Metal hexacyanoferrates-based adsorbents for cesium removal

Enhanced uranium removal from aqueous solution by core-shell Fe0@Fe3O4: Insight into the synergistic effect of Fe0 and Fe3O4

In this study, Fe0@Fe3O4 was synthesized and used to remove U(VI) from groundwater. Different experimental conditions and cycling experiments were used to investigate the performance of Fe0@Fe3O4 in the U(VI) removal, and the XRD, TEM, XPS and XANES techniques were employed to characterize the Fe0@Fe3O4. The results showed that the U(VI) removal efficiency of Fe0@Fe3O4 was 48.5 mg/g that was higher than the sum of removal efficiency of Fe0 and Fe3O4. The uranium on the surface of Fe0@Fe3O4 mainly existed as U(IV), followed by U(VI) and U(V). The Fe0 content decreased after reaction, while the Fe3O4 content increased. Based on the results of experiments and characterization, the enhanced removal efficiency of Fe0@Fe3O4 was attributed to the synergistic effect of Fe0 and Fe3O4 in which Fe3O4 accelerated the Fe0 corrosion that promoted the progressively formation of Fe(II) that promoted the reduction of adsorbed U(VI) to U(IV) and incorporated U(VI) to U(V). The performance of Fe0@Fe3O4 at near-neutrality condition was better than at acidic and alkalic conditions. The chloride ions, sulfate ions and nitrate ions showed minor effect on the Fe0@Fe3O4 performance, while carbonate ions exhibited significant inhibition. The metal cations showed different effect on the Fe0@Fe3O4 performance. The removal efficiency of Fe0@Fe3O4 decreased with the number of cycling experiment. Ionizing radiation could regenerate the used Fe0@Fe3O4. This study provides insight into the U(VI) removal by Fe0@Fe3O4 in aqueous solution.

Physicochemical and pharmacotechnical characterization of Prussian blue for future Prussian blue oral dosage forms formulation

Ferric hexacyanoferrate, Fe4 [Fe(CN)6]3 · xH2O, known as Prussian blue (PB), has proven its effectiveness as an antidote in cases of accidental poisoning or poisoning caused by radioactive materials such as cesium (Cs) and thallium (Tl); which due to their solubility in water, when absorbed by the human body, cause serious damage to vital organs. The local development of a drug with PB as an active ingredient arises as a response to the civil and military needs established within the Ministry's pharmacy request for national defense. This fact contemplates the circumstances related to public health protection in the nuclear, radiological, biological and chemical (NRBQ) of the emergency institutions in health and national security. In this paper and by using various analytical techniques, the characterization of the locally synthesized PB with pharmaceutical quality has been described, as a first step to predict its behavior in the preparation of a drug that contains it as an active ingredient. The research findings demonstrate that locally synthesized PB is suitable for use in oral dosage forms, enabling the local development of drug formulations incorporating PB, thus being able to potentially become a main resource in the treatment of Cs and Tl poisoning in any accidental or intended of the population. This development opens up the possibility of creating drug formulations that incorporate PB at a local level, making it a potentially significant resource in the treatment of Cs and Tl poisoning. The ability to locally produce and utilize PB in oral dosage forms could be crucial in addressing cases of accidental or intentional exposure within the population. This advancement not only contributes to the scientific understanding of PB but also holds promising implications for practical applications in public health and emergency situations.

A Prussian blue analog-based copper-aluminum layered double hydroxide for cesium removal from water: fabrication, density functional theory-based molecular modeling, and the adsorption mechanism

A new type of adsorbent, a Prussian blue analog-based copper-aluminum layered double hydroxide (PBA@CuAl-LDH), was successfully synthesized using a one-step method for the removal of radioactive Cs+ from wastewater. The adsorption performance, characteristics and the underlying adsorption mechanism of PBA@CuAl-LDH were systematically examined. The results showed that PBA@CuAl-LDH exhibited excellent adsorption performance, with a maximum adsorption capacity of 109.2 mg g-1. Over 85% of PBA@CuAl-LDH can be recycled, and the material exhibited only a 6.6% loss in adsorption performance. The adsorption process was well-fitted using the pseudo-second-order kinetic model and the Freundlich isotherm model, revealing the surface heterogeneity of the composite adsorbent. A molecular model of PBA@CuAl-LDH was constructed by combining density functional theory and multiple instrumental characterization techniques. Our results indicate that PBA crystals can be generated between layers and on the surface. Ion exchange was revealed as the main adsorption mechanism of Cs+ by PBA@CuAl-LDH. Specifically, the interstitial spaces of the PBA crystals generated between the layers and on the surface played an important role in ion exchange. These findings provide concrete theoretical support for radioactive pollution control and have significant value in directing the fabrication of cesium removal materials and their future engineering application.

A Prussian-blue analogue (PBA) ion-chromatography-based technique for selective separation of Rb+ (as RbCl) from brines

A new general method is presented for separating pure RbCl(s) from solutions rich in Na+ and K+. The method relies on Rb+ adsorption via ion exchange performed by self-synthesized PES coated Zn-Hexa-Cyanoferrate material. The procedure starts by passing the wastewater through an ion exchange column, which is thereafter regenerated with 1 M NH4Cl. If the Rb+ absorbed on the column does not reach a minimal predetermined value (e.g., 8%, eq-based), the ammonia is removed by sublimation and the remaining salts are passed again through a Na+-preadsorbed column. Once the adsorbed Rb+ is substantial (>8%), a chromatography-based separation between Rb+ and Na+/K+ is performed, using a 2nd column, fully pre-adsorbed with NH4+. First, 0.05M NH4+-solution is used to extract Na+ and K+ out of the first column, along with a small Rb+ mass, which is thereafter partly re-adsorbed on the second column, while Na+/K+ ions are not. Once the exiting eluent solution is devoid of the competing ions, 1M NH4+-solution is used to extract all the remaining Rb+ into the regeneration solution, which is thereafter subjected to water evaporation followed by NH3/HCl sublimation to result in pure RbCl(s) product. We used theoretical simulations corroborated by empirical results to present proof of concept for the suggested approach. A detailed cost analysis (Capex and Opex) reveals that the RbCl(s) production cost does not exceed ∼25% of the current salt price.

Removal of radionuclide 99Tc from aqueous solution by various adsorbents: A review

Technetium isotope 99Tc is a main radioactive waste produced in the process of nuclear reaction, which has the characteristics of long half-life and strong environmental mobility, and can be bio-accumulated in organisms, resulting in serious threat to human health and ecosystem. Adsorption method is widely used in the field of removing radionuclides from water due to the advantages of high treatment rate, simple and mature industrial application. In this review paper, the recent advances in research and application of various adsorption materials for 99Tc pollution treatment were summarized and analyzed for the first time, including inorganic adsorbents, such as activated carbon, zero-valent iron, metallic minerals, clay minerals, layered double hydroxides (LDHs), tin-based materials, and sulfur-based materials; organic adsorbents, such as porous organic polymers (POPs), covalent-organic frameworks (COFs), metal-organic frameworks (MOFs), and ion exchange resin; and biological adsorbents, such as biopolymers (chitosan, cellulose, alginate), and microbial cells. The performance characteristics and the adsorption kinetics and isotherms of various adsorption materials were discussed. This review could deepen the understanding of the adsorptive removal of 99Tc from aqueous solution, and provide a reference for the future research in this field.

Design and Synthesis of Covalently Tethered "IsoG-Star" as Recyclable Host for Selective Cesium Separation

The isoguanosine self-assembled pentamer (isoG-star) has exhibited remarkable selectivity for Cs+ binding over competing alkali and alkali earth metal cation, rendering it a promising extractor for radioactive waste 137Cs separation. However, to make isoG-star a pracrtical material for Cs+ isolation, the development of recyclable isoG-star material is required. In this study, a systematic screening of functional isoG derivatives was performed. By employing well-defined complex formation and post-assembly modification, a covalently tethered isoG5-star was prepared through olefin metathesis, utilizing a designed isoG monomer. The application of this newly developed covalently linked isoG-star enabled selective Cs+ extraction, followed by controled solvent-induced H-bond dessociation. This resulted in the creation of a recyclable Cs+ extractor, demonstrating excellent cation selectivity and good reusability (over seven cycles) the first time. Consequently, this new supramolecular macrocycle offers a practical new platform for the treatment of radiocesium (134Cs and 137Cs) in an environmentally friendly and highly effective manner.

Cation-Intercalated Lamellar MoS2 Adsorbent Enables Highly Selective Capture of Cesium

Highly selective capture of cesium (Cs+) from complex aqueous solutions has become increasingly important owing to its (133Cs) indispensable role in some cutting-edge technologies and the environmental mobility of radioactive nuclide (137Cs) from nuclear wastewater. Herein, we report the development of cation-intercalated lamellar MoS2 as an effective Cs+ adsorbent with the advantages of facile synthesis and highly tunable layer spacing. Two types of cations, including Na+ and NH4+, were employed for the intercalations between adjacent layers of MoS2. The results demonstrated that the adsorption capacity of the NH4+-intercalated material (M-NH4+, 134 mg/g) for Cs+ clearly outperformed the others due to higher loading percentages of cations and larger layer spacing. The cesium partition coefficients for M-NH4+ in the presence of 100-fold competing ions all exceed 1 × 103 mL/g. A simulated complex aqueous solution containing 15.37 mg/L Cs+ and highly excess of competing ions Li+, Na+, K+, Mg2+, and Ca2+ (20-306 times higher) was introduced to prove the practical application potential using our best-performing M-NH4+, showing a good to excellent partition ability of Cs+ among other cations, especially for Cs/K and Cs/Na with separation factors of 58 and 212, respectively. The adsorption and selectivity mechanisms were clearly elucidated using various advanced techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. These results revealed that the good selectivity for Cs+ can be ascribed to the differences in Lewis acidities, hydration energy, cation sizes, and in particular, the divergence of coordination modes which was successfully achieved after tuning the layer distance via the cation intercalation strategy. In addition, the material has fast kinetics (<30 min), wide range of pH tolerance (4-10), and good reusability. Overall, our studies point out that the tunable lamellar MoS2-based materials are promising adsorbents for Cs+ capture and separation.

Sulfate Radical-Based Degradation of Organic Pollutants: A Review on Application of Metal-Organic Frameworks as Catalysts

The degradation of organic pollutants present in domestic and industrial effluents is a matter of concern because of their high persistence and ecotoxicity. Recently, advanced oxidation processes (AOPs) are being emphasized for organic pollutant removal from effluents, as they have shown higher degradation efficiencies when compared to conventional activated sludge processes. Sulfate radical-based methods are some of the AOPs, mainly carried out using persulfate (PS) and peroxymonosulfate (PMS), which have gained attention due to the ease of sulfate radical generation and the effective degradation of organic molecules. PMS is gaining more popularity because of its high reactivity and ability to generate excess sulfate radicals. PMS has been the major focus; therefore, its mechanism has been explained, and limitations have been elaborated. The involvement of metal-organic frameworks for PMS/PS activation applied to organic pollutant removal and recent advances in the application of biochar and hydrogel-assisted metal-organic frameworks have been discussed.

Efficient adsorptive removal of Co2+ from aqueous solution using graphene oxide

This study aimed to utilize synthesized graphene oxide (GO) for adsorptive removal of cobalt ions and investigate the adsorption mechanism using advanced techniques such as X-ray absorption spectra (XAFS). The GO was synthesized via an improved Hummers method, resulting in high surface area (93.7 m2/g) and abundant oxygen-containing functional groups. Various characterizations, including SEM, TEM, Raman, FT-IR, TG, potentiometric titrations, and N2 sorption-desorption measurements, were employed to characterize the GO. The adsorption behavior of GO towards Co2+ was investigated, and the results showed that the adsorption process followed a pseudo-second-order kinetic model and the Langmuir model, with a maximum sorption capacity of 93.7 mg/g. The adsorption process was chemisorption and endothermic, with GO showing adsorption selectivity order of Co2+ > Sr2+ > Cs+. Based on various characterizations such as X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), FT-IR, and XPS, the sorption mechanism of Co2+ onto GO was discussed, with the results indicating that coordination and electrostatic interaction were the primary adsorption mechanisms, with oxygen-containing functional groups playing a vital role. The first coordinating atom for Co2+ was O, and the coordination environment was similar to that of cobalt acetate and CoO. Overall, this study provides comprehensive understanding of the adsorption behavior and mechanism of Co2+ onto GO, highlighting its potential as an effective adsorbent for removing nuclides from aqueous solution.

Electro-adsorption of Cs(I) ions from aqueous solution by capacitive deionization using ACC/MoO3 composite electrode

The separation of Cs⁺ from radioactive wastes is of paramount importance, but still a challenge. In this paper, ACC/MoO₃ composite electrode was prepared and used for the separation of Cs⁺ by capacitive deionization (CDI). The electrode materials were characterized by SEM-EDS, FTIR, XPS before and after adsorption experiments. The composite electrode was composed of ACC and hexagonal tunnel structure of MoO₃, which had a mesoporous structure. The specific surface area, average pore diameter, total pore volume and maximal specific capacitance were 170.4 m² g^-1, 2.127 nm, 0.906 cm³ g^-1 and 76.3 F g^-1, respectively. The adsorption kinetics, isotherms, and the mass transfer process were analyzed, and the possible adsorption mechanism was proposed. The removal efficiency of Cs⁺ increased with the increase of voltage and the decrease of Cs⁺ concentration, which reached 44.7 % after 240 min when voltage was 1.2 V and Cs⁺ concentration was 5 mg L^-1. The Cs⁺ adsorption onto the ACC/MoO₃ composite was multi-layer adsorption and the adsorption to active sites (AAS) was the rate-limiting step. Overall, the ACC/MoO₃ composite was a potential electrode for Cs⁺ separation.

Synthesis of heated aluminum oxide particles impregnated with Prussian blue for cesium and natural organic matter adsorption: Experimental and machine learning modeling

Heated aluminum oxide particles impregnated with Prussian blue (HAOPs-PB) are synthesized for the first time using different molar ratios of aluminum sulfate and PB to improve the adsorption of cesium (¹³³Cs⁺) and natural organic matter (NOM) from an aqueous solution. The Cs⁺ adsorption from various aqueous solutions, including surface, tap and deionized water by synthesized HAOPs-PB, is investigated. The influencing factors such as HAOPs-PB mixing ratio, pH and dosage are studied. In addition, pseudo 1st and 2nd order is tested for adsorption kinetics study. A machine learning model is developed using gene expression programming (GEP) to evaluate and optimize the adsorption process for Cs⁺ and NOM removal. Synthesized adsorbent showed maximum adsorption at a 1:1 M ratio of aluminum sulfate and PB in DI, tap, and surface water. The pseudo 2nd order kinetics model described the Cs ⁺ adsorption by HAOPs-PB more accurately that indicating physiochemical adsorption. Adsorption of Cs⁺ showed an increasing trend with higher HAOPs-PB concentration, while high pH also favored the adsorption. Maximum NOM adsorption is found at a higher HAOPs-PB dosage and a neutral pH value. Furthermore, the proposed GEP model shows outstanding performance for Cs⁺ adsorption modeling, whereas a modified-GEP model presents promising results for NOM adsorption prediction for testing dataset by learning the relationship between inputs and output with R² values of 0.9348 and 0.889, respectively.

The recovery of strontium ions from seawater reverse osmosis brine using novel composite materials of ferrocyanides modified roasted date pits

In this study, three types of adsorbents were used to remove and recover strontium ions (Sr2+) from aqueous and brine solution of seawater reverse osmosis (SWRO), namely roasted date pits (RDP) and RDP modified using copper and nickel salts of potassium hexacyanoferrates to obtain RDP-FC-Cu, and RDP-FC-Ni, respectively. Additionally, the influence of various parameters, including pH, temperature, initial concentration, and co-existing ions was also evaluated. The results revealed that pH 10 was the optimum pH in which the maximum Sr2+ ions were adsorbed. Additionally, all adsorbents had a high adsorption capacity (99.9 mg/g) for removing Sr2+ ions at the highest concentration (100 mg/L) and a temperature of 45 °C was found to be the optimum temperature. A scanning electron microscopy for the adsorbents before and after the adsorption of strontium showed the remarkable pore filling onto the active sites of all adsorbents. The thermodynamics parameter demonstrated that the adsorption occurred in an endothermic environment, and that, the reaction was spontaneous, and favorable at all the temperatures investigated. According to isotherm studies, the Langmuir model was the best-fit isotherm model; indicating that strontium adsorption involved the formation of monolayers and multilayers at higher temperatures (45 °C). Furthermore, high desorption percentages (above 90%) were achieved for all the adsorbents when an HCl concentration of 0.5 M was used. This showed the high reusability of the adsorbents. Lastly, the adsorption of strontium from the SWRO brine containing a number of metal ions was extremely sufficient as all the adsorbents were efficient to adsorb a high amount of Sr2+ despite the presence of other competing ions.

Synthesis of N-isopropyl acrylamide copolymerized acrylic acid caped with Dibenzo-18-crown-6 composite for selective separation of Co-60 radioisotope from radioactive liquid waste containing Cs-137

A new selective polymeric composite capped with crown ether was successfully synthesized using N-isopropyl acrylamide copolymerized acrylic acid paired with Dibenzo-18-crown-6, P(NIPAm-Co-AA-DB 18C-6), by Gamma irradiation and ultrasonic homogenizer polymerization. Scanner electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and dynamic light scattering were used to characterize the selected polymeric composite's chemical and physical constitution. SEM shows a rough irregular surface, and FTIR spectra confirmed the function groups of P(NIPAm-Co-AA-DB 18C-6). Moreover, a systematic study of monomer and crown ether concentration was investigated to enhance the composite's performance. The behavior of the synthetic composite toward the selective separation of Co-60 from Cs-137 in a binary system was evaluated. Effects of pH, contact time, and initial ion concentration were investigated in a batch mode and the maximum capacity reached 108.0 mg/g for Co-60 and 82.0 mg/g for Cs-137. Four Kinetic models were investigated (pseudo-first-order, pseudo-second-order, Elovich, and Intra-particle diffusion). Regarding the calculated parameters, pseudo-second-order and Elovich models are the most describing the sorption process, indicating the chemisorptions process. Six adsorption isotherms were examined, two-parameter models (Langmuir, and Freundlich) and three-parameter models (Redlich-Peterson, Khan, Sips, and Hills). The best-fitted isotherm was identified using three error methodological approaches: the correlation coefficient (R2), the chi-square test (χ2), and the root-mean-square error. Isotherm models fit the experimental values in the following sequence: Khan > Rdlish-Peterson > Hills > Sips. Finally, an application for column separation was conducted, and Co-60 was completely separated from Cs-137 by 0.1 M HNO3. These findings indicate promising applications in the successive separation of Co-60 from radioactive liquid waste containing Cs-137 from Egyptian reactors.

Graphical abstract

Sustainable Removal of Ammonia from the Anaerobic Digester Supernatant Line Using a Prussian Blue Analogue (PBA) Composite Adsorbent

This paper reports on the physico-chemical removal of NH4+ from the supernatant line in municipal wastewater treatment plants (WWTPs), using zinc-hexa-cyano-ferrate (ZnHCF) beads. The work is divided into three parts: First, the characteristics of three (Zn-, Co-, Ni-) types of HCF beads were determined, with a finding that ZnHCF was the most suitable for the purpose of this work. Second, synthetic and actual supernatant wastewater was passed through a ZnHCF column for many cycles until apparent steady-state results were attained. Due to the very high affinity of the beads toward NH4+ and the much lower affinity toward competing cations, the same regeneration solution could be used for many cycles (20 cycles in this work) without affecting the following adsorption breakthrough curve efficiency and the operational capacity, which was >88% at the end of all adsorption steps. Finally, a cost analysis was performed, revealing that the cost of removing ~500 mg/L of ammonia from the supernatant line is ~$0.02 per m3 of raw wastewater flowing into the plant if the ammonia is recaptured and sold as NH4Cl. This may be cost-effective when the WWTP receives a higher-than-planned load, and an incentive exists for alleviating the ammonia load on the oxidation reactor.

Nanocellulose-Based Adsorbents for Heavy Metal Ion

Heavy metal ions in industrial sewage constitute a serious threat to human health. Nanocellulose-based adsorbents are emerging as an environmentally friendly material platform for heavy metal ion removal based on their unique properties, which include high specific surface area, excellent mechanical properties, and biocompatibility. In this review, we cover the most recent works on nanocellulose-based adsorbents for heavy metal ion removal and present an in-depth discussion of the modification technologies for nanocellulose in the process of assembling high-performance heavy ion adsorbents. By introducing functional groups, such as amino, carboxyl, aldehyde, and thiol, the assembled nanocellulose-based adsorbents both remove single heavy metal ions and can selectively adsorb multiple heavy ions in water. Finally, the remaining challenges of nanocellulose-based adsorbents are pointed out. We anticipate that this review will provide indispensable guidance on the application of nanocellulose-based adsorbents for the removal of heavy metal ions.

Rethinking of the intraparticle diffusion adsorption kinetics model: Interpretation, solving methods and applications

Adsorption is a widely used unit process in various fields, such as chemical, environmental and pharmaceutical, etc. The intraparticle diffusion adsorption kinetics model is one of the most widely used adsorption kinetics models. However, the application and solving method of this model have yet to be discussed. This model has two forms (q_t = kt^1/2 and q_t = kt^1/2 + constant, where q_t is the adsorption capacity at time t, k and constant are the model parameters), which have not been unified yet. Moreover, the interpretation of this kinetics model lacks a theoretical basis (if the line passes through the origin point (0, 0), the adsorption is dominated by the intraparticle diffusion; if not, it is a multiple adsorption process). In this study, we analyzed the proper equations of the intraparticle diffusion model and their applications, discussed the interpretation of the mass transfer steps revealed by this model, and provided the solving methods. The result indicated that the piecewise function q_t = k₁t^1/2 (0 ≤ t ≤ t₁); q_t - q_t = t1 = k₂(t - t₁)^1/2 (t₁ < t ≤ t₂) is the proper form of this model. The adsorbate diffusion in the pores inside the adsorbent is the mass transfer step revealed by this model. The statistical parameters should be used to evaluate the fitting results instead of judging whether the model lines pass through the origin point (0, 0). We provide the solving methods to use the Origin and Microsoft EXCEL software to solve the model. Our study established the method for application of the intraparticle diffusion model.

Response of Amaranthus tricolor to cesium stress in hydroponic system: Growth, photosynthesis and cesium accumulation

Remediation of the cesium-contaminated environment is of paramount importance, and phytoremediation is a cost-effective and green technique. In this paper, the response of Amaranthus tricolor to cesium ions in hydroponic solution was investigated at various cesium concentration (0, 0.05, 0.2, 0.4 and 0.6 mM), in terms of the growth weight, height and photosynthesis. The maximal Cs content in stems and leaves of A. tricolor was 13.05 mg/g dry wt under spiked Cs level of 0.4 mM in solution. The maximal transfer factor (TF) and bioconcentration factor (BCF) were 1.87 and 181.25 respectively, when the corresponding Cs content in roots and shoots was 7.04 mg/g and 13.05 mg/g dry wt respectively. TFs are higher than 1 in the conditions of normal plant growth. The growth of A. tricolor was enhanced after the treatment of Cs at low concentrations (0.05 and 0.2 mM), while it was inhibited at 0.4 and 0.6 mM. The leaf number and dry weight of stem, leaf parts and root parts were maximum at the spiked cesium level of 0.2 mM, which significantly increased by 19.19%, 47.56% and 94.56% respectively, compared with the control samples. Under 0.6 mM cesium stress, curl and withering of the leaves occurred, and the plant growth and cesium accumulation dropped to the minimum. Cs at the spiked level of 0.6 mM in solution inhibited the performance of PSII, especially in terms of blockage in electron transfer process beyond Q_A and restraint of P700 reduction. On contrast, the performance of PSII was enhanced by the spiked Cs at level of 0.2 mM, leading to the growing density of reaction centers per excited cross-section and increasing electron transfer process beyond Q_A. In summary, A. tricolor has potential for remediating the Cs-contaminated environment.

Copolymerization of anthranilic acid and o-phenylenediamine by a free radical in the presence of nanoparticles of copper hexacyanoferrates for the removal of cesium ions in aqueous solutions

Core–shell nanocomposite of copper hexacyanoferrate copolymer of anthranilic acid with o-phenylenediamine (CHCF-poly-AA-co-OPD)) was synthesized and used as ion exchanger for the removal of cesium ions from wastewater. The nanocomposite was prepared by implantation of CHCF nanoparticles into the copolymer of poly(AA-co-OPD) during the polymerization process. By transmission electron microscope, scanning electron microscope and Brunauer–Emmett–Teller, the surface morphology and the porous structure were investigated. The physicochemical characterization of the prepared core–shell nanocomposite was carried out by FT-IR spectroscopy, XRD and thermogravimetric analysis. As a function in pH, metal ion concentration, shaking time and temperature, the capacity of the CSNC toward cesium ions and the behaviors of the process were studied. The results illustrated that the maximum capacity was recorded 1.35 mmol g−1 at pH 11, 10 mmol L−1 Cs+ and 25 °C. Also, Langmuir, Freundlich, Temkin and Dubinin–Radushkevich (D–R) isotherms models were studied, in which the data were well fitted with Langmuir model, suggesting that the uptake of Cs+ was monolayer and homogeneous. Also, the adsorption kinetics data were fitted well to pseudo-second-order model. Thermodynamic parameters were calculated in the temperature from 25 to 60 °C, and the data revealed that Cs+ sorption was endothermic, spontaneous and more favorable at higher temperature. Up to 92% desorption of Cs+ was completed with 2 M KCl.

Selective and effective adsorption of cesium ions by metal hexacyanoferrates (MHCF, M = Cu, Co, Ni) modified chitosan fibrous biosorbent

Selective and effective adsorptive removal of radiocesium is of great importance in terms of nuclear waste management and environmental remediation, but is still challenging because of its radioactive and non-complexing nature. Herein, metal hexacyanoferrates (MHCF, M = Cu, Co, or Ni) modified fibrous chitosan was prepared by multiple sequential adsorption and self-assembly approach, and applied for the selective and effective adsorption of Cs⁺. The physically supported MHCF in chitosan fibers showed good crystallinity and stability, and the obtained fibrous composite has high specific surface area (18.2-29.4 m² g^-1). Moreover, MHCF crystals endowed the fibrous chitosan-based adsorbent with a high adsorption capacity and selectivity towards Cs⁺. Its adsorption kinetic and isotherm performance followed the pseudo second-order model and the Sips model. The q_m value of three fibrous MHCF/chitosan (M = Cu, Co, or Ni) composites was 24.9-70.3 mg g^-1. The fibrous CuHCF/chitosan composite had the highest q_m among the three composites. In summary, the modified chitosan can selectively and effectively remove Cs⁺ from complicated aqueous solutions.

Determination, Separation and Application of 137Cs: A Review

In the context of the rapid development of the world's nuclear power industry, it is necessary to establish background data on radionuclides of different samples from different regions, and the premise of obtaining such basic data is to have a series of good sample processing and detection methods. The radiochemical analysis methods of low-level radionuclides ¹³⁷Cs (Cesium) in environmental and biological samples are introduced and reviewed in detail. The latest research progress is reviewed from the five aspects of sample pretreatment, determination, separation, calculation, application of radioactive cesium and the future is proposed.

Highly selective and easily regenerated porous fibrous composite of PSF-Na2.1Ni0.05Sn2.95S7 for the sustainable removal of cesium from wastewater

The removal of ¹³⁷Cs from radioactive wastewater remains a huge challenge due to the interference of many coexisting ions. Several tin chalcogenides (X₂Sn₃Y₇, XNa, K; YTe, Se, S) were synthesized and screened for highly selective cesium removal from radioactive wastewater. It was found that Na₂Sn₃S₇ showed the best adsorption performance for low cesium concentrations. Especially after nickel doping, the adsorption capacity and thermal stability of the adsorbent were significantly enhanced. Its maximum adsorption capacity reached 436.72 mg·g^-1 within only 5 min and adsorption performance kept active in the pH range of 2-12. After being coated with a porous polysulfone (PSF) fiber, the developed PSF-Na_2.1Ni_0.05Sn_2.95S₇ was applied to natural complex water with cesium concentration of 17.58 mg·L^-1. The separation factors between Cs⁺ and competitive ions ranged from 625.21 to 13123.21. It is noteworthy that NaNO₃ was an efficient regenerating agent and can be easily separated from the CsNO₃ mixture for cyclic utilization. Remarkably, only 45 min in each cycle of adsorption and desorption toward cesium was realized, and the adsorption properties hardly decreased even after 50 consecutive cycles. The above advantages make the proposed material an excellent candidate for efficient Cs⁺ removal and enrichment from wastewater.

On the Sintering Behavior of Nb2O5 and Ta2O5 Mixed Oxide Powders

A mixed oxide system consisting of Nb₂O₅ and Ta₂O_5, was subjected to annealing in air/hydrogen up to 950 °C for 1–4 h to study its sintering behavior. The thermogravimetric–differential scanning calorimetry (TGA–DSC) thermograms indicated the formation of multiple endothermic peaks at temperatures higher than 925 °C. Subsequently, a 30% Ta₂O₅ and 70% Nb₂O₅ (mol%) pellet resulted in good sintering behavior at both 900 and 950 °C. The scanning electron microscope (SEM) images corroborated these observations with necking and particle coarsening. The sintered pellets contained a 20.4 and 20.8% mixed oxide (Nb₄Ta₂O₁₅) phase, along with Ta₂O₅ and Nb₂O₅, at both 900 and 950 °C, indicating the possibility of the formation of a solid solution phase. In situ high-temperature X-ray diffraction (XRD) scans also confirmed the formation of the ternary oxide phase at 6 and 19.8% at 890 and 950 °C, respectively. The Hume–Rothery rules could explain the good sintering behavior of the Ta₂O₅ and Nb₂O₅ mixed oxides. An oxide composition of 30% Ta₂O₅ and 70% Nb₂O₅ (mol%) and a sintering temperature of 950 °C appeared adequate for fabricating well-sintered oxide precursors for subsequent electrochemical polarization studies in fused salts.

Adsorption of Co2+ and Sr2+ in aqueous solution by a novel fibrous chitosan biosorbent

In this study, a novel fibrous chitosan biosorbent was prepared using LiOH/KOH/urea/H₂O (4.5:7:8:80.5 by weight) as spinning solvent. The fibrous chitosan exhibited a higher adsorption capacity and a faster adsorption rate for Co²⁺ and Sr²⁺, compared with spherical chitosan due to its high specific surface area (16.9 m² g^-1), uniform fineness (24.1 μm), and good mechanical strength. The adsorption capacity of fibrous chitosan for Co²⁺ and Sr²⁺ was 31.3 mg g^-1 and 20.0 mg g^-1, respectively, which was higher than that of spherical chitosan (22.5 mg g^-1for Co²⁺ and 8.9 mg g^-1 for Sr²⁺). The coordination between -NH₂/-OH of chitosan and the nuclide ions was the rate-limiting step. The improvement of adsorption performance was due to the higher specific surface area which increased the exposure degree of functional groups (adsorptive sites). This new wet-spun fibrous chitosan biosorbent showed great potential in the adsorptive removal of nuclides ions from aqueous solution.

Copper ferrocyanide chemically immobilized onto a polyvinylidene fluoride hollow-fibre membrane surface for the removal of aqueous cesium

A method of chemically bonding copper ferrocynide (CuFC) to the surface of a PVDF hollow-fibre membrane (PVDF-CuFC) was designed and the resulting PVDF-CuFC was applied to the effective removal of aqueous cesium (Cs). In order to chemically immobilize CuFC on the surface of the PVDF hollow-fibre membrane, carboxyl groups were introduced onto the membrane surface (PVDF-COOH) to peptide bond with amine groups from CuFC. The introduction of the carboxyl group onto the surface of the PVDF hollow-fibre membrane was confirmed by Fourier-transform infrared spectroscopy (FT-IR), while the immobilization of CuFC was confirmed by scanning electron microscopy with energy dispersed spectroscopy, FT-IR, and thermogravimetric analysis. The PVDF-CuFC showed higher Cs adsorption kinetics and adsorption capacity than PVDF-COOH. Moreover, as the initial pH increased, the amount of Cs adsorption by PVDF-CuFC also increased. However, the amount of Cs adsorption at pH 10 was slightly less. The applicability of PVDF-CuFC as a filter type adsorbent for the treatment of a Cs-contaminated water source is demonstrated by continuous filtration experiments.

Sodium to cesium ions: a general ladder mechanism of ion diffusion in prussian blue analogs

Prussian blue analogs (PBAs) form crystals with large lattice voids that are suitable for the capture, transport and storage of various interstitial ions. Recently, we introduced the concept of a ladder mechanism to describe how sodium ions inside a PBA crystal structure diffuse by climbing the frames formed by aligned cyanide groups in the host structure. The current work uses semi-empirical tight-binding density functional theory (DFTB) in a multiscale approach to investigate how differences in the size of the monovalent cation affect the qualitative and quantitative aspects of the diffusion process. The results show that the ladder mechanism represents a unified framework, from which both similarities and differences between cation types can be understood. Fundamental Coulombic interactions make all positive cations avoid the open vacant areas in the structure, while cavities surrounded by partially negatively charged cyanide groups form diffusion bottlenecks and traps for larger cations. These results provide a new and quantitative way of understanding the suppression of cesium adsorption that has previously been reported for PBAs characterized by a low vacancy density. In conclusion, this work provides a unified picture of the cation adsorption in PBAs based on the newly formulated ladder mechanism.

Separation of anthropogenic radionuclides from aqueous environment using raw and modified biosorbents

In this study, two types of biosorbents were used to remove ¹³⁷Cs and plutonium isotopes from aqueous solutions - moss (Ptilium crista - castrensis) and oak sawdust (Quercus robur), both in the form of natural and modified state. Sorbent modification significantly increases the sorbent surface area (for moss sorbents - from 4.0 to 47.2 m²/g, and for sawdust sorbents - from 1.1 to 26.3 m²/g), pore volume (from 10^-3 to 10^-2), concentration and amount of basic cations and anions, as well as active functional groups on the sorbent surface. The main functional groups on the surface of natural sorbents modified with iron hydroxide interacting with analytes are carboxyl and hydroxyl groups. For carbonized sawdust and its subsequent activation with concentrated HCl, in addition to carboxyl and hydroxyl groups, acetyl groups also become active. Carbonated sawdust treated with HCl showed the highest average removal efficiency and sorption capacity for radiocesium and plutonium isotopes in laboratory column experiments - for ¹³⁷Cs ∼78.6% and ∼196.6 Bq/g and for ^239+240Pu ∼83% and ∼41.5 Bq/g, respectively. The moss and moss modified with iron hydroxide also showed good properties of adsorbing plutonium isotopes in field (in-situ) experiments. The best results on the sorption of ¹³⁷Cs in field experiments were shown by carbonated sawdust activated with HCl, and for isotopes of plutonium - the raw moss and moss modified with iron hydroxide. The results of the study showed that sorbents can be used not only for purification of water from plutonium isotopes but allow the operational sampling and more accurate measurement of radiocesium and plutonium isotopes in the fresh water reservoirs by the dynamic flow method.

A critical review of various adsorbents for selective removal of nitrate from water: Structure, performance and mechanism

Nitrate is ubiquitous pollutant due to its high water solubility, usually contributing to eutrophication, and posing a threat to aquatic ecosystem and human health. Adsorption approach has been widely used for nitrate removal because of the simplicity, easy operation, and low cost. Adsorbent plays a key role in the adsorptive removal of nitrate. The adsorption performance and adsorption mechanism are determined by the structural feature of adsorbent that is dependent on the preparation method. In this review, various types of adsorbents for nitrate removal were systematically summarized, their preparation, characterization, and adsorption performance were evaluated; the factors influencing the nitrate adsorption performance were discussed; the adsorption isotherm models, kinetic models and thermodynamic parameters were examined; and the possible adsorption mechanisms responsible for nitrate adsorption were categorized; the possible correlation of adsorbent structure to adsorption performance and adsorption mechanism were explained; the potential applications of adsorbents were discussed; finally, the strategies for improving adsorption capacity and selectivity towards nitrate, the challenges and future perspectives for developing novel adsorbent were also proposed. This review will deepen the understanding of nitrate removal by adsorption process and help the development of high-performance adsorbents for selective nitrate removal from water and wastewater.

Core–shell polymer nanocomposite based on free radical copolymerization of anthranilic acid and o-amino phenol in the presence of copper hexacyanoferrates nanoparticles and its adsorption properties

Core–shell polymer nanocomposite (CSNC) of copper hexacyanoferrate-copolymer of anthranilic acid with o-aminophenol (CHCF-poly(AA-co-OAP)) was synthesized and used as ion exchanger for the sorption of cesium ions from aqueous solution. The nanocomposite was prepared by implantation of CHCF nanoparticles into copolymer of poly(AA-co-OAP) during the polymerization process. The surface morphology and the porous structure were investigated through transmission electron microscope (TEM), scanning electron microscope (SEM) and Brunauer–Emmett–Teller (BET). The characterization of the prepared (CSNC) was carried out by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Thermogravimetric (TGA). Which SEM and TEM images confirmed the nano-size of the prepared CSNC. The values of adsorption capacity of CSNC towards cesium ions and the factors influence on the removal of cesium from solutions were investigated as function in pH, metal ion concentration, temperature and contact time. The results illustrated that the highest value of sorption capacity of the prepared CSNC towards Cs+ ions was 2.1 mmol g−1 at pH 11, 10 mmol L−1 Cs+ and 25 °C. Four modeling include on Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) isotherms models were studied. According to the obtained data, Langmuir model considered the most suitable model, which suggest that the uptake of Cs+ was monolayer and homogeneous. Also, the adsorption kinetics data was fitted well to pseudo-second-order model. Thermodynamic parameters were calculated in the temperature from 25 to 60 °C and the data revealed that Cs+ sorption was endothermic, spontaneous, and more favorable at higher temperature. Up to 92% desorption of Cs+ was completed with 2 M KCl.

Non-thermal plasma irradiated polyaluminum chloride for the heterogeneous adsorption enhancement of Cs+ and Sr2+ in a binary system

The natural ecosystem will continually deteriorate for decades by the leakage of Cs and Sr isotopes. The exploration of the new materials or techniques for the efficient treatment of radioactive wastewater is critically important. In this study, a dielectric barrier discharge (DBD) configuration was constructed to operate the non-thermal plasma (NTP). The NTP was incorporated into the synthesis of polyaluminum chloride (PAC) in two different procedures to intensify the synthesis of PAC (NTP-PAC) and enhance the further removal of Cs and Sr from wastewater. The employment of NTP in two procedures both had significantly changed the physicochemical characteristics of PAC materials, which facilitated the further adsorption application of NTP-PAC on the treatment of Cs⁺ and Sr²⁺. Different molecular, morphological, and adsorption characteristics were confirmed to the NTP-PAC materials. The heterogeneous adsorption of the NTP-PAC can be appropriately fitted by both the pseudo-first-order kinetic model and the Elovich model. Both physisorption and chemisorption reaction mechanisms were ensured for the heterogeneous adsorption of the NTP-PAC material towards Cs⁺ and Sr²⁺, which guaranteed the excellent adsorption performance of NTP-PAC materials compared to PAC. The electron collisions caused by NTP with alum pulp created highly reactive growth precursors and intensified the nucleation and hydrolysis polymerization of PAC. The employment of NTP explicitly broadens the reaction pathways between PAC and cationic contaminants in the aqueous environment, which expands the application area of PAC materials in environmental sustainability.

Shape stable poly(vinyl alcohol) hydrogels with immobilized metal hexacyanoferrates for cesium removal from waters

The metal hexacyanoferrates with transition metal ions to replace ferric ions in the face center cubic structure of Prussian blue (PB) crystals are candidate adsorbents for radioactive cesium ions in waters. This study for the first time synthesized the shape stable poly(vinyl alcohol) (PVA) hydrogels with immobilized metal hexacynoferrate (PB analogue) that can be stored at dry and can efficiently adsorb cesium ions from waters after rewetting. A total of eight PB analogue particles in two families M₃[Fe(III)(CN)₆]₂ (MFe(III)) or M₄[Fe(II)(CN)₆]₂ (MFe(II)) with M=Zn, Ni, Cu, or Co were synthesized and were immobilized in the PVA hydrogels following boric acid and sulfate crosslinking. The produced PVA-PB analogue hydrogels are all stable in shape after dry and rewet, and the rewet hydrogels can adsorb cesium ions from waters at much higher rates. As predicted by the diffusion-reaction model, the apparent reaction constants for cesium ion adsorption are 4.2×10^-4 1/s, 3.4×10^-4 1/s, 3.9×10^-4 1/s, 4.1×10^-4 1/s, 4.1×10^-4 1/s, 3.8×10^-4 1/s, 1.1×10^-3 1/s, and 9.6×10^-4 1/s, for ZnFe(III), ZnFe(II), NiFe(III), NiFe(II), CuFe(III), CuFe(II), CoFe(III), and CoFe(II), respectively. The corresponding maximum adsorption capacities based on Langmuir isotherm model at 25 °C are 232.6 mg/g, 389.0 mg/g, 193.9 mg/g, 256.8 mg/g, 388.2 mg/g, 395.1 mg/g, 297.3 mg/g, and 391.2 mg/g, respectively. The use of PVA-CoFe(III) is the candidate for enhanced Cs removal from waters comparing the use of other PB analogues as adsorbent.

Biochar as environmental armour and its diverse role towards protecting soil, water and air

Biochar has been of considerable importance for various environmental applications in recent years. It has exhibited substantial advantages like favourable structural and surface properties, easy process of preparation and widely available feedstocks. These set of exceptional properties make it an efficient, cost-effective and environment friendly source for diversified elimination of pollutants. The heterogeneity of physico-chemical properties offers a possibility for biochar to optimize its efficacy for targeted applications. This review aims to highlight the critical role that biochar plays in various environmental applications, be it in soil, water or air. In particular the article offers a comprehensive review of the recent research findings and updates related to the diversified role of biochar. Also, the interaction of pollutants with biochar functional groups and the impact of variation of parameters on biochar attribute relevant to specific pollutant removal, modifications, mechanisms involved and competence for such removal has been discussed. Different technologies for production of biochar have also been summarized with an emphasis on post treatment of biochar, such as modification and doping. In addition to this, the underlying gaps in the studies carried out so far and recommendations for future research areas in biochar have also been deliberated.

Electrostatic interactions and physisorption: mechanisms of passive cesium adsorption on Prussian blue

The study finds atomic-level physisorption interactions that leads to electrostatic Langmuir adsorption.

Securely anchored Prussian blue nanocrystals on the surface of porous PAAm sphere for high and selective cesium removal

Prussian blue (PB) has been well known as a pigment crystal to selectively sequestrate the radioactive cesium ion released from aqueous solutions owing to PB cage size similar to the cesium ion. Because the small size of PB is hard to deal with, the adsorbents containing PB have been prepared in the form of composites causing low sequestration efficiency of cesium. In this study, securely anchored PB nanocrystals on the surface of millimeter-sized porous polyacrylamide (PAAm) spheres (PB@PAAm) have been prepared by the crystallization of PB on the Fe³⁺ adsorbed PAAm. The securely anchored PB nanocrystals have been demonstrated to be selective and efficient adsorbents for sequestration of the radioactive cesium. The well-interconnected-spherical pores and millimeter-sized diameter of the PB@PAAm adsorbents facilitated permeation of Cs⁺ into the adsorbent and ease of handling respectively. Especially the well-interconnected-spherical pores allowed that PB@PAAm showed 90% of its maximum Cs⁺ adsorption capacity within 30 min. The PB@PAAm showed an outstanding Cs⁺ capture ability of 374 mg/g, high removal efficiency of 85% even at low concentration of Cs⁺ (10 ng/L), and superior selectivity of Cs⁺ against interference ions of Na⁺, K⁺, Mg²⁺, and Ca²⁺.

Selective Separation of Radiocesium from Complex Aqueous Matrices Using Dual Solid-Phase Extraction Systems

The release of radiocesium (r-Cs) into natural aqueous systems is of concern because of its extended solubility as an alkaline metal ion and its facile incorporation into living beings. A technique for the selective separation of Cs from an aqueous matrix using dual solid-phase extraction (SPE) systems in a series is proposed in this paper. The SPEs equipped with chelates (Nobias Chelate-PA1 and Nobias Chelate-PB1), an ion-exchange resin (Nobias Ion SC-1), or macrocycles (MetaSEP AnaLig Cs-01 and MetaSEP AnaLig Cs-02) were evaluated in terms of selectivity and retention/recovery behavior toward Cs and other potentially competing ions (Li, Na, K, Rb, Ba, Ca, Mg, and Sr). The simulated solution of ¹³³Cs, a chemical analog of r-Cs, was used to optimize the separation process. Operating parameters such as pH (3-13), flow rate (0.2-5.0 mL min^-1), and elution behavior (HCl, 0.1-5.0 mol L^-1) were optimized to ensure maximum removal of Cs from the aqueous matrices. The dual SPE system comprised Nobias Chelate-PB1 that minimized the competing impact of ions, while selective Cs retention was attained with MetaSEP AnaLig Cs-02. The proposed process was verified using real r-Cs-contaminated water from Fukushima, Japan, to observe the quantitative separation and preconcentration of r-Cs from the complex matrices.

Novel composite materials of modified roasted date pits using ferrocyanides for the recovery of lithium ions from seawater reverse osmosis brine

In this paper, novel composite materials from modified roasted date pits using ferrocyanides were developed and investigated for the recovery of lithium ions (Li+) from seawater reverse osmosis (RO) brine. Two composite materials were prepared from roasted date pits (RDP) as supporting material, namely potassium copper hexacyanoferrate-date pits composite (RDP-FC-Cu), and potassium nickel hexacyanoferrate-date pits composite (RDP-FC-Ni). The physiochemical characterization of the RO brine revealed that it contained a variety of metals and salts such as strontium, zinc, lithium, and sodium chlorides. RDP-FC-Cu and RDP-FC-Ni exhibited enhanced chemical and physical characteristics than RDP. The optimum pH, which attained the highest adsorption removal (%) for all adsorbents, was at pH 6. In addition, the highest adsorption capacities for the adsorbents were observed at the initial lithium concentration of 100 mg/L. The BET surface area analysis confirmed the increase in the total surface area of the prepared composites from 2.518 m2/g for RDP to 4.758 m2/g for RDP-FC-Cu and 5.262 m2/g for RDP-FC-Ni. A strong sharp infrared peak appeared for the RDP-FC-Cu and RDP-FC-Ni at 2078 cm-1. This peak corresponds to the C≡N bond, which indicates the presence of potassium hexacyanoferrate, K4[Fe(CN)6]. The adsorption removal of lithium at a variety of pH ranges was the highest for RDP-FC-Cu followed by RDP-FC-Ni and RDP. The continuous increase in the adsorption capacity for lithium with increasing initial lithium concentrations was also observed. This could be mainly attributed to enhance and increased lithium mass transfer onto the available adsorption active sites on the adsorbents' surface. The differences in the adsorption in terms of percent adsorption removal were clear and significant between the three adsorbents (P value < 0.05). All adsorbents in the study showed a high lithium desorption percentage as high as 99%. Both composites achieved full recoveries of lithium from the RO brine sample despite the presence of various other competing ions.

Novel One-Pot Solvothermal Synthesis of High-Performance Copper Hexacyanoferrate for Cs+ Removal from Wastewater

Efficient removal of radioactive cesium from complex wastewater is a challenge. Unlike traditional precipitation and hydrothermal synthesis, a novel vast specific surface area adsorbent of copper hexacyanoferrates named EA-CuHCF was synthesized using a one-pot solvothermal method under the moderate ethanol media characterized by XRD, SEM, EDS, BET, and FTIR. It was found that the maximum adsorption capacity towards Cs+ was 452.5 mg/g, which is far higher than most of the reported Prussian blue analogues so far. Moreover, EA-CuHCF could effectively adsorb Cs+ at a wide pH range and low concentration of Cs+ in geothermal water within 30 minutes, and the removal rate of Cs+ was 92.1%. Finally, the separation factors between Cs+ and other competitive ions were higher than 553, and the distribution coefficient of Cs+ reached up to 2.343 × 104 mL/g. These properties suggest that EA-CuHCF synthesized by the solvothermal method has high capacity and selectivity and can be used as a candidate for Cs+ removal from wastewater.

Synthesis and characterization of zinc-hexacyanoferrate composite beads for controlling the ammonia concentration in low-temperature live seafood transports

A new water treatment technology is presented for extending the longevity and increasing the maximal bio-load of container-bound, lucrative live seafood transportations. The technology is designed for removing ammonia and minimizing the bacterial concentration that develop in the water during the transport. This paper focuses on the characteristics of self-synthesized polyether-sulfone (PES) coated Zn-HCF composite beads, which have a high adsorbing capacity for NH₄⁺ in seawater and constitute the heart of the developed technology. Adsorption isotherms show that the operational capacity of the composite material (PES = 20% w/w) at NH₄⁺ concentration of 10 mgN/L at 3.5 °C is ∼3 mgN/g Zn-HCF. The kinetics of the PES-coated beads were shown to be considerably slower than the bare Zn-HCF, but since the retention time in the transport is long (many days), this does not detract from the effectiveness of the adsorption. Simulation experiments with and without live fish showed that the adsorbing material behaved as expected during a 21-d trip and that it did not have any effect on the fish. Repeated adsorption/regeneration (3 and 6 M NaCl) tests proved the composite material's stability and ion-exchange robustness. Electrooxidation of the ammonia in the exhausted regeneration solution was carried out with high efficiency and the treated solution could be used effectively in the following chemical regeneration step. The cost of a treatment unit installed in a 40-foot container was estimated at $40,000 and the ROI at 6 to 12 months.

Adsorptive removal of Sr(II) from aqueous solution by polyvinyl alcohol/graphene oxide aerogel

In this study, a new adsorbent, polyvinyl alcohol (PVA) and graphene oxide (GO), was prepared, characterized and used for the removal of Sr²⁺ from aqueous solution. In PVA/GO composite, the inter-lamellar spacing of adjacent GO layers was dramatically enlarged due to the intercalation of PVA molecules, such a unique architecture significantly mitigated the aggregation of GO layers, which facilitated the accessible exposure of active sites and the mass transfer of strontium ions (Sr²⁺), thus enhancing the adsorption capacity toward Sr²⁺. The adsorption of Sr²⁺ by PVA/GO composite conformed to the pseudo second-order kinetic model (R² = 0.9994), the Langmuir model (R² = 0.9042), and the Freundlich model (R² = 0.9598). The complexation interaction between Sr²⁺ and oxygen atoms/π-electron domain of PVA/GO composite was primarily responsible for the adsorption mechanism, based on the characterization results of X-ray photoelectron spectroscopy (XPS), scanning electron microscope equipped with energy dispersion spectroscopy (SEM-EDS) and powder X-ray diffraction (PXRD).