Behavior Of Rare Earth Elements Research Articles

Facet-Dependent Adsorption of Rare Earth Elements (REEs) and Actinides onto Goethite: REE Pattern Variability and Cerium Anomaly.

Assessing the fate of contaminants in the environment requires a deep understanding of intrinsic adsorption mechanisms on natural minerals such as Fe-oxyhydroxides. In this study, we proposed an innovative approach to probe site heterogeneities on the goethite surface by comparing the adsorption behavior of rare earth elements (REEs, including Sc, Y, and all lanthanides; Ln) except Pm, as well as Th and U. A surface loading-dependent adsorption of Ln and Y was observed, with a shift from (i) preferential middle to heavy REE adsorption and (ii) limited to substantial fractionation between Y and Ho as the loading increased. These observations are likely attributable to the formation of strong and weak complexes onto the (021) and (110)/(100) goethite faces at low and high loadings, respectively. Additionally, Ce-anomaly, characteristic of Ce(III) partial oxidation to Ce(IV), was observed only at high loading. By drawing an analogy with Th(IV) and Sc(III), Ce(IV) is expected to outcompete Ln(III) and Y adsorptions and stabilize primarily at the strong sites on the (021) face, even under conditions of high loading. The outcome of this study, supported by charge distribution-multisite complexation (CD-MUSIC) calculation, provides new insights into the impact of facet-dependent adsorption and redox processes on Fe-oxyhydroxides.

Extraction of Rare Earth Elements from Phalaborwa phosphogypsum

Rare earth elements (REE) are present at concentrations of approximately 0.36 % in phosphogypsum stacks located in Phalaborwa, South Africa. The REE are present in the phosphogypsum in solid solution in the gypsum and as fluorine and aluminium rich precipitates. Recovery of the REE offers opportunities for valorization and reducing the environmental impact of the phosphogypsum waste. This paper presents the results of investigations into the leaching behaviour of rare earth elements and other impurities from phosphogypsum using aqueous sulfuric acid. The effects of acid concentration, temperature, residence time, and the influence of impurities were evaluated for their impact on the solubility of rare earth elements in a sulfate medium. It was found that a significant fraction of the REE can be leached from the phosphogypsum in a range of conditions much less severe than traditional hard rock rare earth processing conditions. The REE were leached at a sulfuric acid concentration of 110 g/l, temperature of 30°C - 40°C and a residence time of approximately 8 hours.

Liquid-liquid extraction and separation of light and heavy rare earth elements from chloride solution using a mixture of tertiary amine and phosphinic acid: recycling strategies for NdFeB magnet

ABSTRACT This piece of work aims to study the extraction behavior of light and heavy rare earth elements, which are often found in permanent magnets, using a mixture of tri-octyl amine and bis-(2,4,4-trimethylpentyl) phosphinic acid from a chloride medium. The study showed that the extraction efficiency of Dy(III) is more than that of Nd(III) and Pr(III). Benzene proved to be an effective diluent. Increasing the pH of the aqueous phase improved the extraction percentages, with maximum extractions of 98.4% for Dy(III), 61.2% for Nd(III), and 58.3% for Pr(III) at pH 5.04 using 0.1 mol/L of each extractant. Adding sodium chloride enhanced the extraction efficiency due to the salting-out effect. The extraction mechanism has been proposed based on the slope analysis and FTIR data. From thermodynamic variables, the process was found to be exothermic. The simulated leach liquor of NdFeB magnets showed the highest separation factors of 67.7 (Dy/Pr) and 56.9 (Dy/Nd) at pH 2.05 with 0.25 mol/L extractants. The counter-current study showed that 4.15 mg/L Dy(III) was left behind in the raffinate indicating 97.4% removal of Dy(III) in two stages at unity phase ratio. Testing with actual leach liquor from hard disk magnets revealed a preference for iron extraction, which impeded REE extraction.

Phosphatization in the São Pedro and São Paulo Archipelago (SPSPA), Equatorial Atlantic, Brazil: Insights from guano leaching and chemical weathering

This research explores the phosphatization process in the São Pedro and São Paulo Archipelago (SPSPA), located in the Equatorial Atlantic, by analyzing the geochemical interactions between guano coatings and the underlying rocks. The study also examines the geochemical characteristics of the substrates, assessing the behavior of major, minor, trace, and rare earth elements, and determines the degree of weathering degradation of guano crusts, speleothems, peridotites and carbonate sedimentary rocks affected by environmental factors as rain, wind and halmyrolysis. The distribution of chemical elements in water-soluble, adsorbed, acid-extractable/exchangeable, readily acid and reducible, acid oxidizable, and residual phases were investigated. The principal findings of this method show that elevated Na levels are leached in water-soluble fractions, thereby highlighting the occurrence of rapid and active geochemical cycling, which is influenced by seawater. In contrast, in more acidic environments (pH close 4.8 to 2.0), considerable amounts of macroelements like P, Fe, Mg, Al, and Mn are found in association with remaining phases, indicating a slower and more incremental geochemical cycle of mature guano in the input and output systems of these nutrients in the archipelago. The mineralogy, as indicated by the presence of mafic minerals such as olivine, augite, and Cr-spinel, as well as phosphates including fluorapatite, collinsite, and spheniscidite, also supports this finding. The findings underscore the complex interplay between biological activities and geochemical processes, which influence the elemental dynamics in the phosphate-rich rocks of the SPSPA at depth. This study not only enhances our understanding of phosphatization processes but also offers important insights into the sustainable management of marine resources in environmentally sensitive areas. The research underscores the necessity of considering biological and environmental variables when examining geochemical cycles, particularly in regions exhibiting distinctive geological and biological interactions that challenge the prevailing models, such as those identified in the ASPSP.

A Comparison Study on the Recovery of REEs from Red Mud by Sulfation Roasting–Water Leaching and Citric Acid Leaching

In this study, the recovery of rare earth elements (REEs) from red mud (bauxite residue) was explored through a combination of citric acid leaching and sulfation roasting–water leaching processes, introducing an innovative approach to the field. The research uniquely investigates the influence of citric acid on the leaching behavior of REEs and impurities in both untreated red mud and red mud subjected to sulfation roasting, providing a direct comparison of these methodologies. A novel aspect of this study is the evaluation of solvent extraction efficiency using DEHPA, highlighting the selective recovery of REEs over impurities from both citric acid and water-leaching solutions. Furthermore, a comprehensive phase analysis using X-ray diffraction (XRD) was conducted to track the transformations of minerals during the sulfation roasting process, an original contribution to the literature. The findings revealed that over 85% of REEs and major elements such as Fe, Al, Ca, and Ti dissolved in water after sulfation at 105 °C, while iron and titanium dissolution significantly decreased following roasting at 725 °C. Importantly, terbium, neodymium, and gadolinium extraction efficiencies were notably affected by roasting temperature. Citric acid leaching results demonstrated that the direct leaching of red mud leads to higher leaching efficiency than leaching it after the roasting process. Solvent extraction demonstrated lower terbium and neodymium recovery from citric acid solutions compared to water leaching solution. Finally, stripping experiments illustrated that 6M H2SO4 solution is capable of stripping more than 80% of rare earth elements, except terbium.

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.

Rare earth elements in fucus algae Barents Sea

Patterns of distribution of rare earth elements (REE) in natural objects are important geochemical indicators of the state of the environment. For the first time, data on REE contents in fucus algae from various horizons of the littoral of the Barents Sea are presented. The behavior of REE in natural processes is controlled by the solubility of their compounds, the ability to complex, and the tetrad effect of fractionation. Natural factors determining REE migration in the sediment–water–macrophytes system are discussed.

Extraction behaviors of minor actinides and rare earth elements with NTA amide extractants

ABSTRACT Nitrilotriacetamide (NTA amide) has been developed as an extractant for the mutual separation of minor actinides (MA; Am and Cm) and rare earth elements (REs) by solvent extraction. NTA amide is a tertiary amine in which the three carboxyl groups of nitrilotriacetic acid are amidated. NTA amides have six hydrophobic long-chain alkyl groups on the side chains, and they have enhanced solubility in organic solvents, thereby allowing for the use of nonpolar diluents, such as n-dodecane. This study examined the extraction behavior of MA and REs using four NTA amides with six side chains comprising n-octyl groups, 2-ethylhexyl groups, and a mixture of these groups. The results showed that the linear-type hexaoctyl NTA amide (HONTA) had the highest extraction ability for MA. Furthermore, the extraction behavior of MA and REs was different under low and high nitrate conditions, and that of scandium (Sc) was found to be considerably different depending on the side chains.

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.

Enhanced enrichment of rare earth elements during pedogenesis under subtropical climate

Rare earth elements (REE) are crucial strategic resources, and weathering-crust rare earth deposits are one of the primary sources. To systematically understand the geochemical behavior (e.g., enrichment and leaching) of REE 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 rare earth elements at 264 (interquartile range (IQR): 278) ppm, 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 (PCA) and Linear mixed-effects models (LME) 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. LME and correlation analysis indicates that the enrichment of REE (Q REE ) shows a trend of initially increasing and then decreasing with rising temperature and precipitation, due to variations host clay minerals. The greatest enrichment occurs in the subtropical region (mean annual temperature (MAT) = 15 ̶ 23 °C; mean annual precipitation (MAP) = 1000 ̶ 2000 mm); weathering-crust type REE deposits are primarily found in the subtropics.

Production of high-grade antimony oxide from smelter slag via leaching and hydrolysis process

This study aimed to investigate the recovery of antimony (Sb) from slag generated in an antimony smelting plant using leaching followed by hydrolysis processes. The leaching behaviors of rare earth elements (REEs) were also examined. The physicochemical properties of the slag were determined using various analytical techniques. The slag (4.12 % Sb) was mainly composed of quartz and minor minerals, including microline, magnetite, hedenbergite, and stibiconite. The Sb types in the slag determined by XPS were found to be in the oxide form. The concentrations of REEs (La, Y, Ce, and Nd) in the slag were 169.21 g/t. Preliminary leaching experiment results indicate that (i) HCl was selected rather than other acids due to its high extraction ability on the Sb from the slag, (ii) a sample with a d50 of < 25 µm should be used, (iii) the slurry should be mixed at 300 rpm. In the following leaching tests, the effects of leaching parameters (HCl acid concentration, amount of tartaric acid, solid-to-liquid ratio, reaction temperature, and time) on the extraction rates of Sb, impurities, and REEs were investigated. At the best leaching conditions (HCl: 8 M, amount of tartaric acid: 1 g/L, stirring speed: 300 rpm, reaction temperature: 75 °C, and time: 180 min), the extraction rates of Sb from the slag were determined to be 91.19 %, but the extraction rates of REEs were measured to be ≤ 50 %. The activation energy (Ea) for Sb leaching was found to be 46.75 kJ/mol, indicating that the reaction was governed by the chemically controlled mechanism. In particular, it was understood from the additional experimental results that the leaching procedure should be carried out for 20 h to extract La with an extraction rate of > 90 %. However, the extraction rate of Sb was negligible in extended times. It was determined that using tartaric acid positively affected La’s leaching mechanism, and the required leaching time for La decreased to 180 min from 20 h with the increase of tartaric acid from 1 g/L to 6 g/L. Hydrolysis tests were conducted using the Taguchi approach (L32, 2^1 4^3). The effects of the alkaline type (NH4OH and NaOH), stirring speed (100, 200, 300, and 400 rpm), temperature (50, 60, 70, and 80 °C), and pH (1.5, 2, 2.5, and 3) on the precipitation of Sb from the PLS were investigated. NH4OH was suggested for use in the hydrolysis test to obtain precipitates with higher purities. The product obtained under the optimal conditions comprised 81.43 % Sb, 16.23 % O, and 2.34 % Fe. The product was identified as antimony oxide by XRD.

Study on the role of microbial metabolites in in-situ noncontact bioleaching of ion-adsorption rare earth ore

Ion adsorption rare earth ore nearly satisfy global market demand for heavy rare earth elements (HREEs). Bio-leaching has important potential for the clean and efficient extraction of ion-adsorption rare earth ore. However, the complexities of in-situ mining restrict the use of contact/direct bio-leaching, and non-contact/indirect bio-leaching would be the best choice. This study explore the potential of fermentation broths prepared by Yarrowia lipolytica (ATCC 30162) for the bio-leaching of ion-adsorption rare earth ore, and three typical metabolites (potassium citrate (K3Cit), sodium citrate (Na3Cit) and ammonium citrate ((NH4)3Cit) of Yarrowia lipolytica were further evaluated in simulated bioleaching (non-contact bioleaching) of ion-adsorption rare earth ore, including leaching behavior, seepage rule and rare earth elements (REEs) morphological transformation. The column leaching experiments shown that direct leaching of REEs using fermentation broths results in incomplete leaching of REEs due to the influence of impurities. Using the purified and prepared metabolites as lixiviant, REEs can be effectively extracted (leaching efficiency >90%) at cation concentration was only 10 % of the commonly used ammonium sulfate concentration (45 mM). Cation type had less effect on leaching efficiency. During the ion-adsorption rare earth ore leaching process, rare earth ions form a variety of complex chelates with citrate, thus transferring rare earth elements from the mineral surface to the leachate. Experimental results showed that pH and concentration together determined the type and form of rare earth chelates, which in turn affect the leaching behavior of REEs and solution seepage rule. This study helps to provide a theoretical basis for the regulation and enhancement of ion-adsorption rare earth ore non-contact bioleaching process.

Anthropogenic impact of rare earth elements on groundwater and surface water in the watershed of the largest freshwater lake in China

Limited knowledge exists regarding the potential risks associated with anthropogenic release of rare earth elements (REEs) in the environment. This study aimed to investigate REE signatures in the watershed Poyang Lake, the largest freshwater lake in China. Samples of surface water, wastewater, and groundwater were collected from five rivers discharging into the lake. Results revealed wastewater from wastewater treatment plants contained total REE concentrations from 231 to 904 μg/L, exceeding those found in surface water (0.4 to 1.3 μg/L) and groundwater (0.5 to 416 μg/L). Samples with elevated REE were found in Ca-Mg-Cl/SO4 type waters and exhibited an 18OD deviation from local meteoric water line. Wastewater exhibited a higher positive Gd anomaly compared to surface water and groundwater, attributed to anthropogenic input of Gd (Gdanth). The determined Gdanth concentration ranged from 0.04 to 0.21 μg/L, and from 0.06 to 0.37 μg/L, accounting for 4 % to 21 % and 49 % to 84 % of total Gd concentrations in groundwater and surface water, respectively. Gdanth concentration in wastewater (0.19 to 0.43 μg/L) remained constant in effluent after wastewater treatment. Surface water displayed relatively complex normalized REE patterns influenced by anthropogenic activities and natural processes (weathering and complexation), while groundwater exhibited heavy REEs enrichment, due to carbonate solution complexation. Additionally, Gdanth concentration showed a positive correlation with ΣREE, Pb, Ni, and Co concentrations in groundwater, indicating a good pollution tracing potential. Health risk assessment using the hazard quotient (HQ) suggested higher HQGd values in groundwater compared to surface water. Residents in the eastern part of Poyang Lake were found to face higher risks associated with Gd in groundwater compared to the western part, with infants and children at greater risk than adult males and females. These findings offer valuable insights into environmental behavior and health risks of REEs in aquatic systems impacted by human activities.

Prevalence of rare earth elements in natural waters of Khanty-Mansiysk

Relevance. New data on the content of lanthanides in the water–rock system are important for understanding the behavior of rare-earth elements in the environment, open up the possibility of using them as indicators of geochemical processes and anthropogenic factor, taking into account the specialities of their migration and fractionation. Aim. Assessment of the quantitative content and distribution of rare-earth elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in the surface and underground waters of Khanty-Mansiysk to identify the main patterns of their behavior. Objects. Surface and underground waters of the natural reserve Samarovsky Chugas, as well as ground deposits and products of secondary mineral formation. Methods. The bulk analysis of water is performed by a standard set of spectral and electrochemical methods. The rare-earth content was determined by inductively coupled plasma mass spectrometry. Chemical composition of ground deposits and secondary mineral formation products – by neutron activation analysis. Results. The paper demonstrates rare-earth elements behavior in aqueous medium, ground deposits and products of secondary mineral formation. Different approaches to rare-earth elements rationing in waters and solid sediments showed comparability of lanthanide distribution spectra to each other and made it possible to identify some features of the rare-earth elements distribution pattern in different environments. In the waters, there are positive anomalies of europium and gadolinium and negative anomaly of cesium. Gadolinium anomalies were detected in ground deposits, and europium in secondary mineral formation products. The high migration activity of the entire considered series of rare-earth elements in the solution coming from the holding deposits was established. During following geochemical processes, mainly middle lanthanides (Sm, Eu, Gd, and Tb) fall out of the solution in the form of secondary mineral formation products.

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.

Improvements in recovery of rare earth elements (REEs) from coal via fluidized-bed combustion: Thermal alteration of REE mineralogy and its impact on element extractability

The extraction of rare earth elements (REE) from coal ash has attracted significant attention, but satisfactory solutions have not yet been achieved. Indeed, the REE extractability is largely determined by the transformation behavior of REE during coal combustion. This study found that the controlled combustion conditions of circulated fluidized-bed boiler (CFB) can both utilize the heating value and enhance the recovery of REE from coal. Tests were conducted using a bituminous coal with REE concentration of approximately 149 ppm in an industrial 35 t/h CFB boiler with controlled boiler loads and coal sources. Advanced automated image analysis by scanning electron microscopy (AIA-SEM) and sequential leaching procedure were employed to clarify the speciation transformation behavior of REE in boilers and investigate the effects of these transformations on the leachability of REE. Approximately 75 % of REE partitioned into fly ash and enriched in particles < 45 μm (∼710 ppm) after combustion. Acid leaching tests under mild conditions (1 M HCl at 60 ℃ and S/L = 1:25) performed on coal, bulk ashes, and sieved ashes revealed an improvement in REE leaching ratio from coal (21.34 %) to fly ash (71.07 %). Particle size played a crucial role in acid extractability, particularly for middle and heavy REE in cyclone ash but had no influence on those in fly ash. The dominant forms of REE in coal including Ca-REE fluorocarbonates (36.7 %), aluminophosphates (12.0 %), and organic-bound REE (approximately 20 %) significantly decreased, contributing to the formation of leachable rare earth oxides (∼65 %) in ash. Furthermore, the small size of REE mineral grains in coal (over 50 % below 5 μm) and extensive mineral fragmentation occurring in boiler resulted in the enrichment and enhanced REY leachability in fine ash.

The mechanism insight into the cooperative coordination of Aza-18-crown-6 ether with diglycolamide by p-benzyl as linkers enhancing the selectivity for heavy REEs(III)

The development of new ligands is crucial for the functional application of REEs(III), because the coordination compounds of rare-earth elements (REEs) have many important applications in pharmaceuticals and nuclear medicine. In this paper, a novel ligand (Cr6-Bz-DGA) with the aza-crown ether and diglycolamide (DGA) units was designed to coordinate with light, medium, and heavy REEs(III). It was found that M/L = 2:2 species (aza-crown ether-REEs(III)-DGA connection) was the thermodynamically stable complex. The stability constants of Nd(III), Eu(III), and Ho(III) complexes were determined by UV–Vis and fluorescence titration, respectively, which were logβNd = 7.49 ± 0.019, logβEu = 7.10 ± 0.013 and logβHo = 8.27 ± 0.032. The variation of fluorescence lifetime suggested that the Eu(III) ion was exclusively coordinated by the ligand with coordination number 9 in the inner sphere of the Eu(III) ion. The shifts of 1H NMR revealed that there are different coordination between the ligand and REEs(III). For larger ionic radii La(III), three O atoms of the DGA unit and five O and one N atoms of the aza-crown ether unit were supplied. While, for Y(III)/Lu(III) with smaller ion radii, the ligand supplied three O atoms from the DGA and one N atom and only two O atoms from the aza-crown ether. The displacement experiment of REEs(III) combined with ligand and the fitted stability constants prove that the smaller ionic radii REEs(III) more strongly bind with ligand than larger ionic radius REEs(III). These results may help understand the coordination behavior of REEs(III) and expand their potential applications.

Exploring Rare Earth Element behavior in the Mount Etna volcanic aquifers (Sicily)

This study presents the first data on REY (Rare Earth Elements plus Yttrium) in the aquifer of Mount Etna (Sicily, Italy). Patterns normalized to chondrites indicate strong water–rock interaction, facilitated by a slightly acidic pH resulting from the dissolution of magma-derived CO2. REY patterns provide insights into the processes of both mineral dissolution and the formation of secondary phases. The relative abundance of light to heavy rare earth elements is compatible with the prevailing dissolution of ferromagnesian minerals (e.g., olivine or clinopyroxenes), reinforced by its strong correlation with other proxies of mineral dissolution (e.g., Mg contents). Pronounced negative Ce anomalies and positive Y anomalies demonstrate an oxidizing environment with continuous formation of secondary iron and/or manganese oxides and hydroxides. The Y/Ho fractionation is strongly influenced by metal complexation with bicarbonate complexes, a common process in C-rich waters. In the studied system, the measured REY contents are always below the limits proposed by Sneller et al. (2000, RIVM report, Issue 601,501, p. 66) for surface water and ensure a very low daily intake from drinking water.

Distribution of trace and rare earth elements in the estuary of Ría de Huelva (SW Spain): Field data and geochemical modeling

The geochemistry of the Ría de Huelva estuary (Spain) has been widely studied owing to its unique conditions due to mixing of acid mine drainage (AMD), river water and seawater, which have been aggravated by the existence of an adjacent phosphate fertilizer plant and its associated phosphogypsum stack.To better understand the complex geochemistry of the overall estuarine system, we make use of (1) measured concentrations of relevant trace elements (rare earth elements (REEs) and metal(loid)s) in the sediments and waters of the estuary and (2) geochemical modeling which combines mixing and adsorption processes.Our study sheds light on the elemental distribution in the sediments and water in the water-mixing area. As seawater neutralizes the acidity of the river water (pH increases to 6.2) colloids of Fe- and Al-oxyhydroxysulphates (schwertmannite and basaluminite, respectively) precipitate as concentrations of aqueous Fe and Al increase. These phases have a high adsorption capacity and play a critical role in the geochemistry of the aquatic system by retaining Cu, Pb, Cr, As, P, REEs and smaller amounts of Zn, Co, Ni and Mn. The geochemical model reproduces the behaviour of the aqueous REEs, requiring high S/L ratios at pH ≥ 3.5 and participation of sediments and colloids in the reactions to match the field data.The evaluation of the effect of the adjacent phosphogypsum stack on the estuarine geochemistry shows that the stack has a notorious impact on the geochemistry of the surrounding estuarine environment owing to the release of high quantities of phosphate.

The Global Biogeochemical Cycle of the Rare Earth Elements

AbstractTo improve our understanding and guide future studies and applications, we review the biogeochemistry of the rare earth elements (REE). The REEs, which form a chemically uniform group due to their nearly identical physicochemical properties, include the lanthanide series elements plus scandium (Sc) and yttrium (Y). These elements, in conjunction with the neodymium isotopes, are powerful tools for understanding key oceanic, terrestrial, biological and even anthropogenic processes. Furthermore, their unique properties render them essential for various technological processes and products. Here, we delve into the characteristics of REE biogeochemistry and discuss normalization procedures and REE anomalies. We also examine the aqueous speciation of REEs, contributing to a better understanding of their behavior in aquatic settings, including the role of neodymium isotopes. We then focus on their environmental distribution, fractionation, and controlling processes in different environmental systems across the land‐ocean continuum. In addition, we analyze sinks, sources, and the mobility of REEs, providing insights into their behavior in these environments. We further investigate the sources of anthropogenic REEs and their bioavailability, bioaccumulation, and transfer along food webs. We also explore the potential effects of climate change on the cycling, mobility and bioavailability of REEs, underlining the importance of current research in this evolving field. In summary, we provide a comprehensive review of REE behavior in the environment, from their properties and roles to their distribution and anthropogenic impacts, offering valuable insights and pinpointing key knowledge gaps.