Robust antibacterial activity of rare-earth ions on planktonic and biofilm bacteria.

Bacterial infections pose a serious threat to human health, with emerging antibiotic resistance, necessitating the development of new antibacterial agents. Cu2+and Ag+are widely recognized antibacterial agents with a low propensity for inducing bacterial resistance; however, their considerable cytotoxicity constrains their clinical applications. Rare-earth ions, owing to their unique electronic layer structure, hold promise as promising alternatives. However, their antibacterial efficacy and biocompatibility relative to conventional antibacterial agents remain underexplored, and the variations in activity across different rare-earth ions remain unclear. Here, we systematically evaluate the antibacterial activity of five rare-earth ions (Yb3+, Gd3+, Sm3+, Tb3+, and La3+) againstStaphylococcus aureusandPseudomonas aeruginosa, benchmarked against well-established antibacterial agents (Cu2+, Ag+) and the antibiotic norfloxacin. Cytotoxicity is also assessed via live/dead staining of fibroblasts after 24 h rare-earth ion exposure. Our findings reveal that rare-earth ions require higher concentrations to match the antibacterial effects of traditional agents but offer the advantage of significantly lower cytotoxicity. In particular, Gd3+demonstrates potent bactericidal efficacy against both planktonic and biofilm bacteria, while maintaining the lowest cytotoxicity toward mammalian cells. Moreover, the tested rare-earth ions also exhibited excellent antifungal activity againstCandida albicans. This study provides a critical empirical framework to guide the selection of rare-earth ions for biomedical applications, offering a strategic direction for the development of novel antimicrobial agents.

Geochemical behavior of rare earth elements in agricultural soils along the Syr Darya River within the Aral Sea Basin.

The widespread use of rare earth elements (REEs) across various industries makes them a new type of pollutant. Additionally, REEs are powerful indicators of geochemical processes. As one of the two main rivers in the Aral Sea, identifying the geochemical behavior of REEs in agricultural soils of the Syr Darya River is of great significance for subsequent indicative studies. In this study, the geochemical characteristics, influencing factors, and potential application significance of REEs in agricultural soils from three sampling areas along the Syr Darya River were analyzed using soil geography and elemental geochemical analyses. The results showed that the highest total concentration of REEs in the agricultural soil was in Area I, with a mean value of 142.49 µg/g, followed by Area III with a mean value of 124.56 µg/g, and the lowest concentration was in Area II with a mean value of 122.48 µg/g. The agricultural soils in the three regions were enriched in light rare earth elements (LREEs), with mean L/H values of 10.54, 10.13, and 10.24, respectively. The differentiation between light and heavy rare earth elements (HREEs) was also high. The concentration of REEs in agricultural soil along the Syr Darya River was primarily influenced by minerals such as monazite and zircon, rather than human activities (the pollution index of all REEs was less than 1.5). The relationship between Sm and Gd can differentiate soils impacted by agricultural activities from natural background soils. The results of this study can serve as a basis for indicative studies of REEs in Central Asia.

Microbial recovery of rare earth elements from various waste sources: a mini review with emphasis on microalgae.

Rare Earth Elements (REEs) are indispensable in contemporary technologies, influencing various aspects of our daily lives and environmental solutions. The escalating demand for REEs has led to increased exploitation, resulting in the generation of diverse REE-bearing solid and liquid wastes. Recognizing the potential of these wastes as secondary sources of REEs, researchers are exploring microbial solutions for their recovery. This mini review provides insights into the utilization of microorganisms, with a particular focus on microalgae, for recovering REEs from sources such as ores, electronic waste, and industrial effluents. The review outlines the principles and distinctions of bioleaching, biosorption, and bioaccumulation, offering a comparative analysis of their potential and limitations. Specific examples of microorganisms demonstrating efficacy in REE recovery are highlighted, accompanied by successful methods, including advanced techniques for enhancing microbial strains to achieve higher REE recovery. Moreover, the review explores the environmental implications of bio-recovery, discussing the potential of these methods to mitigate REE pollution. By emphasizing microalgae as promising biotechnological candidates for REE recovery, this mini review not only presents current advances but also illuminates prospects in sustainable REE resource management and environmental remediation.

Pioneer plants enhance soil multifunctionality by reshaping underground multitrophic community during natural succession of an abandoned rare earth mine tailing.

Spontaneous natural succession in metal mine tailings is fundamental to the rehabilitation of bare tailing. Here, an abandoned rare earth element (REE) mine tailing with spontaneous colonisation by pioneer plants with different functional traits was selected. Soil nutrient cycling, fertility, organic matter decomposition as well as underground organismal communities and their multitrophic networks were investigated. Compared with the bare tailing, the colonisation with Lycopodium japonicum, Miscanthus sinensis, and Dicranopteris dichotoma increased soil multifunction by 222%, 293%, and 525%, respectively. This was accompanied by significant changes in soil bacterial and protistan community composition and increased soil multitrophic network complexity. Rhizospheres of different plant species showed distinct microbial community composition compared to that of bare tailing. Some WPS-2, Chloroflexi, and Chlorophyta were mainly present in the bare tailing, while some Proteobacteria and Cercozoa were predominantly seen in the rhizosphere. Pearson correlation and Random Forest revealed the biotic factors driving soil multifunction. Structural equation modelling further revealed that pioneer plants improved soil multifunction primarily by decreasing the microbial biodiversity and increasing the multitrophic network complexity. Overall, this highlights the importance of subterrestrial organisms in accelerating soil rehabilitation during natural succession and provides options for the ecological restoration of degraded REE mining areas.

Layered rare-earth hydroxides as multi-modal medical imaging probes: particle size optimisation and compositional exploration.

Recently, layered rare-earth hydroxides (LRHs) have received growing attention in the field of theranostics. We have previously reported the hydrothermal synthesis of layered terbium hydroxide (LTbH), which exhibited high biocompatibility, reversible uptake of a range of model drugs, and release-sensitive phosphorescence. Despite these favourable properties, LTbH particles produced by the reported method suffered from poor size-uniformity (670 ± 564 nm), and are thus not suitable for therapeutic applications. To ameliorate this issue, we first derive an optimised hydrothermal synthesis method to generate LTbH particles with a high degree of homogeneity and reproducibility, within a size range appropriate for in vivo applications (152 ± 59 nm, n = 6). Subsequently, we apply this optimised method to synthesise a selected range of LRH materials (R = Pr, Nd, Gd, Dy, Er, Yb), four of which produced particles with an average size under 200 nm (Pr, Nd, Gd, and Dy) without the need for further optimisation. Finally, we incorporate Gd and Tb into LRHs in varying molar ratios (1 : 3, 1 : 1, and 3 : 1) and assess the combined magnetic relaxivity and phosphorescence properties of the resultant LRH materials. The lead formulation, LGd1.41Tb0.59H, was demonstrated to significantly shorten the T2 relaxation time of water (r2 = 52.06 mM-1 s-1), in addition to exhibiting a strong phosphorescence signal (over twice that of the other LRH formulations, including previously reported LTbH), therefore holding great promise as a potential multi-modal medical imaging probe.

Biochemical and biophysical interaction of rare earth elements with biomacromolecules: A comprehensive review.

The growing utilization of rare earth elements (REEs) in industrial and technological applications has captured global interest, leading to the development of high-performance technologies in medical diagnosis, agriculture, and other electronic industries. This accelerated utilization has also raised human exposure levels, resulting in both favourable and unfavourable impacts. However, the effects of REEs are dependent on their concentration and molecular species. Therefore, scientific interest has increased in investigating the molecular interactions of REEs with biomolecules. In this current review, particular attention was paid to the molecular mechanism of interactions of Lanthanum (La), Cerium (Ce), and Gadolinium (Gd) with biomolecules, and the biological consequences were broadly interpreted. The review involved gathering and evaluating a vast scientific collection which primarily focused on the impact associated with REEs, ranging from earlier reports to recent discoveries, including studies in human and animal models. Thus, understanding the molecular interactions of each element with biomolecules will be highly beneficial in elucidating the consequences of REEs accumulation in the living organisms.

Rare Earth Element Adsorption to Clay Minerals: Mechanistic Insights and Implications for Recovery from Secondary Sources.

The energy transition will have significant mineral demands and there is growing interest in recovering critical metals, including rare earth elements (REE), from secondary sources in aqueous and sedimentary environments. However, the role of clays in REE transport and deposition in these settings remains understudied. This work investigated REE adsorption to the clay minerals illite and kaolinite through pH adsorption experiments and extended X-ray absorption fine structure (EXAFS). Clay type, pH, and ionic strength (IS) affected adsorption, with decreased adsorption under acidic pH and elevated IS. Illite had a higher adsorption capacity than kaolinite; however, >95% adsorption was achieved at pH ∼7.5 regardless of IS or clay. These results were used to develop a surface complexation model with the derived binding constants used to predict REE speciation in the presence of competing sorbents. This demonstrated that clays become increasingly important as pH increases, and EXAFS modeling showed that REE can exist as both inner- and outer-sphere complexes. Together, this indicated that clays can be an important control on the transport and enrichment of REE in sedimentary systems. These findings can be applied to identify settings to target for resource extraction or to predict REE transport and fate as a contaminant.

Molding the future: Optimization of bioleaching of rare earth elements from electronic waste by Penicillium expansum and insights into its mechanism.

The recovery of rare earth elements (REE) from electronic waste is crucial for ensuring future demand security, as there is a high supply risk for this group of elements, and mitigating the environmental impacts of conventional mining. This research focuses on extracting REE from waste printed circuit boards through bioleaching, addressing the limited attention given to this source. A strain of Penicillium expansum demonstrated efficient bioleaching under optimal conditions of 7.5 initial pH, 0.1 mM phosphate concentration, and excluding a buffering agent. The study achieved significant improvements in La and Tb extraction and enhancements in Pr, Nd, and Gd recovery, approaching 70 % within 24 h. Fungal mechanisms involved in REE extraction included fungal pH control, organic acid biosynthesis, phosphate bioavailability, and potential fungal proton pump involvement. This approach offers a promising solution for sustainable REE recovery from e-waste, contributing to resource security and circular economy.

Advancing phytomining: Harnessing plant potential for sustainable rare earth element extraction.

Rare earth elements (REEs) are pivotal for advanced technologies, driving a surge in global demand. Import dependency on clean energy minerals raises concerns about supply chain vulnerabilities and geopolitical risks. Conventional REEs productionis resource-intensive and environmentally harmful, necessitating a sustainable supply approach. Phytomining (agromining) utilizes plants for eco-friendly REE extraction, contributing to the circular economy and exploiting untapped metal resources in enriched soils. Critical parameters like soil pH, Casparian strip, and REE valence influence soil and plant uptake bioavailability. Hyperaccumulator species efficiently accumulate REEs, serving as energy resources. Despite a lack of a comprehensive database, phytomining exhibits lower environmental impacts due to minimal chemical usage and CO2 absorption. This review proposes phytomining as a system for REEs extraction, remediating contaminated areas, and rehabilitating abandoned mines. The phytomining of REEs offers a promising avenue for sustainable REEs extraction but requires technological advancements to realize its full potential.

Enhanced removal of rare earth elements from aqueous media: exploring the potential of AM-3 and AM-4 titanosilicates.

This study investigates the impact of three key variables on the performance of nanoporous AM-3 and layered AM-4 titanosilicates in removing nine REEs (Y, La, Ce, Pr, Nd, Eu, Gd, Tb, and Dy) from natural mineral water and identifies optimal operational conditions using Response Surface Methodology (RSM). The experimental conditions were determined by a Box-Behnken Design of 3 factors-3 levels (pH 4, 6, and 8; sorbent dose 20, 100, and 180 mg/L; and element concentration 1, 3, and 5 µmol/L). Three-dimensional response surfaces were used to assess the linear, quadratic, and interaction influences of each factor on the REEs' removal percentage. The pH was the most significant factor in the removal process using AM-3, while the sorbent dose was more important for AM-4. The results highlighted the sorbents' strong capacity for REE removal. The optimal operating conditions obtained by RSM were applied to aqueous solutions with salinity 10 (common in coastal and transitional systems) and 30 (average seawater salinity). The results showed that AM-3 has a strong potential for removing REEs in solutions with salinity 10 and 30, while AM-4 was less efficient due to competition between REEs and other ions present in the solution.

Decomposition of Luminescent Hydroxyapatite Scaffolds in Simulated Body Fluid.

We present a luminescence study investigating the dissolution of rare-earth-doped hydroxyapatite scaffolds in simulated body fluid (SBF), aiming to assess the luminescence stability of Tb-, Ce-, and Eu-doped scaffolds over time. Our findings reveal a consistent decrease in luminescence emission intensity across all samples over a four-week period in which the scaffolds were immersed in the SBF. In addition, energy-dispersive spectroscopy confirms a decrease in rare-earth ion concentration in the scaffolds with respect to time, whereas fluorescence spectroscopy shows the presence of rare-earth ions in the SBF, indicating the partial dissolution of the scaffolds over time. The use of rare-earth ions as luminescence markers provides insights into the mechanisms of apatite formation in hydroxyapatites. Thus, these scaffolds may find wider use in regenerative medicine, particularly in targeted drug delivery systems, where their luminescent properties have the potential to noninvasively track drug release.

RARE-EARTH elements in the topsoils of a Russian industrial city: Sources and human health risk assessment.

Research on rare-earth elements (REEs) in urban soils of Russian industrial cities is extremely limited. This study investigates the potential sources and human health risks of REEs contained in the topsoils of the industrial Russian city of Chelyabinsk. The study also takes into account natural sources of REE as the city is located on the border of granites (Urals) and sedimentary rocks (Western Siberia). We analyzed the concentration and distribution of REEs in the soils of four types of locations: residential courtyards, city parks, roadsides, and industrial locations. The total REE concentrations ranged from 44 to 255 mg/kg, with average concentrations of 140, 124, 113 and 89 mg/kg in the courtyards, roadsides, industrial location and city parks, respectively. The REE content in courtyard soils could be influenced by poor cleaning of fallen leaves. The ratios of light REE (LREE) to heavy REE (HREE) ranged from 9.5 to 10.1, revealing an obvious fractionation between them. The fractionation of LREE and HREE, and the REE/ES (European Shale) pattern showed that REE accumulation in Chelyabinsk soils has been disturbed by human activities. It was shown that the dust from industrial emissions was the main anthropogenic source of REE accumulation in urban soil. The largest amounts of REEs are emitted from an electrometallurgical plant and zinc production plant. Fortunately, the estimated daily intakes of REE from soils for children and adults were well below the safety thresholds. At the same time, in order to prevent social tension and reduce the anthropogenic load on the urban area, it is recommended to use phytoremediation technologies, smart landscaping of industrial and residential areas, more thorough cleaning of fallen leaves and road dust. It is also recommended to move the most dangerous production processes outside the urban area.

Organic-mineral colloids regulate the migration and fractionation of rare earth elements in groundwater systems impacted by ion-adsorption deposits mining in South China.

Ion-adsorption rare earth element (REE) deposits distributed in the subtropics provide a rich global source of REEs, but in situ injection of REEs extractant into the mine can result in leachate being leaked into the surrounding groundwater systems. Due to the lack of understanding of REE speciation distribution, particularly colloidal characteristics in a mining area, the risks of REEs migration caused by in situ leaching of ion-adsorption REE deposits has not been concerned. Here, ultrafiltration and asymmetric flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry (AF4-ICP-MS) were integrated to characterize the size and composition of REEs in leachate and groundwater from mining catchments in South China. Results show that REEs were associated with four fractions: 1) the <1 kDa fraction including dissolved REEs; 2) the 1 - 100 kDa nano-colloidal fraction containing organic compounds; 3) the 100 kDa - 220 nm fine colloids including organic-mineral (Fe, Mn and Al (oxy)hydroxides and clay minerals); 4) the >220 nm coarse colloids and acid soluble particles (ASPs) comprising minerals. Influenced by the ion exchange effect of in situ leaching, REEs in leachate were mostly dissolved (79 %). The pH of the groundwater far from the mine site was increased (5.8 - 7.3), the fine organic-mineral colloids (46 % - 80 %) were the main vectors of transport for REEs. Further analysis by AF4 revealed that the fine colloids can be divided into mineral-rich (F1, 100 kDa - 120 nm) and organic matter-rich (F2, 120 - 220 nm) populations. The main colloids associated with REEs shifted from F1 (64 % ∼ 76 %) to F2 (50 % ∼ 52 %) away from the mining area. For F1 and F2, the metal/C molar ratio decreased away from the mining area and middle to heavy REE enrichment was presented. According to the REE fractionation, organic matter was the predominant component capable of binding REEs in fine colloids. Overall, our results indicate that REEs in the groundwater system shifted from the dissolved to the colloidal phase in a catchment affected by in situ leaching, and organic-mineral colloids play an important role in facilitating the migration of REEs.

Template-free efficacious morphology of electrosynthesized polyaniline/ß-cyclodextrin host-guest complex on Au/rGO modified electrode for removal and recovery of rare-earth and heavy elements from seawater.

Global water pollution and scarcity of water resources are turning increasingly into serious threats to the survival of all living organisms on Earth. This study offers an influent strategy for the electrosynthesis of reduced graphene oxide/polyaniline/ß-cyclodextrin (rGO/PAni/ßCD) nanocomposite and its application to the removal/recovery of heavy elements (HEs) and rare-earth elements (REEs). Besides physicochemical and electrochemical studies, the surface morphological and statistical properties of fabricated nanocomposite electrode were examined. The textural and morphological characteristics of nanocomposite electrode were investigated via AFM data based on statistical, stereometric, and fractal theory. The cohesive, porous, and well-developed morphology of fabricated nanocomposite electrode has enabled the electrodeposition technique to achieve significant simultaneous removal/recovery efficiency of HE and REE ions such as Pb(II), Cu(II), Cd(II), Hg(II), Ce(IV), and Nb(V). Therefore, using rGO/PAni/ßCD, considerable removal of HEs and REEs was achieved under optimized pH, 0.1 M KNO3, and 35 mg L-1 metal ion initial concentration during 20 min. Removal capacity of the nanocomposite electrode is preserved subsequent to 10 cycles of electrodeposition/desorption, according to the desorption investigation through eluted adsorbent at time intervals in deionized water and adjusted acidic pH values. Then, using rGO/PAni/CD nanocomposite, simulated seawater remediation was accomplished successfully. This interdisciplinary approach reveals that the removal/recovery efficiency enhance linearly along with the improvement of well-developed morphology for electrosynthesized composites. Thus, these results suggest how the morphological features of the polymer composites could improve remediation of water resources.

Rare earth elements applied to phytoremediation: Enhanced endocytosis promotes remediation of antimony contamination with different valence levels in Solanum nigrum L.

Antimony (Sb) pollution poses a noteworthy risk to human health and ecosystem sustainability, therefore effective, eco-friendly, and widely accepted restoration methods are urgently needed. This study introduces a new approach of using La(III) foliar application on Solanum nigrum L. (S. nigrum), a cadmium hyperaccumulator, to improve its photosynthetic and root systems under Sb stress, resulting in a higher biomass. Notably, La(III) also enhances endocytosis in root cells, facilitating efficient and non-selective remediation of both Sb(III) and Sb(V) forms. The absorption of Sb by root cell endocytosis was observed visually with a confocal laser scanning microscope. The subcellular distribution of Sb in the cell wall of S. nigrum is reduced. And the antioxidant enzyme activity system is improved, resulting in an enhanced Sb tolerance in S. nigrum. Based on the existing bibliometric analysis, this paper identified optimal conditions for S. nigrum to achieve maximum translocation and bioconcentration factor values for Sb. The foliar application of La(III) on plants treated with Sb(III), Sb(V), and a combination of both resulted in translocation factor values of 0.89, 1.2, 1.13 and bioconcentration factor values of 11.3, 12.81, 14.54, respectively. Our work suggests that La(III)-enhanced endocytosis of S. nigrum root cells is a promising remediation strategy for Sb-contaminated environments.

Artisanal mining of monazite and cassiterite in the Amazon: Potential risks of rare earth elements for the environment and human health.

Artisanal mining is intensely carried out in developing countries, including Brazil and especially in the Amazon. This method of mineral exploration generally does not employ mitigation techniques for potential damages and can lead to various environmental problems and risks to human health. The objectives of this study were to quantify the concentrations of rare earth elements (REEs) and estimate the environmental and human health risks in cassiterite and monazite artisanal mining areas in the southeastern Amazon, as well as to understand the dynamics of this risk over time after exploitation. A total of 35 samples of wastes classified as overburden and tailings in active areas, as well as in areas deactivated for one and ten years were collected. Samples were also collected in a forest area considered as a reference site. The concentrations of REEs were quantified using alkaline fusion and ICP-MS. The results were used to calculate pollution indices and environmental and human health risks. REEs showed higher concentrations in anthropized areas. Pollution and environmental risk levels were higher in areas deactivated for one year, with considerable contamination factors for Gd and Sm and significant to extreme enrichment factors for Sc. Human health risks were low (< 1) in all studied areas. The results indicate that artisanal mining of cassiterite and monazite has the potential to promote contamination and enrichment by REEs.

[Level and health evaluation of rare earth elements in human blood and hair in the mining areas in Northwest Hubei].

OBJECTIVE: To investigate the content of rare earth elements(REs)in blood and hair of residents in a RE mining area in Northwest Hubei, and evaluate the impact of REs on the health status of local residents. METHODS: A total of 191 residents from the core area of RE mining areas and 186 residents from non RE mining areas, aged 20-69, were selected. The content of REs in the blood and hair of the survey subjects was measured using inductively coupled plasma mass spectrometry, and compared with existing literature values. At the same time, blood tests and questionnaire surveys will be conducted on the health status of residents to examine whether human RE enrichment can lead to endemic diseases. RESULTS: The average total content of REs in the blood of residents in the mining area was 60.22 ng/mL, which was 3.35 times that of the control area; The average total content of REs in hair was 1197.91 ng/g, which was 6.32 times higher than the control area. As age increasing, the abundance of REs in the blood and hair of both men and women in mining areas increased. The proportion of Yttrium and Scandium in the blood and hair were much higher than that in the soil. Compared to hair, Yttrium and Scandium were more easily enriched in the blood. There was no significant difference in the probability of fatty liver, hepatitis B, hypoglycemia, hypotension, hypertension and heart disease and the average life span between residents in RE mining areas and those in the control area. CONCLUSION: The high daily average dietary intake of REs in residents leads to a relatively large accumulation of REs in human blood and hair, but no significant and substantial human health damage has been found at present.

Correlation between urinary rare earth elements and liver function in a Zhuang population aged 35-74 years in Nanning.

BACKGROUND: Animal studies have shown that exposure to REEs can cause severe liver damage, but evidence from population studies is still lacking. Therefore, we investigated the relationship between REEs concentrations in urine and liver function in the population. METHODS: We conducted a cross-sectional study on 1024 participants in Nanning, China. An inductively coupled plasma mass spectrometer (ICP-MS) was used to detect the concentrations of 12 REEs in urine. The relationship between individual exposure to individual REE and liver function was analyzed by multiple linear regression. Finally, the effects of co-exposure to 5 REEs on liver function were assessed by a weighted sum of quartiles (WQS) regression model and a Bayesian kernel machine regression (BKMR) model. RESULTS: The detection rate of 5 REEs, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), and dysprosium (Dy), is greater than 60%. After multiple factor correction, La, Ce, Pr, Nd, and Dy were positively correlated with serum ALP, Ce, Pr, and Nd were positively correlated with serum AST, while Ce was negatively correlated with serum TBIL and DBIL. Both WQS and BKMR results indicate that the co-exposure of the 5 REEs is positively correlated with serum ALP and AST, while negatively correlated with serum DBIL. There were potential interactions between La and Ce, La and Dy in the association of co-exposure of the 5 REEs with serum ALP. CONCLUSIONS: The co-exposure of the 5 REEs was positively correlated with serum ALP and AST, and negatively correlated with serum DBIL.

Roles of pH and phosphate in rare earth element biosorption with living acidophilic microalgae.

The increasing demand for rare earth elements (REEs) has spurred interest in the development of recovery methods from aqueous waste streams. Acidophilic microalgae have gained attention for REE biosorption as they can withstand high concentrations of transition metals and do not require added organic carbon to grow, potentially allowing simultaneous sorption and self-replication of the sorbent. Here, we assessed the potential of Galdieria sulphuraria for REE biosorption under acidic, nutrient-replete conditions from solutions containing ≤ 15 ppm REEs. Sorption at pH 1.5-2.5 (the growth optimum of G. sulphuraria) was poor but improved up to 24-fold at pH 5.0 in phosphate-free conditions. Metabolic activity had a negative impact on REE sorption, additionally challenging the feasibility of REE biosorption under ideal growth conditions for acidophiles. We further examined the possibility of REE biosorption in the presence of phosphate for biomass growth at elevated pH (pH ≥ 2.5) by assessing aqueous La concentrations in various culture media. Three days after adding La into the media, dissolved La concentrations were up to three orders of magnitude higher than solubility predictions due to supersaturation, though LaPO4 precipitation occurred under all conditions when seed was added. We concluded that biosorption should occur separately from biomass growth to avoid REE phosphate precipitation. Furthermore, we demonstrated the importance of proper control experiments in biosorption studies to assess potential interactions between REEs and matrix ions such as phosphates. KEY POINTS: • REE biosorption with G. sulphuraria increases significantly when raising pH to 5 • Phosphate for biosorbent growth has to be supplied separately from biosorption • Biosorption studies have to assess potential matrix effects on REE behavior.

Multistep pH-peak-focusing liquid chromatography with a hydrophilic polymer gel column for separation of rare earth elements.

Multistep pH-peak-focusing liquid chromatography with a column packed with a hydrophilic polymer gel (a cross-linked hydroxylated methacrylic polymer gel) was developed for separation of rare earth metal ions. Metal ions in a sample solution introduced to the column are chromatographically extracted into the stationary gel phase at the top of the column equilibrated with a basic solution used as the first mobile phase containing acetylacetone and 1,10-phenanthroline by synergistic extraction effect. After the sample solution is introduced, the mobile phases are delivered into the column by stepwise gradient elution in order of decreasing pH. Each metal ion is concentrated at a pH border formed between the zones of different pH in the column and moves toward the outlet of the column with the pH border. Mutual separation of La(III), Ce(III), Nd(III), Eu(III), Y(III), Tb(III), and Yb(III) was achieved by the present method for an 1-mL sample injection with the column of which the inner volume is 11.8 mL. The multistep pH-peak-focusing liquid chromatography with a hydrophilic polymer gel column developed in this study has great potential as a useful method for the separation of rare earth metal ions on a preparatory scale.