Adsorption Of Rare Earth Elements Research Articles

Gravity-Driven Separation for Enrichment of Rare Earth Elements Using Lanthanide Binding Peptide-Immobilized Resin.

Rare Earth Elements (REEs) constitute indispensable raw materials and are employed in a diverse range of devices, including but not limited to smartphones, electric vehicles, and clean energy technologies. While there is an increase in demand for these elements, there is a global supply challenge due to limited availability and geopolitical factors affecting their procurement. A crucial step in manufacturing these devices involves utilizing highly pure REEs, often obtained through complex and nonsustainable processes. These processes are vital in isolating individual REEs from mixtures containing non-REEs and other REEs. There exists an urgent requirement to explore alternative techniques that enable the selective recovery of REEs through more energy-efficient processes. To overcome the limitations mentioned above, we developed a microbead-based technology featuring immobilized lanthanide binding peptides (LBPs) for the selective adsorption of REEs. This technology does not require the utilization of external stimuli but uses gravity-based separation processes to separate the bound REE from the unbound REE. We demonstrate this technology's potential by enriching two relevant REEs (Europium and Terbium). Additionally, we propose a mechanism whereby REEs bind selectively to a particular LBP, leveraging the distinctive physicochemical characteristics of both the REE and the LBP. Moreover, these LBPs exhibit no binding affinity toward other frequently encountered industrial ions. Finally, we demonstrate the recovery of REEs through a change in system conditions and assess the reusability of the microbeads for subsequent adsorption cycles. We anticipate that this approach will address the challenges of REE recovery and demonstrate the potential of biomolecular strategies in advancing sustainable resource management.

Transport dynamics of rare earth elements in weathering crust soils

In modern industries, rare earth elements (REEs) are considered as essential metals and invaluable natural resources. Ion-adsorption deposits (IADs) are repositories of REE in the weathering crust soils, in which REEs are adsorbed on clay minerals. In the last few decades, the mining of REEs from IADs has caused substantial environmental damage owing to the overuse of leaching agents for the desorption and transport of REEs in weathering crust soils. These environmental issues have sparked extensive research interest in modeling REE transport dynamics in weathering crust soils. Nevertheless, because current models treat REE adsorption and transport independently, they do not accurately describe REE transport dynamics. Therefore, in this study, a unified workflow that synergizes adsorption and transport dynamics is proposed to predict REE transport. The adsorption of REEs on IADs was found to follow the Freundlich isotherm with the coefficient of determination exceeding 0.9826. The adsorption capacities of La3+, Sm3+, Er3+, and Y3+ reach 1.3127, 1.4423, 1.5793, and 1.1061 mg g−1 at 300 ppm, respectively. For the breakthrough curve, an advection–dispersion–adsorption–equation (ADAE) model was developed and utilized to accurately and reliably predict REE transport dynamics in soil columns. It was found the saturation time of REEs in soils is 39.22, 44.15, 50.64, and 32.17 h, respectively at 2 mL min−1 and decreased with the increase of flow velocity. The upper and lower limits of REE transport are ADAE-Freundlich and ADAE-Toth. More importantly, the model was applied to simulate REEs transport in field-scale weathering crusts over 100 years and predict REE accumulation in the highly weathered layered, which is found in natural weathering crusts. The qualitative prediction of REE transport dynamics in weathering crusts may help fundamentally lower the usage of leaching agents and mitigate concomitant the environmental impacts of mining.

Recovery of rare earth elements from mine wastewater using alginate microspheres encapsulated with zeolitic imidazolate framework-8

There is increasing demand and interest in efficient methods for the recovery of rare earth elements (REEs) from wastewater because of the growing concerns associated with the negative impacts of REEs-rich waste discharged on pristine ecosystems. Here, we designed a ZIF-8@ALG composite hydrogel by encapsulating zeolitic imidazolate frameworks-8 (ZIF-8) into sodium alginate and poly (vinyl alcohol) double cross-linked networks (ALG) for the recovery of REEs from mine wastewater. ZIF-8@ALG showed exceptional REEs adsorption performance with the most superior separation factor (Ho/Mn) of 597.5. For the REEs considered, the ZIF-8@ALG composite exhibited a preference for heavy REEs with high adsorption efficiencies (65.3 ∼ 97.2%) and distribution coefficients (2045.5 ∼ 28500.0 mL·g−1). Adsorption involved a combination of electrostatic attraction, complexation and ion exchange mechanisms. REEs adsorbed on ZIF-8@ALG could also be desorbed using sodium citrate via ion-exchange and complexation, thus achieving efficient REEs recovery. In addition, ZIF-8@ALG was stable and reusable, maintaining effective adsorption in wastewater over four consecutive cycles, where the optimal adsorption efficiency reached 80.0%. Overall, this study provided an effective and feasible method for the recovery of REEs in mine wastewater, and confirmed that ZIF-8-based materials have significant potential for REEs recovery applications in wastewater engineering treatment.

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.

Insights into neodymium interaction with carboxylate-graphene-like support in presence of nitrate: A comparative DFT investigation

Recently, we demonstrated that carboxylate mesoporous carbon improved the adsorption of rare earth elements as neodymium (Nd). Here, calculations based on Density Functional Theory were carried out to give insight on binding of the Nd with carboxylates. Different phenyl carboxylate-Nd complexes were first identified, considering nitrate and water molecules as ligands, in order to obtain reliable carboxylate-graphene models. The optimized structures are used to compute the binding and complexation energies then the competition for metal between carboxylate group and solvent was analysed. The results, in agreement with the experimental evidence, indicated that the Nd favors the anchored carboxylate groups compared to the bulk water. Findings showed that, the graphene support did not significantly alter the carboxylate-Nd binding energies. The partial charges revealed the coupling electron-withdrawing effect of the nitrate and water oxygens. The binding and complexation energies provided here can be regarded as references for designing of REE chelating sorbents.

Enrichment and fractionation of rare earth elements (REEs) in ion-adsorption-type REE deposits: Constraints of an iron (hydr)oxide–clay mineral composite

Abstract Ion-adsorption-type rare earth element (REE) deposits are the source of more than 90% of global heavy REEs (HREEs). Thus, understanding the ore genesis of REEs, particularly the distribution characteristics and enrichment mechanisms of HREEs, is vital for efficient exploration and mining of ion-adsorption-type REE deposits worldwide. The characteristics and petrogenesis of bedrock, and the aqueous mobility of REEs, are known to be important factors controlling REE accumulation and fractionation in the weathering crust of REE deposits. However, the effect of REE adsorption on secondary minerals, which is a crucial step in deposit formation, remains poorly understood. This problem was addressed by the study described herein, which involved a systematic analysis of the complete weathering profile (78 m) of the Renju ion-adsorption-type REE deposit in South China and a simulated adsorption experiment. Clay minerals and iron (Fe) (hydr)oxides are the dominant REE adsorbents in the weathering crust and most are micro-to-nanosized particles. Thus, the fine particle fraction (< 2 μm) was separated from field samples, to better disclose their effects on the concentration and redistribution of REEs. Phase compositions and morphologies were characterized by X-ray diffraction, Mössbauer spectrometry, and scanning/transmission electron microscopy (SEM/TEM), which revealed that various clay minerals and Fe (hydr)oxides form composites along the profile of the deposit. Composites of ferrihydrite–kaolinite, goethite–kaolinite/halloysite, and hematite–kaolinite/halloysite were found to be distributed in the semi-weathered, completely weathered, and topsoil layers, respectively, with different sizes and shapes. The concentrations and partition patterns of REEs in different occurrence states were distinguished after sequential extraction. Ion-exchangeable-REEs were the major state and enriched in the upper completely weathered layer. These species were found to be adsorbed onto kaolinite and halloysite via electrostatic attraction, without obvious fractionation. Fe (hydr)oxides were determined to comprise ca. 20% of REEs at most depths and over 50% of REEs in the topsoil and semi-weathered layer. It was found that Fe (hydr)oxides scavenge REEs through complexation and oxidation, resulting in HREE enrichment and a positive cerium (Ce) anomaly, respectively. In addition, compared with crystalline Fe (hydr)oxides, amorphous Fe (hydr)oxides immobilize more REEs but exhibit weaker preferential adsorption of HREEs. The above-described findings are consistent with the results of simulated experiments for REE adsorption onto a clay mineral–Fe (hydr)oxide composite (Bt-60), which was obtained from hydrothermal processing of biotite. Furthermore, the distributions and stabilities of LREEs and HREEs were distinguished by TEM–energy–dispersive spectroscopy (EDS) of Bt-60 before and after REE extraction by ammonium sulfate. The phase transformation pathways of clay minerals and Fe (hydr)oxides, and their different enrichment and fractionation characteristics in REEs, were also discussed in terms of the structure and surface properties of minerals, adsorption mechanisms, and variations in chemical properties across the REE group. The results shed new light on how clay minerals and Fe (hydr)oxides affect the enrichment and fractionation of REEs in ion-adsorption-type deposits.

High efficiency simultaneous adsorption of rare earth elements from aqueous solutions using carbon xerogel-chitosan composite

ABSTRACT This study investigated the simultaneous sorption of rare earth elements (REEs) from acidic media using carbon xerogel functionalised with chitosan. The combined carbon xerogel with chitosan that was synthesised has a sphere-like structure and a larger BET surface area (275 m2 g−1) than pure carbon xerogel alone (228 m2 g−1). To determine the optimal conditions, adsorption of REEs was established under different variables, including pH, contact time, initial concentration, adsorbent wt. and temperature, as well as desorption experiments. The adsorption isotherms showed that both the Freundlich and Langmuir models were followed, in addition to a pseudo-second order kinetic model. The adsorption is likely exothermic, which confirms it is favourable at low temperatures, and a dissociative adsorption process is involved, according to analysis of thermodynamic state functions. Langmuir calculations revealed that the maximum amount of REEs that were adsorbed was 164 mg/g. Because of its superior adsorption capacity and simplicity in using a recycled material following several desorption cycles, carbon xerogel-chitosan is being employed as a novel adsorbent material to remove REEs from aqueous solutions.

Rare earth element behaviors of groundwater in overlying aquifers under the influence of coal mining in northern Ordos Basin, China.

Rare earth elements (REEs) have been used as tracers to reveal the hydrochemical sources and processes in groundwater systems that are usually modified by anthropogenic inputs. However, the REE behaviors in groundwater affected by mining activities have yet to be fully understood. In combination of REE geochemistry with general hydrochemical and isotopic (δ2H and δ18O) methods, this study investigated the concentration and fractionation of REEs in alkaline groundwater from two coal mines with similar aquifer lithology but different mining histories in the Northern Ordos Basin. One of the coal mines started mining in March 2009 (Ningtiaota coal mine, NTT), while the other started mining in December 2018 (Caojiatan coal mine, CJT). Results show that the primary hydrochemical type is HCO3-Ca in NTT groundwater with pH value ranging between 7.68 and 8.60, while CJT groundwater was dominated by the HCO3-Na type with higher pH of 9.09-10.00. The average values of ΣREEs were lower, and the NASC-normalized pattern reflected more intense fractionation in NTT groundwater than those in CJT groundwater. The evident differences are caused by the distinctions in water-rock interaction, complexation of inorganic species, and adsorption of REEs in NTT and CJT groundwater. Furthermore, these processes were closely related to the pH of groundwater that was different in two coal mines, which is likely linked to the different durations of coal mining activities that led to differences in development of rock fractures and pyrite oxidation. It is expected that REEs, combined with other indicators such as pH, can be used to trace and help better understand the hydrochemical changes in groundwater caused by mining.

Rare earth element distribution patterns in Lakes Huron, Erie, and Ontario

Rare earth elements (REE) are increasingly used in industrial applications, consumer electronics and green technologies, but their baseline concentrations and distribution patterns in the North American Great Lakes remain poorly understood. Here, we report dissolved REE concentrations in > 70 surface water samples from Lakes Huron, Erie, and Ontario (2021 and 2022) and assess their spatial distribution patterns and governing biogeochemical controls. Dissolved (<0.22 µm-filtered) REE concentrations were spatially heterogeneous (up to 3 orders-of-magnitude) across the lakes and did not systematically increase upstream-to-downstream through the basin. Nearshore-to-offshore decreases in dissolved REE levels were observed for all lakes and appeared the result of REE adsorption to colloids and subsequent sedimentation. Combined with enrichment of light over heavy REE, particularly in samples closer to shore, our data suggests that riverine input is a major pathway by which REE are loaded to the lakes. Finally, we used normalization and pattern-filling to assess REE anomalies in the lake surface waters. Anomalies for Gd (>20 % across the lakes) were notably higher than those of the other REE but varied significantly spatially, and also showed enrichment nearshore, particularly near urban centers and in Lake Ontario. This work provides new surveillance data to further develop our understanding of REE dynamics in the Great Lakes.

New insights into rare earth element-induced microalgae lipid accumulation: Implication for biodiesel production and adsorption mechanism

A coupling technology for lipid production and adsorption of rare earth elements (REEs) using microalgae was studied in this work. The microalgae cell growth, lipid production, biochemical parameters and lipid profiles were investigated under different REEs (Ce3+, Gd3+and La3+). The results showed that the maximum lipid production was achieved at different concentrations of REEs, with lipid productivities of 300.44, 386.84 and 292.19 mg L−1 d−1 under treatment conditions of 100 μg L−1 Ce3+, 250 μg L−1 Gd3+ and 1 mg L−1 La3+, respectively. Moreover, the adsorption efficiency of Ce3+, Gd3+ and La3+exceeded 96.58 %, 93.06 % and 91.3 % at concentrations of 25–1000 μg L−1, 100–500 μg L−1 and 0.25–1 mg L−1, respectively. In addition, algal cells were able to adsorb 66.2 % of 100 μg L−1 Ce3+, 48.4 % of 250 μg L−1 Gd3+ and 59.9 % of 1 mg L−1 La3+. The combination of extracellular polysaccharide and algal cell wall could adsorb 25.2 % of 100 μg L−1 Ce3+, 44.5 % of 250 μg L−1 Gd3+ and 30.5 % of 1 mg L−1 La3+, respectively. These findings indicated that microalgae predominantly adsorbed REEs through the intracellular pathway. This study elucidates the mechanism of effective lipid accumulation and adsorption of REEs by microalgae under REEs stress conditions. It establishes a theoretical foundation for the efficient microalgae lipid production and REEs recovery from wastewater or waste residues containing REEs.

Adsorption of rare earth elements on a magnetic geopolymer derived from rice husk: studies in batch, column, and application in real phosphogypsum leachate sample.

There is a growing need to develop new strategies for rare earth element (REE) recovery from secondary resources. Herein, a novel approach to utilize biogenic silica (from rice husk) and metakaolin was employed to fabricate magnetic geopolymer (MGP) by incorporating metallic iron. The fabricated MGP adsorbent material was used to uptake Ce3+, La3+, and Nd3+ from synthetic solutions and real phosphogypsum leachate in batch and column modes. The MGP offers a negatively charged surface at pH above 2.7, and the uptake of REEs rises from pH 3 to 6. The kinetic study validated that the kinetics was much faster for Nd3+, followed by La3+ and Ce3+. A thermodynamic investigation validated the exothermic nature of the adsorption process for all selected REEs. The desorption experiment using 2mol L-1 H2SO4 as the eluent demonstrated approximately 100% desorption of REEs from the adsorbent. After six adsorption-desorption cycles, the MGP maintained a high adsorption performance up to cycle five before suffering a significant decrease in performance in cycle six. The effectiveness of MGP was also assessed for its applicability in recovering numerous REEs (La3+, Ce3+, Pr3+, Sm3+, and Nd3+) from real leachate from phosphogypsum wastes, and the highest recovery was achieved for Nd3+ (95.03%) followed by Ce3+ (86.33%). The operation was also feasible in the column presenting suitable values of the length of the mass transfer zone. The findings of this investigation indicate that MGP adsorbent prepared via a simple route has the potential for the recovery of REEs from synthetic and real samples in both batch and continuous operations modes.

Stripped: contribution of cyanobacterial extracellular polymeric substances to the adsorption of rare earth elements from aqueous solutions.

The transformation of modern industries towards enhanced sustainability is facilitated by green technologies that rely extensively on rare earth elements (REEs) such as cerium (Ce), neodymium (Nd), terbium (Tb), and lanthanum (La). The occurrence of productive mining sites, e.g., is limited, and production is often costly and environmentally harmful. As a consequence of increased utilization, REEs enter our ecosystem as industrial process water or wastewater and become highly diluted. Once diluted, they can hardly be recovered by conventional techniques, but using cyanobacterial biomass in a biosorption-based process is a promising eco-friendly approach. Cyanobacteria can produce extracellular polymeric substances (EPS) that show high affinity to metal cations. However, the adsorption of REEs by EPS has not been part of extensive research. Thus, we evaluated the role of EPS in the biosorption of Ce, Nd, Tb, and La for three terrestrial, heterocystous cyanobacterial strains. We cultivated them under N-limited and non-limited conditions and extracted their EPS for compositional analyses. Subsequently, we investigated the metal uptake of a) the extracted EPS, b) the biomass extracted from EPS, and c) the intact biomass with EPS by comparing the amount of sorbed REEs. Maximum adsorption capacities for the tested REEs of extracted EPS were 123.9-138.2 mg g-1 for Komarekiella sp. 89.12, 133.1-137.4 mg g-1 for Desmonostoc muscorum 90.03, and 103.5-129.3 mg g-1 for Nostoc sp. 20.02. A comparison of extracted biomass with intact biomass showed that 16% (Komarekiella sp. 89.12), 28% (Desmonostoc muscorum 90.03), and 41% (Nostoc sp. 20.02) of REE adsorption was due to the biosorption of the extracellular EPS. The glucose- rich EPS (15%-43% relative concentration) of all three strains grown under nitrogen-limited conditions showed significantly higher biosorption rates for all REEs. We also found a significantly higher maximum adsorption capacity of all REEs for the extracted EPS compared to cells without EPS and untreated biomass, highlighting the important role of the EPS as a binding site for REEs in the biosorption process. EPS from cyanobacteria could thus be used as efficient biosorbents in future applications for REE recycling, e.g., industrial process water and wastewater streams.

Chemical modification of zeolites for the recovery of rare earth elements evaluated by machine learning algorithms

Rare earth elements (REE) are a significant group of valuable elements used in diverse and relevant applications in our daily lives. The mining and processing of the original ores, as well as the final wastes disposal, produce wastewater with variable concentrations of REE to be recovered. Sorbent materials like zeolites have been employed in adsorption processes to capture diverse pollutants from wastewater. The objective of this study is to identify the most effective modified zeolite for the adsorption and desorption of REE from aqueous solutions. To achieve this, the processes evaluation by machine learning (ML) algorithms was explored through both supervised and unsupervised analyses. The purpose of the usage of such tools was to assist in the selection of the optimal zeolite for REE recovery and to assess the predictive capabilities of the models. Modified zeolites were obtained by acid and alkali treatments in order to increase their sorption capacity compared to the controls and they were characterized by SEM/EDS, FTIR and pH zero point charge. Kinetic modelling and desorption assays were also performed, these last ones to evaluate the REE leaching from the sorbent for the best suitable modified zeolites. An overall removal of 80% for adsorption and over 90% recovery for desorption were achieved for the best modified zeolites. ML algorithms helped to classify the adsorption results and allowed the selection of the best suitable modified zeolites. It is concluded that alkali modification of the zeolites surfaces increases their natural adsorption capacity for recovering REE.

Adsorption Behaviors of Lanthanum (III) and Yttrium (III) Ions on Gibbsite

The enrichment process of rare earth elements in ion-adsorbed rare earth ores and bauxite is potentially related to the adsorption of rare earth elements by gibbsite. In this paper, lanthanum and yttrium were selected as surrogates of light rare earth elements and heavy rare earth elements, respectively. The effects of adsorption time, solution pH, and background electrolyte concentration on the adsorption of rare earth ions by gibbsite were investigated through batch adsorption experiments. The results showed that the adsorption of rare earth ions by gibbsite can approach equilibrium in 72 h. There is mainly electrostatic repulsion between gibbsite and rare earth ions at pH 4–7, and the adsorption efficiency increases with the increase in solution pH value and background electrolyte concentration. The adsorption process of rare earth ions by gibbsite is more consistent with the pseudo-second-order kinetic and Langmuir single-layer adsorption models. Moreover, based on the structural correlation between clay minerals and gibbsite, the causes for the differences in the adsorption behaviors of rare earth elements on the minerals are discussed. The results of this study help to understand the role of aluminum hydroxide in the migration and fate of rare earth elements in epigenetic environments.

Exploring Optimization of Zeolites as Adsorbents for Rare Earth Elements in Continuous Flow by Machine Learning Techniques.

Unsupervised machine learning (ML) techniques are applied to the characterization of the adsorption of rare earth elements (REEs) by zeolites in continuous flow. The successful application of principal component analysis (PCA) and K-Means algorithms from ML allowed for a wide range assessment of the adsorption results. This global approach permits the evaluation of the different stages of the sorption cycles and their optimization and improvement. The results from ML are also used for the definition of a regression model to estimate other REEs' recoveries based on the known values of the tested REEs. Overall, it was possible to remove more than 70% of all REEs from aqueous solutions during the adsorption assays and to recover over 80% of the REEs entrapped on the zeolites using an optimized desorption cycle.

Fabrication of sodium alginate-doped carbon dot composite hydrogel and its application for La (III) adsorption and enhanced the removal of phosphorus.

Adsorption is an effective method for the removal of hazardous substances from wastewater. In this work, a low-cost and environmental-friendly composite hydrogel material of sodium alginate doped with nitrogen doped carbon dots (SA@NCDs) was fabricated by impregnation for lanthanide and enhanced phosphorus adsorption in wastewater. The effects of NCDs doping amount, dosage, pH, initial solution concentration, adsorption time and temperature on the process of La (III) adsorption by SA@NCDs were investigated. The adsorption isotherms fitted to Langmuir isotherm model (R2 = 0.9970-0.9989) and the adsorption kinetics followed pseudo-second-order kinetic model (R2 = 0.9992). The maximum adsorption capacity of the adsorbent for La (III) was 217.39mg/g according to the Langmuir model at 298.15K. After five cycles, the removal efficiency of La (III) adsorbed by SA@NCDs was still 85.1%. Moreover, the loaded La (III) enhanced the adsorption of phosphorus. The La (III)-SA@NCDs-5 hydrogel adsorbent greatly improved the adsorption capacity for phosphorus compared with the La (III)-free adsorbent, and the adsorption amount can reach 9.64mg-P/g. The SA@NCDs complex hydrogels for rare earth adsorption were prepared by introducing NCDs rich in amino group into SA hydrogels. The introduction of NCDs increases the adsorption sites of hydrogels, and also overcomes the problem that NCDs itself is difficult to recover in wastewater treatment applications. The lanthanide adsorbed material has a stable structure and can be used to remove phosphorus to deal with waste using the waste. It indicates the SA@NCDs hydrogel composite adsorbent have good potential for wastewater treatment.

Synthesis, characterization and uptake studies of diglycolamic acid and diglycolamide analogs adsorbents for extraction of rare earth elements

Tetraalkyldiglycolamides are known for their high extracting efficiency of rare earth elements (REEs) from nitric acid solutions (1–6 mol/L). Nevertheless, solid-phase extractants based on diglycolamides (DGA) are poorly studied for REEs extraction. This paper explores the design and synthesis of novel REEs adsorbents by grafting silica with diglycolic acid-based ligands. The newly developed solid-phase materials were investigated for their potential to effectively separate REEs from various media. The functionalization of the silica with different ligands was quantified, and the adsorbents' extraction capacities and selectivity for REEs over Calcium (Ca2+), Aluminium (Al3+) and Iron (Fe3+) were evaluated. Si-NH-DGA emerged as the most efficient adsorbent for Gd3+ extraction, exhibiting a remarkable capacity of 44 mg/g at pH 4–6. However, modifications involving ether oxygen substitution with a methylamino group or sulfur led to reduced extraction efficiencies. Si-NH-DGA-NMe2 demonstrated strong binding of REEs in nitric acid solutions (1–3 mol/L HNO3) with corresponding adsorption capacities for Y3+, La3+, Gd3+ and Yb3+ being 16.3, 14.2, 22.8, and 30.2 mg/g, respectively. Furthermore, it displayed remarkable selectivity for REEs over Ca2+. The equilibrium extraction for Gd occurred within 60 min for Si-NH-DGA and Si-NH-DGA-NMe2 under their respective optimal conditions. Disodium EDTA solution demonstrated a high stripping efficiency for Gd3+ in the Si-NH-DGA-NMe2 column extraction, yielding a significant concentration factor (CF = 85). In the same column, following five cycles of loading/stripping of Gd3+, there was an average capacity loss of 6%. Si-NH-DGA-NMe2 emerged as a promising material for solid-phase extraction from concentrated nitric acid solutions, characterized by high capacity and good selectivity towards middle and heavy REEs. This structure has the potential to be further optimized for the development of a solid-phase extraction column for REEs separation and purification. The findings also highlight the potential of Si-NH-DGA-NMe2 as a candidate for REEs adsorption for potential industrial applications and the purification of acidic waste solutions.

Surface structure regulating of silica adsorbent for the selective adsorption of heavy rare earth

Rare earth element (REE) is a strategic metal resource, heavy REE owns higher economic and strategic value compared with light rare earth elements. However, it is a great challenge for the separation of heavy rare earth ion efficiently in the solution with mixed rare earth ions due to the similar physicochemical properties of heavy and light REE. In this paper, the diglycolamide (DGA) modified silica adsorbents were prepared and applied to the selective adsorption of heavy earth ion Dy3+. The structure of DGA on the silica surface was regulated during the modifying processes to obtain DGAb-SiO2 and DGAs-SiO2 adsorbent, which was verified by FTIR and NMR characterization results. The adsorption results showed that the DGAb-SiO2 adsorbent owned a much higher distribution coefficient (Kd) value for the selective adsorption of Dy3+ than the DGAs-SiO2 adsorbent. The higher adsorption selectivity is likely due to the fixed carbon chain of the DGA group on the surface of DGAb-SiO2 adsorbent formed rigid spatial structures of the oxygen atoms, which will be favorable for the selective coordination of Dy3+. Besides its effectiveness in adsorption behavior, the DGAb-SiO2 adsorbent displayed excellent stability. The Kd value of DGAb-SiO2 for Dy3+ selective adsorption maintained a high level after four successive recycling runs. The adsorption kinetics results displayed that the adsorption of Dy3+ followed pseudo-second-order kinetic, and the adsorption process fitted the Langmuir isotherm model. Additionally, the same adsorption rules for the rare earth ions were observed over DGA-KIT-6 adsorbent, indicating the high universality of the surface modification to the adsorbent support, which will provide an intentional reference for the surface modification to other adsorbent support.

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.

Improved recovery selectivity of rare earth elements from mining wastewater utilizing phytosynthesized iron nanoparticles

While rare earth elements (REEs) play key roles in many modern technologies, the selectivity of recovering of REEs from mining wastewater remains a critical problem. In this study, iron nanoparticles (FeNPs) synthesized from euphorbia cochinchinensis extracts were successfully used for selective recovery of REEs from real mining wastewater with removal efficiencies of 89.4% for Y(III), 79.8% for Ce(III) and only 6.15% for Zn(Ⅱ). FTIR and XPS analysis suggested that the high selective removal efficiency of Y(III) and Ce(III) relative to Zn(Ⅱ) on FeNPs was due to a combination of selective REEs adsorption via complexing with O or N, ion exchange with H+ present in functional groups contained within the capping layer and electrostatic interactions. Adsorptions of Y(III) and Ce(III) on FeNPs conformed to pseudo second-order kinetics and the Langmuir isotherm model with maximum adsorption capacities of 5.10 and 0.695 mg∙g−1, respectively. The desorption efficiencies of Y(III) and Ce(III) were, respectively, 95.0 and 97.9% in 0.05 M acetic acid, where desorption involved competitive ion exchange between Y(III), Ce(III) and Zn(Ⅱ) with H+ contained in acetic acid and intraparticle diffusion. After four consecutive adsorption-desorption cycles, adsorption efficiencies for Y(III) and Ce(III) remained relatively high at 52.7% and 50.1%, respectively, while desorption efficiencies of Y(III) and Ce(III) were > 80.0% and 95.0%, respectively. Overall, excellent reusability suggests that FeNPs can practically serve as a potential high-quality selectivity material for recovering REEs from mining wastewaters.