Removal of radionuclide Sr2+ ions from aqueous solution using synthesized magnetic chitosan beads

Removal of Co, Sr and Cs ions from simulated radioactive wastewater by forward osmosis

The removal of Co, Sr and Cs ions form simulated radioactive wastewater using forward osmosis (FO) process was investigated. The effect of various factors on nuclide transport was examined, including membrane orientation, NaCl concentration, flow velocity, and the main factors were identified by correlation analysis. The mechanisms of nuclides transfer through membrane were explored. The results indicated that the active layer facing draw solution (AL-DS) had higher nuclide flux than AL-FS. At AL-FS mode, the highest flux of Co, Sr and Cs were only 1.54, 10.22 and 15.63 mg m^-2 h^-1 respectively by cellulose triacetate with embedded polyester screen support (CTA-ES) membrane. At AL-DS mode, the flux of Co and Cs increased when NaCl concentration and flow velocity increased. Convection, diffusion and electrostatic interactions were found to influence the nuclide transport all together. The Pearson correlation and partial correlation analysis identified that the diffusion coefficient of nuclides and reverse NaCl flux were the most important factors affecting nuclide flux through cellulose triacetate membrane. The water flux, NaCl concentration, flow velocity and partition coefficient were not the main affecting factors for nuclide flux.

Uranium biosorption by immobilized active yeast cells entrapped in calcium-alginate-PVA- GO-crosslinked gel beads

A novel biosorbent, i. e. Saccharomyces cerevisiae entrapped in graphene oxide (GO), polyvinyl alcohol (PVA) and alginate and cross-linked in CaCl2- boric acid solution, was prepared, characterized and applied for U (VI) biosorption. The performance of U sorption and cations release (Na, K, Ca and Mg ions) was investigated under different contact time, initial uranium concentration and initial pH. Uranium sorption equilibrium basically achieved after 360 min. The kinetic data of U biosorption and Ca release were best described by the pseudo first-order equation. Both Langmuir and Freundlich models could fit the U sorption isotherm data. With increase of initial uranium (3.7 ~ 472.2 μmol/L) and sodium concentration (78.8 ~ 3911.7 μmol/L), the cations release ((Na + K)/2 + (Ca + Mg)) decreased from 116.9 to 30.1 μmol/g when the corresponding U sorption increased from 0.6 to 77.3 μmol/g. Initial solution pH at 3 was favorable for U sorption when pH ranged from 3 to 7. With increase of uranium concentration, ion exchange played a less role in U removal. The maximum U sorption capacity reached 142.1 μmol/g, calculated from the Langmuir model at initial pH 5. The O-containing functional group, such as carboxyl on the gel bead played an important role in U adsorption according to FTIR and XPS analysis. XPS analysis showed the existence of U (VI) and U (IV) on the surface of gel bead. Ion exchange, complexation and uranium reduction involved in uranium adsorption by the immobilized active dry yeast gel beads.

Synthesis of core-shell magnetic titanate nanofibers composite for the efficient removal of Sr(ii)

We report a facile approach for the fabrication of Fe₃O₄@titanate fibers magnetic composite through a hydrothermal method and sol-gel process. The structure and morphology were characterized by X-ray diffraction (XRD), transmission electron microsphere (TEM), scanning electron microscope (SEM) and energy-dispersive X-ray analysis (EDX). Owing to the high ion exchange capacity of the functional titanate layer, the obtained core-shell structured magnetic microspheres exhibited high removal efficiency towards strontium from wastewater. The effects of contact time and Sr(ii) concentration on the uptake amount of strontium were systematically investigated. The results indicated that the adsorption equilibrium can be reached within 30 min, and the maximum exchange capacity was approximately 37.1 mg g^-1. Moreover, the captured Sr(ii) can be eluted using 5 wt% of EDTA(Na), which contributed to the reduction of waste volume. Based on the experimental results of ion exchange process and X-ray photoelectron spectroscopy (XPS), a possible adsorption mechanism was proposed. This work provided a facile approach to synthesize magnetic functional nanocomposites for wastewater treatment.

Characterization and Adsorption Behavior of Strontium from Aqueous Solutions onto Chitosan-Fuller's Earth Beads

Fuller's earth spherical beads using chitosan as a binder were prepared for the removal of strontium ions from aqueous solution. The adsorbents were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed the porous nature of the beads. The Brunauer⁻Emmett⁻Teller (BET) surface area of the beads was found to be 48.5 m²/g. The adsorption capacities of the beads were evaluated under both batch and dynamic conditions. The adsorption capacity was found to be ~29 mg/g of adsorbent at 298 K when the equilibrium concentration of strontium in the solution was 925 mg/L at pH 6.5. The X-ray photoelectron spectroscopy (XPS) data suggest that strontium uptake by the beads occurs mainly through an ion-exchange process. Kinetic data indicate that the sorption of strontium onto the beads follows anomalous diffusion. Thermodynamic data suggest that the ion-exchange of Sr²⁺ on the bead surface was feasible, spontaneous and endothermic in nature.

Algal sorbent derived from Sargassum horneri for adsorption of cesium and strontium ions: equilibrium, kinetics, and mass transfer

An algal sorbent derived from Sargassum horneri was prepared and used to adsorb cesium and strontium ions from aqueous solution. The phenomenological mathematical models associated to the predicted equilibrium isotherms were developed to determine the rate-limiting steps of the adsorption process. The maximum adsorption capacity of cesium ion and strontium ion was calculated to be 0.358 and 1.72 mmol g-1, respectively. The adsorption kinetics followed to the pseudo-second-order equation. It was found that adsorption of cesium or strontium ions onto the active sites of the biosorbent was the rate-limiting step. In addition, the external mass transfer and the internal mass transfer cannot be neglected for the adsorption of strontium ion based on the error analysis. The functional groups relevant to the adsorption were carboxyl and sulfate groups.

Strontium in the environment: Review about reactions of plants towards stable and radioactive strontium isotopes

Radiostrontium is released to the environment from routine and accidental discharge and acts on living organisms either from external sources or after absorption. When incorporated by plants, it enters the food chain and causes primary threat to human health and the environment. Understanding the mechanisms of plants for strontium uptake and retention is therefore essential for decision making concerning agriculture: are uptake rates low enough so that plants can serve as food? Or is radiostrontium accumulated so that plants should not be eaten but could be probably used for extracting strontium from water and soil in hot spots of pollution? The review presents a summary of studies about the origin of stable and radioactive strontium in the environment and effects coming from both internal and external exposure of plants. Mobility and availability of strontium to plant roots in soil are controlled by external factors such as chemical composition of the soil and pH, temperature and agricultural soil cultivation as well as soil biological networks built by microbial communities. Plant surfaces may receive input of strontium from deposition induced by atmospheric pollution or by acquisition from water through the whole immersed surface. Cells have entry mechanisms for strontium such as plasma membrane transporters for calcium and potassium. Part of absorbed strontium can be lost via processes discussed in this review. We give examples on strontium transfer factors for 149 plants to estimate plant absorption capacity for strontium from soil, water and air. Uptake efficiency of terrestrial and aquatic plants is deciding about their remediation potential to either remove radiostrontium by accumulation and rhizofiltration or to retain it in roots or aerial parts. Data of strontium content in soils after fallout and edible plants from long-term monitoring support the evaluation of the potential hazards posed by strontium input to the food chain.

Adsorption of Sr(II) from water by mercerized bacterial cellulose membrane modified with EDTA

The treatment of low-level radioactive wastewater is a critical and considerable challenge. Bacterial cellulose membrane (BCM) modified with ethylenediaminetetraacetic acid (EDTA) using (3-aminopropyl) triethoxysilane (APTES) as a crosslinker were used to remove Sr²⁺ in this work. SEM, XPS, and FTIR were used to characterize the morphology, structure, chemical shift, and functional groups of the as-prepared adsorbent. The synthesized BCM@APTES-EDTA presented a three-layer structure of membrane-net-membrane with nano-sized fibers (<100 nm). The adsorption of Sr²⁺ onto BCM@APTES-EDTA was investigated as a function of contact time and initial concentration of Sr²⁺. Results showed that the adsorption of Sr²⁺ followed the pseudo second-order kinetic model (R² = 0.999), and fitted well with the Langmuir isotherm model (R² = 0.996). The maximum adsorption capacity was calculated to be 44.86 mg g^-1, which was comparable to other adsorbents. Additionally, the mechanism of Sr²⁺ adsorbed by the as-prepared adsorbent was studied through FTIR and XPS analysis, which indicated that the tertiary amines and carboxylate from grafted EDTA participated in the adsorption of Sr²⁺.

Comparison of sustainable biosorbents and ion-exchange resins to remove Sr2+ from simulant nuclear wastewater: Batch, dynamic and mechanism studies

Removal of Sr²⁺ from aqueous media presents particular challenges, especially in complex wastes such as nuclear industry liquors. Commercial sorbents while effective, can be highly expensive and subject to negative effects from competing ions. Here we evaluate two potential biosorbents (crab carapace and spent distillery grain) as potential alternatives and compare their performance to two commercial sorbents for Sr²⁺ removal at industrially relevant concentrations (low mg/L). Physical and structural characterization of the materials was undertaken, and batch and dynamic studies were performed on Sr²⁺ solutions and simulated nuclear wastewater. Sorption performance was quantified with respect to contact time, initial concentration and ion-competition. Removal efficiencies were 20-70% for the biosorbents compared to 55-95% for the commercial materials. Results indicated sorption was predominantly through monolayer coverage on homogenous sites and could be described using a pseudo-second-order kinetic model. Studies with the simulant liquor showed Sr²⁺ sorption was reduced by 10-40% due to ion-competition for sites. Characterization of biosorbents before and after Sr²⁺ sorption suggested that outer-sphere complexation and ion-exchange were the primary Sr²⁺ removal mechanisms. The efficiency of crab carapace for Sr²⁺ removal from aqueous media (with adsorption capacity 3.92 mg/g.) at industrially relevant concentrations, together with its mechanical stability, implementation and disposal cost, makes it a competitive option compared to other biosorbents and commercial materials reported in the literature.

New Chitosan/Iron Oxide Composites: Fabrication and Application for Removal of Sr2+ Radionuclide from Aqueous Solutions

Here, we discuss the fabrication and problems of application of chitosan-based composite materials for the removal of hazardous metal ions from tap water and wastewater. The chitosan-based composites containing iron oxides for the uptake of Sr²⁺ ions were fabricated via a co-precipitation method with variation of the iron/chitosan ratio and pH of the medium. The morphology and composition of the fabricated sorbents were characterized using scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX) and X-ray diffraction (XRD) analysis. We have shown that the suggested fabrication approach allows for a homogeneous distribution of the inorganic phase in the polymer matrix. Investigations of the sorption performance of the composites have shown that they are efficient sorbents for ⁹⁰Sr radionuclides uptake from tap water. The composite sorbent containing amorphous iron oxide in a chitosan matrix and calcined at 105 °C showed the best sorption characteristics. We have also demonstrated that there is an optimal iron oxide content in the composite: with increasing oxide content, the efficiency of the sorbents decreases due to poor stability in solution, especially in alkaline media. The alternative approach yielding magnetic chitosan-based composites with sufficiently good sorption performance and stability in neutral and weakly alkaline media is suggested.

A new technique for removing strontium from seawater by coprecipitation with barite

Strontium (Sr) removal from seawater has recently attracted attention from an environmental perspective after the Fukushima Nuclear Power Plant accident, but there is a lack of effective removal techniques for removing Sr from seawater. In the present study, we looked at the removal efficiency of Sr by using barite (BaSO₄) under various experimental conditions to develop techniques for the direct removal of Sr from seawater. The effects of pH, saturation state, ionic strength, competitive ions, and [Ba²⁺]/[SO₄^2-] ratio in the initial aqueous solution were examined. Among them, Sr uptake by barite was found to be dependent on pH, saturation state, and [Ba²⁺]/[SO₄^2-] ratio in initial aqueous solution, showing that most of the aqueous Sr can be removed from the aqueous solution by adjusting these parameters. However, the effects of ionic strength and competitive ions were negligible, suggesting the effectiveness of its application to removal of Sr from seawater. Batch experiments were also conducted in a seawater system, and a rather high removal efficiency of Sr from seawater (more than 90%) was achieved. Considering its high removal and retention efficiency of Sr in seawater systems, barite is a reliable material for the removal of Sr from seawater.

Preparation of alginate fibers coagulated by calcium chloride or sulfuric acid: Application to the adsorption of Sr2

The adsorption behavior of Sr²⁺ over alginate (Alg) fibers prepared by wet spinning was investigated. Different grades of sodium alginate (Alg-Na) were chosen. The Alg fibers were obtained by coagulation of 1% H₂SO₄ (Alg-acid) or 5% CaCl₂ (Alg-Ca) solutions. In addition, the Sr²⁺ adsorption percentages of the spherical Alg-Ca beads with a 0.672-mm-diameter was 70.64% which was significantly lower than that Alg-Ca fibers (79.49%). These results suggested that the fibrous shape is more suitable than the spheres as an adsorbent from sea water. For Sr²⁺ adsorption capacities using different Alg fibers, the Alg-acid fibers obtained from 12% IL-2 and 8% I-2 grade solutions reached adsorption equilibrium at 99.88 and 99.27%, respectively, within 3 min. However, the Alg-Ca fiber obtained from 8% I-2 grade solution reached equilibrium at 80.01% within 30 min. Moreover, the Alg-acid fiber obtained from 8% I-2 grade solution adsorbed up to 34 mg/g of Sr²⁺ at an initial concentration of 1700 mg/L solutions. However, when Sr²⁺ co-existing cations (Ca²⁺, Na⁺, and mixtures of them) the adsorption capacity of the Alg-Ca fiber obtained from 8% I-2 grade solution slightly decreased since the egg-box structure of Alg-Ca fiber favored the selective Sr²⁺ adsorption and subsequent ion exchange with Ca²⁺.

Surface interactions of Cs+ and Co2+ with bentonite

Uptake of radioactive metal species from soils and solutions by clay particles could be a treatment option due to simplicity of operation and economic cost. In this concern, adsorption behavior of Cs⁺ or Co²⁺ onto bentonite as a function of contact time, pH, initial metal concentration, ionic strength, and temperature was studied by batch adsorption technique. Adsorption isotherm data were interpreted by Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. Bentonite exhibited maximum adsorption capacity of 83.3 mg g^-1 for Cs⁺ and 15.9 mg g^-1 for Co²⁺. Presence of humic acid (HA) as a representative model of organic matter did not significantly affect the adsorption capacity of bentonite for Cs⁺, whereas it increased the adsorption capacity of bentonite for Co²⁺. Thermodynamic parameters, standard enthalpy (ΔH°), standard entropy (ΔS°), and standard free energy (ΔG°) were determined through batch adsorption experiments performed at four different temperatures of 288, 298, 318, and 338 K. Co²⁺ adsorption onto bentonite showed an endothermic reaction (ΔH° = 13.6 kJ mol^-1) whereas Cs⁺ adsorption displayed an exothermic nature (ΔH° = -4.65 kJ mol^-1). Negative values of ΔG° and positive values of ΔS° indicated the feasibility and spontaneous nature of adsorption processes and more disordered form after adsorption.

Magnetite-based adsorbents for sequestration of radionuclides: a review

As a result of extensive research efforts by several research groups, magnetite-based materials have gained enormous attention in diverse fields including biomedicine, catalysis, energy and data storage devices, magnetic resonance imaging, and environmental remediation. Owing to their low production cost, ease of modification, biocompatibility, and superparamagnetism, the use of these materials for the abatement of environmental toxicants has been increasing continuously. Here we focus on the recent advances in the use of magnetite-based adsorbents for removal of radionuclides (such as 137Cs(i), 155Eu(iii), 90Sr(ii), 238U(vi), etc.) from diverse aqueous phases. This review summarizes the preparation and surface modification of magnetite-based adsorbents, their physicochemical properties, adsorption behavior and mechanism, and diverse conventional and recent environmental technological options for the treatment of water contaminated with radionuclides. In addition, case studies for the removal of radionuclides from actual contaminated sites are discussed, and finally the optimization of magnetite-based remedial solutions is presented for practical application.

Polymer-based nanocomposites for heavy metal ions removal from aqueous solution: a review

A review of versatile polymer-based composites containing different functional organic and/or inorganic counterparts for the removal of hazardous metal ions from wastewater solutions.

Core–shell zeolite@Alg–Ca particles for removal of strontium from aqueous solutions

A core–shell zeolite@Alg–Ca adsorbent was synthesized by a simple method of coaxial electrospinning and applied for the removal of Sr(ii) ions from aqueous solution.

Immobilization of Metal Hexacyanoferrate Ion-Exchangers for the Synthesis of Metal Ion Sorbents--A Mini-Review

Metal hexacyanoferrates are very efficient sorbents for the recovery of alkali and base metal ions (including radionuclides such as Cs). Generally produced by the direct reaction of metal salts with potassium hexacyanoferrate (the precursors), they are characterized by ion-exchange and structural properties that make then particularly selective for Cs(I), Rb(I) and Tl(I) recovery (based on their hydrated ionic radius consistent with the size of the ion-exchanger cage), though they can bind also base metals. The major drawback of these materials is associated to their nanometer or micrometer size that makes them difficult to recover in large-size continuous systems. For this reason many techniques have been designed for immobilizing these ion-exchangers in suitable matrices that can be organic (mainly polymers and biopolymers) or inorganic (mineral supports), carbon-based matrices. This immobilization may proceed by in situ synthesis or by entrapment/encapsulation. This mini-review reports some examples of hybrid materials synthesized for the immobilization of metal hexacyanoferrate, the different conditionings of these composite materials and, briefly, the parameters to take into account for their optimal design and facilitated use.

Fundamental studies of novel zwitterionic hybrid membranes: kinetic model and mechanism insights into strontium removal

A series of zwitterionic hybrid membranes were prepared via the ring opening of 1,3-propanesultone with the amine groups in the chains of TMSPEDA and a subsequent sol-gel process. Their kinetic models for strontium removal were investigated using three two-parameter kinetic equations (i.e., Lagergren pseudo-first order, pseudo-second order, and Elovich models). Adsorption mechanism was evaluated using intraparticle diffusion model, diffusion-chemisorption model, and Boyd equation. It was found that the adsorption of strontium ions on these zwitterionic hybrid membranes fitted well with the Lagergren pseudo-second order model. Mechanism insights suggested that diffusion-chemisorption was one of the main adsorption mechanisms. Boyd equation exhibited that film-diffusion mechanism might be the control process during the starting period. These findings are very useful in strontium removal from the stimulated radioactive wastewater.

Chitosan-based biosorbents: modification and application for biosorption of heavy metals and radionuclides

Heavy metal pollution is a serious environmental problem in the world, especially in developing countries. Among different treatment technologies, biosorption seems a promising alternative method. Chitosan-based biosorbents are potential and effective for heavy metal removal from aqueous solution. The preparation and characterization of the natural polymer chitosan, modified chitosan and chitosan composites, and their application for the removal or recovery of toxic heavy metals, precious metals and radionuclides from wastewater were introduced. Chitosan structures and their properties, chitosan modifications (physical conditioning and chemical modification), blends and composites as well as the metal sorption by chitosan-based biosorbents were briefly presented. The metal sorption capacities, influence of intrinsic nature of metal ions, pH and contact time, desorbing agents, isotherm and kinetics models, biosorption mechanisms were discussed.

Investigation of strontium and uranium sorption onto zirconium-antimony oxide/polyacrylonitrile (Zr-Sb oxide/PAN) composite using experimental design

A study on the sorption of strontium (Sr(2+)) and uranium (UO2(2+)) onto zirconium-antimony oxide/PAN (Zr-Sb oxide/PAN) composite was conducted. The zirconium-antimony oxide was synthesized and was then turned into composite spheres by mixing it with polyacrylonitrile (PAN). The single and combined effects of independent variables such as initial pH, temperature, initial ion concentration and contact time on the sorption of Sr(2+) and UO2(2+) were separately analyzed using response surface methodology (RSM). Central composite design (CCD) was separately employed for Sr(2+) and UO2(2+) sorption. Analysis of variance (ANOVA) revealed that all of the single effects found statistically significant on the sorption of Sr(2+) and UO2(2+). Probability F-values (F=2.45 × 10(-08) and F=9.63 × 10(-12) for Sr(2+) and UO2(2+), respectively) and correlation coefficients (R(2)=0.96 for Sr(2+) and R(2)=0.98 for UO2(2+)) indicate that both models fit the experimental data well. At optimum sorption conditions Sr(2+) and UO2(2+) sorption capacities of the composite were found as 39.78 and 60.66 mg/g, respectively. Sorption isotherm data pointed out that Langmuir model is more suitable for the Sr(2+) sorption, whereas the sorption of UO2(2+) was correlated well with the Langmuir and Freundlich models. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° indicate that Sr(2+) and UO2(2+) sorption processes are endothermic and spontaneous.

Application of magnetic chitosan composites for the removal of toxic metal and dyes from aqueous solutions

Magnetic chitosan composites (MCCs) are a novel material that exhibits good sorption behavior toward various toxic pollutants in aqueous solution. These magnetic composites have a fast adsorption rate and high adsorption efficiency, efficient to remove various pollutants and they are easy to recover and reuse. These features highlight the suitability of MCCs for the treatment of water polluted with metal and organic materials. This review outlines the preparation of MCCs as well as methods to characterize these materials using FTIR, XRD, TGA and other microscopy-based techniques. Additionally, an overview of recent developments and applications of MCCs for metal and organic pollutant removal is discussed in detail. Based on current research and existing materials, some new and futuristic approaches in this fascinating area are also discussed. The main objective of this review is to provide up-to-date information about the most important features of MCCs and to show their advantages as adsorbents in the treatment of polluted aqueous solutions.