Fractionation Of Rare Earth Elements Research Articles

Hyper-enrichment of heavy rare earth elements in highly evolved granites through multiple hydrothermal mobilizations

Abstract Highly evolved granites can be important hosts of rare earth element (REE) resources, and more importantly, they commonly serve as the protolith for regolith-hosted REE deposits to form during weathering. Highly evolved granites in the Zudong pluton, South China, are extremely rich in the heavy (H)REE (up to 8000 ppm total HREE), and display significant REE fractionation. Moreover, the HREE enrichment is positively correlated with the degree of REE fractionation, indicating a unique process in preferentially enriching the HREE during the evolution of the granites. Multiple stages of hydrothermal re-mobilization of the REE can account for the HREE mineralization, and these are recorded in the texture and composition of the zircon. In these processes, fluctuations in the F activity of the fluid caused alternating dissolution-reprecipitation and continuous growth of the zircon. REE were repeatedly mobilized and enriched in the fluid to precipitate the major HREE mineral synchysite-(Y), and partially incorporated into the growth zone of zircon, while other elements were largely lost to the fluid during the extensive dissolution of the rock-forming minerals. LREE were also likely substantially mobilized in the late hydrothermal stage and lost through complexation with Cl, causing the significant LREE depletion and, thus REE fractionation. This process continuously enriched host granites in the HREE to a potentially economic grade, making them favorable protoliths for subsequent supergene regolith-hosted HREE deposits.

Impact of Systematic Modeling Uncertainties on Kilonova Property Estimation

The precise atomic structure and therefore the wavelength-dependent opacities of lanthanides are highly uncertain. This uncertainty introduces systematic errors in modeling transients like kilonovae and estimating key properties such as mass, characteristic velocity, and heavy metal content. Here, we quantify how atomic data from across the literature as well as choices of thermalization efficiency of r-process radioactive decay heating impact the light curve and spectra of kilonovae. Specifically, we analyze the spectra of a grid of models produced by the radiative transfer code Sedona that span the expected range of kilonova properties to identify regions with the highest systematic uncertainty. Our findings indicate that differences in atomic data have a substantial impact on estimates of lanthanide mass fraction, spanning approximately 1 order of magnitude for lanthanide-rich ejecta, and demonstrate the difficulty in precisely measuring the lanthanide fraction in lanthanide-poor ejecta. Mass estimates vary typically by 25%–40% for differing atomic data. Similarly, the choice of thermalization efficiency can affect mass estimates by 20%–50%. Observational properties such as color and decay rate are highly model dependent. Velocity estimation, when fitting solely based on the light curve, can have a typical error of ∼100%. Atomic data of light r-process elements can strongly affect blue emission. Even for well-observed events like GW170817, the total lanthanide production estimated using different atomic data sets can vary by a factor of ∼6.

Discrimination of brewing technologies and assessment of health risks based on rare earth elements: Evidence of fingerprint in Chinese famous vinegars

Considering the essential influence of vinegar brewing processes on human health, this study determined the content and fractionation of rare earth elements (REEs) in 40 Chinese vinegar products to assess food safety and probe the application of REEs in tracing brewing processes. The total REEs contents in different products exhibited great variations (1.66 μg/kg to 124.54 μg/kg), which should be attributed to the difference in brewing techniques. Vinegars produced by solid brewing fermentation normally contain higher REEs contents than those produced by liquid brewing fermentation. The REEs contents in vinegars from inland areas were higher than those from coastal areas. The health risk assessment indicated that REEs contents were below the daily intake standards; however, considerable attention should be paid on the risk to children. This study contributes foundational data for understanding REEs behavior in vinegars, which is crucial for ensuring food safety and identifying the actual vinegar production process.

Controls on the distribution and fractionation of rare earth elements in recent sediments from the rivers along the west coast of India

Controls on the distribution and fractionation of rare earth elements in recent sediments from the rivers along the west coast of India

Mobility and fractionation of rare earth elements during black shale weathering: Implications from acid rock drainage and sequential extraction study

Black shale is a type of sedimentary rocks that are enriched in rare earth elements (REEs). It is of both economic importance and environmental significance to understand REE mobility during black shale weathering. The present study approaches to this by analysing REEs in acid rock drainage (ARD) from black shale weathering system, fresh and weathered black shales, soils derived from black shales, and sequential extractants from black shales at Dongping town in Hunan province (China). Results showed that REEs had variable high concentrations in ARD as shown by total REE + Y (∑REY) concentrations from 162 to 4074 (μg/L). REEs in ARD displayed hat-shape NASC-normalized patterns with significant enrichments of middle REEs (MREE) relative to light REEs (LREE) and heavy REEs (HREE), and had significant negative Ce (Ce/Ce⁎ = 0.6) and positive Y (Y/Y⁎ = 1.5) anomalies. MREE enrichment in ARD could be evaluated using MREE/MREE⁎ values, which varied from 1.43 to 1.81 with a mean of 1.65, distinctly higher than those of whole rocks (around 1.0). 1 M HCl extraction results suggested that REEs were integratedly mobilized during shale weathering, while six-step extraction studies identified that REEs in ARD resulted from exchangeable and Fe-oxide fractions with MREE and HREE enrichment in shales respectively. MREE in exchangeable and HREE in Fe-oxide fractions were preferentially released during weathering, as illustrated by plots of MREE/MREE⁎ against HREE/LREE ratios of ARD and six-step extractants. Therefore, geochemical processes for REE mobility during black shale weathering included integrated mobilization and preferential release. Integrated REE mobilization resulted from the dissolution of REE-bearing minerals and oxidation of sulfides. Preferential REE release resulted from acid fluids produced by sulfide oxidation during weathering. Thus, a new model was proposed for interpreting geochemical processes of REE mobility during black shale weathering, and for understanding REE distribution in ARD from natural and anthropogenic systems.

Migration and controlling factors of rare earth elements in geothermal systems on the southern Tibetan Plateau

Rare earth elements (REE) serve as effective tracers of water-rock interactions, a crucial process in the evolution of geothermal systems. However, the geochemical behavior of REE during their migration within geothermal systems, particularly the fractionation mechanism, remains poorly understood. In this study, we focus on the geochemical characteristics of REE in hot springs, host rocks, and sinters from various hot spring systems in the Yadong-Gulu rift (YGR), the largest extensional rift in the southern Tibetan Plateau. The objective is to explore the factors that control REE concentrations in hot springs and elucidate the fractionation of REE during their migration. The concentrations of REE are significantly influenced by pH, Fe oxides (oxyhydroxides), and HCO3− concentrations in central and southern hot springs, whereas high reservoir temperatures contribute to higher ΣREE concentrations in northern hyperthermal springs. REE speciation calculations show that LnO2− and LnO2H are dominant complexes in northern alkaline hot springs, while carbonate complexes (LnCO3+ and Ln(CO3)2−) prevail in central and southern spring samples. Additionally, weakly acidic hot springs exhibit a prevalence of Ln3+, LnF2+, and LnSO4+ species. The chondrite-normalized REE patterns of all hot spring samples display enrichment in MREE, which is significantly distinct from the patterns observed in host rocks and sinters enriched in LREE. The fractionation of REE in the YGR hot spring systems is primarily controlled by the following processes: (1) Temperature, pH, and relative abundance of complexing agents influence the complexation of REE and further regulate their fractionation in hot springs; (2) During water-rock interaction, preferential leaching of HREE and MREE from host rocks can lead to their enrichment in alkaline hot springs. The dissolution of iron-rich sediments plays a significant role in generating the distinctive MREE bulge pattern in acid-neutral hot springs compared to host rocks; (3) The higher stability of MREE and HREE complexes in water, as well as the preferential coprecipitation of unstable LnCO3+ complexes formed by LREE with carbonates, are key factors responsible for LREE enrichment in sinters.

Uptake time and enrichment mechanism of rare earth elements in deep-sea bioapatite

Bioapatite is widely recognized as the primary carrier for rare earth elements and yttrium (REY) in deep-sea REY-rich muds. The incorporation of REY into bioapatite occurs at the water-sediment interface, which has the potential to serve as a proxy for reconstructing paleoenvironmental conditions. The timing of REY uptake and the fractionation of rare earth elements (REEs) within bioapatite are crucial factors to understanding the application of these proxies. In this study, we present in-situ geochemical data for bioapatite obtained from surface sediments in the high sedimentation rate Somali Basin of the northwestern Indian Ocean (NWIO), as well as fish teeth within nodules from the low sedimentation rate in the northwestern Pacific Ocean (NWPO). Our findings indicate that the uptake time of REY occurred rapidly, with the ΣREY content reaching 7265 μg/g in bioapatite from the surface sediments in the NWIO within several thousand years. The bone fragments exhibited a high ΣREY content, which was primarily attributed to substitution processes. This led to a notably elevated proportion of middle rare earth elements (MREE) compared to fish teeth. In contrast, the adsorption and substitution mechanisms responsible for REY incorporation decreased from the root to the tip in fish teeth, resulting in a pronounced decline in ΣREY content. The adsorption mechanism was identified as the primary process responsible for REY uptake in the fish teeth within the studied nodules from the NWPO. The fractionation pattern of REEs in these teeth exhibited similarities to that of fish teeth from the NWIO. Therefore, we inferred that the fish teeth within the studied nodules may preserve the original information during late diagenesis. The variation of REY contents in the nodules was influenced by the redox environment, and there is no evidence to support the migration of REY from the nodules into the fish teeth.

Surface complexation of rare earth elements on goethite in sea-floor hydrothermal environment: Insight from first principles simulations

Deep-sea mud shows tremendous resource potential for rare earth elements (REEs) and its formation is closely associated with sea-floor hydrothermal activities. Iron (oxyhydr)oxides link the sources and sinks of REEs in sea-floor hydrothermal systems. However, the complexation mechanisms of REEs on iron (oxyhydr)oxides have not been well understood yet. In this study, by using the first principles molecular dynamics technique, we first calculated the pKa’s of surface groups on goethite (110) surface at elevated temperatures relevant to sea-floor hydrothermal systems and then evaluated the complexation structures and free energies of REEs on goethite (110) and (010) surfaces using the method of constraint by taking Sc3+, Y3+, and La3+ as model REE cations. The results show that REE complexation occurs in mildly acidic to neutral conditions. The most thermodynamically stable complexes of REEs are bidentate complexes on two neighboring FeOH sites on goethite (110) surface and tridentate complexes on two neighboring FeOH sites plus one Fe2OH site on goethite (010) surface. Sc3+ complexes match the goethite lattice and can be incorporated into the lattice. The stabilities of REE complexes increase with the distance from hydrothermal vents. Complexation of Y3+ is less favored on goethite compared to other REEs whereas Sc3+ prefers complexation on goethite (010) surface and La3+ exhibits similar stabilities on both (010) and (110) surfaces. The derived atomic level complexation mechanisms would be helpful for the interpretation of experimental data and the prediction of REEs’ behavior in the sea-floor. The findings presented here provide valuable insights into REEs fractionation and enrichment in deep-sea muds.

The yengejeh diasporic karst bauxite deposit, NW Iran: Constraints on distribution and fractionation of major and rare earth elements

The Yengejeh diasporic karst bauxite deposit (NW Iran) was developed as discontinuous layers and lenses along the contact of dolomitic limestone of the Ruteh Formation (middle-upper Permian) and dolomite of the Elika Formation (Triassic). This deposit is constituted by two conspicuous subset layers, (1) green bauxite (GB) and (2) red bauxite (RB). The XRD analytic data revealed that diaspore is accompanied by chlorite and anatase in the GB subset and by hematite in the RB subset. Minerals such as pyrophyllite, kaolinite, illite, and rutile are present within the both subsets. The antithetical distributions of Al with Fe and Al with Ti in the deposit are indicative of the controlling role of climatic changes of the depositional environment and the function of post-formation diagenetic processes. The increment in certain geochemical ratios like La/Y, (La/Yb)N, and (LREE/HREE)N from the top toward the bottom of the horizon is designative of pH increase in depositional milieu by buffering of the percolating solutions, and of preferential scavenging of LREE by hematite. The positive Ce anomaly in the GB subset took place as the result of change in the oxidation state of this element from Ce3+ to Ce4+. However, the positive Ce anomalies in the RB subset implicates preferential scavenging of Ce onto hematite. The marked variation range in anomaly values of Eu/Eu* (0.38–1.01) at Yengejeh reveals that this index acted as non-conservative during the evolution of this deposit, and this behavior is related most likely to influences of post-formation diagenetic processes.

The Characteristics and Enrichment Process of Dabu Ion-Adsorption Heavy Rare-Earth Element (HREE) Deposits in Jiangxi Province, South China

Ion-adsorption rare-earth deposits supply over 90% of the global market’s heavy rare-earth elements (HREEs). The genesis of these deposits, particularly HREE deposits, has garnered significant attention. To elucidate the metallogenic mechanisms of HREE deposits, a comprehensive study of the weathering profile of granite was conducted in Jiangxi Province, South China. This study focuses on the following two aspects: the petrogeochemistry of HREE-rich granite and the enrichment and fractionation of rare-earth elements (REEs) during the weathering process. The results suggest that the Dabu granites are a typical peraluminous, high-K, calc-alkaline granite series with high silica content (SiO2: 74.5%–76.4%), relatively low phosphorus content (P2O5: <0.05%), and high HREE content (ΣLREE/ΣHREE: 0.16–0.66). Weathering advances the decomposition of minerals and the release of elements. REEs are mainly fixed in the regolith by scavengers, mainly clays, Fe–Mn oxides, and carbonates, and ΣREE can reach 799 ppm in the B horizon. However, HREEs tend to migrate further and preferentially combine with Fe–Mn oxides and carbonates as compared to LREEs, leading to a significant fractionation of REEs in the regolith (ΣLREE/ΣHREE = 0.2–1.1). Additionally, the differential weathering of REE-bearing minerals and the precipitation of secondary REE-bearing minerals are also vital for REE fractionation.

Potential for high-grade recovery of rare earth elements and cobalt from acid mine drainage via adsorption to precipitated manganese (IV) oxides

High demand for rare earth elements (REEs) has increased interest in their recovery from unconventional sources, such as acid mine drainage (AMD). AMD contains elevated concentrations of Mn, Fe, and Al, which precipitate as (oxy)hydroxide minerals as pH is raised. These precipitates can remove cations including REEs and Co from solution via sorption and/or coprecipitation. In this study we developed a method to recover these critical minerals by sorption to MnO2, precipitated by oxidation of in situ Mn (II) with added KMnO4 at acidic pH. MnO2 solids were prepared with varying concentrations of KMnO4, SO42−, and Cl−, to elucidate the effects of excess KMnO4, SO42− concentration, and ionic strength on adsorption. When using a stoichiometric ratio of Mn (II) and KMnO4, 100% removal of REEs and Co occurred at approximately pH 3.5, nearly 2 pH units lower than was observed by sorption to Fe and Al hydroxysulfates. When using excess KMnO4 nearly 100% removal of REEs and Co was accomplished at approximately pH 2, although SO42− was found to inhibit REE sorption. From these results, we developed a two-stage process for recovery of REEs from AMD; a preliminary pH adjustment to remove Fe and Al hydroxy-sulfates, followed by adding KMnO4, precipitating MnO2, enabling recovery of REEs and Co. We tested this process in a representative synthetic AMD, achieving a grade of 6.16 mg REEs per g of solid, which is 65 % of the maximum possible grade based on solution composition. Fractionation of REEs was observed, with light REEs (LREEs) preferentially sorbed to MnO2 relative to both medium REEs (MREEs) and heavy REEs (HREEs). In contrast, preferential sorption of HREEs was observed for sorption to Fe and Al oxyhydroxides at all pH ranges. These results suggest the mechanisms of REE sorption differ among the solids and warrant further study.

Vital effects and the fractionation of rare earth elements and yttrium during uptake by and transfer within freshwater bivalves and their shells

Mussels are commonly used as bioarchives in environmental monitoring, yet the impact of vital effects on the trace element or isotope ratios used as biogeochemical proxies is often only ill constrained. A prime example of such trace elements are the Rare Earth elements and Yttrium (REY) which have become (micro)contaminants in freshwater systems worldwide. We here report on the distribution of REY in different soft tissues and in the shells of freshwater bivalve A. anatina, commonly known as “duck mussel”, from the Danube River in Hungary and the Vistula River in Poland. Both rivers are contaminated with anthropogenic Gd from contrast agents used in magnetic resonance imaging (MRI). Regardless of the mussels' origin, all of their compartments show very similar shale-normalised REY patterns. None of the samples show any anthropogenic Gd anomaly, implying that in freshwater anthropogenic Gd from MRI contrast agents is either not bioavailable or that REY from ambient river water are insignificant for the REY budget of freshwater mussels. Compared to ambient water, the bivalves bioaccumulate the REY with preferential uptake of Ce and of light REY over heavy REY. However, REY concentrations in mussels are similar to or lower than those in their potential food source, with minor fractionation along the REY series besides slight preferential uptake of La and Y. Comparison of shells and tissues reveals the systematic oxidative decoupling of Ce from its REY neighbours, probably due to the presence of Ce(IV) solution-complexes in the mussels' extrapallial fluid. Despite possible REY fractionation during their initial uptake, vital effects do not impose any major control on REY fractionation during REY transfer within the mussels or during formation of their shells. Mussel shells may, therefore, conveniently be used for environmental monitoring of REY without major disturbance from vital effects.

Crustal Melting Recorded by Dykes along the Gold-bearing Melanson Brook Fault, Northern New Brunswick Appalachians

Dykes intruding along the Melanson Brook Fault record two magmatic episodes in northern New Brunswick. Dykes at the South Gold Zone of the Elmtree gold deposit are aphanitic and magnesian-calcic, whereas those at Ellis Brook (2.5 km to the west) are ilmenite-series and weakly peraluminous with hornblende- and plagioclase-porphyritic phases. Elevated 147Sm/44Nd generated by partial melting, titanium depletion, absence of rare earth element fractionation, and trondhjemite-like compositions indicate the South Gold Zone dykes were sourced from low-volume fluid fluxed melting of gabbroic crust. A Sm-Nd depleted model mantle age of 1.1 Ga for the Ellis Brook dykes suggests that they were sourced from melting of Ganderian crustal rocks rather than the sinking Acadian slab. 143Nd/144Nd evolution curves for the South Gold Zone dykes intersect that of the Ellis Brook dykes at 432 Ma and 427 Ma. This suggests that the magma from which the South Gold Zone dykes crystallized was extracted from a similar source area as the magma that generated the Ellis Brook dykes. Evidence of fluid exsolution in the Ellis Brook dykes indicates they could be a potential source for reduced intrusion-related gold mineralization. The Ellis Brook dykes yielded a U-Pb zircon age of 391 ± 5 Ma, which is consistent with the timing of oceanic slab break-off at the end of the Acadian orogenic cycle. Extraction of South Gold Zone magma occurred up to 40 Myr earlier, likely during the Salinic orogenic cycle.

Indigenous microbial influence on REE enrichment and fractionation in South China weathering crusts: Insights from experimental simulations

The activity of microorganism plays an important role on the enrichment, migration and fractionation of rare earth elements (REEs) in the supergene environment. To investigate the characteristics of indigenous microorganisms on the enrichment and fractionation of REEs, we studied the adsorption efficiencies of REEs by 30 indigenous microbial strains that were isolated and cultured from the weathering profile of a regolith-hosted REE deposit in South China. Most microbial strains exhibited high adsorption efficiencies for REEs, ranging from 2.3 to 42.9 mg g−1. Notably, the taxonomic classification of microorganisms significantly influenced the adsorption selectivity. Gram-positive bacteria exhibited a pronounced enrichment of the heavy REEs, while gram-negative bacteria showed no obvious adsorption preference. The tetrad effects were observed in REE adsorption patterns of gram-negative bacteria and fungi; however, fungi demonstrated a much higher affinity for light and medium REEs. Chemically modified microbial cells were employed to investigate the adsorption mechanism, revealing that distinct functional groups of microbial cells corresponded to the adsorption preference of microorganisms towards REE. Carboxyl and phosphate groups contributed to a relatively high adsorption capacity for light REEs and heavy REEs, respectively. The findings of our study suggest that the distinct composition of microbial groups may exert a significant influence on the biogeochemical cycle of REE in weathering profiles.

Features of Distribution of Rare-Earth Elements in Coals of the Far East

For the first time, the distribution of rare earth elements (REE) has been studied in detail for a number of coal facilities (30 deposits, 650 samples of coal and 210 samples of carbonaceous rocks). The ubiquitous presence of elevated concentrations of REE in coals has been noted. The REE mineral cluster in coals includes the association: ash content of coals – SiO2 – K2O – Al2o3 – TiO2 – Sc – Y – Dy – Ho – Er – Tm – Yb – Lu, and the association La – Ce – Pr – Nd – Sm – Eu – Gd – Tb. The presence of these elements of the mineral part of the coals is preferably in the composition of phosphate minerals – monazite and apatite (according to electron microscopy with microanalysis, the correlation of REE with P2o5). The content of individual REE in humic acids isolated from coals and fractions of coals of different densities has been studied. The specific role of organic matter(s) in the concentration of REE, their presence in the humus component of S and in low-ash coals is shown. Selective accumulation (fractionation) of heavy REE by organic matter has been experimentally established for the first time. Two genetic types of REE mineralization have been identified in coals: mainly terrigenous (hydrogenic) and tufogenic. The increased concentrations of REE in coals are due to the influence of the petrofund. The deposits were ranked according to the degree of prospects for REE based on an assessment of the resource potential of associated REE in the coals of the studied brown coal deposits. REE raw materials (lanthanides in coal ash) differ significantly from traditional types of rare earths ores by an incomparably large relative amount of heavy REE (on average 3–4 times), sometimes reaching 46% of the total REE content. Thus, coal ash is a unique non–traditional source of heavy lanthanides – more rare, valuable and expensive. The coals of the studied deposits should be considered as associated raw materials for rare earths.

Fractionation of rare earth elements in the weathering processes of granodiorite and basalt

Fractionation of rare earth elements in the weathering processes of granodiorite and basalt

Fate and potential ecological risk of rare earth elements in 3000-year reclaimed soil chronosequences

The introduction of anthropogenic inputs into natural systems may lead to enduring alterations in the innate characteristics of Rare Earth Elements (REEs). Against this backdrop, the evolutionary processes and environmental drivers of REEs in soil remain uncertain. A 3000-year soil chronosequence with uniform parent material was established in reclaimed farmland along the Yangtze River, reconstructing, for the first time, the dynamic processes of REE accumulation and fractionation over a long-time scale. Analysis of 122 soil samples showed REE concentrations ranging from 146.00 to 216.56 μg/g. Based on reclamation duration, three significant stages of REE evolution were identified: natural leaching, rapid accumulation, and stable accumulation with differentiation. Reclaimed soil after 3000 years exhibited a 14.1 % increase in REE concentrations compared to fresh sediments, attributed to anthro -pedogenic processes. Moreover, Heavy Rare Earth Elements (HREEs) accumulated faster than Light Rare Earth Elements (LREEs), particularly in deeper soils (60–100 cm), where HREE concentrations rose by 34.3 %, mainly due to acidic environments promoting HREE fixation. Additionally, the potential ecological risk posed by REEs heightened with reclamation duration, with HREEs exhibiting a sensitivity of 83 % to 94 %. Our findings stress the urgency of carefully monitoring exogenous REEs introduced through anthropogenic activities, particularly HREEs.

Grain size control on organo-clay complexation and REE fractionation in the Paleozoic strata of the Permian Basin (West Texas, U.S.A.)

As a major component of mudstone, clay minerals are known to conserve organic matter (OM) as well as a range of trace elements through the mechanisms of adsorption, encapsulation, and/or intercalation. The associations of the clay minerals on one hand and trace elements and OM on the other hand impact the diagenetic evolution of such rocks and is of substantial importance for their characterization and assessment. Subsurface core samples collected from Late Paleozoic mudstone within the Permian Basin of Texas were separated into four grain size fractions (>2 µm, 2 to 1 µm, 1 to 0.6 µm, and <0.6 µm) to determine the clay mineralogy, OM abundances, and rock geochemistry using a suite of diffraction, spectroscopic, and chemical analysis. All separates were largely consisted of illite-smectite (I-S), illite-tobelite-smectite (I-T-S), mica/illite and chlorite coupled with some minor quartz and feldspar. The smectite component of I-S was shown to increase with decreasing grain size fractions. Additionally, t he rise in the content of smectite interlayers correlated with an increase in the total organic carbon (TOC) content towards the finest grain size separates in all samples. This suggested that a significant portion of the TOC content resided in the fraction below 2 µm and that smectite interlayers promoted the preservation of OM. Rare earth elements (REE) concentrations were found to be the highest in the finest grain size separates and align with an increased content of smectite interlayers, denoting a plausible interaction between the two. Further on, REE and TOC concentrations display a significant positive correlation in all size fractions and increase with respect to smectite interlayer content. This three-component relation suggests the REE adsorption to illite-smectite was likely promoted by OM. Understanding the close relation between the clay minerals, OM, and trace element content is indicative of polyvalent cationic bridging, ligand exchange, and organo-metallic complexation, which eventually l eads to the enrichment of OM and fractionation of REE in mudstone.

Quantitative evaluation of anthropogenic sources and health risks of rare earth elements in airborne particulate matter

Rare earth elements (REEs) have emerged as contaminants in airborne particulate matter (PM); however, their anthropogenic sources remain poorly quantified, and associated health risks are unknown. This study investigates the REE distribution across eight sizes of airborne PM during July and December in Qingdao, a major Chinese port city. Our results reveal a single coarse-mode distribution with REE concentrations. In contrast, fine PM (size: 0.43–2.1 μm) exhibits notable enrichment of La and Ce compared to Al and other REEs. This study traces La and Ce enrichment to fluid catalytic cracking catalysts (FCCC)-related sources, including refinery and ship emissions, by comparing the REE fractionation in samples with potential sources. We quantify the contributions from FCCC-related sources to La (July: 33.6 % ± 3.2 %, Dec.: 46.4 % ± 5.2 %) and Ce (July: 16.5 % ± 14.3 %, Dec.: 30.3 % ± 12.2 %) by comparing measured concentrations with predictions derived from neighboring REEs, a method previously used exclusively in aquatic systems. For the first time, supply ratios of refinery and ship to FCCC-related La are calculated using a two-component mixing model based on the [La]FCCC/[V]anth, revealing the dominance of refinery emissions (July: 97.3 % ± 0.6 %, Dec.: 99.6 % ± 0.1 %). Furthermore, a global review of La and Ce anomalies that integrates published REE data with our findings reveals a widespread distribution of positive anomalies. The significantly positive correlation between La and Ce anomalies underscores FCCC-related emissions as a global source in fine PM, contributing 0–92 % (mean: 35 % ± 33 %) for La and 0–72 % (mean: 21 % ± 24 %) for Ce. Although the non-carcinogenic health risks of Ce are generally low globally, concerns should be raised in areas near source emissions, where Ce health risks sharply increased along with its concentrations. There is urgently need to establish a threshold value for La, owing to its global enrichment. This study provides novel insights into the sources and health implications of REEs in airborne PM.

Rare earth elements and yttrium along eastern Atlantic estuaries

Rare earth elements (REE) are widely used as tracers of geochemical and anthropogenic processes across diverse environments. We investigated the abundances, sources, and fractionation of REE and Y in 12 estuaries along the Southwest Atlantic Coast. Additionally, we assessed the concentrations of Al, Fe, Mn, and organic carbon (OC) to elucidate the influence of diagenetic remobilization and facilitate comparison between estuaries. The ƩREEY varied widely, ranging from 6 mg kg-1 (Santa Cruz Channel; > 90% sand) to 337 mg kg-1 (Piraquê-Açú; 30% silt+clay). Normalized REE abundances relative to post-Archean Australian shale (PAAS) revealed enrichment of light REE (LREE) over heavy REE (HREE). Moreover, the northern estuaries of the Todos os Santos Bay (São Paulo, Mataripe, Subaé), Vitória Bay, and the Doce River exhibited enrichment of medium REE (MREE) over HREE. Positive correlation between ƩREEY and Al, Fe, and Mn were observed in 5 of the studied estuaries. LREE showed a positive correlation with Al (r2 > 0.7) and Fe (r2 > 0.8) across most of the areas studied. Additionally, REE were significantly correlated with Mn (r2 > 0.8) in only 5 out of the 12 estuaries, while a positive correlation with OC (r2 > 0.8) was observed in 8 estuaries. The concentration of REEY, Al, Mn, Fe, and OC depends on the bottom types and position along the estuarine zones. The observed REEY abundances contribute to the characterization of estuaries along the east coast of Brazil and can serve as a baseline reference for the region.