SiO2-based glasses on their mechanical and radiation shielding properties, particularly focusing on the inclusion of heavy metal oxides (HMO) and rare earth elements (REE) like neodymium (Nd). Through the systematic investigation of fifteen distinct glass samples with varying concentrations of specific oxides and elements, we investigate the compositional changes and their influence on physical properties and their effectiveness in attenuating radiation. Our findings demonstrate that the incorporation of Nd significantly enhances the glass's radiation shielding capabilities. Glasses doped with Nd exhibited higher effective atomic numbers and electron densities, which translate to superior attenuation characteristics at lower photon energies. This is highlighted by the exceptional performance of the 20Nd sample, showing the lowest exposure build-up factors (EBF) at 10 mean free paths (mfp), indicating its potential as a premier candidate for shielding applications against various energy levels of radiation. Moreover, the variation in the Elastic Modulus of the glass samples underscores the significant impact of the glass matrix composition on its mechanical properties, suggesting a delicate balance between network formers and modifiers in determining the glass properties. It can be concluded that the neodymium-doped SiO2-based glasses may be considered as targeted compositions in fine-tuning material properties to meet specific application requirements. As the demand for efficient radiation shielding materials grows across medical, industrial, and space exploration sectors, our findings provide a solid foundation for the development of new glass formulations tailored for enhanced mechanical properties and superior radiation protection levels.

Influence of Organic Matter Thermal Maturity on Rare Earth Element Distribution: A Study of Middle Devonian Black Shales from the Appalachian Basin, USA

This study focuses on understanding the association of rare earth elements (REE; lanthanides + yttrium + scandium) with organic matter from the Middle Devonian black shales of the Appalachian Basin. Developing a better understanding of the role of organic matter (OM) and thermal maturity in REE partitioning may help improve current geochemical models of REE enrichment in a wide range of black shales. We studied relationships between whole rock REE content and total organic carbon (TOC) and compared the correlations with a suite of global oil shales that contain TOC as high as 60 wt.%. The sequential leaching of the Appalachian shale samples was conducted to evaluate the REE content associated with carbonates, Fe–Mn oxyhydroxides, sulfides, and organics. Finally, the residue from the leaching experiment was analyzed to assess the mineralogical changes and REE extraction efficiency. Our results show that heavier REE (HREE) have a positive correlation with TOC in our Appalachian core samples. However, data from the global oil shales display an opposite trend. We propose that although TOC controls REE enrichment, thermal maturation likely plays a critical role in HREE partitioning into refractory organic phases, such as pyrobitumen. The REE inventory from a core in the Appalachian Basin shows that (1) the total REE ranges between 180 and 270 ppm and the OM-rich samples tend to contain more REE than the calcareous shales; (2) there is a relatively higher abundance of middle REE (MREE) to HREE than lighter REE (LREE); (3) there is a disproportionate increase in Y and Tb with TOC likely due to the rocks being over-mature; and (4) the REE extraction demonstrates that although the OM has higher HREE concentration, the organic leachates contain more LREE, suggesting it is more challenging to extract HREE from OM than using traditional leaching techniques.

Petrogenesis of Miocene volcanism in the Central Anatolia: Geochemical, isotopic and geochronological evidence

This paper presents the first 40Ar/39Ar age data, new bulk-rock major-trace element compositions and NdSr isotope geochemistry, combined with detailed geological mapping of Galatia Volcanic Province (GVP) in the northwest Central Anatolia (Turkey). Here, there are voluminous extrusive rocks in a wide compositional range: a basalt, andesite and trachyte suite, and their pyroclastic equivalents. 40Ar/39Ar dating of two whole-rock samples from the GVP yielded plateau ages of 21.76 ± 0.8 Ma and 20.97 ± 0.5 Ma, constrain the volcanic activity at ca. 21 Ma (Aquitanian). The samples show by sub-parallel light rare earth element (LREE)-enrichment and relatively flat heavy rare earth element (HREE) patterns and moderate fractionation [average (La/Yb)N = 13.5]. Their initial 87/86Sr values vary between 0.704619 and 0.704998, while initial 143/144Nd values lie between 0.512673 and 0.512755. Integration of the geochemical and geochronological with geological data we propose that the volcanic rocks in the northern area of GVP with calc-alkaline affinity were produced by a lithospheric mantle magma in an extensional setting.

Recovery of rare earth elements from mine wastewater using alginate microspheres encapsulated with zeolitic imidazolate framework-8

There is increasing demand and interest in efficient methods for the recovery of rare earth elements (REEs) from wastewater because of the growing concerns associated with the negative impacts of REEs-rich waste discharged on pristine ecosystems. Here, we designed a ZIF-8@ALG composite hydrogel by encapsulating zeolitic imidazolate frameworks-8 (ZIF-8) into sodium alginate and poly (vinyl alcohol) double cross-linked networks (ALG) for the recovery of REEs from mine wastewater. ZIF-8@ALG showed exceptional REEs adsorption performance with the most superior separation factor (Ho/Mn) of 597.5. For the REEs considered, the ZIF-8@ALG composite exhibited a preference for heavy REEs with high adsorption efficiencies (65.3 ∼ 97.2%) and distribution coefficients (2045.5 ∼ 28500.0 mL·g−1). Adsorption involved a combination of electrostatic attraction, complexation and ion exchange mechanisms. REEs adsorbed on ZIF-8@ALG could also be desorbed using sodium citrate via ion-exchange and complexation, thus achieving efficient REEs recovery. In addition, ZIF-8@ALG was stable and reusable, maintaining effective adsorption in wastewater over four consecutive cycles, where the optimal adsorption efficiency reached 80.0%. Overall, this study provided an effective and feasible method for the recovery of REEs in mine wastewater, and confirmed that ZIF-8-based materials have significant potential for REEs recovery applications in wastewater engineering treatment.

Nephrite from Xinjiang Qiemo Margou Deposit: Gemological and Geochemical Insights

The nephrite belt in the Altun Mountain–Western Kunlun Mountain region, which extends about 1300 km in Xinjiang, NW China, is the largest nephrite deposit in the world. The Qiemo region in the Altun Mountains is a crucial nephrite-producing area in China, with demonstrated substantial prospects for future exploration. While existing research has extensively investigated secondary nephrite deposits in the Karakash River and native black nephrite deposits in Guangxi Dahua, a comprehensive investigation of black nephrite from original deposits in Xinjiang is lacking. Margou black-toned nephrite was recently found in primary deposits in Qiemo County, Xinjiang; this makes in-depth research on the characteristics of this mine necessary. A number of technical analytical methods such as polarizing microscopy, Ultra-Deep Three-Dimensional Microscope, electron microprobe, back-scattered electron image analysis, X-ray fluorescence, and inductively coupled plasma mass spectrometry were employed for this research. An experimental test was conducted to elucidate the chemical and mineralogical composition, further clarifying the genetic types of the black and black cyan nephrite from the Margou deposit in Qiemo, Xinjiang. The results reveal that the nephrite is mainly composed of tremolite–actinolite, characterized by Mg/(Mg + Fe2+) ratios ranging from 0.86 to 1.0. Minor minerals include diopside, epidote, pargasite, apatite, zircon, pyrite, and magnetite. Bulk-rock rare earth element (REE) patterns exhibit distinctive features, such as negative Eu anomalies (δEu = 0.00–0.17), decreasing light REEs, a relatively flat distribution of heavy REEs, and low total REE concentrations (1.6–38.9 μg/g); furthermore, the Cr (6–21 μg/g) and Ni (2.5–4.5 μg/g) contents are remarkably low. The magmatic influence of granite appears to be a fundamental factor in the genesis of the magnesian skarn hosting Margou nephrite. The distinctive black and black cyan colors are attributed to heightened iron content, mainly associated with FeO (0.08~6.29 wt.%). Analyses of the chemical composition allow Margou nephrite to be classified as typical of magnesian skarn deposits.

Bioleaching ion-unexchangeable rare earth in ion-adsorption type rare earth waste tailing

Ion-adsorption type rare earth ores (IREO) in China serve as the primary source of medium and heavy rare earth globally. With the rapidly growing demand for rare earth elements (REEs) and the dwindling supply of premium IREO, enhancing the recovery of REEs, especially the ion-unexchangeable REEs with ultra-low content and ambiguous speciation from IREO or its tailing, has become a critical trend and challenge. This study identified the occurrences of ion-unexchangeable REEs, primarily detected in Fe-enriched minerals, xenotime, and monazite of IREO using TESCAN integrated mineral analyzer (TIMA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) analysis. To extract these elusive REEs, a bioleaching technique utilizing Aspergillus niger (A. niger) metabolites was proposed, achieving a leaching yield of 31.4 wt%. Complementary sequential chemical extraction methods (SCEM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations further elucidate the underlying mechanism, involving the carboxylic acid produced by the metabolic process of microbes that dissolves goethite by disrupting FeO bonds and liberating REEs, which complexed with carboxylate (RCOO), to promote further dissolution. This work offers insight into enhancing the recovery of ion-unexchangeable REEs from IREO or its tailing, paving the way for sustainable and efficient rare earth mining practices.

Effect of Fractionation Columns on the Elution of Rare Earth Elements Recovered from Acid Mine Drainage

Rare earth elements (REE) can be found in expressive contents in different secondary sources, such as acid mine drainage (AMD). This work evaluated separation of light and heavy rare earth elements (REE) from an acid mine drainage (AMD) generated in a former uranium mine in Brazil by using ion exchange. This AMD presents pH 3.50, total REE content of 97 mg L−1 and 1.3 g L−1 of sulfate and was used in the REE loading experiments. Loading experiments were carried out in columns using a commercial strong acid cation (SAC) exchange resin. Elution was performed with 0.01 mol L−1 NH4EDTA in systems with one, two and three columns. Regarding the loading step, the resin presented a total loading capacity of 0.58 mmol g−1. The resin proved to be more selective for light REE with adsorption efficiency of 78% and 48% for heavy REE. Regarding elution, high efficiencies between 90 and 100% were achieved for REE. The final REE solution is approximately 10 times more concentrated in the liquor related to the acid mine water. Better fractionation results were achieved for the system with three columns. Although the complete separation of the REE into pure elements was not possible, two distinct fractions of heavy and light REE could be obtained, and La was completely separated from the other REE. In order to improve fractionation and separate the REE into individual ones, the concentrated fractions can proceed to subsequent ion exchange systems.

Neoarchean high-Mg basalt and rhyolite bimodal complex in the Yinshan Block, North China Craton: Petrogenesis and tectonic implications

Plate tectonics plays an important role in Earth’s evolution, but it is a difficult and controversial issue to trace the operation of plate tectonics in the Archean. Calc-alkaline magmas are a diagnostic feature of modern subduction-related magmatism and thus identification of Archean subduction-related calc-alkaline magmas is crucial for understanding when Archean plate tectonics operated. Here we present zircon U-Pb, whole-rock geochemical and Sr-Nd isotopic data for a metamorphosed Neoarchean calc-alkaline bimodal volcanic complex from the Yinshan Block, the North China Craton. Zircon U-Pb dating results indicate that these meta-volcanic rocks were erupted in the late Neoarchean (∼2570 Ma). Its mafic unit is characterized by high contents of K2O (0.68–4.20 wt%), MgO (Mg# = 62.0-73.4), Cr (332-904 ppm), Ni (105-269 ppm), and is enriched in light rare earth elements (REEs), but depleted in heavy REEs and Nb, Ta and Ti. These geochemical features are similar to those of high-Mg basalts in the Phanerozoic arc setting. They have positive εNd(t) values (+1.3 to + 2.4), indicating that they were derived from the depleted mantle wedge. The felsic unit has variable K2O content (1.42–4.95 wt%) and K2O/Na2O ratios of 0.23–1.36 with positive εNd(t) values (+0.7 to + 3.1). They show characteristics of modern adakites with high Sr/Y and LaN/YbN ratios, suggesting that they were generated by partial melting of the thickened juvenile mafic lower crust. We conclude that the studied Neeoarchean bimodal meta-volcanic complex was formed during subduction-zone retreating and root delamination in a Neoarchean arc. Our results further indicate that plate tectonics had already operated in the Neoarchean in the Yinshan Block.

Rare Earth Elements in Shells of Black Sea Molluscs: Anomalies and Biogeochemical Implications

Rare earth elements (REE) are a class of increasingly used high-tech product components and new emerging environmental pollutants, which are accumulated, in particular, in marine biota. In this study, REE contents were estimated in shells of several molluscs common in the Black Sea. The summed REE contents in mollusc shells decreased in the following order of species: Magallana gigas = Anadara kagoshimensis > Flexopecten glaber ponticus ≥ Rapana venosa > Mytilus galloprovincialis, ranging from 0.46 to 1.9 mg·kg−1. Canonical analysis of principal coordinates allowed for the correct identification of species based on the REE composition in no fewer than 67% of the samples. The mollusc shells were anomalously enriched in Sc, Y, La, Eu and Tb, most likely due to anthropogenic contamination. The Y/Ho ratios in all samples were represented by two fit values: 23.2 (chondritic) and 67.6 (superchondritic, mainly associated with A. kagoshimensis). A new universal relationship linking the contents of three light and heavy REE in Black Sea mollusc shells was proposed: Ce0.3 Er0.7/Yb = 2.00 ± 0.46 (mean ± standard deviation).

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.

A cost-effective dual-layer grain boundary diffusion strategy to significantly enhance coercivity of sintered Nd-Ce-Fe-B magnets

In an attempt to obtain cost-effective sintered Nd-Ce-Fe-B magnet and overcome the coercivity-remanence trade-off challenge caused by heavy rare earth (HRE) diffusion, a novel dual-layer coating method has been proposed for the grain boundary diffusion process (GBDP). A high coercivity increment of 8.56 kOe is achieved by dual-layer coated DyHx/Pr80Al20 (DH/PA) diffusion with 0.8 wt% DyHx and a slight remanence reduction from 12.85 to 12.71 kG. Although the DyHx diffused magnet has a coercivity increment of 9.24 kOe, it consumes twice as much DyHx as the DH/PA diffused magnet at the great sacrifice of remanence. This can be attributed to the formation of continuous grain boundary phase and thin Dy-rich shell via microstructural observations. Further TEM characterization indicates that the amorphous triple junction grain boundary phase (TJP) gradually transforms into the crystalline Nd2O3 structure after GBDP. The coexistence of cubic-Nd2O3 phase and hexagonal-Nd2O3 phase found in the dual-layer coated Pr80Al20/DyHx (PA/DH) diffused magnet creates a more intricate grain boundary phase structure, hindering the diffusion of Dy. Comparably, the formation of single cubic-Nd2O3 (Ia3̅ structure) grain boundary phase in the DH/PA and DyHx diffused magnets is an important reason for the significant increase in coercivity. Based on the evaluation of magnetic performance and cost, the DH/PA diffused magnet achieves a higher price-performance ratio (PPR). This cost-effective bilayer grain boundary diffusion strategy provides a valuable reference for high PPR Nd-Ce-Fe-B magnet fabrication.

A hydrous sub-arc mantle domain within the northeastern Neo-Tethyan ophiolites: Insights from cumulate hornblendites

Being a part of the large-scale Indus-Tsangpo suture zone ophiolites of the Alpine-Himalayan orogenic system, the Neo-Tethyan ophiolites of eastern Arunachal Himalaya, northeast India, are important in understanding the formation and evolution of the Neo-Tethyan lithosphere. This study focuses on the hornblendite dykes occurring within serpentinized peridotites of the Mayodia ophiolites in eastern Arunachal Himalaya, to ascertain the origin and evolution of such hydrous mineral cumulates within the ophiolite complex. Texturally and chemically, the hornblendites contain three types of amphiboles, Amp1 (pargasite), Amp2 (Mg-hornblende), and Amp3 (actinolite). The pargasites occur as large cm-sized phenocrysts and show cumulate textures while Mg-hornblende appears as both intercumulus grains between cumulus pargasites and surrounding partially resorbed clinopyroxene grains. Actinolite occurs along the breakdown zone of pargasite and is associated with other secondary minerals. The hornblendites are characterized by high MgO (~12–20 wt%) and low SiO2 (~42–44 wt%) with depleted light rare earth elements (REE) [(La/Sm)N = 0.29–0.52] and almost flat heavy REE [(Gd/Yb)N) = 0.89–1.11]. Moreover, the samples are characteristically depleted in high field strength elements (Nb, Ta, Ti, Hf) while being enriched in Pb. Geothermobarometric calculations yield high magmatic temperatures of ~950 and ~840 °C for pargasite and Mg-hornblende, respectively, and variable pressures with pargasite having the highest pressures (1.6–1.7 GPa) followed by Mg-hornblende (1.1–1.2 GPa) and finally actinolite (~0.55 GPa). Furthermore, fO2 calculations for the cumulus pargasites revealed highly oxidizing conditions (ΔNNO+2) and water content of parental melts (H2Omelt% = ~14.25 %). Parental melt calculations using whole-rock REE concentrations suggest formation from a hydrous sub-alkaline basaltic melt. Whole-rock initial SrNd isotopic ratios of the hornblendites reveal a primary signature for them, falling in the mantle array in proximity to the high-μ (HIMU) mantle reservoir. All these signatures point towards a magmatic arc affinity for these hornblendites. The host peridotite unit shows highly enriched REE concentrations (ƩREE = 18.13 ppm) with flat REE patterns compared to the other peridotites of the locality, which show depleted signatures. Olivine chemistry of the host peridotite unit depicts primary compositions falling in the mantle array. The olivine-liquid thermometer yields temperatures ~1000 °C, which are much lower than those of peridotites occurring in spreading centers (MOR or back-arc). These evidence suggest that the hornblendites and their host peridotite unit represent an island arc root complex, which further imply the hydrous nature of the Neo-Tethyan sub-arc mantle.