Removal Of Rare Earth Elements Research Articles

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.

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

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

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 76.80mg/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.

Relict soil evidence for post-Miocene aridification in the Atacama Desert of South America

Deep exposures of soil profiles on Miocene or Mio-Pliocene alluvial deposits were studied along a 500 km N-S transect in the Atacama Desert. These ancient deposits, with excellent surface preservation, now stand many meters above a broad incised Plio-Pleistocene alluvial terrain. Total geochemical analyses and mass balance calculations allowed the establishment of elemental gains, losses, and redistribution in the soils. From north to south (presently hyperarid to arid), the ancient soils reveal an increase in losses of rock-forming elements (Si, Al, Fe, K, Mg). Additionally, rare earth elements (REE) show losses with increasing southerly latitude and systematic patterns with soil depth. Some REEs appear to be unique chemical tracers of exogenous dust and aerosol additions to the soils. The removal of major elements and REEs is impossible in the present climate (one of salt and dust accumulation), revealing that for a significant period following the deposition of the alluvium, soils were exposed to rainfall, chemical weathering, and mass loss—with a geographical pattern that mirrors the present rainfall gradient in the region. Following the cessation of weathering, the pre-weathered soils have undergone enormous dust and salt accumulations, with the rates and types of salt accumulation consistent with latitude: (1) carbonate in the south and (2) sulfate, chlorides, and nitrates to the north. The quantity, and apparent rates, of salt accumulation have a strong latitudinal trend. Isotopes of sulfate have predictable depth patterns based on isotope fractionation via vertical reaction and transport. The relict hyperarid soils are geochemically similar to buried Miocene soils (ca. 10−9 Ma) in the region, but they differ from older Miocene soils, which formed in more humid conditions. The overall soil record for the Atacama Desert appears to be the product of changes in Pacific Ocean sea surface temperatures over time, and resulting changes in rainfall. The mid-Miocene was relatively humid based on buried soil chemistry and evidence of fluvial activity. The mid to late Miocene cooling (ca. 10−5.5 Ma) appears to have aridified the region based on paleosol soil chemistry. Pliocene to earliest Pleistocene conditions caused weathering of the relict soils examined here, and regional fluvial activity. Since the earliest Pleistocene, the region has largely experienced the accumulation of salts and, except for smaller scale oscillations (glacial-interglacial), has experienced protracted hyperaridity.

Optimizing the Recovery of Rare Earth Elements from Spent Fluorescent Lamps by Living Ulva sp.

Given the significant industrial applications of rare earth elements (REEs), supply chain constraints, and negative environmental impacts associated with their extraction, finding alternative sources has become a critical challenge. Previously, we highlighted the potential of living Ulva sp. in the removal and pre-concentration of Y from a solution obtained by sequential acid leaching of spent fluorescent lamps (SFLs). Here, we extended that study to other REEs extracted from SFLs and evaluated the effect of pH (4.5-9.0), light exposure (absence, natural and supplemented with artificial light), and Hg (presence and absence). The results showed small differences in the removal of Y (23-30%) and other REEs at the different pH values, opening the scope of the methodology. However, Ulva sp. relative growth rate (RGR) was negatively affected in the higher acidity condition, without any visible signs of decay. In the absence of light, the RGR also decreased, which was accompanied by a halving of the removal efficiency compared to that with artificial light supplementation (40% for Y). Although Hg had minimal influence on the removal and concentration of REEs by Ulva sp., its presence in the enriched biomass is undesirable. Therefore, this contaminant was selectively removed from the solution using Fe3O4@SiO2/SiDTC nanoparticles before contact with the macroalgae (70% removal in 30 min; 99% in 72 h). In addition to easy solubilization, macroalgae enriched with REEs have a simpler composition compared to SFLs. Calcination of the biomass allowed the REEs to be further concentrated, with concentrations (130 mg/g for Y) up to 240 times higher than in typical apatite ore. This highlights enriched biomass as a sustainable alternative to traditional mining for obtaining these critical raw materials.

Highly selective recovery of rare earth elements from mining wastewater using phyto-synthesized biochar dispersed iron nanoparticles

Recovery of rare earth elements (REEs) from secondary sources such as mining wastewater has attracted much recent attention due to the rising global demand for REEs and the need to environmentally protect potentially contaminated mine sites. One significant issue it that most adsorbents proposed for removal and/or recovery of REEs are not generally selective for REEs. In this study, biochar dispersed iron nanoparticles synthesized using a plant extract (BC-FeNPs) were successfully used for the selective recovery of REEs from mining wastewater, where the Kd values were Nd(III) (918 mL∙g−1), Eu(III) (1253 mL∙g−1), Tb(III) (1119 mL∙g−1), Dy(III) (1032 mL∙g−1), Lu(III) (1898 mL∙g−1), compared to only 23.9 mL∙g−1 for Zn(II). The maximum adsorption efficiency of REEs for the composite was higher than the constituent parts being 88.4 % for BC-FeNPs, but only 8.72 % for biochar and 82.4 % for FeNPs, respectively. FTIR, XPS and Zeta potential analysis suggested that the observed selective adsorption of REEs, involved interactions of REEs with O and N, as well as ion-exchange with H+ from the biochar and capping layer, as well as electrostatic interactions. The desorption efficiency of bound REEs from BC-FeNPs was > 85 % when using acetic acid, and was attributed to efficient competitive ion exchange. Pearson correlation analysis further demonstrated that the adsorption mechanism included ion complexation, ion exchange and electrostatic adsorption, while the desorption mechanism was mainly via ion exchange. Overall, BC-FeNPs has significant potential to practically recover REEs from mining wastewater having demonstrated excellent reusability after five adsorption–desorption cycles.

G-C3N4 modified natural low-grade dolomite-palygorskite: Removal capacity and adsorption mechanism for Gd3+

Rare earth elements (REEs) pose significant environmental challenges due to the wastewater generated during their extraction. Developing efficient adsorbents with simple, economical and eco-friendly methods for removing and recovering REEs from wastewater is highly demanded but full of challenges. This study creates a novel adsorbent (g-C3N4/0.5DPal) for efficient REEs removal and recovery by integrating the low-grade mineral dolomite-palygorskite with g-C3N4 through a "one-pot" calcination method. Characterization techniques including SEM, XRD, FT-IR, XPS, etc., were employed to analyze the structure of the g-C3N4/0.5DPal composite. Batch adsorption experiments focusing on Gd3+ from among the REEs were conducted to evaluate the adsorption performance. The results reveal a remarkable 3.34 times increase in Gd3+ adsorption capacity of g-C3N4/0.5DPal (192.46 mg/g) compared to raw dolomite-palygorskite (57.62 mg/g) at 298 K, highlighting the effectiveness of the modification. The adsorption mechanism involves electrostatic interactions, surface complexation, and cation-π interactions. It is worth noting that g-C3N4 facilitates the conversion of dolomite to calcite during the preparation process, enhancing the Gd3+ adsorption of g-C3N4/0.5DPal. This work offers a promising solution for the removal and recovery of REEs and the high-value utilization of low-grade minerals, addressing both environmental concerns and resource sustainability.

Template-free efficacious morphology of electrosynthesized polyaniline/β-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/β-cyclodextrin (rGO/PAni/βCD) 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/βCD, 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.

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.

Highly selective recovery of yttrium from mining wastewater using biosynthetic iron sulfide nanoparticles

The selective recovery of rare earth elements (REEs) from mining wastewater has become a hot research topic due to the increasing industrial value of REEs. Herein, biosynthetic iron sulfide nanoparticles (nFeS) were deployed as a superior adsorbent to selectively recover Y(Ⅲ) from mining wastewater. The maximum adsorption efficiency achieved for of Y(Ⅲ) by nFeS was 81.2 % compared to only 38.7 % for Eu(Ⅲ) and 20.8 % for Mn(Ⅱ), demonstrating that nFeS had a high selective adsorption for Y(Ⅲ). To understand the origins of the high selectivity of nFeS, the removal of REEs by the capping layer and the FeS-core were separately investigated. Specifically, given the hard and soft acid base principle (HASB) and the square antiprism coordination geometry of Y(Ⅲ), the adsorption of Y(Ⅲ) by the capping layer was predominantly attributed to CO and –NH2 serving as a monodentate ligand to strongly chelate with Y(Ⅲ), while Y(Ⅲ) interacted with Fe–O on the FeS-core and –COOH more via ion-exchange with Y(Ⅲ). Collectively, cooperative interactions between the capping layer and FeS-core resulted in the overall highly selective adsorption of Y(Ⅲ) by nFeS, suggest this approach has significant potential for future practical remediation and recovery applications to Y(Ⅲ) rich mining wastewaters.

Influence of experimental parameters on the sorption behavior of Rare Earth Elements on manganese ferrite nanoparticles

Rare Earth Elements (REE) are nearly irreplaceable in many technologies, but their supply is limited by geopolitical factors. Additionally, their exploration and refinement bring serious environmental consequences. Therefore, alternative sourcing of these elements through methods such as sorption has recently been attempted. Nanoparticles are exceptional REE sorbents, however, difficulties in material separation post-sorption have fueled an interest in the use of magnetic nanoparticles, which can be easily separated from the solution by applying an external magnetic field. In this study, we explore the influence of sorbent dosage, pH and matrix complexity in the removal of trivalent cations of nine REE (Y, La, Ce, Pr, Nd, Eu, Gd, Tb and Dy) using manganese ferrite nanoparticles (MnFe2O4); herein the abbreviation REE is employed to indicate such elements including the trivalent cations. The REE removal increased for higher sorbent dosages and pH. More than 90% of REE in mono-elemental solutions were removed from water at pH 6 and 8. Removal below 10% was observed for pH < 4, due to the positive surface charge of the sorbent, which did not favor interaction with cationic REE species. Increasing the complexity of the matrix, the removal of REE from water decreased considerably, which can be attributed to an increase of total REE concentration and the limited number of sorption sites in the sorbent. Further sorption inhibition was reported in increased ionic strength scenarios (mineral and saline water), possibly due to competition with Na+, which may limit the application of this material in complex matrices.

Removal of REE and Th from solution by co-precipitation with Pb-phosphates

The supply of technologically important rare earth elements (REE) is a concern in Europe, hence the recovery of REE from alternative sources has recently become widely investigated. One of the problems is the lack of cost-effective technologies for REE recovery from leaching solutions. The present work investigated the potential for recovering REE and Th from leaching solutions by co-precipitation with Pb phosphates. A set of four experiments were conducted using analytical reagent grade chemicals to analyze the effects of Pb and different pH on the efficiency of REE and Th removal from aqueous solutions. After selecting the best conditions, two additional experiments were performed using solutions obtained from leaching REE-rich apatite mine waste.The precipitates resulting from the experiments as well as the solutions before and after precipitation were analyzed. It was found that the formation of a crystalline mixture of REE- and Th- enriched pyromorphite, Pb5(PO4)3Cl, and Pb-phosphates, about which little has been known so far, was responsible for complete (>99%) removal of REE and Th from aqueous solutions at pH 4 and 6. At lower pH, the removal is incomplete except for Sc and Th, which probably form a distinct phases. Besides that, no fractionation of LREE and HREE was observed. The experiments included the study of solutions resulting from the leaching of REE-rich apatite waste, which may contribute to the development of new technologies for REE recovery from wastes.

Uptake the rare earth elements Nd, Ce, and La by a commercial diatomite: kinetics, equilibrium, thermodynamic and adsorption mechanism

This study addresses the application and evaluation of diatomite as a low-cost, natural, abundant, and highly efficient adsorbent of Nd3+, Ce3+, and La3+ rare earth elements (REEs). The results revealed that the diatomite was porous and cylindrical, with a specific surface area of 150 m2/g. The diatomite displayed a point of zero charge equal to 1.8, maintaining its surface negatively charged at pH values higher than 1.8, which was beneficial for cationic REEs uptake. At pH 1, all three REEs had their lowest uptake values; at pHs 2–6, the REEs removal efficiency practically did not change. The uptaken percentage increased in the order of La3+ (50%), Ce3+ (77%), and Nd3+ (92%), influenced by the electronegativity of the ions. The Avrami-fractional order (AFO) and Liu isotherm model better fit the kinetic and equilibrium process (qmax = La3+ (22.8 mg g−1), Ce3+ (56.2 mg g−1), and Nd3+ (100.9 mg g−1)). Since the diatomite is highly porous, pore filling/pore-surface diffusion was the main mechanism for REEs adsorption, as well as ion exchange and chelation. The reusability tests revealed that the diatomite could be reused 8 times without losing performance. This research shows that diatomite is an efficient strategy for designing effective, low-cost, sustainable adsorbents to recover REEs from synthetic and real effluents.

Eco-friendly methodology for removing and recovering rare earth elements from saline industrial wastewater.

In this study, response surface methodology (RSM) was applied with a Box-Behnken design to optimize the biosorption (removal and bioconcentration) of rare earth elements (REEs) (Y, La, Ce Eu, Gd, Tb) by living Ulva sp. from diluted industrial wastewaters (also containing Pt and the classic contaminants Hg, Pb, Zn, Cu, Co, and Cd). Element concentration (A: 10-190 μg/L), wastewater salinity (B: 15-35), and Ulva sp. dosage (C: 1.0-5.0 g/L) were the operating parameters chosen for optimization. Analysis of the Box-Behnken central point confirmed the reproducibility of the methodology and p-values below 0.0001 validated the developed mathematical models. The largest inter-element differences were observed at 24 h, with most REEs, Cu, Pb and Hg showing removals ≥ 50 %. The factor with the greatest impact (positive) on element removal was the initial seaweed dosage (ANOVA, p< 0.05). The optimal conditions for REEs removal were an initial REEs concentration of 10 μg/L, at a wastewater salinity of 15, and an Ulva sp. dosage of 5.0 g/L, attaining removals up to 88% in 24 h. Extending the time to 96 h allowed seaweed dosage to be reduced to 4.2 g/L while achieving removals ≥ 90%. The high concentrations in REE-enriched biomass (∑REEs of 3222 μg/g), which are up to 3000 times higher than those originally found in water and exceed those in common ores, support their use as an alternative source of these critical raw materials.

Highly efficient removal of rare earth elements by two-dimensional titanium carbide nanosheets as impacted via water chemistry.

The separation and recycling of rare earth elements (REEs) are very important owing to the high demand, limited resource, specific usages, and environmental issues. In this work, two-dimensional Ti3C2Tx MXene was introduced to remove REEs (Nd(III) and La(III)) from water, and its physicochemical properties were conducted by HRTEM, SEM-EDS, XRD, FTIR, and XPS. Various parameters, such as initial pH, REEs initial concentration, contact time, and temperature, were investigated by batch experiment, respectively. Furthermore, the adsorption kinetic and isotherm were examined to analyze the adsorption behavior and adsorption mechanism. Nd(III) and La(III) have a good affinity with Ti3C2Tx MXene surface functional groups (-F, -OH, and containing oxygen groups). The maximum adsorption capacities of Ti3C2Tx MXene for Nd(III) and La(III) were 229.85 mg/g and 175.83 mg/g at T = 333 K, respectively. The adsorption data of Nd(III) on Ti3C2Tx MXene fitted well with the Freundlich isotherms model and pseudo-second-order kinetic model. However, the best fitting for La(III) adsorption on Ti3C2Tx MXene was described by both pseudo-first-order and pseudo-second-order model. Thermodynamic study of Nd(III) and La(III) adsorption on Ti3C2Tx MXene showed that the reaction was a spontaneous and endothermic process. These results indicated Ti3C2Tx MXene had a great potential in extracting REEs from an aqueous solution.

Adsorptive capacity and kinetic studies of PK216 resin for the extraction of Pr, Gd, and Dy rare earth elements

AbstractBACKGROUNDThe removal of rare earth elements (REE) ions from aqueous solutions is a challenging task, and it requires a cost‐effective and readily available adsorbent material with excellent performance. In this study, PK216 resin was utilized for the adsorption kinetics and mechanism studies of REE ions owing to its outstanding performance, low cost, and easy availability.RESULTSThe findings revealed that higher loading resulted in increased adsorption capacity, while pH and temperature adjustments had minimal effects on the adsorption process, which remained constant within the pH range of 1–6 and a temperature range of 25–85 °C. Moreover, the thermodynamic parameters showed that the adsorption reaction for praseodymium (Pr) and gadolinium (Gd) was spontaneous and exothermic, whereas for dysprosium (Dy) it was endothermic due to its high hydration enthalpy. This characteristic nature of Dy requires additional energy from the surroundings to dissociate from the aqueous phase and proceed to the PK216 resin surface compared to Pr and Gd. The Langmuir model and pseudo‐second‐order reaction were found to be the fitting models for the adsorption process on PK216 resin. Additionally, the chemisorption of Pr, Gd, and Dy resulted in monolayer coverage. The diffusion process was found to be intraparticle and film diffusion, as it fitted the Boyd kinetic model as opposed to the Weber–Morris intraparticle model.CONCLUSIONThe results indicate that higher loading enhances the adsorption capacity, and the Langmuir model and pseudo‐second‐order reaction are the most suitable models for the adsorption process on PK216 resin. © 2023 Society of Chemical Industry

Nickel-aluminium layered double hydroxide as an efficient adsorbent to selectively recover praseodymium and samarium from phosphogypsum leachate

This study aimed to synthesize a green powdered layered double hydroxide (LDH) based on nickel-aluminum (Ni–Al-LDH) to evaluate its efficiency in the removal of rare earth elements (REEs), Praseodymium (Pr3+) and Samarium (Sm3+), from synthetic effluents and real leachate using phosphogypsum as a secondary source of REEs. Several characterization techniques were employed to evaluate the physicochemical properties of Ni-Al-LDH adsorbent, such as specific surface area and porosity, functional surface groups and phases, and point of zero charge. The characterization results indicated that Ni-Al-LDH exhibited a typical layered structure confirming the successful synthesis. The effect of key adsorption variables, such as pH, contact time, initial concentration, and temperature, on the REEs adsorption was extensively studied in single-factor experiments separately. The kinetic and equilibrium adsorption data agreeably fitted the Avrami and Sips models, respectively. The maximum adsorption capacities for Pr3+ and Sm3+ adsorption were 18.13 and 15.68 mg g−1 at 298 K, respectively. The thermodynamic parameters (ΔH0, ΔS0, ΔG0) indicated that the adsorption was spontaneous, favorable, and exothermic for both Pr3+ and Sm3+. The interactions between Pr3+ and Sm3+ onto Ni-Al-LDH suggest that multiple adsorption mechanisms are involved, such as ion exchange, precipitation, chelation, and pore filling. Finally, the Ni-Al-LDH could selectively recover REEs, specially Pr3+ and Sm3+, from the real phosphogypsum leachate. It has been demonstrated that Ni-Al-LDH is a promising adsorbent material that could be used as an adsorbent for the recovery of REEs from synthetic and real effluents.

Removal of rare-earth elements from aqueous solutions by microporous titanosilicate ETS-4

The mining of Rare-Earth Elements (REE) is an unsustainable practice that raises environmental, economic, and societal concerns. As a result, there is a need to develop suitable technologies for the removal of these elements from contaminated waters. Sorption is a clean and efficient method for decontaminating water, and microporous titanosilicates have shown promise for REE removal. However, the influence of solution parameters on this process remains poorly understood. In this study, the effect of pH (4–8), concentration (1–5 μM), and sorbent amount (20–180 mg L−1) on the removal of a mixture of REE3+ (Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy) from water by the microporous titanosilicate ETS-4 (Na9Ti5Si12O38(OH)·12H2O) was assessed. A Box-Behnken design was used to investigate the experimental conditions, and the results were presented as three-dimensional response surfaces. The removal mechanism involves the ion exchange of Na+ by REE3+, with pH being the main variable in the process due to competition with H+. Increasing pH resulted in higher removal, with 100% removal achieved at ETS-4 amounts of 180 mg L−1 and REE concentrations of 1 μM. Most REE3+ removal occurs within the first 15 min, with little difference between metals (except for Y, which exhibits lower removal). At ETS-4 amounts of 20 mg L−1, REE are highly concentrated in the sorbent, reaching 145 mg g−1 (15% of the sorbent's mass, post-sorption). These results demonstrate that even low amounts of ETS-4 have the potential to remove high concentrations of REE3+ from aqueous solutions with pH levels similar to those found in natural systems.

Tailoring abundant active-oxygen sites of Prussian blue analogues-derived adsorbents for highly efficient Yb(III) capture.

The removal of rare earth elements in mineral processing wastewater is highly desirable but still challenging. In this study, three bimetallic Prussian blue analogues (PBA) and six corresponding oxides are prepared by co-precipitation and calcination methods, and then utilized to adsorb aqueous Yb(III) solution. The results of XRD, SEM, BET, and XPS indicate the successful synthesis of all the adsorbents. Among them, three PBA-oxide samples (PBO-800) exhibit the superior adsorption capacities (˃250mg/g). The adsorption processes of Yb(III) are in accordance with the pseudo-second-order kinetic model and Langmuir model, simultaneously showing the spontaneous and endothermic thermodynamics. Moreover, PBO-800 can be reused after alkaline solution regeneration with less than 10% degradation after five consecutive adsorption-desorption cycles. More importantly, PBO-800 exhibits the impressive separation selectivity of Yb(III) and most light rare earth ions (e.g., 5.51 of Yb/La, 4.03 of Yb/Pr), as well as the selectivity of Yb(III) and alkali metal ions (e.g., 300.5 of Yb/Na, 256.2 of Yb/Ca). According to the characterization analysis and DFT calculation, the adsorption mechanism of Yb(III) by PBO-800 is mainly attributed to the strong interaction between the abundant active-oxygen sites and Yb(III), and the significant electrostatic attraction.

Recovery and removal of rare earth elements from mine wastewater using synthesized bio-nanoparticles derived from Bacillus cereus

The efficient removal and recovery of rare earth elements (REEs) from mine wastewater is highly desirable due to the increasing public demands to both protect the environment and recover valuable REEs resources. In this study, bio-nanoparticles (BC@FeNPs-EPS), which combined extracellular polymeric substances (EPS) and iron nanoparticles (FeNPs) were synthesized via Bacillus cereus and used to remove REEs such as Eu(III) from mine wastewaters. The removal efficiency of BC@FeNPs-EPS (90.2%) was consistently higher than the removal efficiencies of the three constituent components alone, FeNPs (85%), Free cell (67%) and EPS (10%) exhibited. SEM and XPS analysis indicated the existence of substantial organic capping agents derived from microorganisms on the FeNPs, where comparison of FTIR spectra before and after exposure to Eu(III) showed changes in both wavenumber and peak intensity of these various organic functional groups suggesting the formation of surface complexes with Eu(III), whereas Zeta potential measurements of the material also supported electrostatic interactions between Eu(III) and BC@FeNPs-EPS. Adsorption kinetics almost perfectly correlated with the non-linear pseudo-second-order model. Collectively, these results indicated that the removal mechanism for Eu(III) by BC@FeNPs-EPS involved both surface complexation and ion exchange and the additive effect removal of Eu(III) by FeNPs, Free cell and EPS. In addition, the practical removal efficiency of a range of REEs from real mine wastewaters by BC@FeNPs-EPS was consistently high being 88% for Eu(III), 89% for Tb(III) and 89% for Ce(III). The material produced was also highly reusable, maintaining a high Eu(III) removal rate (69%) even after 5 consecutive removal cycles.