Total Rare Earth Elements Content Research Articles

Rare Earth Elements in the Seagrass Zostera noltei and Sediments from the Black Sea Coast of Crimea

In the present work, we assessed the contents of rare earth elements (REEs), including yttrium and scandium, in rhizomes and leaves of the widespread seagrass Zostera noltei Hornemann 1832 and in the nearby sediments from the Black Sea coast. The total REE content in the sediments was found to be much higher than in Z. noltei. The order of decrease in the major REE contents in the sediments and the seagrass rhizomes was identical, except for La and Y. La was the most abundant in the sediments, and Y in the rhizomes. The contents of all REEs in rhizomes of Z. noltei were 1.5–10 times higher than in the leaves. The highest difference in the REE contents was found for the minor elements (Sm–Lu). The translocation factors for Sc and the minor elements (excluding Tb) from the sediments to the rhizomes and from the rhizomes to the leaves turned out to be pairwise equal, which indicates the similarity of the REE translocation mechanisms. Comparing our results with the literature data, it is possible to conclude that the seagrass Z. noltei does not have an advantage in the REE accumulation over marine macroalgae. At the same time, large coastal deposits of this seagrass after storms allow us to consider it as a possible source of REEs in the future.

Fluid-mineral dynamics at the Rincón de la Vieja volcano—hydrothermal system (Costa Rica) inferred by the study of major, minor and rare earth elements in the hyperacid crater lake

Volcanic lakes are complex natural systems and their chemical composition is related to a myriad of processes. The chemical composition of major, minor, Rare Earth Elements (REE) and physico-chemical parameters at the hyperacid crater lake of Rincón de la Vieja volcano (Costa Rica) are here investigated during February 2013–August 2014. The study of the lake chemical composition allows to identify the main geochemical processes occurring in the lake and to track the changes in the volcanic activity, both important for active volcanoes monitoring. The total REE concentration (∑REE) dissolved in the crater lake varies from 2.7 to 3.6 mg kg−1 during the period of observation. REE in the water lake samples normalized to the average volcanic local rock (REEN-local rock) are depleted in light REE (LREE). On the contrary REEN-local rock in the solids precipitated (mainly gypsum/anhydrite), from lake water samples in laboratory at 22°C, are enriched in LREE. The low variability of (La/Pr)N-local rock and (LREE/HREE)N-local rock ratios (0.92–1.07 and 0.66–0.81, respectively) in crater lake waters is consistent with the low phreatic activity (less than 10 phreatic eruptions in 2 years) observed during the period of observation. This period of low activity precedes the unrest started in 2015, thus, it could be considered as a pre-unrest, characterized by infrequent phreatic eruptions. No clear changes in the REE chemistry are associated with the phreatic eruption occurred at mid-2013. The results obtained investigating water-rock interaction processes at the Rincón de la Vieja crater lake show that rock dissolution and mineral precipitation/dissolution are the main processes that control the variability of cations composition over time. In particular, precipitation and dissolution of gypsum and alunite are responsible for the variations of REE in the waters. Despite the low variations of (La/Pr)N-local rock and (LREE/HREE)N-local rock ratios, this study allows to suggest that REE can be used, together with major elements, as practical tracers of water-rock interaction processes and mineral precipitation/dissolution at active hyperacid crater lakes over time, also during periods of quiescence and low phreatic activity.

Dataset of rare earth elements distribution in soils and vegetables

This paper presents a comprehensive data set on rare earth elements (REE) and their distribution in soils and vegetables in an area where the soil background is enriched with these elements. The study examined REE distribution in six vegetables commonly grown in local residents' gardens, including fennel, garlic, lettuce, parsley, onion, and raddichio, and each plant was analyzed for REE composition in its root, stem, and leaf or bulb. In addition to total REE concentrations in soils and plants, the data set includes transfer factors and fractionation indices for REE in soils, as well as normalized curves. This dataset may be useful in the field of soil geochemistry and research on the uptake of lanthanides into plants and the food chain, as well as their potential effects on human health.

High-temperature magnetic performance and corrosion resistance of hot-deformed and sintered Nd-Fe-B magnets with similar room-temperature magnetic properties

Both hot-deformed (HD) and sintered Nd-Fe-B magnet have huge prospect in the application of permanent magnet servomotor, but its magnetic performance is often influenced by increased working temperature and corrosion environment. Hereby, the high-temperature magnetic performance and corrosion resistance of HD magnets and sintered magnets with similar room-temperature magnetic properties were investigated. The melt-spun Nd-Fe-B powders of MQU-F and MQU-G have been used to prepare the HD magnets without (HDF) and with (HDG) heavy rare earth of Dy element. The sintered magnets of 45H grade (S45H) and 35UH grade (S35UH) were used as reference magnets to evaluate the high-temperature magnetic performance and corrosion resistance of HDF and HDG, respectively. The results show that both HDF and HDG have superior temperature coefficient of coercivity (β), irreversible flux loss (hirr) and corrosion resistance to the same-grade sintered magnets. The analysis on microstructure and element composition reveals that the difference in β and hirr between HD and sintered magnets is mainly resulted from grain size and Pr content. The nanograins in HD magnets are much smaller than the micrograins in sintered magnets. Consequently, |β| and hirr reduces significantly with the decrease of grain size. Meanwhile, the Pr-contained sintered magnets of S45H and S35UH consist of both Pr2Fe14B and Nd2Fe14B phases. As the magneto-crystalline anisotropy of Pr2Fe14B decreases faster than that of Nd2Fe14B with the increased temperature. |β| and hirr of the HDF and HDG are better than those of the same-grade sintered magnets. In addition, the difference in corrosion resistance is primarily caused by the grain boundary (GB) width, the total rare earth (TRE) content and Co content. The corrosion on Nd-Fe-B magnet initiates from and propagates along GB and the boundary of flake particles at the surface of HD and sintered magnets. The narrower GB width, lower TRE content and higher Dy content all play important role in better corrosion resistance of HD magnets.

Zircons in NYF-type pegmatites in the Emeishan large igneous province, SW China: A record of Nb and REE mineralization processes

The metallogenic mechanism of Nb and rare earth elements (REEs) during the magmatic-hydrothermal evolution of alkaline rocks remains ambiguous. Zircon is a common accessory mineral occurring in both barren aplite and the Nb-Y-F mineralized pegmatite (NFY-type) in Miyi County of the Pan-Xi area, the central zone of the Permian Emeishan large igneous province (ELIP) in SW China. Here, we present in situ geochemical analyses on these zircons to reveal the Nb-REE mineralization processes during magmatic-hydrothermal evolution, as well as the prospecting potential of plume-related NYF-type pegmatites. Four types of zircons are identified in the Miyi aplite and pegmatite. Zrn-I with well-developed oscillatory zoning (OZ) represents magmatic zircons in the aplite. Zrn-II and Zrn-III are magmatic zircons in the pegmatite. Zrn-II is closely associated with albite and is restricted to the center of an individual crystal, indicating early crystallization. There are abundant nanoscale britholite and thorite inclusions in Zrn-II, indicating that the primary melt is enriched in Ca, Y, REEs, Nb, Th, and F. Zrn-III presents as the rim of Zrn-II, with a sharp boundary between them. Zrn-IV is a metamict zircon formed through hydrothermal alteration after its structure was destroyed due to high Th and/or U contents. In situ zircon U-Pb dating of both Zrn-I and Zrn-III yields concordant ages of ca. 258 Ma, coeval with the felsic magmatism in the ELIP. For positive εHf(t) values of Zrn-I and Zrn-III (1.8–5.8 and 1.5–9.1, respectively), the Miyi pegmatite is also plume-related and might be derived from magma resembling A-type granite in the ELIP. Both Zrn-I and Zrn-III show negative Eu anomalies, and there is a decrease in Sc contents from Zrn-I to Zrn-III, indicating that the Miyi pegmatite formed from a highly evolved magma. Furthermore, the synchronous increases in Na, Nb, Y and total REEs from Zrn-I to Zrn-III indicate that excess Na in the melt plays an essential role in the further enrichment of Nb, Y, and REEs. In addition, a dramatic decrease in Nb, Y and total REE contents and LREE (light REE)/HREE (heavy REE) ratios from Zrn-III to Zrn-IV illustrates that Na- and F-rich hydrothermal fluids can leach and facilitate the precipitation of these elements, particularly LREEs. Therefore, there are two-stage Nb and REE mineralization processes related to magmatic-hydrothermal evolution in the Miyi pegmatite, which may be a general model for the mineralization of plume-related NFY-type pegmatites.

Rare earth elements in sands collected from Southern California sea beaches

Rare earth elements (REEs) are considered the limiting resources for advancing clean technologies and electronics. Because global REEs reserve is limited, non-conventional and secondary sources are being investigated for recovery. Here, we investigated wet and dry sand from seven Southern California beaches for sixteen REEs. These include five light REEs, two medium REEs, and nine heavy REEs, separated by their atomic weight. The mass of the magnetically separated compounds ranged from 15.19 to 129.91 g per kg of dry sand in the studied sea beaches in Southern California. The total REEs concentration ranged from 1168.1 to 6816.7 μg per kg of wet sand (dry sand basis) and 1474.7–7483.8 μg per kg of dry sand. Cerium (Ce) and Yttrium (Y) were the most prevalent REEs in these beaches ranging from 387.4 to 2241.1 μg kg−1 and 104.5–2302.3 μg kg−1 of sand respectively. This study found light REEs concentration accounted for 70–80% of total rare earth elements in the studied beaches. The concentrations of the analyzed REEs were significantly different (p < 0.05) from each other in the studied beaches. Additionally, Pearson correlation showed that the REEs were strongly correlated (r ≥ 0.83) with each other in the reported sea beaches, indicating a similar origin of the REEs. The dominant heavy metals in the studied samples were Vanadium (V), Chromium (Cr), Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn), and Strontium (Sr). Dominant minerals identified in sands were quartz, anorthite, ilmenite, and xenotime. All the beaches are lowly enriched with REEs, and any of the REEs caused no ecological risk or pollution. Similarly, no pollution/ecological risk was observed for the analyzed heavy metals. This study identified beach sand as a potential REEs source and demonstrated an easy separation of REEs containing magnetic compounds from sand.

Evolution of strength with rare-earth content in highly-alloyed Mg-Gd-Y alloys

Mechanical properties of extruded Mg-Gd-Y alloys are investigated as a function of rare-earth content within the high concentration range. The strength is found to change non-monotonously with the total rare-earth content. A maximum of tensile yield strength (275 MPa) and ultimate tensile strength (348 MPa) is achieved at ∼18 wt. % rare-earth content. While grain refinement and solid solution strengthening mechanism are found to primarily contribute to the value of yield strength, the change of solid solution strengthening due to the competitive balance of solid solubility between the alloying species is demonstrated to dominate the non-monotonous evolution of tensile yield strength upon rare-earth content. In addition, the increased block precipitates deteriorate the capacity of plastic deformation and decrease tensile strength at high rare-earth content. The present findings provide helpful guidance for the intelligent design of highly-alloyed Mg alloys.

Abundant off-axis hydrothermal activity in the 29–30 ridge segment of the Southwest Indian Ridge: evidence from ferromanganese crusts

In the ultra-slow spreading mid-ocean ridge, seafloor hydrothermal ventings mostly occur in the off-axis region. The plume of hydrothermal venting provides Fe, Mn and other metal materials for the growth of ferromanganese crust in the surrounding seamounts, showing unique geochemical characteristics that are different from that of hydrogenetic crust. Based on five samples of ferromanganese crusts, major, trace and rare earth element analysis was carried out to identify their material sources. Combined with the investigation data of water column and seafloor camera photos by deep towed hydrothermal detection system, the potential of hydrothermal activity in the 29–30 ridge segment of the Southwest Indian ridge was evaluated. The results showed that the ferromanganese crust in the study area had significantly higher Fe/Mn value (average 1.9), relatively higher Si and Al contents, and significantly higher Ca/P value (average 9.3),without significant phosphorylation. ferromanganese crust in the study area have significantly lower Co and Ni contents (about 1600 mg/kg on average), and relatively lower Sr, Ba, Pb, Cu, Zr and Mo contents (between 100-1000 mg/kg on average). The contents of W, Th and Te are also relatively low (average content between 10–50 mg/kg); The total rare earth element content of the crust in the study area is relatively low (about 928 mg/kg on average), and the light rare earth is relatively enriched. The standardized rare earth curve of the shale shows a left-leaning pattern as a whole, showing the enrichment of heavy rare earth relative to the shale. The Co content and rare earth element content of the ferromanganese crusts in this area are significantly lower than those of hydrogenetic crusts. The discrimination diagrams of ternary and bivariate material sources reveal that they have mixed hydrothermal and hydrogenetic origins. The three crust samples of S1, S2, and S5 are located within 2 km of the known hydrothermal fields, indicating a correlation between ferromanganese crust and the location of hydrothermal activity. There is no known hydrothermal field near the S3 and S4 stations. Altered rocks and water column turbidity anomalies were found near S3 station, and large areas of altered rocks and suspected hydrothermal biological remains were also found near S4 station, indicating that hydrothermal activity may exist in both areas. In addition to the two new hydrothermal fields identified in this article, the spatial frequency of hydrothermal activity in the study area reaches 15 sites/100 km, which is significantly higher than other well investigated oceanic ridges. Out of the eight hydrothermal fields in the study area, seven are located in the off axis region, mainly because the hydrothermal activity in this area is controlled by high angle and large offset normal faults and one-way detachment faults. This also indicates that the off-axis region of the Southwest Indian Ridge has high potential for hydrothermal activity.

Arsenic contamination and rare earth element composition of acid mine drainage impacted soils from South Africa

Acid mine drainage (AMD) impacted soils occur as soils near weathered pyritic mine tailings, directly receiving AMD or in proximity to AMD polluted waters. They pose environmental and human health risks and present challenges to restoration strategies for better land use management. This study investigated the chemical composition and geochemical evidence of AMD impact in four top soils from gold and coal mining regions near Johannesburg, South Africa with a focus on characterising metal contamination and rare earth element (REE) content. Soil physico-chemical properties (pH, electrical conductivity, texture, cation exchange capacity, carbon content, and sulfate) were measured and analysed and pseudo-total elemental contents were determined from a microwave digestion analysed by ICP-MS. The results showed evidence of soil acidification and exceedingly high sulfate (>7000 mg kg−1) and calcium (>200 g kg−1) contents. High arsenic contents (>300 mg kg−1) were found for some of the samples, exceeding the national soil screening value of 23 mg kg−1. Total REE content ranged from 51.7 to 110 mg kg−1 and favoured the light over heavy rare earth elements. The results suggest that there are complex dynamics between AMD and soil element fractions. Arsenic was unexpected as it had not previously been well documented in AMD polluted groundwater, surface waters, or mine seepage from the region, and REEs, with which AMD is often enriched, were not retained in the topsoil samples. These novel findings indicate major challenges to post-mining land rehabilitation.

Distribution, source and contamination of rare earth elements in sediments from lower reaches of the Xiangjiang River, China

Rare earth elements (REEs) are emerging micropollutants in aquatic environments. In this study, concentrations of REEs and major elements, and mineralogical compositions of sediments from lower reaches of the Xiangjiang River (China) were analyzed using ICP-MS technique. The results suggested that sediments were characterized by terrigenous compositions TiO2, SiO2, Al2O3, K2O, Na2O and P2O, and contained high concentrations of REEs with mean total REE concentrations (∑REE) of 318.7 mg/kg. REEs were moderately enriched in upper river sediments, and slightly or less enriched in downriver sediments. The normalized REE distribution pattern for sediments was characterized by flat shalelike and Eu depleted V-shape REE patterns, which indicated REEs in sediments were lithologically contributed from sedimentary rocks and granites distributed in the watershed respectively. REEs in sediments were hosted mainly in Fe–Mn oxides, and sulfide and organic matters that were characterized by middle REEs (MREE) enrichments relative to light REEs (LREE) and heavy REEs (HREE), and the distribution and differentiation of REEs in sediments were controlled by clays, Fe–Mn oxides, organic matters and finer grains; and also by accessory minerals (e.g., zircon) from granite. The distribution features of REEs in sediments and BCR extraction results suggested that the sediment REE enrichment resulted from additional REE input from anthropogenic sources, including those in discharges from sulfide-ore smelting industries at Zhuzhou city and from phosphate fertilizer plants at Xiangtan city along the river. Thus, sediments were contaminated with REEs in moderate degree in upper river area, and REE contamination was then formed by superimposing anthropogenic REEs on lithological residues. Finally, concentrations of Ce > 100 mg/kg, Gd > 8.12 mg/kg, ∑REE >274.9 mg/kg, ∑LREE >252.3 mg/kg and ∑HREE >28.8 mg/kg here were recommended as the REE contamination levels that represented as REE indices for identifying and rating REE contamination in this mining impacted river.

Extraction of rare earths from coal and coal by-products as a non-traditional source

Rare earth elements (REEs) are one of the critical metals used for modern technological applications and green technologies. Due to growing demand and limited availability, there is a huge supply risk associated with REEs. The primary resources of rare earths in India are limited and associated with many processing challenges. In this scenario, it is important and timely to explore the non-traditional sources of rare earths to meet the domestic demand of country in the future. India is rich in coal deposits. The studies are very limited and there is scarcity of the research work carried out on the extraction of rare earths from Indian coal and coal by-products. Therefore, the objective of the present research article is to highlight the presence of REEs in Indian coal along with coal by-products. The objective is to identify the sweet pots of rare earths in coal and coal by-products. The concentration of total REEs is in the range of 150–200 ppm in coal samples. Furthermore, coal ash contains the concentration of total REEs which is more than 600 ppm in the samples of study area. It is aimed to review the several methods to recover rare earths that can be economically applied for the extraction of rare earths from coal and its by-products. Column leaching experiments achieve a 50% recovery rate of REEs from coal, while thermal treatment of coal enhances the recovery rate by one and a half times compared to untreated samples. Process optimization experiments demonstrate the superiority of the flocculator jar test apparatus, resulting in a significant increase in REE recovery (52% from coal samples). It was found that there is a huge work is still needed to be done for the development of an energy efficient and economical recovery of rare earths from coal and its by-products.

Geology and Rare Earth Element Geochemistry of Magnesian Granitoids Within Proterozoic Schist Belt of Southwest Nigeria

Abstract The increased global demand for and price of rare earth elements (REEs) has led to intensive search for them in rocks of the upper continental crust all over the world. This study is aimed at characterising the granitoids at Okeho within Southwestern Nigeria using geochemical data and assessing their potential for REE enrichment. Ten representative rock samples of the Proterozoic intrusives, syenite and granodiorite, were studied for their mineralogical and elemental compositions. Elemental concentrations were analysed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Average major oxide concentrations revealed SiO2 (57.53 wt. %), Al2O3 (13.25 wt. %), CaO (5.05 wt. %), and MgO (5.59 wt. %) for the syenite and SiO2 (62.39 wt. %), Al2O3 (14.98 wt. %), CaO (3.67 wt. %), and MgO (3.25 wt. %) for the granodiorite. Total Alkali–Silica (TAS), Aluminum Saturation Index (ASI), and La/10-Y/15-Nb/8 plots discriminated the granitoids as metaluminous monzonite-syenite and peraluminous diorite-granodiorite. Average total REE concentrations in the syenite (625.06 ppm) and porphyritic-granodiorite (364.51 ppm) were above values reported for the granites in some mines in Jiangxi Province, Southern China.

Geochemistry and Mineralogy of Rare-Earth Elements in Ferruginous Deposits and Bottom Sediments of the Laptev Sea

Abstract —The geochemical and mineralogical aspects of the distribution of rare-earth elements (REE) in ferruginous deposits (FD) and bottom sediments of the southeastern Laptev Sea are analyzed. The FD are dominated by biomorphs developed after polychaete tubes. The REE patterns depend on the proportion of ore and non-ore substances. The ore substance is represented mainly by iron hydroxides (limonite). It is a product of suboxic diagenesis enhanced by bioturbation and determines the slight enrichment of FD in MREE and cerium deficiency (Cean = 0.94). The non-ore substance comes from terrigenous sediments and has an (alumino)silicate composition. It controls the scandium content and is the source of REE mineral grains, among which monazite-(Ce) prevails. The sediments demonstrate a common similarity in REE patterns to shales and suspended material transported to the Laptev Sea by the Lena River, with elevated LREE and MREE contents and the value of Ce anomaly almost equal to unity (Cean = 1.06). In the sediments, REE minerals occur mostly in the silt fraction (&amp;lt;63 μm in size). The high content of organic matter (Corg of up to 2.15%) of predominantly terrigenous origin (OMter of up to 85%) in the sediments explains the oxygen deficiency and weak diagenetic mineral formation with low accumulation of trace elements, including REE, in the FD. The total REE content in the FD is lower than that in the sediments (on average, 173 ppm against 206 ppm).

Rare earth elements in tea garden soils and their bioavailability to tea buds in Taiwan

Tea (Camellia sinensis) is a widespread beverage plant that prefers aluminum-enriched acidic soils. However, rare earth elements (REEs) might be highly phyto-available in these soils. With the increasing demands for REEs in high-technology industries, understanding the dynamics of REEs in the environment is essential. Thus, this study identified the total concentration of REEs in the root-zone soils and corresponding tea buds (n = 35) collected from tea gardens in Taiwan. Additionally, the labile REEs in the soils were extracted with 1 M KCl, 0.1 M HCl, and 0.05 M ethylenediaminetetraacetic acid (EDTA) to elucidate the fractionation tendency of REEs in the soil-plant system and the relationships between REEs and Al in the tea buds. The concentration of light REEs (LREEs) was higher than those of medium REEs (MREEs) and heavy REEs (HREEs) in all soil and tea bud samples. According to the upper continental crust (UCC) normalization, MREEs and HREEs were more abundant than LREEs in the tea buds. Furthermore, REEs remarkably increased with increasing Al in the tea buds, whereas the linear correlations between Al and MREEs and HREEs were stronger than between LREEs. Compared with LREEs, the extractabilities of MREEs and HREEs by all single extractants in the soils were higher, coinciding with their higher UCC-normalization-based enrichments in the tea buds. Moreover, the 0.1 M HCl- and 0.05 M EDTA-extractable REEs were affected by soil properties and significantly correlated with the total REEs in the tea buds. The concentration of REEs in the tea buds was successfully predicted by empirical equations of extractable REEs with 0.1 M HCl and 0.05 M EDTA, as well as general soil properties including pH, organic carbon, dithionite-citrate-bicarbonate-extractable iron, aluminum, and phosphorus. However, this prediction should be further verified using many soil and tea types in the future.

Rare-Earth Minerals in Kaolin Ore, Mine Tailings, and Sands – Central Georgia, Upper Coastal Plain

AbstractThe total concentrations of rare-earth elements (REE) in the mined kaolin (0.02–0.06 wt.%), kaolin mine tailings (0.03–1.9 wt.%), and the kaolin-associated Marion Member sand lithology (0.03–4.6 wt.%) opened questions regarding the modes of occurrence of the REE and the role(s) of chemical weathering and secondary processes to explain the presence of REE in these materials. The REE were hosted primarily by phosphate minerals (monazite, xenotime) based on mineralogic analyses (scanning electron microscopy, X-ray diffraction). Enrichments in the light rare-earth elements (LREE: La–Gd) and the high correlation coefficient values were noted between P and the total REE concentrations (r2 = 0.99) for the sands and the mine tailings. Lower correlation coefficient values were noted between total REE concentrations and Zr (r2 = 0.31). The coarse fractions of the mined kaolins were enriched in the heavy rare-earth elements (HREE: Y, Tb–Lu) relative to the kaolin-associated sand lithologies. The REE inventory cannot be explained solely by mineral inheritance within the mined kaolins. Lower correlation coefficient values between P and total REE, positive Eu/Eu* anomalies, and the presence of xenotime overgrowths on zircon showed the importance of the role of chemical weathering of the detrital minerals during post-depositional processes (such as diagenesis) leading to redistributed and fractionated REE within the mined kaolin. The possibility of adsorption of the REE to kaolin mineral surfaces in the fine fraction of the mined kaolins remains open and permits further study to characterize fully the multi-modal fractionation of REE possible in the Georgia kaolin deposits.

Rare Earth Elements Transfer from Soil to Vegetables and Health Risks Associated with Vegetable Consumption in a Former Mining Area

Rare earth elements (REEs) and 18 other elements in the vegetables (carrot, parsley, cabbage, potato, onion) and soils from two villages near tailings management facilities in the Baia Mare area, NW Romania, were measured. The soil-to-plant transfer and the health risks posed by the consumption of these vegetables were also assessed. The pseudo-total concentrations of elements varied widely in the soil and vegetables, with the lowest concentrations being found for Ta (2.1 µg/kg) and the highest for Fe (9219 mg/kg). The concentration of total light REEs (LREEs) was considerably higher than that of heavy REEs (HREEs). The percentages of available elements were &lt;20% of the pseudo-total concentration, except for Zn, Cd, and Pb, where the available fractions were much higher. Generally, the soil-to-plant transfer factors decreased in the following order: parsley &gt; onion &gt; cabbage &gt; carrot &gt; potato, and varied from element to element. The LREEs were less absorbed than the HREEs in all investigated vegetable species. Pearson correlations revealed strong positive correlations between the lanthanides, except for Eu, in the soil and vegetables. No important health risks following the consumption of vegetables were found for REEs, the estimated daily intake of REEs through vegetable consumption being much lower than the acceptable daily intake.

Magnesium isotope fractionation in differentiation of mafic-alkaline-carbonatitic magma and Fe-P-REE-rich melt at Bayan Obo, China

The Bayan Obo area in the North China Craton (NCC) contains the largest rare earth element (REE) resources in the world. The key to this gigantic and efficient REE accumulation has been the focal point of century-long research efforts. Intense differentiation of mantle-derived alkaline magmas is envisaged as a highly viable process for REE enrichment based on the first discovery of mafic-alkaline-carbonatitic suite in the Bayan Obo region. Geochronological and Sr-Nd-Hf-O isotopic analyses revealed that these rocks derived from a common mantle source and evolved with magmatic differentiation at 1.31 Ga to 1.32 Ga. Elemental geochemistry and Mg isotopes in this magma series (alkaline diabase sill, syenite dyke and carbonatite) unambiguously support the differentiation model. The earliest ferrocarbonatite, with nearly undifferentiated REE concentrations, has mantle-like δ26Mg (−0.27 ± 0.03‰), and therefore can be considered as the original product of the mantle derived alkaline magma at Bayan Obo. The subsequent magnesiocarbonatites have a LREE enrichment feature, which is consistent with the alkaline diabase sills. The magnesiocarbonatites possess light Mg isotopic composition (from − 0.42‰ to − 0.50‰), whereas the alkaline diabase sills have heavy Mg isotopic composition (from − 0.03‰ to − 0.05‰). This rock assemblage should present two end members, which differentiated likely by immiscibility in the chamber from a common alkaline magma. The subsequent syenite dyke has no obvious Mg isotopic variation (from − 0.44‰ to − 0.39‰) during differentiation from the above alkaline magma. Notably, as the most important REE hosts, fine-grained ferrocarbonatites show large Mg isotopic variations (from − 0.85‰ to + 0.13‰) and present positive correlations with total MgO and CaO contents, but negative with total Fe2O3, P2O5 and REE contents. In fine-grained ferrocarbonatite, closely associated apatite, monazite, hematite and magnetite minerals occur as a special intergrowth texture. This unique paragenetic assemblage is likely the mineralization record of a Fe-P-REE-rich melt, which shows particular affinity of hydrothermal fluid and light Mg isotope in carbonatitic magma. By contrast, magnesian siderite phenocrysts as the early cumulates in carbonatitic magma are enriched in heavy Mg isotope (from − 0.07‰ to + 0.21‰). Immiscibility of Fe-P-REE-rich melt and fractional crystallization of carbonate minerals are responsible for large Mg isotope fractionation and giant REE enrichment in the Bayan Obo deposit.

Insight study of rare earth elements in PM2.5 during five years in a Chinese inland city: Composition variations, sources, and exposure assessment

The booming development of rare earth industry and the extensive utilization of its products accompanied by urban development have led to the accelerated accumulation of rare earth elements (REEs) as emerging pollutants in atmospheric environment. In this study, the variation of REEs in PM2.5 with urban (a non-mining city) transformation was investigated through five consecutive years of sample collection. The compositional variability and provenance contribution of REEs in PM2.5 were characterized, and the REEs exposure risks of children and adults via inhalation, ingestion and dermal absorption were also evaluated. The results showed an increase in the total REEs concentration from 46.46 ± 35.16 mg/kg (2017) to 81.22 ± 38.98 mg/kg (2021) over the five-year period, with Ce and La making the largest contribution. The actual increment of industrial and traffic emission source among the three pollution sources was 1.34 ng/m3. Coal combustion source displayed a downward trend. Ingestion was the main exposure pathway for REEs in PM2.5 for both children and adults. Ce contributed the most to the total intake of REEs in PM2.5 among the population, followed by La and Nd. The exposure risks of REEs in PM2.5 in the region were relatively low, but the trend of change was of great concern. It was strongly recommended to strengthen the concern about traffic-related non-exhaust emissions of particulate matter.

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.

Geochemical Characteristics and Factors of Transfer and Accumulation of Rare Earth Elements in Rock-Soil-Tea of the Mengku Tea Region in Yunnan Province, China

Rare earth elements (REEs) in tea are usually determined by the soil, but their transfer characteristics and influencing factors have been rarely studied and reported. In order to determine the transfer and accumulation characteristics of REEs, rock, soil, and tea samples were collected in the Mengku tea region. Levels of 15 REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) in samples were determined by inductively coupled plasma atomic emission spectrometry (ICP-MS). The results showed that light rare earth elements (LREEs) were easily enriched in rock, soil, and tea. The average total concentration of REEs in investigated rocks was 199 mg·kg−1, which was lower than the element abundance of China’s continental crust but higher than the standard value of element abundance in the upper continental crust (UCC). The average total REE concentration in the investigated soil was 225 mg·kg−1, which was lower than the background value of soil in Yunnan Province. The chondrite-normalized levels of Ce and Eu in rocks and Eu in soil showed negative anomalies, while Ce levels in soil showed slightly positive anomalies. The total amount of REEs in tea was relatively low and the chondrite-normalized values of Eu in tea showed significantly positive anomalies. Eu anomalies in tea were closely correlated with soil pH (pH &lt; 5, negative anomalies; pH &gt; 5, positive anomalies). K, Na, Ca, and Mg were the main factors affecting the transfer of REEs. LREEs were mainly enriched in tea through Na+ channels. Mg and K affected the differentiation and enrichment of heavy rare earth elements (HREEs) in tea. Calcium showed a significantly positive correlation with Eu in tea. The human health risk assessment showed that the risk of drinking tea to the human body was far below the reference value. Ce, Y, and La in tea were the main elements that affected non-carcinogenic risk and carcinogenic risk.