Adsorption Properties toward Trivalent Rare Earths by Alginate Beads Doping with Silica

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.

Recent advances in alginate-based composite gel spheres for removal of heavy metals

The discharge of heavy metal ions from industrial wastewater into natural water bodies is a consequence of global industrialisation. Due to their high toxicity and resistance to degradation, these heavy metal ions pose a substantial threat to human health as they accumulate and amplify. Alginate-based composite gels exhibit good adsorption and mechanical properties, excellent biodegradability, and non-toxicity, making them environmentally friendly heavy metal ion adsorbents for water with promising development prospects. This paper introduces the basic properties, cross-linking methods, synthetic approaches, modification methods, and manufacturing techniques of alginate-based composite gels. The adsorption properties and mechanical strength of these gels can be enhanced through surface modification, multi-component mixing, and embedding. The main production processes involved are sol-gel and cross-linking methods. Additionally, this paper reviews various applications of alginate composite gels for common heavy metals, rare earth elements, and radionuclides and elucidates the adsorption mechanism of alginate composite gels. This study aimed to provide a reference for synthesising new, efficient, and environmentally friendly alginate-based adsorbents and to contribute new ideas and directions for addressing the issue of heavy metal pollution.

Magnetic Hydrogel Beads as a Reusable Adsorbent for Highly Efficient and Rapid Removal of Aluminum: Characterization, Response Surface Methodology Optimization, and Evaluation of Isotherms, Kinetics, and Thermodynamic Studies

Biopolymers such as alginate and gelatin have attracted much attention because of their exceptional adsorption properties and biocompatibility. The magnetic hydrogel beads produced and used in this study had a core structure composed of magnetite nanoparticles and gelatin and a shell structure composed of alginate. The combination of the metal-ion binding ability of alginate and the mechanical strength of gelatin in magnetic hydrogel beads presents a new approach for the removal of metal from water sources. The beads were designed for aluminum removal and fully characterized using various methods, including Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, vibrating sample magnetometry, microcomputed tomography, and dynamic mechanical analysis. Statistical experimental designs were employed to optimize the parameters of the adsorption and recovery processes. Plackett-Burman Design, Box-Behnken Design, and Central Composite Design were used for identifying the significant factors and optimizing the parameters of the adsorption and recovery processes, respectively. The optimum parameters determined for adsorption are as follows: pH: 4, contact time: 30 min, adsorbent amount: 600 mg; recovery time: reagent 1 M HNO3; and contact time: 40 min. The adsorption process was described by using the Langmuir isotherm model. It reveals a homogeneous bead surface and monolayer adsorption with an adsorption capacity of 5.25 mg g-1. Limit of detection and limit of quantification values were calculated as 4.3 and 14 μg L-1, respectively. The adsorption process was described by a pseudo-second-order kinetic model, which assumes that chemisorption is the rate-controlling mechanism. Thermodynamic studies indicate that adsorption is spontaneous and endothermic. The adsorbent was reusable for 10 successive adsorption-desorption cycles with a quantitative adsorption of 98.2% ± 0.3% and a recovery of 99.4% ± 2.6%. The minimum adsorbent dose was determined as 30 g L-1 to achieve quantitative adsorption of aluminum. The effects of the inorganic ions were also investigated. The proposed method was applied to tap water and carboy water samples, and the results indicate that magnetic hydrogel beads can be an effective and reusable bioadsorbent for the detection and removal of aluminum in water samples. The recovery values obtained by using the developed method were quantitative and consistent with the results obtained from the inductively coupled plasma optical emission spectrometer.

Alginate Beads Containing Cerium-Doped Mesoporous Glass and Curcumin: Delivery and Stabilization of Therapeutics

Cancer is a leading cause of death worldwide, its genesis and progression are caused by homeostatic errors, and reactive oxygen species play a major role in promoting aberrant cancer homeostasis. In this scenario, curcumin could be an interesting candidate due to its versatile antioxidant, anti-inflammatory, anti-tumor, anti-HIV, and anti-infection properties. Nonetheless, the major problem related to its use is its poor oral bioavailability, which can be overcome by encapsulating it into small particles, such as hydrogel beads containing mesoporous silica. In this work, various systems have been synthesized: starting from mesoporous silica glasses (MGs), cerium-containing MGs have been produced; then, these systems have been loaded with 4 to 6% of curcumin. Finally, various MGs at different compositions have been included in alginate beads. In vitro studies showed that these hybrid materials enable the stabilization and effective delivery of curcumin and that a synergic effect can be achieved if Ce³⁺/Ce⁴⁺ and curcumin are both part of the beads. From swelling tests, it is possible to confirm a controlled curcumin release compartmentalized into the gastrointestinal tract. For all beads obtained, a curcumin release sufficient to achieve the antioxidant threshold has been reached, and a synergic effect of cerium and curcumin is observed. Moreover, from catalase mimetic activity tests, we confirm the well-known catalytic activity of the couple Ce³⁺/Ce⁴⁺. In addition, an extremely good radical scavenging effect of curcumin has been demonstrated. In conclusion, these systems, able to promote an enzymatic-like activity, can be used as drug delivery systems for curcumin-targeted dosing.

Biosorption of rare-earth and toxic metals from aqueous medium using different alternative biosorbents: evaluation of metallic affinity

Currently, the world faces difficulties related to the quantity and quality of water because of industrial expansion, population growth, and urbanization intensification. Biosorption is considered a promising technology that can be applied to remove toxic metals (TMs) and rare-earth metals (REMs) in wastewater at low concentrations, due to its efficiency and low cost. In this work, we investigated different non-conventional biosorbents to remove metallic ions (TMs and REMs) in biosorptive affinity tests. Metallic affinity assays among lanthanum and different biosorbents showed that greater affinities were found for sericin-alginate beads crosslinked with polyvinyl alcohol (SAPVA) (0.280 mmol/g) and polyethylene glycol diglycidyl ether (SAPEG) (0.277 mmol/g), expanded vermiculite (0.281 mmol/g), Sargassum filipendula seaweed (0.287 mmol/g), and seaweed biomass waste (0.289 mmol/g). Among the biosorbents evaluated, SAPVA and SAPEG beads, besides to sericin-alginate beads crosslinked with proanthocyanidins (SAPAs) were selected for affinity assays with other REMs and TMs. Compared to other particles, SAPVA beads showed higher potential for biosorption by REMs with the following order of affinity: Yb3+ > Dy3+ > Nd3+ > Ce3+ > La3+. Additionally, the biosorptive affinity of TMs by SAPVA beads followed the order: Al3+ > Cr3+ > Pb2+ > Cu2+ > Cd2+ > Zn2+ > Ni2+.

Novel benzylphosphate-based covalent porous organic polymers for the effective capture of rare earth elements from aqueous solutions

It has been a major challenge to develop stable and cost-effective porous materials that efficiently recover heavy rare earth elements (HREEs) due to ever-increasing demand, low availability and high cost of HREEs. This study presents two novel benzylphosphate-based covalent porous organic polymers (BPOP-1 and BPOP-2) that were prepared by facile one-pot Friedel-Crafts reactions. Various analytical techniques are used to investigate the successful syntheses of BPOP materials and establish their material properties, which include an unusual crystalline nature, large surface area, hierarchical pore structure, and superior chemical stabilities. The BPOPs effectively adsorb, and thus remove HREEs from aqueous media. In particular, BPOP-1 had higher phosphate content and exhibits superior adsorption capacities (Eu³⁺: 289.5; Gd³⁺: 292.7; Tb³⁺: 294.4; Dy³⁺: 301.9 mg/g) than BPOP-2, while BPOP-2 had higher mesoporosity and correspondingly supports faster adsorption kinetics. Remarkably, both BPOP materials exhibit some of the highest HREE adsorption capacities reported to date, the selective capture of Dy³⁺ ions, and excellent cyclic adsorption/desorption properties. We provide a potential adsorption mechanism for Dy³⁺ capture by the BPOP adsorbent. These demonstrate that introducing phosphate functionality into a robust porous polymer backbone with high surface area is a promising strategy for selective HREEs capture from wastewater.

Equilibrium, Thermodynamic, Reuse, and Selectivity Studies for the Bioadsorption of Lanthanum onto Sericin/Alginate/Poly(vinyl alcohol) Particles

In a scenario of high demand, low availability, and high economic value, the recovery of rare-earth metals from wastewater is economically and environmentally attractive. Bioadsorption is a promising method as it offers simple design and operation. The aim of this study was to investigate lanthanum bioadsorption using a polymeric bioadsorbent of sericin/alginate/poly(vinyl alcohol)-based biocomposite. Batch system assays were performed to evaluate the equilibrium, thermodynamics, regeneration, and selectivity of bioadsorption. The maximum capture amount of lanthanum at equilibrium was 0.644 mmol/g at 328 K. The experimental equilibrium data were better fitted by Langmuir and Dubinin-Radushkevich isotherms. Ion exchange mechanism between calcium and lanthanum (2:3 ratio) was confirmed by bioadsorption isotherms. Thermodynamic quantities showed that the process of lanthanum bioadsorption was spontaneous (-17.586, -19.244, and -20.902 kJ/mol), endothermic (+15.372 kJ/mol), and governed by entropic changes (+110.543 J/mol·K). The reusability of particles was achieved using 0.1 mol/L HNO₃/Ca(NO₃)₂ solution for up to five regeneration cycles. The bioadsorbent selectivity followed the order of lanthanum > cadmium > zinc > nickel. Additionally, characterization of the biocomposite prior to and post lanthanum bioadsorption showed low porosity (9.95 and 12.35%), low specific surface area (0.054 and 0.019 m²/g), amorphous character, and thermal stability at temperatures up to 473 K. This study shows that sericin/ alginate/poly(vinyl alcohol)-based biocomposites are effective in the removal and recovery of lanthanum from water.

Efficient Recovery of Rare Earth Elements (Pr(III) and Tm(III)) From Mining Residues Using a New Phosphorylated Hydrogel (Algal Biomass/PEI)

With the target of recovering rare earth elements (REEs) from acidic leachates, a new functionalized hydrogel was designed, based on the phosphorylation of algal/polyethyleneimine beads. The functionalization strongly increased the sorption efficiency of the raw material for Pr(III) and Tm(III). Diverse techniques were used for characterizing this new material and correlating the sorption performances and mechanisms to the physicochemical structure of the sorbent. First, the work characterized the sorption properties from synthetic solutions with the usual procedures (study of pH effect, uptake kinetics, sorption isotherms, metal desorption and sorbent recycling, and selectivity from multi-element solutions). Optimum pH was found close to 5; sorption isotherms were fitted by the Langmuir equation (maximum sorption capacities close to 2.14 mmol Pr g−1 and 1.57 mmol Tm g−1). Fast uptake kinetics were modeled by the pseudo-second order rate equation. The sorbent was highly selective for REEs against alkali-earth and base metals. The sorbent was remarkably stable for sorption and desorption operation (using 0.2 M HCl/0.5 M CaCl2 solutions). The sorbent was successfully applied to the leachates of Egyptian ore (pug leaching) after a series of pre-treatments (precipitation steps), sorption, and elution. The selective precipitation of REEs using oxalic acid allows for the recovery of a pure REE precipitate.

Influence of carbohydrate polymer shaping on organic dye adsorption by a metal–organic framework in water

A thorough analysis and comparison was conducted of the Orange II and Rhodamine B dye adsorption properties of unshaped MIL-100(Fe) (MIL) particles and alginate polymer-shaped MIL beads (MIL-alg).

Crosslinked alginate/sericin particles for bioadsorption of ytterbium: Equilibrium, thermodynamic and regeneration studies

Sericin is a soluble globular protein, present in Bombyx mori silkworm cocoons. Sericin's properties can be improved to expand its application by producing blends with other substances, such as alginate polysaccharide and crosslinking agent poly(vinyl alcohol). This study evaluates the use of alginate and sericin particles chemically crosslinked with poly(vinyl alcohol) (SAPVA) for batch bioadsorption of rare-earth element ytterbium from aqueous medium. The equilibrium study showed that the maximum bioadsorption capacity for ytterbium was 0.642 mmol/g at 55 °C. Equilibrium data fit both Langmuir and Dubinin-Radushkevich models. The estimation of thermodynamic parameters showed that there was an increase in the entropy change, and that the bioadsorption process is endothermic and spontaneous. Characterization analyzes revealed that SAPVA particles, even after ytterbium bioadsorption, showed spherical shape, homogeneous composition, amorphous structure, low surface area, macropores, and low porosity. After the first regeneration cycle, the amount of captured ytterbium ions showed a slight increase (about 0.01 mmol/g) and calcium ions were completely released by SAPVA particles. Bioadsorbent particles separated selectively ytterbium from synthetic effluent containing different toxic metal ions. These results show that the SAPVA particles can be used as an effective bioabsorbent to remove and recover ytterbium from wastewater.

Biological, biomolecular, and bio-inspired strategies for detection, extraction, and separations of lanthanides and actinides

Lanthanides and actinides are elements of ever-increasing technological importance in the modern world. However, the similar chemical and physical properties within these groups make purification of individual elements a challenge. Current industrial standards for the extraction, separation, and purification of these metals from natural sources, recycled materials, and industrial waste are inefficient, relying upon harsh conditions, repetitive steps, and ligands with only modest selectivity. Biological, biomolecular, and bio-inspired strategies towards improving these separations and making them more environmentally sustainable have been researched for many years; however, these methods often have insufficient selectivity for practical application. Recent developments in the understanding of how lanthanides are selectively acquired and used by certain bacteria offer the opportunity for a newer, more efficient take on these designs, as well as the possibility for fundamentally new designs and strategies. Herein, we review current cell-based and biomolecular (primarily small-molecule and protein-based) methods for detection, extraction, and separations of f-block elements. We discuss how the increasing knowledge regarding the selective recognition, uptake, trafficking, and storage of these elements in biological systems has informed and will continue to promote development of novel approaches to achieve these ends.

Lanthanide recovery by silica-Cyanex 272 material immobilized in alginate matrix

Mesoporous silica impregnate with Cyanex 272 (bis/2,4,4-trimethylpentyl/phosphinic acid) extractant was immobilized into an alginate matrix to obtain a composite sorbent easy to use and applicable in fixed-bed column continuous systems. The sorption efficiency of this material was tested for the recovery of Eu(III) ions from aqueous solutions in batch and continuous mode. The competition among rare earths ions (europium, lanthanum, and lutetium) and among rare earths and calcium or sodium ions was investigated. High calcium concentrations strongly reduce the sorption capacity of the alginate matrix that composes the hybrid material and the Cyanex 272 impregnated into silica powder improves the rare earths' sorption performance in this calcium charged media. The experimental breakthrough curves obtained were satisfactory fitted by Thomas model.

Adsorption of rare earth metals from wastewater by nanomaterials: A review

Rare earth elements are widely used in chemical engineering, the nuclear industry, metallurgy, medicine, electronics, and computer technology because of their unique properties. To fulfil ever increasing demands for these elements, recycling of rare-earth-element-containing products as well as their recovery from wastewater is quite important. In order to recover rare earth elements from wastewater, their adsorption from low-concentration aqueous solutions, by using nanomaterials, is investigated due to technological simplicity and high efficiency. This paper is a review of the state-of-the-art adsorption technologies of rare earth elements from diluted aqueous solutions by using various nanomaterials. Furthermore, desorption and reusability of rare earth metals and nanomaterials are discussed. On the basis of this review it can be concluded that laboratory testing indicates promising adsorption capacities, which depend significantly on nanomaterial type and adsorption conditions. The adsorption process, which mostly follows the Langmuir, Freundlich, Sips, and Temkin isotherms, is typically endothermic and spontaneous. Furthermore, pseudo-second order, pseudo-first order, and intra-particle diffusion models are the best models to describe the kinetics of adsorption. The dominant adsorption mechanisms are surface complexation and ion exchange. More investigation, however, will be required in order to synthesize appropriate, environmentally friendly, and efficient nanomaterials for adsorption of rare earth elements from real wastewater.

Terbium Ion Adsorption from Aqueous Solution by Using Magnetic γFe2O3-NH4OH@SiO2 Nanoparticles Functionalized with Amino Groups

New magnetic stabilized and functionalized core@shell nanoparticles (NPs) were synthesized in a simple way and characterized in order to adsorb Tb³⁺ from aqueous solution with a very low Tb³⁺ concentration. For the fluorescence determination of adsorption efficiency and capacity, tiron monohydrate as a ligand was used. The obtained results confirm the potential of the synthesized magnetic γ-Fe₂O₃-NH₄OH@SiO₂ NPs, functionalized with (3-Aminopropyl) trimethoxysilane (APTMS), to be used for adsorption of Tb³⁺ from aqueous solution, with the possibility of its removal from aqueous solution via an external magnet. The endothermic and spontaneous adsorption follows a pseudo-second-order kinetic model, and the adsorption equilibrium data fit the Temkin isotherm well. The maximum adsorption efficiency from aqueous solution with a 2 × 10^-6 M concentration of Tb³⁺ is over 90% at pH 7.

Biosorption of dysprosium (III) using raw and surface-modified bark powder of Mangifera indica: isotherm, kinetic and thermodynamic studies

In this paper, we have used HDTMA-Br- and NaOH-treated bark powder of Mangifera indica as bio-sorbents for the removal of dysprosium (III) from its aqueous solution. The adsorption process was investigated at different experimental parameters such as contact time, temperature, pH, adsorbent dose, and initial metal concentration. The amount of chemically modified bark powder required was almost two times lesser than raw bark to get a higher percentage removal of the metal ion. The kinetics results revealed the adsorption process follows the nonlinear form a pseudo-second-order model. The negative values of Gibbs free energy change (∆G°) indicated the spontaneity of the adsorption process. The enthalpy change (∆H°) and entropy change (∆S°) of adsorption were 60.97 kJ/mol and 0.48 J/mol K, respectively signified it as an endothermic process. The maximum adsorption capacity was found to be 55.04 mg/g for sorption of Dy (III) on NaOH-treated bark powder and was better fitted to Langmuier model. It was confirmed to follow physisorption process and the activation energy of the system was found to be 41.07 kJ/mol. The possibility of adsorbent and adsorbate interactions were indicated by the FTIR and SEM/EDX analysis.

Sorption and Desorption Studies of Pb(II) and Ni(II) from Aqueous Solutions by a New Composite Based on Alginate and Magadiite Materials

A new composite material based on alginate and magadiite/Di-(2-ethylhexyl) phosphoric acid (CAM-D2EHPA) was successfully prepared by previous impregnation of layered magadiite with D2EHPA extractant, and then immobilized into the alginate matrix. Air dried beads of CAM-D2EHPA were characterized by FTIR and SEM⁻EDX techniques. The sorbent was used for the separation of lead and nickel from nitrate solutions; the main parameters of sorption such as contact time, pH of the solution, and initial metal concentration were studied. The beads recovered 94% of Pb(II) and 65% of Ni(II) at pH 4 from dilute solutions containing 10 mg L-1 of metal (sorbent dosage, S.D. 1 g L-1). The equilibrium data gave a better fit using the Langmuir model, and kinetic profiles were fitted using a pseudo-second order rate equation. The maximum sorption capacities obtained (at pH 4) were 197 mg g-1 and 44 mg g-1 for lead and nickel, respectively. The regeneration of the sorbent was efficiently carried out with a dilute solution of HNO₃ (0.5 M). The composite material was reused in 10 sorption⁻elution cycles with no significant differences on sorption uptake. A study with synthetic effluents containing an equimolar concentration of both metals indicated a better selectivity towards lead ions.

Functionalized Magnetic Silica Nanoparticles for Highly Efficient Adsorption of Sm3+ from a Dilute Aqueous Solution

Separation of Sm³⁺ from a dilute solution via conventional solvent extraction is often plagued by emulsion and third phase formation. These problems can be overcome with functionalized magnetic nanoparticles that can capture the target species and be separated from the raffinae phase rapidly and efficiently on application of a magnetic field. Magentic silica nanoparticles (Fe₂O₃/SiO₂) were synthesized by a modified Stöber method and functionalized with carboxylate (Fe₂O₃/SiO₂/RCOONa) and phosphonate (Fe₂O₃/SiO₂/R₁R₂PO₃Na) groups to achieve high adsorption capacity and fast adsorption kinetics. The adsorbents were characterized by X-ray diffraction analysis, transmission electron microscopy, BET measurements, magnetization property evaluation, Fourier infrared spectroscopy, and thermogravimetric analysis. Equilibrium adsorption of Sm³⁺ on Fe₂O₃/SiO₂/RCOONa particles was attained within 10 min and within 20 min on Fe₂O₃/SiO₂/R₁R₂PO₃Na nanoparticles. The kinetic data were correlated well with a pseudo-second-order model. Adsorption capacities of Fe₂O₃/SiO₂/RCOONa and Fe₂O₃/SiO₂/R₁R₂PO₃Na were 228 and 180 mg/g, respectively. The recovery of the adsorbed Sm³⁺ using 2 mol/L HCl as desorption agent was evaluated. The adsorption mechanism is discussed based on FTIR analysis, carboxylate group/Sm³⁺ molar ratio, phosphonate group/Sm³⁺ molar ratio, and pH. The adsorbents show significant potential for Sm³⁺ recovery in industrial applications.

Praseodymium sorption on Laminaria digitata algal beads and foams

Algal (Laminaria digitata) beads and algal foams have been prepared by a new synthesis mode and the sorbents were tested for praseodymium sorption in batch and fixed-bed like systems (recirculation or one-pass modes), respectively. Metal binding occurs through ion-exchange with Ca(II) ions used for ionotropic gelation of alginate contained in the algal biomass and eventually with protons. Sorption isotherms at pH 4 are described by the Langmuir and the Sips equations with maximum sorption capacities close to 110-120mgPrg-1. Uptake kinetics are fitted by the pseudo-second order reaction rate equation for both beads and foams; in the case of beads the Crank equation also gives good fit of experimental data. Metal is successfully desorbed using 2M HCl/0.05M CaCl2 solutions and the sorbent can be efficiently re-used for a minimum of 5 cycles with negligible decrease in sorption/desorption properties and appreciable concentrating effect (around 8-10 times the initial metal concentration). Tested in continuous mode, the algal foam shows typical breakthrough curves that are fitted by the Yan method; desorption is also efficient and allows under the best conditions to achieve a concentration factor close to 8.

Efficent removal of nickel(II) salts from aqueous solution using carboxymethylchitosan-coated silica particles as adsorbent

Three types of organo-mineral composites have been probed as adsorbents for the removal of Ni(II) ions from aqueous solution. Native Aerosil 200 silica particles have been encapsulated with carboxymethylchitosan (CM-CS) providing SiO₂+CM-CS, surface-silanized silica particles SiO₂NH₂+CM-CS were obtained by treatment with APTES and subsequent encapsulation by CM-CS. Alternatively, surface-carboxylated Aerosil 200 was coated by CM-CS affording SiO₂CO₂H+CM-CS. The materials have been characterized by various techniques. The effects of counter ions (Cl^-, Br^-, CH₃COO^-, NO₃^- and SO₄^2-), pH and initial Ni(II) concentration on the adsorption capacities have been systematically investigated. The maximum adsorption capacity q_m of CM-CS-coated silica was determined using the Langmuir adsorption isotherm. For SiO₂CO₂H+CM-CS, SiO₂+CM-CS and SiO₂NH₂+CM-CS, they decrease at pH 7 in the order 256mg/g>140mg/g>105mg/g. The adsorption kinetic fits well with a pseudo-second order model. These carbohydrate-derived biosorbents are excellent adsorbents with capacities superior to most other adsorbents reported in the literature.

Biosorption of Cu(II) by immobilized microalgae using silica: kinetic, equilibrium, and thermodynamic study

Immobilized microalgae using silica (IMS) from Micractinium reisseri KGE33 was synthesized through a sol-gel reaction. Green algal waste biomass, the residue of M. reisseri KGE33 after oil extraction, was used as the biomaterial. The adsorption of Cu(II) on IMS was tested in batch experiments with varying algal doses, pH, contact times, initial Cu(II) concentrations, and temperatures. Three types of IMSs (IMS 14, 70, and 100) were synthesized according to different algal doses. The removal efficiency of Cu(II) in the aqueous phase was in the following order: IMS 14 (77.0%) < IMS 70 (83.3%) < IMS 100 (87.1%) at pH 5. The point of zero charge (PZC) value of IMS100 was 4.5, and the optimum pH for Cu(II) adsorption was 5. Equilibrium data were described using a Langmuir isotherm model. The Langmuir model maximum Cu(II) adsorption capacity (q m) increased with the algal dose in the following order: IMS 100 (1.710 mg g(-1)) > IMS 70 (1.548 mg g(-1)) > IMS 14 (1.282 mg g(-1)). The pseudo-second-order equation fitted the kinetics data well, and the value of the second-order rate constant increased with increasing algal dose. Gibbs free energies (ΔG°) were negative within the temperature range studied, which indicates that the adsorption process was spontaneous. The negative value of enthalpy (ΔH°) again indicates the exothermic nature of the adsorption process. In addition, SEM-energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses of the IMS surface reveal that the algal biomass on IMS is the main site for Cu(II) binding. This study shows that immobilized microalgae using silica, a synthesized biosorbent, can be used as a cost-effective sorbent for Cu(II) removal from the aqueous phase.

Adsorption of Rare Earths(Ⅲ) Using an Efficient Sodium Alginate Hydrogel Cross-Linked with Poly-γ-Glutamate

With the exploitation of rare earth ore, more and more REEs came into groundwater. This was a waste of resources and could be harmful to the organisms. This study aimed to find an efficient adsorption material to mitigate the above issue. Through doping sodium alginate (SA) with poly-γ-glutamate (PGA), an immobilized gel particle material was produced. The composite exhibited excellent capacity for adsorbing rare earth elements (REEs). The amount of La3+ adsorbed on the SA-PGA gel particles reached approximately 163.93 mg/g compared to the 81.97 mg/g adsorbed on SA alone. The factors that potentially affected the adsorption efficiency of the SA-PGA composite, including the initial concentration of REEs, the adsorbent dosage, and the pH of the solution, were investigated. 15 types of REEs in single and mixed aqueous solutions were used to explore the selective adsorption of REEs on gel particles. Scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy analyses of the SA and SA-PGA gel beads suggested that the carboxyl groups in the composite might play a key role in the adsorption process and the morphology of SA-PGA changed from the compact structure of SA to a porous structure after doping PGA. The kinetics and thermodynamics of the adsorption of REEs were well fit with the pseudo-second-order equation and the Langmuir adsorption isotherm model, respectively. It appears that SA-PGA is useful for recycling REEs from wastewater.

A comprehensive review on biosorption of heavy metals by algal biomass: materials, performances, chemistry, and modeling simulation tools

Heavy metals contamination has become a global issue of concern due to their higher toxicities, nature of non-biodegradability, high capabilities in bioaccumulation in human body and food chain, and carcinogenicities to humans. A series of researches demonstrate that biosorption is a promising technology for removal of heavy metals from aqueous solutions. Algae serve as good biosorbents due to their abundance in seawater and fresh water, cost-effectiveness, reusability and high metal sorption capacities. This article provides a comprehensive review of recent findings on performances, applications and chemistry of algae (e.g., brown, green and red algae, modified algae and the derivatives) for sequestration of heavy metals. Biosorption kinetics and equilibrium models are reviewed. The mechanisms for biosorption are presented. Biosorption is a complicated process involving ion-exchange, complexation and coordination. Finally the theoretical simulation tools for biosorption equilibrium and kinetics are presented so that the readers can use them for further studies.