Novel application of nanozeolite for radioactive cesium removal from high-salt wastewater

Cesium adsorption from an aqueous medium for environmental remediation: A comprehensive analysis of adsorbents, sources, factors, models, challenges, and opportunities

Considering the widespread and indispensable nature of nuclear energy for future power generation, there is a concurrent increase in the discharge of radioactive Cs into water streams. Recent studies have demonstrated that adsorption is crucial in removing Cs from wastewater for environmental remediation. However, the existing literature lacks comprehensive studies on various adsorption methods, the capacities or efficiencies of adsorbents, influencing factors, isotherm and kinetic models of the Cs adsorption process. A bibliometric and comprehensive analysis was conducted using 1179 publications from the Web of Science Core Collection spanning from 2014 to 2023. It reviews and summarizes current publication trends, active countries, adsorption methods, adsorption capacities or efficiencies of adsorbents, tested water sources, influencing factors, isotherm, and kinetic models of Cs adsorption. The selection of suitable adsorbents and operating parameters is identified as a crucial factor. Over the past decade, due to their notable capacity for Cs adsorption, considerable research has focused on novel adsorbents, such as Prussian blue, graphene oxide, hydrogel, and nanoadsorbents (NA). However, there remains a need for further development of application-oriented laboratory-scale experiments. Future research directions should encompass exploring adsorption mechanisms, developing new adsorbents or their combinations, practical applications of lab-scale studies, and recycling radioactive Cs from wastewater. Drawing upon this literature review, we present the most recent research patterns concerning adsorbents to remove Cs, outline potential avenues for future research, and delineate the obstacles hindering effective adsorption. This comprehensive bibliometric review provides valuable insights into prevalent research focal points and emerging trends, serving as a helpful resource for researchers and policymakers seeking to understand the dynamics of adsorbents for Cs removal from water.

Advancing in Cesium Retention: Application of Magnesium Phosphate Cement Composites

A serious risk that harms the safe use of water and affects aquatic ecosystems is water pollution. This occurs when the water's natural equilibrium is disrupted by an excessive amount of substances, both naturally occurring and as a byproduct of human activities, that have varied degrees of toxicity. Radiation from Cs isotopes, which are common components of radioactive waste and are known for their long half-lives (30 years), which are longer than the natural decay processes, is a major source of contamination. Adsorption is a commonly used technique for reducing this kind of contamination, and zeolite chabazite has been chosen as the best adsorbent for cesium in this particular situation. The purpose of this research is to investigate a composite material based on magnesium phosphate cement (MPC). Magnesium oxide (MgO), potassium dihydrogen phosphate (KH2PO4), and properly selected retarders are used to create the MPC. The optimal conditions for this composite material are investigated through the utilization of X-ray diffraction, scanning electron microscopy, BET surface area analysis, and atomic absorption spectroscopy. The principal aim is to enable innovations in the elimination of radioactive waste-contaminated water using effective cesium removal. The most promising results were obtained by using KH2PO4 as an acid, and MgO as a base, and aiming for an M/P ratio of two or four. Furthermore, we chose zeolite chabazite as a crucial component. The best adsorption abilities for Cs were found at Qads = 106.997 mg/g for S2 and Qads = 122.108 mg/g for S1. As a result, zeolite is an eco-friendly material that is a potential usage option, with many benefits, such as low prices, stability, and ease of regeneration and use.

Eco-friendly natural mineral biotite as a cesium adsorbent: Utilizing low-concentration acid and hydrogen peroxide

Biotite, a phyllosilicate mineral, possesses significant potential for cesium (Cs) adsorption owing to its negative surface charge, specific surface area (SSA), and frayed edge sites (FES). Notably, FES are known to play an important role in the adsorption of Cs. The objectives of this study were to investigate the Cs adsorption capacity and behavior of artificially weathered biotite and identify mineralogical characteristics for the development of an eco-friendly geologically-based Cs adsorbent. Through various analyses, it was confirmed that the FES of biotite was mainly formed by mineral structural distortion during artificial weathering. The Cs adsorption capacity is improved by approximately 39% (from 20.53 to 28.63 mg g-1) when FES are formed in biotite through artificial weathering using a low-concentration acidic solution mixed with hydrogen peroxide (H2O2). Especially, the Cs selectivity in Cs-containing seawater, including high concentrations of cations and organic matter, was significantly enhanced from 203.2 to 1707.6 mL g-1, an increase in removal efficiency from 49.5 to 89.2%. These results indicate that FES of artificially weathered biotite play an essential role in Cs adsorption. Therefore, this simple and economical weathering method, which uses a low-concentration acidic solution mixed with H2O2, can be applied to natural minerals for use as Cs adsorbents.

Immobilization of 137Cs as a crystalline pollucite surrounded by amorphous aluminosilicate

To date, radiocesium (¹³⁷Cs) has been considered stable in the form of pollucite mineralized through high-temperature heat treatment. This study presented a possibility through experimental results that the entire medium exists as amorphous aluminosilicate at a relatively low temperature, but cesium is partially and preferentially converted from a composite adsorbent into pollucite. Cesium lowers the eutectic point within the system and initiates the nucleation of pollucite prior to other elements. We confirmed that the partial mineral phase of cesium showed the same chemical stability as when the entire medium was converted to pollucite. X-ray absorption spectroscopy provided direct evidence for this phenomenon; also, the stability results of radioactive cesium shown through a series of sintering experiments supported the conclusion. This method can be applied as a method to immobilize radioactive cesium under relatively mild temperature conditions of atmospheric pressure, while eliminating the problem of diffusion due to its volatilization.

A low-cost photo-evaporation inorganic membrane preparation and treatment of the simulated high salinity radioactive waste water

Solar-driven desalination is an energy-saving and environmentally benign wastewater treatment technology. A method of in situ self-reduction of graphene oxide (rGO) by cheap geopolymer was introduced, and a photo evaporation membrane device (rGOPGC) for treatment of the simulated high salt liquid radioactive waste (HSLRW) was prepared in the present study. Compared with other rGO based photo evaporation membrane materials, geopolymer matrix has the advantages of low cost, reductant free, simple preparation process and mild conditions. After desalination of simulated seawater, the concentrations of Na⁺, K⁺, Ca²⁺ and Mg²⁺ ions reached the WHO standard, and the removal rates of radioactive I^-, Cs⁺ and Sr²⁺ in the simulated high salinity wastewater reached 99.62%, 99.71% and 99.99% respectively; The evaporation rate of rGOPGC remained stable at 1.5 kg/m²/h after 16 cycles in high salinity environment. There was no obvious salt accumulation on the upper surface of the device, indicating its high stability. Furthermore, the evaporation performance at high temperature near the nuclear power plant (NPP) waste water was simulated and tested. Under one solar intensity and 35 °C ambient temperature, the evaporation rate of 1.75 kg/m²/h and the evaporation efficiency of 98.51% were achieved. The results indicated that the rGOPGC device is potential in the concentration evaluation of HSLRW.

Applications of Nano-Zeolite in Wastewater Treatment: An Overview

Nano-zeolite is an innovative class of materials that received recognition for its potential use in water and tertiary wastewater treatment. These applications include ion-exchange/sorption, photo-degradation, and membrane separation. The aim of this work is to summarize and analyze the current knowledge about the utilization of nano-zeolite in these applications, identify the gaps in this field, and highlight the challenges that face the wide scale applications of these materials. Within this context, an introduction to water quality, water and wastewater treatment, utilization of zeolite in contaminant removal from water was addressed and linked to its structure and the advances in zeolite preparation techniques were overviewed. To have insights into the trends of the scientific interest in this field, an in-depth analysis of the variation in annual research distribution over the last decade was performed for each application. This analysis covered the research that addressed the potential use of both zeolites and nano-zeolites. For each application, the characterization, experimental testing schemes, and theoretical analysis methodologies were overviewed. The results of the most advanced research were collected, summarized, and analyzed to allow an easy visualization and comparison of these research results. Finally, the gaps and challenges that face these applications are concluded.

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⁺.

Response surface methodology for strontium removal process optimization from contaminated water using zeolite nanocomposites

The effective removal of strontium from polluted water is an emerging issue worldwide, especially in Japan, after the destruction of Fukushima's Daiichi Nuclear Power Plant. In the strontium removal process, statistical optimization of associated factors is needed to reduce the quantity of chemicals and the number of experimental trials. In this study, response surface methodology based on the central composite design was employed for assessing the influence of different factors and their interaction effects on the efficiency of strontium removal. We have considered nanoscale zero-valent iron-zeolite (nZVI-Z) and nano-Fe/Cu zeolite (nFe/Cu-Z) as adsorbents for the effective removal of strontium. The results suggested that the studied three factors such as pH, contact time, and concentration are positively related to the adsorption of strontium. That is, the maximum strontium removal occurred at pH, initial concentration, and contact time of 12, 200 mg L^-1, and 30 min, respectively. The experimental maximum strontium adsorption capacity of nZVI-Z and nFe/Cu-Z adsorbents is 32.5 mg/g and 34 mg/g, respectively. The present study also showed that the most statistically significant potential contributor was initial concentration, followed by contact time in the removal process. The study indicated that the interaction effect between contact time and initial concentration was statistically important, suggesting the need for a multi-mechanism technique in the removal phase of strontium. Tόth, Langmuir, Dubinin-Astakhov (D-A), Freundlich, and Hill isotherm models were also fitted with the experimental strontium adsorption data, in which the Tόth model fitted best compared to the other models based on the RMSD and R².

Effective removal of 137Cs ions from radioactive wastewater by Melamine-Styrene based Polymer (MSP)

Cesium (Cs) is a major product of uranium fission, which is one of the most existed radionuclides in radioactive wastes. Removal of Cs-137 has a critical role in the decontamination of liquid radioactive waste due to its half-life of 30.17 years. Concordantly, melamine styrene based conjugated polymer (MSP) was designed, synthesized, and characterized with FTIR, TGA, SEM and BET measurements. The novelty of the study is that the MSP adsorbent is designed as a highly conjugated structure to have better interaction with Cs over the Cs-π bond of the benzene groups of the adsorbent. In this work, the adsorption behavior and rate of MSP were investigated as parameters of adsorbent amount, pH, contact time, particle size, initial Cs⁺ concentration, and temperature. Besides, the adsorption efficiency of Cs-137 was examined by Gamma Spectroscopy. Adsorption results were fitted to three different isotherms which were Freundlich, Langmuir and Dubinin-Radushkevich (D-R). The maximum adsorption capacity of polymer for Cs⁺ ion was found from Langmuir isotherm as 78 mg g^-1. As a part of kinetic parameters, pseudo first and second orders were investigated and in terms of the correlation coefficient pseudo second order was much more appropriate for adsorption of Cs-137 onto MSP.

Effective cesium removal from Cs-containing water using chemically activated opaline mudstone mainly composed of opal-cristobalite/tridymite (opal-CT)

Opaline mudstone (OM) composed of opal-CT (SiO2·nH2O) has high potential use as a cesium (Cs) adsorbent, due to its high specific surface area (SSA). The objective of this study was to investigate the Cs adsorption capacity of chemically activated OM and the adsorption mechanism based on its physico-chemical properties. We used acid- and base-activation methods for the surface modification of OM. Both acid- and base- activations highly increased the specific surface area (SSA) of OM, however, the base-activation decreased the zeta potential value more (- 16.67 mV), compared to the effects of acid-activation (- 6.60 mV) or non-activation method (- 6.66 mV). Base-activated OM showed higher Cs adsorption capacity (32.14 mg/g) than the others (acid: 12.22 mg/g, non: 15.47 mg/g). These results indicate that base-activation generates pH-dependent negative charge, which facilitates Cs adsorption via electrostatic attraction. In terms of the dynamic atomic behavior, Cs cation adsorbed on the OM mainly exist in the form of inner-sphere complexes (IS) containing minor amounts of water molecules. Consequently, the OM can be used as an effective Cs adsorbent via base-activation as an economical and simple modification method.

Statistical techniques for the optimization of cesium removal from aqueous solutions onto iron-based nanoparticle-zeolite composites

Statistical optimization of performance determining factors is essential for the development of a cesium removal system from aqueous solutions. Therefore, factorial experimental design and multiple regression techniques were employed to assess the primary and interaction effects of the pH, initial concentration, and contact time in the cesium removal process using nanoscale zero-valent iron-zeolite (nZVI-Z) and nano-Fe/Cu-zeolite (nFe/Cu-Z) as an adsorbent. The optimum region of cesium removal was identified by constructing a contour plot. The study revealed that initial concentration was the most significant factor followed by contact time. The study also suggested that maximum cesium removal occurred at pH, initial concentration, and contact time of 6, 200 mg/L, and 30 min, respectively. Moreover, the statistically significant interaction effect was observed between contact time and initial concentration. The experimental data were also fitted with Tόth, Langmuir, Dubinin-Astakhov (D-A), Freundlich, and Hill models and found that the Tόth model fitted better compared with the other four models based on Akaike information criterion (AIC) and root-mean-square deviation (RMSD). The findings of this paper can undoubtedly contribute to constructing the optimum statistical process of removing hazardous pollutants from the water, which significantly impacts on human health and the environment. Graphical abstract.

Enhanced removal of Co(II) and Ni(II) from high-salinity aqueous solution using reductive self-assembly of three-dimensional magnetic fungal hyphal/graphene oxide nanofibers

Layer-structured graphene oxide excellent carrier for modifications; however, its poor recoverability and stability preclude its application in wastewater treatment fields. Herein, three-dimensional magnetic fungal hyphal/graphene oxide nanofibers (MFHGs) were assembled by a reductive self-assembly (RSA) strategy for the efficient capture of Co(II) and Ni(II) from high-salinity aqueous solution. The RSA strategy is inexpensive, eco-friendly and easy to scale up. The obtained MFHGs enhanced the dispersity and stability of graphene oxide and exhibited excellent magnetization and large coercivity, leading to satisfactory solid-liquid separation performance and denser sediment. The results of batch removal experiments showed that the maximum removal capacity of MFHGs for Ni(II) and Co(II) was 97.44 and 104.34 mg/g, respectively, in 2 g/L Na₂SO₄ aqueous solution with a pH of 6.0 at 323 K, and the effects of initial pH and ionic strength on Co(II) and Ni(II) removal were explored. Yield residue analysis indicated that the high porosity and oxygen-containing functional groups of MFHGs remarkably improved their Co(II)- and Ni(II)-removal capacities. According to the analysis, hydroxyl groups and amine groups participated in the chemical reaction of Co(II) and Ni(II) removal, and cation-exchange chemical adsorption was dominant during the Co(II)- and Ni(II)-removal process. Based on the attributes of MFHGs, a continuous-flow recycle reactor (CFRR) was proposed for emergency aqueous solution treatment and exhibited satisfactory removal efficiency and regeneration performance. The combination of MFHGs and the proposed CFRR is a promising water treatment strategy for rapid treatment applications.

A two-step process for pre-hydrolysis of hemicellulose in pulp-impregnated effluent with high alkali concentration to improve xylose production

The viscose fiber production process is accompanied by the accumulation of pulp-impregnated effluent (PIE), including hemicellulose and large amounts of alkali, and discharge of PIE will cause environment pollution. This paper aims to relieve the inhibition of high concentration of alkali on xylose production from hydrolysis of hemicellulose in PIE. Based on the fact that solid acid uses H⁺ at the acid sites to exchange with cations in PIE and can be recycled, a two-step method including an extra pretreatment process before pre-hydrolysis (SPP) is proposed. After the alkali was removed by the H⁺ dissociated from solid acid in the extra pretreatment process, the pH of PIE dropped from 14 to 4, and the content of Na⁺ and proteins was reduced by 99.13 % and 78.51 %, respectively. After SPP, the polymerization degree of the hemicellulose decreased by 73.4 %, and the subsequent enzymatic hydrolysis process was promoted. Finally, the xylose yield of SPP followed by enzymatic hydrolysis reached 57.15 g/L, which was 145.38 % more than that of enzymatic hydrolysis alone. The load of a downstream ion purification procedure was relieved compared to that of inorganic acid hydrolysis. The development of SPP contributes to the resource utilization of high alkali concentration wastewater.

Cesium removal using acid- and base-activated biotite and illite

Biotite and illite have excellent cesium (Cs) adsorption capacity due to their negative charges in addition to adsorption sites of the planar, interlayer, and frayed edge sites (FES). The aim of this study is to investigate the Cs adsorption capacity using acid- and base-activated biotite and illite based on their mineralogical characteristics. The acid-activated biotite and base-activated illite exhibited high Cs removal efficiency from the low-level Cs-containing DI water (97.5 % and 97.3 %, respectively). The acid-activation of biotite increased the specific surface area (SSA, 12.08 → 43.04 m²/g), Fe(III)/Fe(II) ratio (0.56 → 0.76), and wedge zone d-spacing (1.017 → 1.065 nm), while the zeta potential (-4.06 → -4.82 mV) decreased. The base-activation of illite resulted to a decrease in the SSA (22.14 → 18.49 m²/g), zeta potential (-7.68 → -31.64 mV), and Fe(III)/Fe(II) ratio (0.92 → 0.79). However, only acid-activated biotite appeared to have a high capacity of Cs removal from Cs-containing seawater (73.9 %; base-activated illite: 26.1 %). These results indicate that the FES of biotite owing to acid-activation showed better results in regards to Cs adsorption as compared to the pH-dependent negative charges of the base-activated illite.

Cesium removal from a water system using a polysulfone carrier containing nitric acid-treated bamboo charcoal

Laboratory scale sorption and desorption experiments were performed to investigate the cesium (Cs) removal efficiency of a bead-shaped polysulfone carrier containing HNO₃-treated bamboo charcoal (BC). The average Cs removal efficiency of BC only and of polysulfone carrier without BC after 1 h sorption reaction was 53 and 18%, respectively. However, the Cs removal efficiency for the polysulfone carrier with 5% HNO₃-treated BC (P-5N-BC) after 1 h and 24 h reaction was 66 and 98%, respectively. The Cs removal efficiency after 24 h reaction remained >85% over a wide range of pH and temperature conditions, suggesting that using P-5N-BC as the Cs adsorbent is feasible in a variety of aquatic environments. The maximum Cs sorption capacity (q_m) of P-5N-BC, as calculated from a Langmuir isotherm model, was 60.9 mg/g, which is much higher than those of other adsorbents from previous studies for 1 h of sorption time. The Cs desorption rate of P-5N-BC for 24 h desorption time was <17%, showing that the Cs was stably enough attached to the HNO₃-treated BC for long-term use. The results of continuous column experiments showed that the total amount of treated water from the column packed with P-5N-BC increased more than nine times when compared with that from the only BC-granule-packed column. The P-5N-BC maintained more than 68% Cs removal efficiency after 90 pore volumes of flushing, suggesting that only 15 g of P-5N-BC (with only 0.75 g of HNO₃-treated BC) could clean 5 L of Cs-contaminated water (initial Cs concentration: 1.0 mg/L; effluent concentration: < 0.09 mg/L). The present results demonstrate that P-5N-BC has remarkable potential for removal of Cs from diverse water systems.

Effective removal of radioactive cesium from contaminated water by synthesized composite adsorbent and its thermal treatment for enhanced storage stability

A composite adsorbent for the removal of radioactive cesium (¹³⁷Cs) was synthesized by immobilizing potassium cobalt ferrocyanide in the micro pores of the zeolite chabazite. The synthetically optimized composite adsorbent demonstrates a rapid cesium adsorption rate under both salt-free and high-salt conditions with a high distribution coefficient of cesium (≥10⁵ mL/g). Although both components have the same ion-exchange reaction between potassium and cesium, the reaction by ferrocyanide component was predominant, which derived hundred times higher distribution coefficient of the composite adsorbent than that of pure chabazite. A thermal stabilization process was studied for improving the storage and/or disposal stability of the spent adsorbent. The formation of a eutectic system within the spent adsorbent reduced the stabilization temperature to 1000 °C from 1200 °C. Accordingly, the leaching of cesium was remarkably reduced by the remineralization to the stable pollucite. The stable impregnation of ferrocyanide component in the chabazite pores derived the reduction of cesium volatility enabling the high temperature stabilization method. Our experimental results provide evidence that the composite adsorbent has clear advantages on the cesium removal from contaminated water and its stabilization via thermal-treatment.

Removal of heavy metals and radionuclides from water using nanomaterials: current scenario and future prospects

There is an increase in concern about the hazardous effects of radioactivity due to the presence of undesirable radioactive substances in our vicinity. Nuclear accidents such as Chernobyl (1986) and Fukushima (2011) have further raised concerns towards such incidents which have led to contamination of water bodies. Conventional methods of water purification are less efficient in decontamination of radioisotopes. They are usually neither cost-effective nor environmentally friendly. However, nanotechnology can play a vital role in providing practical solutions to this problem. Nano-engineered materials like metal oxides, metallic organic frameworks, and nanoparticle-impregnated membranes have proven to be highly efficient in treating contaminated water. Their unique characteristics such as high adsorption capacity, large specific surface area, high tensile strength, and excellent biocompatibility properties make them useful in the field of water purification. This review explores the present status and future prospects of nanomaterials as the next-generation water purification systems that can play an important role in the removal of heavy metals and radioactive contaminants from aqueous solutions.

Shape-selective adsorption mechanism of CS-Z1 microporous molecular sieve for organic pollutants

A self-made microporous molecular sieve CS-Z1 has been found to have excellent adsorption performance for small molecular nitrile and pyridine pollutants in acrylonitrile production wastewater. In order to explore its adsorption mechanism, the adsorption kinetics, isotherms and thermodynamics of CS-Z1 for eight nitrile and pyridine organic pollutants with different structures and properties were investigated. Meanwhile, the analysis of molecular dynamics simulation based on density functional theory was conducted to revel the adsorption-diffusion process of different organic pollutants on the surface and in the pores of CS-Z1. Both the experimental and simulated results verified the shape-selective adsorption mechanism of CS-Z1 for these organic pollutants. The adsorption processes of CS-Z1 for these pollutants were spontaneous physical adsorption, and the adsorption efficiency of CS-Z1 mainly depended on the molecular size of pollutant. Benefitting from the flexible crystalline structure of CS-Z1 and the breathing vibration of CS-Z1 orifices, it could adsorb some pollutants with slightly larger size than its pore diameter. Molecular dynamics simulation results visually display the shape-selective adsorption process of CS-Z1 for these pollutants through the respiratory effect of CS-Z1 molecular sieve orifices.

Zeolites as Carriers of Antitumor Ribonuclease Binase

Natural and synthetic zeolites have many applications in biomedicine and nutrition. Due to its properties, zeolites can absorb therapeutically active proteins and release them under physiological conditions. In this study we tested the clinoptilolite, chabazite, and natrolite ability to be loaded by antitumor ribonuclease binase and the cytotoxicity of the obtained complexes. We found the optimal conditions for binase loading into zeolites and established the dynamic of its release. Cytotoxic effects of zeolite-binase complexes toward colorectal cancer Caco2 cells were characterized after 24 and 48 h of incubation with cells using MTT-test. Zeolites were toxic by itselfs and reduced cells viability by 30% (clinoptilolite), 40% (chabazite), and 70% (natrolite) after 48 h of incubation. Binase complexes with clinoptilolite as well as chabazite always demonstrated enhanced toxicity (up to 57 and 60% for clinoptilolite and chabazite, respectively) in comparison with binase and zeolites separately. Our results contribute to the perspective development of binase-based complexes for therapy of colorectal cancer for or the treatment of malignant skin neoplasms where the complexes can be used in pasty form.

Biosorption of radioactive cesium from contaminated water by microalgae Haematococcus pluvialis and Chlorella vulgaris

The biosorption properties of water-soluble radioactive cesium (¹³⁷Cs) by microalga Haematococcus pluvialis were evaluated with different cell conditions, and its cesium-uptake rate was compared with that by other microalgae, Chlorella vulgaris and Anabaena sp. Photo-induced H. pluvialis red cyst rapidly removed radioactive cesium from the solution by bioaccumulation. We showed that the effectiveness of ¹³⁷Cs uptake is dependent on the specific cell condition of even the same microalgal species. While the H. pluvialis red cyst removed almost 95% of the soluble ¹³⁷Cs in 48 h, both H. pluvialis intermediate cells and C. vulgaris showed 90% uptake efficiency of ¹³⁷Cs with slow uptake rate. The energy dispersive spectrometer data demonstrated that the cesium uptake acceleration by inducing astaxanthin in H. pluvialis red cyst involves the cesium accumulation through the potassium transport channel. The long-term monitoring experiments of the cesium uptake showed that only 40% of ¹³⁷Cs remained in collapsed H. pluvialis cell fragments after 12 months.

Removal of Cs-137 and Sr-90 from reactor actual liquid waste samples using a new synthesized bionanocomposite-based carboxymethylcellulose

A new biosorbent containing vinylsulphonic acid and 2-acryloamido-2-methyl-1-propanesulphonic acid in the presence of magnetic nanoparticles, iron (III) oxide, grafted to carboxymethylcellulose sodium salt P(VSA/AMPSO3H/MNPs)-g-CMC bionanocomposite material (BNC) has been synthesized by γ radiation induced grafting copolymerization technique. The effect of comonomer, crosslinker, CMC concentration and the absorbed dose (kGy) on the grafting efficiency and swelling degree was studied. The BNC has been successfully synthesized and the structure of the prepared BNC was confirmed by Fourier transform infrared (FTIR), thermal analysis (TGA and DTA), X-ray powder diffraction (XRD), high-resolution 1H NMR spectroscopy and scanning electron microscopy (SEM) micrograph. Batch studies relevant to adsorption of Cs-137 and Sr-90 from the reactor actual liquid waste samples by the BNC were performed as a function of contact time, solution pH, metal ion concentration, and temperature in simulation studies using the γ emitting isotopes Cs-134 and Sr-85 as representatives of Cs-137 and Sr-90, respectively. Those studies were used to find out the best conditions for isolation of Cs-137 and Sr-90 from reactor actual liquid waste. The isotherms and kinetics were analyzed using different models at 25 °C. The maximum capacity of BNC was found to be 297 and 330 mg g−1 for Cs(I) and Sr(II) metal ions, respectively.

A novel approach for the removal of radiocesium from aqueous solution by ZSM-5 molecular sieve

Finding an approach for pretreatment of radionuclides from contaminated water are interesting topics of research. In present work, the ZSM-5 molecular sieve was characterized with different techniques such as zeta potential, SEM, FT-IR and XRD to clarify the surface properties of sample and applied as a sorbent to concentrate and recover Cs(I) from aqueous solution. The effect of environmental conditions such as contact time, ionic strength, content of sorbent and solution pH on Cs(I) uptake were optimized using batch techniques. Different kinetic and isotherm models were utilized to evaluate the experimental data and the correlation parameters were obtained. Based on the sorption/desorption experiment, it can be deduced that the ZSM-5 molecular sieve has potential application for the rapid and quantitative recovery of radiocesium from wastewater.

Impact of alkali cations on properties of metakaolin and metakaolin/slag geopolymers: Microstructures in relation to sorption of 134Cs radionuclide

Radio-cesium constitutes major environmental threats. Sorption of hazardous species onto geopolymeric sorbents is relatively recent and may give information about the retention mechanisms when geopolymers are applied to immobilize radwastes. Here, Na-MK, K-MK, Na-MKBFS, and K-MKBFS geopolymeric sorbents were synthesized from metakaolin (MK) and blast furnace slag (BFS) and were characterized using XRD, XRF, FT-IR, DTA/TGA and SEM. FT-IR/XRF results clarified the impact of mono-valent alkali cation (M⁺) in dividing the sorbents into Al-rich (sodium-based) and Si-rich (potassium-based). All sorbents were amorphous to semi-crystalline containing mica-phyllosilicates (greater in Si-rich), tobermorites (greater in MKBFS-based), gehlenite, calcite, quartz, hematite and hydrotalcite. Isotherms of ¹³⁴Cs radionuclide sorption were constructed, being regular with a positive temperature effect. Al-rich sorbents gave higher sorption capacities than Si-rich ones. Na-MK sorbent recorded the more distinctive sorption capacity (74.95mg/g; at 333K). Langmuir, Freundlich and D-R models were used to disclose the capacities and mechanisms governing the sorption processes. Sorption of Cs⁺ onto the examined sorbents was favorable. All systems were controlled by ion exchange mechanism, except ¹³⁴Cs/K-MK system which was controlled by physi- sorption mechanism. ¹³⁴Cs/Na-MK GP system was the only spontaneous among all. The endothermic natures were the common denominator between the tested systems.

Computer simulation of water desalination through boron nitride nanotubes

Development of high-efficiency and low-cost seawater desalination technologies is critical to solving the global water crisis. Herein we report a fast water filtering method with high salt rejection by boron nitride nanotubes (BNNTs). The effect of the radius of BNNTs on water filtering and salt rejection was investigated by molecular dynamics (MD) simulation. Our simulation results demonstrate that fast water permeation and high salt rejection could be achieved by BNNT(7,7) under both high pressure and low pressure. The potential of mean force (PMF) of Na⁺ ion and water molecule through BNNT(7,7) further revealed the mechanism of seawater desalination by BNNT(7,7). Using BNNT(7,7) array, a 10 cm² nanotube membrane with 1.5 × 10¹³ pores per cm² will produce freshwater with a flow rate of 98 L per day per MPa under 100 MPa. Our study shows the potential application of BNNTs membrane for fast and efficient desalination.

Decontamination of radioactive cesium ions using ordered mesoporous monetite

We report herein the fabrication of an environmentally friendly, low-cost and efficient nanostructured mesoporous monetite plate-like mineral (CaHPO₄) as an adsorbent for removal of radioactive cesium ions from aqueous solutions. The phase and textural features of the synthesized mesoporous monetite were well characterized by XRD, FTIR, SEM, HRTEM, DLS, TGA/TDA, and N₂ adsorption/desorption techniques. The results indicate that the cesium ions were effectively adsorbed by the mesoporous monetite ion-exchanger (MMT-IEX) above pH 9.0. Different kinetic and isotherm models were applied to characterize the cesium adsorption process. The fabricated monetite exhibited a monolayer adsorption capacity up to 60.33 mg g⁻¹ at pH of 9.5. The collected data revealed the higher ability of CaHPO₄ for the removal of Cs(i) from aqueous media in an efficient way.

This study involves the identification of environmentally friendly, low-cost and efficient nanostructured mesoporous monetite plate like mineral as an adsorbent for removal of cesium from aqueous solutions.

Effect on Cs removal of solid-phase metal oxidation in metal ferrocyanides

Metal ferrocyanides (MFCs) have been studied for many years and are regarded as efficient adsorbents for the selective removal of radioactive cesium (Cs) from contaminated aqueous solutions. Although their efficiency has been demonstrated, various investigations on the physicochemical, thermal, and radiological stability of the solids of MFCs are required to enhance the applicability of MFCs in the treatment process. We observed that the Cs adsorption efficiencies of cobalt and nickel ferrocyanides decreased as their aging period increased, while the Cs adsorption efficiencies of copper and zinc ferrocyanides did not decrease. The tendencies of these ferrocyanides were accelerated by exposure of the solids at a higher temperature for a longer time. Our comprehensive analyses demonstrated that only the oxidizable metals in the MFCs can be oxidized by aging time and increasing temperature; also, this affects the Cs removal efficiency by decreasing the exchangeable sites in the solids. The chemical stability of MFCs is very important for the optimization of the synthesis and storage conditions.