Behavior Of Rare Earth Elements Research Articles

Rare earth element and yttrium behaviour during metabolic transfer and biomineralisation in the marine bivalve Mytilus edulis: Evidence for a (partially) biological origin of REY anomalies in mussel shells.

Rare Earth Elements and Yttrium (REY) are widely used as proxies for environmental conditions and biogeochemical processes, but have also become (micro)contaminants of surface waters worldwide. Soft tissues and shells of mussels are increasingly used in environmental science and geology as bioarchives for REY, but REY fractionation by and in these organisms is still not well understood. We report on the distribution of REY in different compartments of marine M. edulis mussels from Norway, and in their ambient water and food (plankton). The shale-normalised REY patterns of all compartments studied decrease from light to heavy REY (LREY and HREY, respectively), while the LREY depletion occasionally reported in the literature cannot be observed. The bivalves show REY concentrations up to five orders of magnitude higher than those in ambient water (with preferential uptake of Ce and of LREY over HREY) but lower than those in their potential plankton food (with minor REY fractionation, except for preferential uptake of La and Y). While metabolic REY fractionation within the bivalves is minor, vital effects affect the REY distribution in the shells of M. edulis mussels. Rejection and decoupling of Ce during shell formation occurs due to Ce oxidation and formation of Ce(IV) solution-complexes in the extrapallial fluid (EPF). While discrimination against HREY incorporation results from strong solution-complexation of the HREY, preferential uptake of La, Gd and Y during shell formation is due to the less stable solution-complexes of these ions. These observations are compatible with the presence of siderophores in the EPF, suggesting that in contrast to freshwater mussel A. anatina, vital effects can to some extent affect the size of anomalies in the REY patterns of marine M. edulis shells. This implies that these anomalies are (partially) of biological origin, which limits their use as paleo-redox proxies.

On the prospects of identifying rare and rare earth metals in the black shale sequence of the Eastern segment of the Greater Caucasus

The expansion, updating, and comprehensive utilization of the mineral resource base for rare and rare-earth metals necessitate the search for and development of new deposits of non-traditional genetic types, including those localized within black shale formations. This study examines the distribution of rare and rare-earth elements (REE) in the black shale formation of the Eastern segment of the Greater Caucasus, where extensive research and exploratory drilling have led to the discovery of several deposits and occurrences of non-ferrous metals. The results of geochemical and mineralogical investigations reveal a high concentration of rare and rare-earth elements (REE) and other metals within the black shale formation. All lithological types of rocks constituting the black shale formation, as well as rocks from the near-deformation and hydrothermally metasomatized zones, were tested for this study. Comparative studies of the behavior of rare and rare-earth elements across various rock types indicated significant variations in their elemental spectrum and concentrations. Notably, elevated concentrations of rare-earth elements were observed in clay-rich rocks, attributed to the sorptive capacity of clay minerals. Analysis of the distribution of microelements in the rocks and main minerals of the black shale formation highlighted a considerable presence of rare, rare-earth, and other elements, with concentrations exceeding their Clarke values by several times. Distinct anomalous zones were identified for Au, Mo, Cs, La, Ce, Nd, Sm, and U, while anomalous zones were noted for Cd, Se, Hf, Yb, Lu, Eu, Tb, and Th. The geochemical characteristics related to the concentration of these elements were also determined. The findings indicate that the unique properties of graphitized clay shales and accessory minerals within the formation significantly influence the processes of concentration of rare and rare-earth elements, serving as sources of associated metals. This study further analyzes the geochemical and mineralogical characteristics of the black shale formation and delineates zones of mobilization and concentration for rare, rare-earth, and other elements.

Extraction and recovery of rare earth elements from NdFeB waste using bismuth reinforced by supergravity

NdFeB stands as the foremost utilized material in permanent magnet applications, generating substantial quantities of NdFeB magnet waste annually. These wastes contain 20−30 wt. % rare earth elements (REEs) and are valuable secondary resources. In this paper, Bi was used as extractant to recover REEs in NdFeB waste by pyrometallurgy, and excess Bi was separated by supergravity technology for recycling. The migration and diffusion behaviors of REEs during the extraction process were investigated, with the diffusion coefficient of REEs in Bi obtained. The influence of Bi-to-waste mass ratio on rare earth extraction efficiency in smelting process, alongside the effect of temperature and gravity coefficient on the Bi recovery rate in supergravity centrifugation process were delineated. Findings revealed that the diffusion of Nd in Bi and NdFeB conformed to Fick's second law. Notably, with a Bi-to-waste mass ratio surpassing 1:1, spontaneous separation occurred between the Bi and Fe phases, facilitating the migration of almost all REEs from NdFeB waste into the Bi phase. Under the optimal conditions (Bi/NdFeB mass ratio of 4:3, separation temperature of 500°C and a gravity coefficient of 1000), the recovery rate of REEs during the smelting stage reached 99.6%, while the Bi recovery rate during the supergravity stage was 74.7%. Additionally, the overall REE recovery rate and Bi recovery rate during the entire process reached 99.3% and 70.3%, respectively. The successful development of this process has opened up a new way for recycling REEs from NdFeB waste.

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.

Effects of alkaline extraction on behavior of rare earth elements in coal ashes

The effects of alkaline extraction on the behavior of rare earth elements in coal ashes were investigated in the present study. Independent variables are the concentration of extractant and particle size of coal ashes. Sodium hydroxide was used as an extractant, and the molarity of the solvents varied from 1.0 to 7.0 M. The coal ashes used here were fly and bottom ashes. Fly and bottom ashes were classified into four samples by particle size, with each categorized at both 45 and 300 µm. The particle size distribution and crystalline characteristics of coal ashes, leaching, and the contents of rare earth elements in coal ashes after alkaline extraction were investigated, and the effects of independent variables on the content of rare earth elements in coal ashes were discussed. The test results showed that the dissolution of amorphous phase in coal ashes mainly occurred when the molarity was not more than 3 M, while dissolution and precipitation such as geopolymerization and the formation of zeolite occurred simultaneously when the molarity was more than 5 M. The dissolution and formation of precipitates such as geopolymer in the present study affected the variation of the rare earth element contents in the ashes. Besides, the ashes being smaller in size was more favorable for an increase in the rare earth elements in coal ashes.

Enhanced enrichment of rare earth elements during pedogenesis under subtropical climate

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

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.

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.