Rare Earth Element Values Research Articles

Enhanced enrichment of rare earth elements during pedogenesis under subtropical climate

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

The correlation between Rare Earth Elements and tin in granite, quartz vein, and weathered granite samples, in South Bangka, Bangka Belitung Islands, Indonesia

The presence of Rare Earth Elements (REEs) is often correlated with tin (Sn), particularly at placer deposits in the Bangka Belitung Islands. However, there is limited information on the correlation between Sn and REEs. Therefore, this study aimed to investigate the correlation between REEs and Sn using data analysis of Sn-W, REEs, Y, Th, and U in granite, quartz veins, and weathered granite samples from South Bangka. The statistical analysis carried out using the Pearson correlation coefficient and multivariate processing showed that Sn-REEs have a weakly negative correlation. The examination of genetic aspects through chemical analysis, mineralogy, and Scanning Electron Microscope (SEM) data, showed that Sn and REE originated from the same magmatic fluids but different depositional phases due to magmatic-hydrothermal processes. The results show that REEs were formed during the early magmatic crystallization as mineral and stannite (Cu-Sn) in granite, while Sn was enriched as cassiterite in the deposition of late-stage hydrothermal fluid in parental granite. Moreover, the variation in deposition stage and temperature during the formation process is depicted in statistically uncorrelated values for Sn and REEs.

Secondary Enrichment of REE in Weathered Granite, South Bangka, Indonesia

Rare earth elements (REEs) are essential materials for the manufacture of advanced technology. Secondary REE indications were found in alluvial and lateritic tin deposits within Southeast Asia Tin Belt. This study aims at the REE enrichment of weathering profiles underlain by Toboali Pluton of the main range S-type granite of this belt. Granite and weathering samples were collected and analyzed using XRF, ICP-MS/OES, XRD, SEM-EDX, and EPMA. The Chondrite-normalized REE patterns of granite in Toboali showed enrichment in REE with the highest value of 1,126 ppm. The Toboali Pluton is enriched in LREE and depleted in HREE. The enrichment of REE from the upper to lower horizon of weathering profiles was pointed out by the increase in REE values from a range of 156-188 ppm (horizon B) to 196-268 ppm (horizon C) in Toboali, and from a range of 230-330 ppm (horizon B) to 342-450 ppm (horizon C) in Air Gegas. These coincided with the presence of kaolinite with elevated REE and CeO2 in horizon C of weathering profile. Leaching test result proved that kaolinite plays a role in REE enrichment in the weathering profile through ion adsorption mechanisms in the Air Gegas. The weathering process of REE fluoro-carbonate (bastnäsite-(Ce)) and parisite-(Ce) in granite is believed to contribute in enrichment due to its high dissolution rate, which enhances kaolinite adsorption. In contrast, REE phosphates such as monazite-(Ce) and xenotime-(Y), because of their strong resistance and low solubility, are thought to be only slightly soluble, and most of these minerals remain in Toboali weathering products.

Spatial distribution of trace and rare earth elements of bottom sediments in Lake Ostrowite, Bory Tucholskie National Park, Poland

AbstractLake pollution has attracted concerns worldwide; especially the excessive accumulation of trace elements (TEs) and rare earth elements (REEs) in bottom sediments can pose a serious threat to ecosystem health. However, there is still a knowledge gap on the level of sediment pollution in lakes isolated from the direct impact of pollution sources, their spatial variability, and also on the factors influencing this state. The aim of this study is to investigate the level and spatial variability of TEs and REEs concentrations, as well as to determine their source and the factors determining their distribution in the bottom sediments of Lake Ostrowite. Lake Ostrowite is the largest and deepest water body located in the Bory Tuholskie National Park (in northern Poland), which completely isolates the lake from the direct impact of pollution sources. The study covered analyses of 32 surface samples of bottom sediments. The concentrations of 24 TEs and 14 REEs were determined using inductively coupled plasma mass spectrometry (ICP‐QQQ‐MS). The assessment of the enrichment of bottom sediments in TEs and REEs employed geochemical background values (GBV) that provided the basis for the calculation of relative concentrations and geochemical indices. The determination of their sources and supply routes was based on the cluster analysis and principal component analysis. The obtained results point to the enrichment of the bottom sediments with TEs and REEs. Relative concentration values of TEs and REEs in reference to geochemical background values were in ranges from 0.01 to 7.31, at an average of 0.99, and from 0.03 to 4.29, averaging 1.76, respectively. The enrichment factor values show moderately severe enrichment of sediments at the study sites. This was primarily determined by the concentrations of Ag (from the TEs group) and Lu (from the REEs group). The metal pollution index values showed an approximate spatial distribution of points in terms of the presence of TEs and REEs. The lowest concentrations of TEs and REEs occurred on the eastern shore of the western basin of Lake Ostrowite. TEs and REEs concentrations in sediments are positively correlated with the content of organic matter and depth and negatively correlated with distance of the sampling point from the river outflow from Lake Ostrowite. On the eastern shore of the western basin, TEs and REEs concentrations are additionally shaped by wind, predominantly from the western direction. With water wave action, organic matter is transported to the central part of the western basin, where it is accumulated. Since the lake is isolated from point and nonpoint pollution sources, relevant from a biogeochemical point of view are dry and wet depositions from the atmosphere as well as aquatic vegetation, shoreline vegetation, forest litter, soil, and groundwater.

Pre-concentration of REE values from nepheline syenite rocks of western Odisha, India

ABSTRACT The rare-earth elements (REEs) have gained enormous economic and scientific attention due to their distinct properties and new applications. Nepheline syenite rock is an important primary source of rare earth minerals. The nepheline syenite rocks from the Rairakhol area, western Odisha, have been characterized for their rare earth mineralogical and textural characteristics. Preliminary beneficiation studies of these rocks were carried out to upgrade the REE values using falcon gravity separation and floatation technique. Hornblende, biotite, K-feldspar, albite, and nepheline are the major mineral constituents of the nepheline syenite where REE-bearing minerals occur as accessory minerals. The REE mineral phases present are zircon, sphene, apatite, allanite, britholite, and REE phosphate, with grain sizes ranging from 10 to 50 microns. Allanite and britholite occupy the intergranular spaces of major mineral phases and occur as thin lines or veins whereas sphene and zircon occur as inclusions within major mineral phases. The flotation study shows that the total REE content of the froth product could be enriched to 1696 ppm, which is three times more than the total REE content (563 ppm) of the feed sample.

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.

Origin of calcite cements in the Permian Lucaogou Formation tight reservoirs, Jimsar sag, Junggar basin, NW China: Constraints from geochemistry

Understanding the diagenetic evolution of carbonate cementation in hydrocarbon reservoirs is critical to better reconstruct the history of fluid flow during petroleum accumulation. The extensive occurrence of carbonate cements within the lower Permian Lucaogou Formation tight reservoirs is regarded as a major diagenetic factor that causes strong hydrocarbon reservoir heterogeneities. Petrographic and geochemical analyses, including optical microscopy fitted with cathodoluminescence, scanning electron microscopy, carbon and oxygen stable isotopes, in situ rare earth element, as well as fluid inclusion microthermometry, were carried out to decipher the origin of calcite cementation and understand its control on reservoirs quality. Petrography shows that the precipitating cements mostly consist of pore-filling blocky/mosaic calcite, with a dull orange luminescence color. Chondrite-normalized rare earth element (REE) patterns and C–O isotopic compositions of these calcite cements exhibit strongly negative Eu and Tb anomalies, enrichment in light REE, positive carbon (δ13CPDB = 0.58‰–7.45‰) and negative oxygen (δ18OPDB = −11.38‰ to −8.61‰) isotopic values, similar to the dolostone and micritized peloidal grains, suggesting that the calcite-precipitating fluids were derived from dissolution of lacustrine depositional carbonates. The relative timing of calcite precipitation in reservoirs was constrained based on the thermal-burial history of the study region and precipitation temperatures obtained from fluid inclusions. The results show that this cementation episode mainly occurred during the Late Triassic to Early Jurassic, which was synchronous with the tectonic uplift event. Moreover, homogenization temperatures of fluid inclusions and geochemical signatures of the calcite cement are similar to those of the fracture-fillings, suggesting that these two calcite phases may be genetically related and form coevally within one fluid flow system. It can be interpreted as a response to the compressional tectonic deformation given by the collision of the Qiangtang Block with the Eurasia Plate. This tectonic deformation event is regarded as the driver for calcite precipitation during the early burial stage, resulting in a considerable reduction of reservoir quality. Calcite cementation is pervasive and may play a main role in halting hydrocarbon migration through some of the permeable pathways in reservoirs.

Formation of barite in the Ab Torsh deposit, Kerman province, Iran: Insights from rare earth elements, O and S isotopes, and fluid inclusions

Barite can form in a variety of geological environments, as it occurs in a wide range of mineral deposits. To determine the origin and physicochemical conditions under which the Ab Torsh barite deposit formed, an extensive study was conducted using petrographic, Rare Earth Element (REE) geochemical, O and S isotopic, and fluid inclusion methods. Barite mineralization occurs at Ab Torsh as a stratabound vein in the Senonian carbonate rock units. Barite-quartz is accompanied by subordinate malachite, chrysocolla, Fe-Mn oxide-hydroxides, galena, azurite, fluorite, pyrite, and bornite. The ∑REE values are very low in barite (5.32–14.56 ppm), with chondrite-normalized patterns showing enrichment of Light Rare Earth Elements (LREE) relative to Heavy Rare Earth Elements (HREE). The low ∑REE content and REE element ratios (Ce/La, (La/La*)N, and (Gd/Gd*)N) indicate that seawater with a highly altered geochemical signature (connate water) acted as a Ba ore-forming fluid. The δ18O and δ34S values in barite (+10.4–+11.1 ‰ and +27.3–+27.8 ‰, respectively) and the δ34S values in galena (+6.3 and + 7.9 ‰) indicate that the sulfate (and thus sulfur) originated from sulfate-bearing connate waters and/or evaporites. Thermochemical Sulfate Reduction (TSR) was the most likely mechanism for the formation of the reduced sulfur in galena. The salinity and homogenization temperatures in the aqueous fluid inclusions of barite and quartz (2.7–19.3 wt% NaCl equivalent and 110–275 °C, respectively) indicate that basinal fluids containing a meteoric water component were the source of the mineralizing solutions. The fluid inclusion data demonstrate that two fluid mixing have occurred: one between the hot basinal brines and cold meteoric waters, and another between heated and cold meteoric waters. It is estimated that the hot fluids derived from a maximum depth of about 9 km. The Ab Torsh deposit is classified here as a structure (unconformity)-related barite deposit. It is concluded that intense faulting and brecciation of the host rocks caused by post-Cretaceous compressional tectonics probably provided the channels necessary for the upward migration of deep mineralizing fluids from a basinal brine source. Barite formed where these ascending hot, Ba-bearing hydrothermal fluids encountered cooler, sulfate-bearing connate waters trapped in the overlying Senonian strata and/or the descending cold meteoric waters that dissolved evaporite-bearing rock units.

Studies on hydrometallurgical recovery of rare earth elements as mixed fluoride compound from coal fly ash using environmentally friendly organic acid

ABSTRACT Coal fly ash (CFA) emerged as one of the potential secondary source of rare earth elements (REEs). This paper discusses development of a process scheme for the recovery of REE from a CFA sample, assaying total REE of about 0.2% using environmentally benign lactic acid (LA) as leachant. The CFA is generated at a lignite coal-based thermal power plant. The REE occurs dominantly in an ion-exchangeable form and also as bound to iron oxides. Nearly 25% of total REE is constituted of heavy rare earth elements (HREEs). About 89% of REE values were found leachable with LA at 80°C in 2 h of reaction time at 10% solids content. Kinetic analysis of leaching process shows that the reaction between CFA and LA is chemical reaction controlled with activation energy of 42–45 kJ/mol. The dissolved REE values were extracted quantitatively from leachate using D2EHPA solvent diluted in kerosene and stripped back with 6 N HCl. The REE in strip liquor was precipitated as mixed REE-fluoride concentrate of purity 86% with precipitation efficiency of 98%. A scheme for quantitative recovery of LA from barren stream was developed for its recycle in leaching circuit.

Trace element, rare earth element and trace carbon compounds in Subglacial Lake Whillans, West Antarctica

Whillans Subglacial Lake (SLW) lies beneath 801 m of ice in the lower portion of the Whillans Ice Stream (WIS) in West Antarctica and is part of an extensive and active subglacial drainage network. Here, the geochemical characterization of SLW rare earth elements (REE), trace elements (TE), free amino acids (FAA), and phenolic compounds (PC) measured in lakewater and sediment porewater are reported. The results show, on average, higher values of REEs in the lakewater than in the porewater, and clear changes in all REE concentrations and select redox sensitive trace element concentrations in porewaters at a depth of ~15 cm in the 38 cm lake sediment core. This is consistent with prior results on the lake sediment redox conditions based on gas chemistry and microbiological data. Low concentrations of vanillyl phenols were measured in the SLW water column with higher concentrations in porewater samples and their concentration profiles in the sediments may also reflect changing redox conditions in the sediments. Vanillin concentrations increased with depth in the sediments as oxygenation decreases, while the concentrations of vanillic acid, the more oxidized component, were higher in the more oxygenated surface sediments. Collectively these results indicate redox changes occurring with the upper 38 cm of sediment in SLW and provide support for the existence of a seawater source, already hypothesized, in the sediments below the lowest measured depth, and of a complex and dynamic geochemical system beneath the West Antarctic Ice Sheet.Our results are the first to detail geochemical properties from an Antarctic subglacial environment using direct sampling technology. Due to their isolation from the wider environment, subglacial lakes represent one of our planets last pristine environments that provide habitats for microbial life and natural biogeochemical cycles but also impact the basal hydrology and can cause ice flow variations.

Rare earth element bioaccumulation and cerium anomalies in biota from the Eastern Canadian subarctic (Nunavik)

Recent increases in the demand for rare earth elements (REE) have contributed to various countries' interest in exploration of their REE deposits, including within Canada. Current limited knowledge of REE distribution in undisturbed subarctic environments and their bioaccumulation within northern species is addressed through a collaborative community-based environmental monitoring program in Nunavik (Quebec, Canada). This study provides background REE values (lanthanides + yttrium) and investigates REE anomalies (i.e., deviations from standard pattern) across terrestrial, freshwater, and marine ecosystems in an area where a REE mining project is in development. Results are characteristic of a biodilution of REE, with the highest mean total REE concentrations (ΣREE) reported in sediments (102 nmol/g) and low trophic level organisms (i.e., biofilm, macroalgae, macroinvertebrates, common mussels, and reindeer lichens; 101–102 nmol/g), and the lowest mean concentrations in higher-level consumers (i.e., goose, ptarmigan, char, whitefish, cod, sculpin and seal; 10−2 - 101 nmol/g). The animal tissues are of importance to northern villages and analyses demonstrate a species-specific bioaccumulation of REE, with mean concentrations up to 40 times greater in liver compared to muscle, with bones and kidneys presenting intermediate concentrations and the lowest in blubber. Further, a tissue-specific fractionation was presented, with significant light REE (LREE) enrichment compared to heavy REE (HREE) in consumer livers (LREE/HREE ≅ 101) and the most pronounced negative cerium (Ce) anomalies (<0.80) in liver and bones of fish species. These fractionation patterns, along with novel negative relationships presented between fish size (length, mass) and Ce anomalies suggest metabolic, ecological, and/or environmental influences on REE bioaccumulation and distribution within biota. Background concentration data will be useful in the establishment of REE guidelines; and the trends discussed support the use of Ce anomalies as biomarkers for REE processing in animal species, which requires further investigation to better understand their controlling factors.

Rare Earth Partition Characteristics and Sedimentary Diagenetic Response in Layered Argillaceous Limestone: Taking the Shale of Upper Es4 in the Nx55 Well Area as an Example

Taking the layered argillaceous limestone in the upper Es4 in the Dongying Sag as the research object, the geochemical analysis of major, trace, and rare earth elements (REEs) established the response relationship between REE distribution characteristics and sedimentary diagenesis. The average values of total light REE ( Σ LREE )/total heavy REE ( Σ HREE ) of micrite calcite and argillaceous laminae are 6.75 and 4.06, respectively. The LREEs and HREEs are differentiated, consistent with the distribution pattern of REEs in the crust. Th and U elements are more enriched in the sediments in the lacustrine sedimentary environment than in the diagenetic calcite veins. In primary sediments (argillaceous clay and micrite calcite laminae), LREEs are more enriched, HREEs are depleted, and Eu shows positive anomaly-enrichment characteristics. The LREEs and HREEs of the sparry calcite veins are lower than those of the original sediment argillaceous clay and micrite calcite, showing characteristics of a negative anomaly depletion. Sparry calcite veins originate from diagenetic fluid crystallization and precipitation and have the characteristics of low Th and U, evident positive anomalies of Sr and Eu, and substantial depletion of La. The distribution patterns of REEs within the four components of the laminated argillaceous sparry limestone reflect the order of REE distribution from primary sediment laminae (argillaceous clay and micrite calcite) to diagenetic laminae (calcite veins). Compared with the North American shale, the four components of the contact surface between the argillaceous and bright crystalline laminae, the micrite calcite, the calcite veins, and the argillaceous laminae all showed weak negative δ Ce anomalies and positive δ Eu anomalies. The fractionation degree between LREEs and HREEs reflected by La / Sm cn and Gd / Yb cn is in descending order: the interface between the argillaceous lamina and sparry calcite lamina, micritic calcite, calcite vein, and argillaceous lamina. The argillaceous laminar material has the characteristics of basalt REEs, indicating that the terrestrial debris and argillaceous lacustrine shale in the upper Es4 member of the Niuzhuang subsag are primarily derived from the basic extrusive rocks of the Qingtuozi bulge. REE differentiation is most noticeable at the interface between the argillaceous lamina and calcite vein, proving the directionality of REE differentiation from the original sedimentary lamina to the diagenetic lamina. Shale in the study area is primarily deposited below the redox interface of water at a certain depth, and the deposition rate is stable and slow, providing good conditions for preserving organic matter.

Organic-matter-rich Pennsylvanian Black Shales as a Source of Critical Minerals

This study examines Pennsylvanian shales in Indiana as a potential source of selected critical elements: rare earth elements (REE), vanadium (V), zinc (Zn), arsenic (As), and cadmium (Cd). Widespread, organic-matter-rich marine Desmoinesian black shales are the main target, but other discontinuous shale horizons were also sampled in 11 locations. In total, 39 shale samples were analyzed in this study. The shales are early mature and represent the early oil generation window. The average concentrations of REE in the marine shales studied vary from 164.9 ppm in the Excello Shale to 338.7 ppm in the Carrier Mills Shale. REE distribution patterns show that most shales have REE values roughly representative of the upper continental crust (UCC). Only one sample of the Carrier Mills Shale was enriched compared to the upper continental crust (REE concentration/UCC&gt;5). The shales are characterized by high uranium (U) content, with averages for marine shales from 70.8 ppm in the Excello Shale to 133.8 ppm in the Veale Shale. In contrast, non-marine shales grouped under “other shales” category had the lowest U concentration of 3.3 ppm. Molybdenum (Mo) concentrations in the marine shales are very high at places exceeding 1000 ppm. Among the shales studied, the Mecca Quarry Shale is the most enriched in Mo (average 1103.8 ppm), followed by the Veale Shale (876.7 ppm). The “other shales” category has the lowest Mo content (2.5 ppm) due to deposition under oxygenated conditions. The marine shales are highly enriched in Zn, As, and Cd. Specifically, the Mecca Quarry Shale is the most enriched in Zn, with some samples having content as high as 5480 ppm. Furthermore, the Excello Shale and the Veale Shale have Zn concentrations more than ten times higher than the UCC (~70 ppm). The As content is the highest in the Veal Shale, averaging 61.7 ppm, and some samples reach more than 200 ppm — highly enriched compared to 1.8 ppm in UCC. The Excello Shale, Mecca Quarry Shale, and Veale Shale are all strongly enriched in Cd (76.1, 74.2, and 49.2 ppm on average, respectively), and the Carrier Mills Shale has the lowest average value of 8.5 ppm. These data demonstrate that Pennsylvanian marine black shales are a potential resource of V, Zn, As, and Cd, whereas in non-marine shales, the concentrations of these elements are much lower. In turn, the REE potential needs further investigation; more data are needed to better understand REE concentrations and their associations.

Hydrometallurgical Studies for the Recovery of Rare Earths from Micro-Granite Ore Deposit of Bhatikhera, Rajasthan, India

Abstract This paper presents results on the characterization and hydrometallurgical studies for the recovery of Rare Earth Elements (REE) from micro-granite type hard rock REE deposit of Bhatikheda, Siwana Ring Complex, Rajasthan, India. The total REE (TREE) content of the ore is 0.36%. Heavy REE (HREE) constitutes about 40% of the TREE by weight. Allanite, zircon and gittinsite were identified as the major REE bearing phases. The nature of occurrence of REE phases in the ore is widely varying with the presence of fully liberated grains to those which occur very finely disseminated in lighter gangue minerals. Physical beneficiation using gravity-based separation techniques gave suboptimal performance. Agitation leaching of ground ore with different mineral acids gave good solubilisation of light REE (LREE), about 75%, but the leach recovery of HREE was only 40%. However, sulfation roasting followed by aqueous leaching (SRAL) yielded leach recovery of 85% of total REE under optimised conditions. The lean tenor of TREE in the leachate coupled with its complex solution chemistry necessitated use of ion exchange (IX) process with strong cationic resin in lieu of conventional solvent extraction based separation and purification. The dissolved REE values from the purified liquor were quantitatively precipitated in the form of TREE fluoride using HF as the precipitant. The final product was about 90% pure on dry weight basis. An integrated process scheme for the recovery of TREE values from the Bhatikhera hard rock deposit is designed-

An acid baking approach to enhance heavy rare earth recovery from bituminous coal-based sources

The recovery of rare earth elements (REEs) from secondary resources, particularly coal-based materials, has recently received attention due to supply and demand imbalance. Research reported to date indicates that a high REE recovery can be realized when treating bituminous coal sources using strong acid solutions of approximately100 g/L or higher. This study introduces an approach to enhance the total rare earth recovery (TREE), especially for heavy rare earth elements (HREEs), from these coal sources at significantly lower acid concentrations. Based on the presence of REE minerals like monazite and xenotime, a detailed investigation was undertaken to quantify three pre-leach treatment methods, i.e., 1) roasting, 2) direct acid baking, and 3) acid baking after roasting. Roasting tests at 600 °C revealed that the recovery of light REEs (LREEs) was enhanced while the recovery of HREEs remained relatively unaffected. LREE and HREE recovery values of 38.3% and 21.3%, respectively, were achieved using a 50 g/L (0.5 M) sulfuric acid solution at 5% solid concentration and a solution temperature of 75 °C for 2 h. Comparatively, direct acid baking at 250 °C provided substantial increases in LREE and HREE recovery values to approximately 49.4% and 53.0%, respectively, using an equivalent acid dosage. Recoveries were maximized to 77.0% and 79.6% for LREE and HREE, respectively, by roasting followed by acid baking. Similar results were obtained from the treatment of a second bituminous coal source. Due to strong correlations between REE and Al recovery values, tests were performed on kaolinite and illite, which were prominent clay minerals within the source coals. These experiments revealed that the REE recovery improvements were likely a result of dehydroxylation of clays and subsequent release and decomposition of REE-bearing minerals such as monazite, xenotime and zircon.

Geochemistry and environmental effects of rare-earth elements in laterites from Yunnan province, SW China

Rare-earth elements (REEs) in soils are influenced by pedogenic processes and anthropogenic activities. To interpret the fractionation and migration of REEs during weathering in (sub-)tropical regions, the distribution, fractionation patterns and environmental effects of REEs in laterites were investigated in this study. Soil samples from two laterite profiles (labelled S1 and S2) were collected and the concentrations of REEs were measured with an inductively coupled plasma mass spectrometer. The results suggest that the Σ REEs of S2 (119 ± 10 mg kg –1 to 209 ± 10 mg kg –1 ) have a higher concentration and a wider variation than those of S1 (114 ± 5 mg kg –1 to 154 ± 8 mg kg –1 ). The REEs in both laterite profiles are enriched in the order HREEs &gt; LREEs &gt; MREEs. The distribution patterns of laterite profiles show evidence of inheritance from parent granites. The laterites preferentially incorporated HREEs, and secondary Fe 2 O 3 and clay minerals were likely to affect the fractionation of REEs in laterites. The enrichment factor of REEs varied from 11.1 to 18.9 for S1 and 10.0 to 27.6 for S1, indicating potential pollution by REEs. The accumulation of REEs in laterites by mining activity should be a concern of government environmental agencies. Supplementary material: Table S1, Reference values of REEs and Fe 2 O 3 in standard materials (GSS-18 and GSS-20); Table S2, Measurement parameters of ICP-MS; Table S3, Concentrations of REEs and Fe 2 O 3 in laterite profiles from Yunnan province, SW China; Table S4, The enrichment factor for the laterite profiles from Yunnan province, SW China are available at https://doi.org/10.6084/m9.figshare.c.5609234

Coal characterization and occurrence of rare earth elements in coal and coal-ash of Sohagpur Coalfield, Madhya Pradesh, India

ABSTRACT Coal is a valuable source for power energy as well as for metal contents within it. Coal and its by-product are considered a promising resource for the critical elements and rare earth elements (REEs). The study of REEs in coal is in its infancy. This paper focuses on REEs’ occurrence, qualitative, and quantitative in coal and its by-products (shale coal, shale coal ash, and coal ash) of Sohagpur Coalfield, Madhya Pradesh, India. The collected coal samples were analyzed by scanning electron microscope with energy-dispersive X-ray analysis, inductively coupled plasma mass spectrometry, bomb calorimeter, thermogravimetric analysis, and ultimate analysis. The REEs’ concentration of Sohagpur Coalfield was also compared with the Chinese coal, US coal, and world coal average. The average content of critical REEs for Y is 51.49 ppm, for Nd is 79.34 ppm, for Eu is 2.67 ppm, for Tb is 1.71 ppm, and for Dy is 9.76 ppm in samples. The highest average values of REEs reported for Ce are 58.15 ppm in coal and 187 ppm in coal ash by-products. Coal by-products of the collected samples are a good resource for REEs than the Chinese coal, US coal, and world coal averages.

Selective incorporation of rare earth elements by seaweeds from Cape Mondego, western Portuguese coast

This study examined the mechanism of incorporation of the rare earth elements (REEs), La, Ce, Nd, Eu, Gd, Tb, Yb, into green (Codium tomentosum, Ulva rigida), red (Gracilaria gracilis, Osmundea pinnatifida, Porphyra sp), and brown seaweeds (Saccorhiza polyschides, Undaria pinnatifida) collected from a single site near the coastline of the Cape Mondego, western Portugal. The concentrations of REEs, Mg, Ca, Al, Fe, Zn, and Cu in the biomasses were determined by inductively-coupled plasma mass spectrometry (ICP-MS). The species showed differences in their incorporation and fractionation of REEs from the same environment: the sum of REEs was higher in U. rigida, C. tomentosum, G. gracilis, and O. pinnatifida (0.7–1.7 μg g−1) than in Porphyra sp., S. polyschides, and U. pinnatifida (0.1–0.2 μg g−1). Ratios of Ce/Yb ranged from 13 (in S. polyschides) to 103 (in U. rigida), indicating different proportions of light and heavy REEs among species. Good correlations were found between Al and Fe (R2 = 0.98), and between these elements and La, Ce, Nd, Gd (R2 = 0.88–0.97) and Yb (R2 = 0.66–0.71) for all species except C. tomentosum and G. gracilis. Profiles of REE values normalised to average upper-continental crust composition indicated positive anomalies of Eu and Tb that reinforced the singularity of these elements in the REE group. Correlations between the REEs and Al or Fe suggest that detrital terrigenous particles, adhered to seaweed walls, may be an important mechanism for the incorporation of REEs by seaweeds. Different patterns for C. tomentosum and G. gracilis may also be indicative of the higher influence of cell wall composition on REE incorporation.

Distribution of rare earth elements in soils of contrasting geological and pedological settings to support human health assessment and environmental policies.

Establishing quality reference values (QRVs) for rare earth elements (REEs) in soils is essential for the screening of these emergent contaminants. Currently, Brazil has the second-largest reserve of REEs, but data regarding background concentrations and distributions in soils remain scarce. The aim of this study was to establish the QRVs and assess the spatial distribution of REEs in soils, including REE fractionations and anomalies in (Piauí) state (251,529.186 km2), northeastern Brazil. This study reports the most detailed data on REE geochemistry in Brazilian soils. A total of 243 composite soil samples was collected at 0-20cm depth. The mean background concentrations in soils followed the abundance of the earth's upper crust: Ce > La > Nd > Pr > Sm > Dy > Gd > Er > Yb > Eu > Tb > Lu. The ∑REEs (mg kg-1) showed the following order based on the individual mesoregions of Piauí state: Southeast (262.75) > North and Central-North (89.68) > Southwest (40.33). The highest QRVs were observed in the Southeast mesoregion. The establishment of QRVs based on the mesoregion scale improves data representativeness and the monitoring of natural REE values by identifying hot spots. Geostatistical modeling indicated significant local variability, especially in the Southeast mesoregion. The levels of these elements in this spatial zone are naturally higher than the other values across Piauí state and the mesoregion itself and indicate a high potential to exceed the QRVs. Our approach provides much needed data to help strengthen policies for both human health and environmental protection.

Genesis of the Yingzuihongshan Tungsten Deposit, Western Inner Mongolia Autonomous Region, North China: Constraints from In Situ Trace Elements Analyses of Scheelite

In situ analyses of trace elements and rare-earth elements (REEs) were performed by use of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on scheelite samples from the Yingzuihongshan tungsten deposit in western Inner Mongolia Autonomous Region, China. The contents of trace elements Nb, Ta and Mo of scheelite indicate that the ore-forming fluid is magmatic hydrotherm and is exsolved from highly fractionated granitic melt. The scheelite has high REE contents and ∑REE values, and a very inhomogeneous distribution of REEs exists in different scheelite grains or even in one scheelite grain. The cathodoluminescence (CL) images of scheelite grains display well-developed zoning or fine oscillatory zoning. Development of zoning is closely related to the variable contents of REEs, and the darkness of shade of CL images are mainly determined by ∑REE values, but they have no correlation with the distribution patterns of REEs. The chondrite-normalized REE distribution patterns of scheelite are classified as the middle REEs (MREEs)-enriched type, except for a strong negative Eu-anomaly, which could be a REE-flat type and or a MREEs-depleted type. Trace element composition of scheelites from the Yinzuihongshan tungsten deposit reflect that the ore-forming materials mainly came from the crust and the ore-forming fluids are dominantly derived from the granitic magma in an oxidizing environment, in which very dynamic conditions of the hydrothermal system prevailed during precipitation of scheelite. On the basis of the above understanding and field geological featured, we considered that the Yingzuihongshan tungsten deposit is the quartz-vein-hosted tungsten type that is genetically associated with monzonitic granite.