Microbial green synthesis of luminescent terbium sulfide nanoparticles using E. Coli: a rare earth element detoxification mechanism.

BACKGROUND: Rare-earth sulfide nanoparticles (NPs) could harness the optical and magnetic features of rare-earth ions for applications in nanotechnology. However, reports of their synthesis are scarce and typically require high temperatures and long synthesis times. RESULTS: Here we present a biosynthesis of terbium sulfide (TbS) NPs using microorganisms, identifying conditions that allow Escherichia coli to extracellularly produce TbS NPs in aqueous media at 37 °C by controlling cellular sulfur metabolism to produce a high concentration of sulfide ions. Electron microscopy revealed ultrasmall spherical NPs with a mean diameter of 4.1 ± 1.3 nm. Electron diffraction indicated a high degree of crystallinity, while elemental mapping confirmed colocalization of terbium and sulfur. The NPs exhibit characteristic absorbance and luminescence of terbium, with downshifting quantum yield (QY) reaching 28.3% and an emission lifetime of ~ 2 ms. CONCLUSIONS: This high QY and long emission lifetime is unusual in a neat rare-earth compound; it is typically associated with rare-earth ions doped into another crystalline lattice to avoid non-radiative cross relaxation. This suggests a reduced role of nonradiative processes in these terbium-based NPs. This is, to our knowledge, the first report revealing the advantage of biosynthesis over chemical synthesis for Rare Earth Element (REE) based NPs, opening routes to new REE-based nanocrystals.

Noise pollution assessment and management in rare earth mining areas: a case study of Kollam, Kerala, India.

Noise pollution is an unintentional consequence of mining activities, needing rigorous assessment, monitoring, and mitigation techniques to reduce its impact on local residents and ecosystems. The study specifically examines the noise pollution from rare earth mining activities in the Neendakara-Kayamkulam (NK) coastal belt, Kollam, Kerala, India, a region rich in ilmenite, rutile, sillimanite, zircon, and monazite. Despite the known environmental and health impacts of noise pollution, there is limited specific data on its magnitude and sources in this region, as well as a lack of effective mitigation strategies tailored to rare earth mining operations. Studies have indicated that mining operations, such as the movement of heavy mineral sands, considerably elevate noise levels, which have an effect on the environment's quality and public health. This study seeks to fill the gap by geospatial mapping and assessing the noise levels and recommend measures to effectively mitigate noise pollution. Systematic noise measurements were conducted at 48 suitable locations within the NK coastal belt, including residential, commercial, industrial, coastal, and silence zones. The noise levels vary from 49.1 dB(A) near a religious place to 82.4 dB(A) near the local industry. The study employs geospatial noise mapping and land cover superimposition to implement class-specific mitigation measures for noise pollution in a coastal vicinity mixed land use area, including natural and vegetative barriers, operational scheduling, zoning, and land use planning.

Upconversion and NIR-II luminescent rare earth nanoparticles combined with machine learning for cancer theranostics.

How to develop contrast agents for cancer theranostics is a meaningful and challenging endeavor, and rare earth nanoparticles (RENPs) may provide a possible solution. In this study, we initially modified RENPs through the application of photodynamic agents (ZnPc) and targeted the bevacizumab antibody for cancer theranostics, which was aimed at improving the therapeutic targeting and efficacy. Subsequently, we amalgamated anthocyanin with the modified RENPs, creating a potential cancer diagnosis platform. When the spectral data were obtained from the composite of cells, the crucial information was extracted through a competitive adaptive reweighted sampling feature algorithm. Then, we employed a machine learning classification model and classified both the individual spectral data and fused spectral data to accurately predict distinctions between breast cancer and normal tissue. The results indicate that the amalgamation of fusion techniques with machine learning algorithms provides highly precise predictions for molecular-level breast cancer detection. Finally, in vitro and in vivo experiments were carried out to validate the near-infrared luminescence and therapeutic effectiveness of the modified nanomedicine. This research not only underscores the targeted effects of nanomedicine but also demonstrates the potent synergy between optical spectral technology and machine learning. This innovative approach offers a comprehensive strategy for the integrated treatment of breast cancer.

Self-flocculating Spirulina platensis CMB-02 to efficiently treat ammonia nitrogen of rare earth elements wastewater.

The study aimed to evaluate the cyanobacteria Spirulina platensis CMB-02 (S. platensis CMB-02) with self-flocculation properties to treat the ammonia nitrogen of rare earth elements (REEs) wastewater. The results demonstrated that S. platensis CMB-02 could effectively remove total ammonia nitrogen (TAN) and total inorganic nitrogen within 5 days. Simultaneously, a self-flocculation efficiency of 82.59 % was achieved by microalga in 30 min after wastewater treatment. The pH, tightly bound extracellular polymeric substances (TB-EPS), and cell morphology of S. platensis CMB-02 were identified as key factors influencing its self-flocculation capabilities. Moreover, the established semi-continuous process with a 20 % renewal rate showed a stable treatment effect, representing a TAN degradation rate of 10.9 mg/(L·d). These obtained findings could conclude that the developed approach mediated with self-flocculating S. platensis CMB-02 was a promising way for REEs wastewater treatment.

Toxicity of rare earth elements (REEs) to marine organisms: Using species sensitivity distributions to establish water quality guidelines for protecting marine life.

A lack of chronic rare earth element (REE) toxicity data for marine organisms has impeded the establishment of numerical REE water quality benchmarks (e.g., guidelines) to protect marine life and assess ecological risk. This study determined the chronic no (significant) effect concentrations (N(S)ECs) and median-effect concentrations (EC50s) of eight key REEs (yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), gadolinium (Gd), dysprosium (Dy) and lutetium (Lu)) for 30 coastal marine organisms (encompassing 22 phyla and five trophic levels from temperate and tropical habitats). Organisms with calcifying life stages were most vulnerable to REEs, which competitively inhibit calcium uptake. The most sensitive organism was a sea urchin, with N(S)ECs ranging from 0.64 µg/L for Y to 1.9 µg/L for La and Pr, and EC50s ranging from 4.3 µg/L for Y to 14.4 µg/L for Pr. Conversely, the least sensitive organism was a cyanobacterium, with N(S)ECs ranging from 121 µg/L for Y to 469 µg/L for Pr, and EC50s ranging from 889 µg/L for Y to 3000 µg/L for Pr. Median sensitivity varied 215-fold across all organisms. The two-fold difference in median toxicity (µmol/L EC50) among REEs (Y âˆ¼ Gd > Lu âˆ¼ Nd âˆ¼ Dy âˆ¼ Ce > La ∼ Pr) was attributed to offset differences in binding affinity (log K) to cell surface receptors and the percentage of free metal ion (REE3+) in the test waters. The toxicity (EC50) of the remaining REEs (samarium, europium, terbium, holmium, thulium and ytterbium) was predicted using a combination of physicochemical data and measured EC50s for the eight tested REEs, with good agreement between predicted and measured EC50s for selected organisms. Numerical REE water quality guidelines to protect marine life were established using species sensitivity distributions (e.g., for 95 % species protection, values ranged from 1.1 µg/L for Y to 3.0 µg/L for La, Pr or Lu).

Rare earth metallic elements in plants: assessing benefits, risks and mitigating strategies.

Rare earth elements (REEs) comprises of a uniform group of lanthanides and scandium (Sc) and yttrium (Y) finding their key importance in agriculture sectors, electronic and defense industries, and renewable energy production. The immense application of REEs as plant growth promoters has led to their undesirable accumulation in the soil system raising concerns for REE pollution as upcoming stresses. This review mainly addresses the chemistry of REEs, uptake and distribution and their biphasic responses in plant systems and possible plausible techniques that could mitigate/alleviate REE contamination. It extends beyond the present understanding of the biphasic impacts of rare earth elements (REEs) on physio-biochemical attributes. It not only provides landmarks for further exploration of the interrelated phytohormonal and molecular biphasic nature but also introduces novel approaches aimed at mitigating their toxicities. By delving into innovative strategies such as recycling, substitution, and phytohormone-assisted mitigation, the review expands upon existing knowledge of REEs whilst also offering pathways to tackle the challenges associated with REE utilization.

From screens to seas: Tech contaminants in tiger sharks.

The potential negative impacts of Technology-Critical Elements (TCEs) on the environment and wildlife, despite increasingly recognized, remain largely overlooked. In this sense, this study aimed to investigate the concentrations of several TCEs, including rubidium (Rb), titanium (Ti) and various Rare Earth Elements (REEs), in different tissues of tiger sharks. Sharks incidentally caught by artisanal fleets in southern Brazil were opportunistically sampled and liver, gills, kidneys, heart, muscle, eyes, brain, skin, and teeth were analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Significant Rb concentration variations were observed across different tissues, with higher levels detected in kidneys and lower levels in the liver. Titanium concentrations also exhibited significant differences, with higher levels detected in teeth and lower levels in liver. Although no statistical differences were observed for the analyzed REEs, a trend of higher accumulation in the liver, gills, and skin was noted. Light Rare Earth Elements (LREEs) were found predominantly in all organs, with neodymium, lanthanum, and cerium as the most significant REEs detected. Several statistically significant correlations were identified between Rb and REEs, as well as between Ti and REEs, indicating systemic transport of these elements across different tissues. These findings indicate that the growing extraction and disposal of metallic elements, driven by technological advancements, may lead to their assimilation by marine fauna, particularly at higher trophic levels. The potential harmful effects on these organisms remain unknown and require urgent investigation. Additionally, as mining activities intensify globally, precise legislative measures are essential to address environmental concerns, species conservation, and human health considerations.

Various microbes used for the recovery of rare earth elements from mine wastewater.

Microbes used for the recovery of rare earth elements (REEs) from mining wastewater indicated traces of Escherichia coli (E. coli, 2149.6 µg/g), Bacillus sphaericus (1636.6 µg/g), Bacillus mycoides (1469.3 µg/g), and Bacillus cereus (1083.9 µg/g). Of these, E. coli showed an affinity for REEs than non-REEs (Mn and Zn). The amount of heavy REEs adsorbed (1511.1 µg/g) on E. coli was higher than light REEs (638.0 µg/g) due to the process of increasing adsorption with decreasing ionic radius. Additionally, E. coli demonstrated stability in the recovery of REEs from mining wastewater, as evidenced by 4 cycles. SEM-EDS, XPS and FTIR showed that REEs had a disruptive effect on cells, REEs absorbed and desorbed on the cell surface including ion exchange with ions such as Na+, ligand binding with functional groups like -NH2. Finally, the cost assessment confirmed the economically feasible of E. coli in recovery of REEs from mining wastewater.

Structure-driven development of a biomimetic rare earth artificial metalloprotein.

The 2011 discovery of the first rare earth-dependent enzyme in methylotrophic Methylobacterium extorquens AM1 prompted intensive research toward understanding the unique chemistry at play in these systems. This enzyme, an alcohol dehydrogenase (ADH), features a La3+ ion closely associated with redox-active coenzyme pyrroloquinoline quinone (PQQ) and is structurally homologous to the Ca2+-dependent ADH from the same organism. AM1 also produces a periplasmic PQQ-binding protein, PqqT, which we have now structurally characterized to 1.46-Å resolution by X-ray diffraction. This crystal structure reveals a Lys residue hydrogen-bonded to PQQ at the site analogously occupied by a Lewis acidic cation in ADH. Accordingly, we prepared K142A- and K142D-PqqT variants to assess the relevance of this site toward metal binding. Isothermal titration calorimetry experiments and titrations monitored by UV-Vis absorption and emission spectroscopies support that K142D-PqqT binds tightly (Kd = 0.6 ± 0.2 µM) to La3+ in the presence of bound PQQ and produces spectral signatures consistent with those of ADH enzymes. These spectral signatures are not observed for WT- or K142A-variants or upon addition of Ca2+ to PQQ ⸦ K142D-PqqT. Addition of benzyl alcohol to La3+-bound PQQ ⸦ K142D-PqqT (but not Ca2+-bound PQQ ⸦ K142D-PqqT, or La3+-bound PQQ ⸦ WT-PqqT) produces spectroscopic changes associated with PQQ reduction, and chemical trapping experiments reveal the production of benzaldehyde, supporting ADH activity. By creating a metal binding site that mimics native ADH enzymes, we present a rare earth-dependent artificial metalloenzyme primed for future mechanistic, biocatalytic, and biosensing applications.

Enhanced Tribodegradation of a Tetracycline Antibiotic by Rare-Earth-Modified Zinc Oxide.

Tribocatalysis is an emerging advanced oxidation process that utilizes the triboelectric effect, based on friction between dissimilar materials to produce charges that can initiate various catalytic reactions. In this study, pure and rare-earth-modified ZnO powders (La2O3, Eu2O3, 2 mol %) were demonstrated as efficient tribocatalysts for the removal of the tetracycline antibiotic doxycycline (DC). While the pure ZnO samples achieved 49% DC removal within 24 h at a stirring rate of 100 rpm, the addition of Eu2O3 increased the removal efficiency to 67%, and La2O3-modified ZnO powder exhibited the highest removal efficiency, reaching 80% at the same stirring rate. Additionally, increasing the stirring rate to 300 and 500 rpm led to 100% DC removal in the ZnO/La case within 18 h, with the pronounced effect of the stirring rate confirming the tribocatalytic effect. All tribocatalysts exhibited excellent recycling properties, with less than a 3% loss of activity over three cycles. Furthermore, a scavenger assay confirmed the importance of superoxide radical generation for the overall reaction rate. The results of this investigation indicate that the rare-earth-modified ZnO tribocatalysts can effectively utilize mechanical energy to decompose pollutants in contaminated water.

Association between Exposure of Rare Earth Elements and Outcomes of In Vitro Fertilization-Embryo Transfer in Beijing.

Objective: The study aimed to investigate the impact of rare earth elements (REEs) exposure on pregnancy outcomes of in vitro fertilization-embryo transfer (IVF-ET) by analyzing samples from spouses. Methods: A total of 141 couples were included. Blood and follicular fluid from the wives and semen plasma from the husbands, were analyzed for REEs using inductively coupled plasma mass spectrometry (ICP-MS). Spearman's correlation coefficients and the Mann-Whitney U test were used to assess correlations and compare REE concentrations among three types of samples, respectively. Logistic models were utilized to estimate the individual REE effect on IVF-ET outcomes, while BKMR and WQS models explored the mixture of REE interaction effects on IVF-ET outcomes. Results: Higher La concentration in semen (median 0.089 ng/mL, P = 0.03) was associated with a lower fertilization rate. However, this effect was not observed after artificial selection intervention through intracytoplasmic sperm injection (ICSI) ( P = 0.27). In semen, the REEs mixture did not exhibit any significant association with clinical pregnancy. Conclusion: Our study revealed a potential association between high La exposure in semen and a decline in fertilization rate, but not clinical pregnancy rate. This is the first to report REEs concentrations in follicular fluid with La, Ce, Pr, and Nd found at significantly lower concentrations than in serum, suggesting that these four REEs may not accumulate in the female reproductive system. However, at the current exposure levels, mixed REEs exposure did not exhibit reproductive toxicity.

Rare earth elements and warming: Implications for adult mussel health and sperm quality.

The present study aimed to investigate the effects of europium (Eu) exposure (10 µg/L), warming (a 4 °C increase), and their combination on Mytilus galloprovincialis. Biochemical and histopathological changes in adult mussels were evaluated after a 28-day exposure period. Additionally, biochemical and physiological alterations in sperm were measured following a 30-min exposure period. The overall responses to each treatment were assessed using the Integrated Biological Response index version 2 (IBRv2). In adult mussels, warming elevated metabolism and activated glutathione S-transferases (GSTs), leading to redox imbalance and cellular damage. Europium exposure alone slightly enhanced metabolism and GSTs activity, resulting in cellular damage and histopathological injuries in digestive tubules. The combined exposure to Eu and warming was the most detrimental treatment for adults, as indicated by the highest IBRv2 value. This treatment slightly increased metabolism and uniquely elevated the activity of antioxidant enzymes, as well as GSTs and carboxylesterases. Despite these responses, they were inadequate to prevent redox imbalance, cellular damage, and histopathological injuries in digestive tubules and gills. Regarding sperm, warming reduced reactive oxygen species (ROS) production but raised lipid peroxidation levels. Sperm exposed to this treatment also increased their oxygen consumption and exhibited reduced velocity. The IBRv2 indicated that Eu was the most harmful treatment for sperm, significantly increasing ROS production and notably decreasing sperm velocity. When combined with warming, Eu elevated superoxide anion (O2-) production, lowered sperm velocity, and increased oxygen consumption. This study underscores the importance of investigating the effects of rare earth elements and their interaction with climate change-related factors.

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.

Removal of Rare Earth Elements from complex mixtures by using manganese ferrite nanoparticles: Optimization through surface response methodology.

The crucial role of Rare Earth Elements (REEs) in the development of hi-tech in addition to their limited availability have urged countries to develop sustainable alternatives to their conventional primary sources (ore mining). Sorption technologies using magnetic materials such as spinel ferrite nanoparticles provide efficient removal of REEs from contaminated solutions and ease of separation through application of an external magnetic field. However, there is still limited knowledge available regarding the optimal operational conditions in which to use these materials, especially in complex aqueous mixtures with different REEs. In this study, we have used Surface Response Methodology (SRM) applied to MnFe2O4 nanosorbents to identify their ideal sorption conditions of pH (4-8), REEs concentration (1-5 µM) and sorbent mass (20-180 mg L-1) in a mixture of nine REEs in water samples of distinct salinity (NaCl: 0-30 g L-1). Our results indicated that high pH favored REEs sorption because of the material's surface charge, which promoted interactions with REEs ions at pH 6-8. Yttrium was the least removed element, but total removal was achieved for lowest REEs concentration using 151 mg L-1 of sorbent. High removals were also obtained for the concentration of 5 µM (100 % removal, except for Y and La). Salinity did not impair sorption significantly (<10 %), which was owed to the high sorbent mass used in those assays. An increase in sorbent mass and initial REEs concentration also promoted faster kinetics. The spinel type MnFe2O4 nanoparticles showed great promise in a realistic application, which is the next proposed step in this line of research.

Optimization and mechanism studies for the biosorption of rare earth ions by Yarrowia lipolytica.

Research on the recovery of rare earth elements from wastewater has attracted increasing attention. Compared with other methods, biosorption is a simple, efficient, and environmentally friendly method for rare earth wastewater treatment, which has greater prospects for development. The objective of this study was to investigate the biosorption behavior and mechanism of Yarrowia lipolytica for five rare earth ions (La3⁺, Nd3⁺, Er3⁺, Y3⁺, and Sm3⁺) with a particular focus on biosorption behavior, biosorption kinetics, and biosorption isotherm. It was demonstrated that the biosorption capacity of Y. lipolytica at optimal conditions was 76.80 mg/g. It was discovered that the biosorption process complied with the pseudo-second-order kinetic model and the Langmuir biosorption isotherm, indicating that Y. lipolytica employed a monolayer chemical biosorption process to biosorb rare earth ions. Characterization analysis demonstrated that the primary functional groups involved in rare earth ion biosorption were amino, carboxyl, and hydroxyl groups. The cooperative biosorption of rare earth ions by Y. lipolytica was facilitated by means of surface complexation, ion exchange, and electrostatic interactions. These findings suggest that Y. lipolytica has the potential to be an effective biosorbent for the removal of rare earth elements from wastewater.

Virus-Based Separation of Rare Earth Elements.

The utilization of biomaterials for the separation of rare earth elements (REEs) has attracted considerable interest due to their inherent advantages, including diverse molecular structures for selective binding and the use of eco-friendly materials for sustainable systems. We present a pioneering methodology for developing a safe virus to selectively bind REEs and facilitate their release through pH modulation. We engineered the major coat protein of M13 bacteriophage (phage) to incorporate a lanthanide-binding peptide. The engineered lanthanide-binding phage (LBPh), presenting ∼3300 copies of the peptide, serves as an effective biological template for REE separation. Our findings demonstrate the LBPh's preferential binding for heavy REEs over light REEs. Moreover, the LBPh exhibits remarkable robustness with excellent recyclability and stability across multiple cycles of separations. This study underscores the potential of genetically integrating virus templates with selective binding motifs for REE separation, offering a promising avenue for environmentally friendly and energy-efficient separation processes.

Establishing carbon dots assisted high speed countercurrent chromatography and its application for efficient separation of rare earth element ions.

Rare earth elements with unique magnetic properties and optical properties, known as the 'industrial vitamin', has a very high commercial value. As a secondary resource of rare earth elements, low-concentration solution includes mixed rare earth ions, which need to realize efficient separation and recovery urgently. High speed countercurrent chromatography is suitable for the separation and purification of rare earth element ions due to its advantages of large loading, good tolerance to samples, and simple pretreatment. In this study, a carbon dots assisted high speed countercurrent chromatography method was designed and established, the carbon dots were applied to the mobile phase of high speed countercurrent chromatography for the first time. The low concentration of REEs solution was enriched, and the effective separation of La (III), Ce (III), Gd (III) and Er (III) was successfully achieved. The complete separation of La (III), Ce (III), Gd (III) and Er (III) was achieved with a solvent system of 0.05 mol L-1 P507 (PE), 0.05 mol L-1 HNO3, and 0.1 mol L-1 CDs2 carbon dots (1:1:0.01, v/v/v), the upper phase as stationary phase, the lower phase as mobile phase. Density functional theory result showed that the binding energy of REEs (III)-CDs2 was larger than that of REEs (III)-P507, so the affinity of CDs2 to REEs (III) was stronger than that of P507. Therefore, with the addition of CDs2, the ability of mobile phase to elute REEs from the stationary phase was enhanced, and the separation effect was improved.

Efficient Self-cleaning and antibacterial ceramics with active sites fully exposed obtained from rare earth waste.

The utilization of rare earth polishing powder waste (RPW) to prepare antibacterial ceramics can effectively avoid problems of pollution in the recycling process and waste of rare earth resources. Herein, a novel RPW-based antibacterial ceramics was developed, which possesses the core-shell structure with ceramics as the cores and the CeO2/BiOCl as the superficial coating. The antibacterial ceramics display notable antibacterial activity, and the inactivation rates of 3.3 log under visible light irradiation in 30 min and 2.4 log under darkness in 1 h were achieved, and the zone of inhibition values was found to be 16.6 mm for E.coil. The hardness of antibacterial ceramics was measured to be 897 (±38) HV, higher than commercial porcelain's hardness (600 HV). The antibacterial mechanism was verified by the Ce ion release, reactive species, and fluorescence-based live/dead cells. This study presents a novel antibacterial ceramic structure and green economic reuse method of rare earth waste.

Distribution and migration of rare earth elements in sediment profile near a decommissioned uranium hydrometallurgical site in South China: Environmental implications.

Rare earth elements have garnered increasing attention due to their strategic properties and chronic toxicity to humans. To better understand the content, migration, and ecological risk of rare earth elements in a 180 cm depth sediment profile downstream of a decommissioned uranium hydrometallurgical site in South China, X-ray powder diffraction (XRD) and High-resolution transmission electron microscope (HRTEM) were additionally used to quantify and clarify the mineral composition features. The results showed a high enrichment level of total rare earth elements in the sediment depth profile (range: 129.6-1264.3 mg/kg); the concentration variation of light rare earth elements was more dependent on depth than heavy rare earth elements. Overall, there was an obvious enrichment trend of light rare earth elements relative to heavy rare earth elements and negative anomalies of Ce and Eu. The fractionation and anomaly of rare earth elements in sediments were closely related to the formation and weathering of iron-bearing minerals and clay minerals, as confirmed by the correlation analysis of rare earth elements with Fe (r2 = 0.77-0.90) and Al (r2 = 0.50-0.71). The mineralogical composition of sediments mainly consisted of quartz, feldspar, magnetite, goethite, and hematite. Pollution assessment based on the potential ecological risk index, pollution load index (PLI), enrichment factor, and geological accumulation index (Igeo) showed that almost all the sediments had varying degrees of pollution and a high level of ecological risk. This study implied that continued environmental supervision and management are needed to secure the ecological health in terms of rare earth elements enrichment around a decommissioned uranium hydrometallurgical site. The findings may provide valuable insights for other uranium mining and hydrometallurgical areas globally.

Selective Capacitive Recovery of Rare-Earth Ions from Wastewater over Phosphorus-Modified TiO2 Cathodes via an Electro-Adsorption Process.

Large amounts of wastewater containing low-concentration (<10 ppm) rare-earth ions (REIs) are discharged annually in China's rare-earth mining and processing industry, resulting in severe environmental pollution and economic losses. Hence, achieving efficient selective recovery of low-concentration REIs from REIs-containing wastewater is essential for environmental protection and resource recovery. In this study, a pseudocapacitance system was designed for highly efficient capacitive selective recovery of REIs from wastewater using the titanium dioxide/P/C (TiO2/P/C) composite electrode, which exhibited over 99% recovery efficiency for REIs, such as Eu3+, Dy3+, Tb3+, and Lu3+ in mixed solution. This system maintained high efficiency and more than 90 times the enrichment concentration of REIs even after 100 cycles. Ti4+ of TiO2 was reduced to Ti3+ of Ti3O5 under forward voltage in the system, which trapped the electrons of phosphorus site and caused it to be oxidized to phosphate with a strong affinity for REIs, thus improving the selectivity of REIs. Under reverse voltage, Ti3O5 was oxidized to TiO2, which transferred electrons to phosphate and transformed to the phosphorus site, resulting in the desorption and enrichment of REIs and the regeneration of the electrode. This study provides a promising method for the efficient recovery of REIs from wastewater.