Decontamination of radioactive wastewater: State of the art and challenges forward

Screening diluents to optimize cesium contaminant separation using t-BAMBP extractant

The widespread use of nuclear energy has raised concerns about nuclear safety and radioactive waste management, particularly due to the release of radioactive cesium. This study investigates the use of t-BAMBP (4-tert-butyl-2-(α-methylbenzyl) phenol) for the extraction and separation of cesium from simulate high concentration cesium containing wastewater, focusing on the selection of suitable diluents to enhance the efficiency of the process. We performed a systematic study using density functional theory (DFT) calculations to evaluate the intrinsic properties and interactions of various common diluents with t-BAMBP. The diluents studied include aromatic hydrocarbons (benzene, toluene, xylene), alkanes (cyclohexane, hexane, heptane), and alcohols (hexanol, octanol). Our computational results revealed that cyclohexane is the most suitable diluent due to its moderate solvation-free energy, high nonpolarity, and optimal balance between solubility and reactivity. Experimental validation confirmed the computational findings. The cyclohexane-diluted t-BAMBP system achieved the highest cesium extraction efficiency of over 94 %, with a separation factor (βCs/K) of 767.67. Cyclohexane demonstrated the lowest toxicity and cost among the diluents evaluated, making it a safer and more economical choice for practical applications. The results of this study provide a comprehensive theoretical and experimental basis for the selection of diluents in the t-BAMBP extraction system, offering insights for the sustainable utilization of cesium resources and effective management of radioactive waste.

Recent trends in the phytoremediation of radionuclide contamination of soil by cesium and strontium: Sources, mechanisms and methods: A comprehensive review

This comprehensive review examines recent trends in phytoremediation strategies to address soil radionuclide contamination by cesium (Cs) and strontium (Sr). Radionuclide contamination, resulting from natural processes and nuclear-related activities such as accidents and the operation of nuclear facilities, poses significant risks to the environment and human health. Cs and Sr, prominent radionuclides involved in nuclear accidents, exhibit chemical properties that contribute to their toxicity, including easy uptake, high solubility, and long half-lives. Phytoremediation is emerging as a promising and environmentally friendly approach to mitigate radionuclide contamination by exploiting the ability of plants to extract toxic elements from soil and water. This review focuses specifically on the removal of 90Sr and 137Cs, addressing their health risks and environmental implications. Understanding the mechanisms governing plant uptake of radionuclides is critical and is influenced by factors such as plant species, soil texture, and physicochemical properties. Phytoremediation not only addresses immediate contamination challenges but also provides long-term benefits for ecosystem restoration and sustainable development. By improving soil health, biodiversity, and ecosystem resilience, phytoremediation is in line with global sustainability goals and environmental protection initiatives. This review aims to provide insights into effective strategies for mitigating environmental hazards associated with radionuclide contamination and to highlight the importance of phytoremediation in environmental remediation efforts.

Simulation and calibration of radiation monitoring of nuclear power plant containment sump waste liquid

Waste liquid stored in the containment sumps of nuclear power plants may contain a variety of radionuclides. Real-time monitoring of containment sump waste liquid can ensure that accidents, such as leakage of cooling water, can be avoided. This paper presents the design of a radioactive monitoring system for waste liquid in a containment sump. The detector and the lead-shield in the measurement unit are optimized through Monte Carlo simulations. Experimental verification showed that the background count rate of the measurement chamber in the system was 418.3 cps, and the detection limit of the detection system was 3.01 Bq/L. Distinct gamma-ray characteristic peaks were also observable, demonstrating the system's ability to identify radioactive nuclides in the waste.

Adsorption of uranyl ion on hexagonal boron nitride for remediation of real U-contaminated soil and its interpretation using random forest

Acid leaching has been widely applied to treat contaminated soil, however, it contains several inorganic pollutants. The decommissioning of nuclear power plants introduces radioactive and soluble U(VI), a substance posing chemical toxicity to humans. Our investigation sought to ascertain the efficacy of hexagonal boron nitride (h-BN), an highly efficient adsorbent, in treating U(VI) in wastewater. The adsorption equilibrium of U(VI) by h-BN reached saturation within a mere 2 h. The adsorption of U(VI) by h-BN appears to be facilitated through electrostatic attraction, as evidenced by the observed impact of pH variations, acidic agents (i.e., HCl or H2SO4), and the presence of background ions on the adsorption performance. A reusability test demonstrated the successful completion of five cycles of adsorption/desorption, relying on the surface characteristics of h-BN as influenced by solution pH. Based on the experimental variables of initial U(VI) concentration, exposure time, temperature, pH, and the presence of background ions/organic matter, a feature importance analysis using random forest (RF) was carried out to evaluate the correlation between performances and conditions. To the best of our knowledge, this study is the first attempt to conduct the adsorption of U(VI) generated from real contaminated soil by h-BN, followed by interpretation of the correlation between performance and conditions using RF. Lastly, a. plausible adsorption mechanism between U(VI) and h-BN was explained based on the experimental results, characterizations, and a. comparison with previous adsorption studies on the removal of heavy metals by h-BN.

Freshwater Recovery and Removal of Cesium and Strontium from Radioactive Wastewater by Methane Hydrate Formation

As human society has advanced, nuclear energy has provided energy security while also offering low carbon emissions and reduced dependence on fossil fuels, whereas nuclear power plants have produced large amounts of radioactive wastewater, which threatens human health and the sustainability of water resources. Here, we demonstrate a hydrate-based desalination (HBD) technology that uses methane as a hydrate former for freshwater recovery and for the removal of radioactive chemicals from wastewater, specifically from Cs- and Sr-containing wastewater. The complete exclusion of radioactive ions from solid methane hydrates was confirmed by a close examination using phase equilibria, spectroscopic investigations, thermal analyses, and theoretical calculations, enabling simultaneous freshwater recovery and the removal of radioactive chemicals from wastewater by the methane hydrate formation process described in this study. More importantly, the proposed HBD technology is applicable to radioactive wastewater containing Cs+ and Sr2+ across a broad concentration range of low percentages to hundreds of parts per million (ppm) and even subppm levels, with high removal efficiency of radioactive chemicals. This study highlights the potential of environmentally sustainable technologies to address the challenges posed by radioactive wastewater generated by nuclear technology, providing new insights for future research and development efforts.

Kapok fiber composites minimizing secondary waste and disposal costs for large-scale radioactive liquid treatment

Conventional liquid treatments for large-scale, low-level radioactive wastewater, such as ion exchange and waste solidification, face challenges due to the large amounts of secondary waste and high disposal costs. A new large-scale decontamination method is proposed that uses kapok fiber composites for rapid radionuclide adsorption and high volume reduction to minimize secondary waste. The composite consists of natural zeolite and kapok holocellulose, which has high water-soaking ability and low-temperature pyrolysis. The kapok composites, fabricated using a commercial wet-laid nonwoven manufacturing process, absorbs 99% of low-level radioactive cesium in 20 min, reducing the volume by 98% and the weight by 47% at 300 °C. The low-temperature pyrolysis process below 300 °C prevents cesium desorption and gasification by avoiding zeolite destruction. The mass-producible kapok composites can be used for adsorbing various radionuclides in large-scale wastewater by attaching specific adsorbents for target isotopes to the composites.

CO2 competes with radioactive chemicals for freshwater recovery: Hydrate-based desalination

Here, we introduce CO2 hydrate-based desalination (CHBD) technology for freshwater recovery from radioactive wastewater, for water particularly containing Cs and Sr. The hydrate equilibrium curves of CO2 hydrates shift towards lower temperature and higher pressure regions as the concentrations of CsCl and SrCl2 increase. X-ray diffraction and Raman spectroscopy measurements found that neither CsCl nor SrCl2 can affect the structure of CO2 hydrates. The high-pressure micro-differential scanning calorimetric results demonstrate that CO2 hydrates in the presence of CsCl and SrCl2 started to dissociate at lower temperatures due to the enrichment of CsCl and SrCl2 in the remaining solutions. The formation kinetics results indicate that increases in the concentrations of the radioactive chemicals lead to a decrease in the initial reaction rate and sub-cooling temperature. Solid-state nuclear magnetic resonance spectroscopy was utilized to confirm the exclusion of radioactive isotopes from solid gas hydrates. Importantly, the CHBD technology proposed in this study is applicable to radioactive wastewater containing Cs+ and Sr2+ across broad concentration ranges, spanning from a percent to hundreds of parts per million (ppm), and even sub-ppm levels, with comparable recovery efficiency. This study presents new insights into the potential of environmentally sustainable technologies to overcome the challenges posed by radioactive wastewater.

Chitosan-minerals-based composites for adsorption of caesium, cobalt and europium

Currently, there is a growing interest in the use of natural materials in various fields of science, technology and environmental protection due to their availability, low-cost, non-toxicity and biodegradability. Chitosan, natural clay of local origin, montmorillonite, zeolite, cross-linking agents (epichlorohydrin, sodium tripolyphosphate, glutaraldehyde) and plasticisers (glycerol) were used to synthesise composites. The composites were characterised by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction analysis (XRD) and scanning electron microscope (SEM), tested for their antibacterial activity and used in batch experiments to study the adsorption of caesium, cobalt and europium ions. The maximum capacities for adsorption of caesium, cobalt and europium on the composites were 1400 mg/g, 900 mg/g and 18 mg/g, respectively. The experimental data fit better the Langmuir isotherm model and indicate favourable monolayer adsorption of Cs+, Co2+ and Eu3+ at homogeneous sites of the composites. The experimental data were in better agreement with the pseudo-second-order non-linear kinetic model for most elements and adsorbents. Adaptive neuro-fuzzy inference system proved to be a practical tool with good performance and generalisation capability for predicting the adsorption capacity of composites for caesium, cobalt, and europium ions. It was found that the predicted data were very close to the experimental data.

Well-designed protein amyloid nanofibrils composites as versatile and sustainable materials for aquatic environment remediation: A review

Amyloid nanofibrils (ANFs) are supramolecular polymers originally classified as pathological markers in various human degenerative diseases. However, in recent years, ANFs have garnered greater interest and are regarded as nature-based sustainable biomaterials in environmental science, material engineering, and nanotechnology. On a laboratory scale, ANFs can be produced from food proteins via protein unfolding, misfolding, and hydrolysis. Furthermore, ANFs have specific structural characteristics such as a high aspect ratio, good rigidity, chemical stability, and a controllable sequence. These properties make them a promising functional material in water decontamination research. As a result, the fabrication and application of ANFs and their composites in water purification have recently gained considerable attention. Despite the large amount of literature in this field, there is a lack of systematic review to assess the gap in using ANFs and their composites to remove contaminants from water. This review discusses significant advancements in design techniques as well as the physicochemical properties of ANFs-based composites. We also emphasize the current progress in using ANFs-based composites to remove inorganic, organic, and biological contaminants. The interaction mechanisms between ANFs-based composites and contaminants are also highlighted. Finally, we illustrate the challenges and opportunities associated with the future preparation and application of ANFs-based composites. We anticipate that this review will shed new light on the future design and use of ANFs-based composites.

High efficiency removal of organic and inorganic iodine with ferrate[Fe(VI)] through oxidation and adsorption

I- is a halogen species existing in natural waters, and the transformation of organic and inorganic iodine in natural and artificial processes would impact the quality of drinking water. Herein, it was found that Fe(VI) could oxidize organic and inorganic iodine to IO3-and simultaneously remove the resulted IO3- through Fe(III) particles. For the river water, wastewater treatment plant (WWTP) effluent, and shale gas wastewater treated by 5 mg/L of Fe(VI) (as Fe), around 63 %, 55 % and 71 % of total iodine (total-I) had been removed within 10 min, respectively. Fe(VI) was superior to coagulants in removing organic and inorganic iodine from the source water. Adsorption kinetic analysis suggested that the equilibrium adsorption amount of I- and IO3- were 11 and 10.1 μg/mg, respectively, and the maximum adsorption capacity of IO3- by Fe(VI) resulted Fe(III) particles was as high as 514.7 μg/mg. The heterogeneous transformation of Fe(VI) into Fe(III) effectively improved the interaction probability of IO3- with iron species. Density functional theory (DFT) calculation suggested that the IO3- was mainly adsorbed in the cavity (between the γ-FeOOH shell and γ-Fe2O3 core) of Fe(III) particles through electrostatic adsorption, van der Waals force and hydrogen bond. Fe(VI) treatment is effective for inhibiting the formation of iodinated disinfection by-products in chlor(am)inated source water.

Recent advancement in nanomaterials for the detection and removal of uranium: A review

Uranyl ions U(VI), are the common by-product of nuclear power plants and anthropogenic activities like mining, excess utilization of fertilizers, oil industries, etc. Its intake into the body causes serious health concerns such as liver toxicity, brain damage, DNA damage and reproductive issues. Therefore, there is urgent need to develop the detection and remediation strategies. Nanomaterials (NMs), due to their unique physiochemical properties including very high specific area, tiny sizes, quantum effects, high chemical reactivity and selectivity have become emerging materials for the detection and remediation of these radioactive wastes. Therefore, the current study aims to provide a holistic view and investigation of these new emerging NMs that are effective for the detection and removal of Uranium including metal nanoparticles, carbon-based NMs, nanosized metal oxides, metal sulfides, metal-organic frameworks, cellulose NMs, metal carbides/nitrides, and carbon dots (CDs). Along with this, the production status, and its contamination data in food, water, and soil samples all across the world are also complied in this work.

Efficient Co-Adsorption and Highly Selective Separation of Cs+ and Sr2+ with a K+ -Activated Niobium Germanate by the pH Control

¹³⁷ Cs and ⁹⁰ Sr are hazardous to ecological environment and human health due to their strong radioactivity, long half-life, and high mobility. However, effective adsorption and separation of Cs⁺ and Sr²⁺ from acidic radioactive wastewater is challenging due to stability issues of material and the strong competition of protons. Herein, a K⁺ -activated niobium germanate (K-NGH-1) presents efficient Cs⁺ /Sr²⁺ coadsorption and highly selective Cs⁺ /Sr²⁺ separation, respectively, under different acidity conditions. In neutral solution, K-NGH-1 exhibits ultrafast adsorption kinetics and high adsorption capacity for both Cs⁺ and Sr²⁺ (q_m ^Cs  = 182.91 mg g^-1 ; q_m ^Sr  = 41.62 mg g^-1 ). In 1 M HNO₃ solution, K-NGH-1 still possesses q_m ^Cs of 91.40 mg g^-1 for Cs⁺ but almost no adsorption for Sr²⁺ . Moreover, K-NGH-1 can effectively separate Cs⁺ from 1 M HNO₃ solutions with excess competing Sr²⁺ and M^{n +} (M^{n +}  = Na⁺ , Ca²⁺ , Mg²⁺ ) ions. Thus, efficient separation of Cs⁺ and Sr²⁺ is realized under acidic conditions. Besides, K-NGH-1 shows excellent acid and radiation resistance and recyclability. All the merits above endow K-NGH-1 with the first example of niobium germanates for radionuclides remediation. This work highlights the facile pH control approach towards bifunctional ion exchangers for efficient Cs⁺ /Sr²⁺ coadsorption and selective separation.

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.

Impact of microbial processes on the safety of deep geological repositories for radioactive waste

To date, the increasing production of radioactive waste due to the extensive use of nuclear power is becoming a global environmental concern for society. For this reason, many countries have been considering the use of deep geological repositories (DGRs) for the safe disposal of this waste in the near future. Several DGR designs have been chemically, physically, and geologically well characterized. However, less is known about the influence of microbial processes for the safety of these disposal systems. The existence of microorganisms in many materials selected for their use as barriers for DGRs, including clay, cementitious materials, or crystalline rocks (e.g., granites), has previously been reported. The role that microbial processes could play in the metal corrosion of canisters containing radioactive waste, the transformation of clay minerals, gas production, and the mobility of the radionuclides characteristic of such residues is well known. Among the radionuclides present in radioactive waste, selenium (Se), uranium (U), and curium (Cm) are of great interest. Se and Cm are common components of the spent nuclear fuel residues, mainly as 79Se isotope (half-life 3.27 × 105 years), 247Cm (half-life: 1.6 × 107 years) and 248Cm (half-life: 3.5 × 106 years) isotopes, respectively. This review presents an up-to-date overview about how microbes occurring in the surroundings of a DGR may influence their safety, with a particular focus on the radionuclide-microbial interactions. Consequently, this paper will provide an exhaustive understanding about the influence of microorganisms in the safety of planned radioactive waste repositories, which in turn might improve their implementation and efficiency.

Efficient Iodine Removal by Porous Biochar-Confined Nano-Cu2O/Cu0: Rapid and Selective Adsorption of Iodide and Iodate Ions

Iodine is a nuclide of crucial concern in radioactive waste management. Nanomaterials selectively adsorb iodine from water; however, the efficient application of nanomaterials in engineering still needs to be developed for radioactive wastewater deiodination. Artemia egg shells possess large surface groups and connecting pores, providing a new biomaterial to remove contaminants. Based on the Artemia egg shell-derived biochar (AES biochar) and in situ precipitation and reduction of cuprous, we synthesized a novel nanocomposite, namely porous biochar-confined nano-Cu₂O/Cu⁰ (C-Cu). The characterization of C-Cu confirmed that the nano-Cu₂O/Cu⁰ was dispersed in the pores of AES biochar, serving in the efficient and selective adsorption of iodide and iodate ions from water. The iodide ion removal by C-Cu when equilibrated for 40 min exhibited high removal efficiency over the wide pH range of 4 to 10. Remarkable selectivity towards both iodide and iodate ions of C-Cu was permitted against competing anions (Cl^-/NO₃^-/SO₄^2-) at high concentrations. The applicability of C-Cu was demonstrated by a packed column test with treated effluents of 1279 BV. The rapid and selective removal of iodide and iodate ions from water is attributed to nanoparticles confined on the AES biochar and pore-facilitated mass transfer. Combining the advantages of the porous biochar and nano-Cu₂O/Cu⁰, the use of C-Cu offers a promising method of iodine removal from water in engineering applications.

Tannic acid-assisted in-situ interfacial formation of Prussian blue-assembled adsorptive membranes for radioactive cesium removal

There is a growing interest in advanced materials that can effectively treat wastewater contaminated with radioactive cesium (¹³⁷Cs), which is an extremely hazardous material. Here, we report a new class of Cs-adsorptive membranes compactly assembled with Cs-adsorptive Prussian blue (PB) particles. The PB particle assembly was formed via an in-situ interfacial reaction between two PB precursors in the presence of tannic acid (TA) as a binder on a porous support. While the interfacial reaction enabled the formation of a defect-less PB network, TA enhanced the PB-PB and PB-support compatibilities, consequently producing a uniform, densely packed PB assembly near the support surface. The fabricated TA-assisted PB membrane (PB/TA-M) synergistically rejected Cs via a combination of adsorption and membrane filtration, although adsorption predominantly determined Cs rejection initially. Hence, the PB/TA-M membrane showed considerably higher Cs removal performance than commercial nanofiltration (NF) and reverse osmosis (RO) polyamide (PA) membranes for a sufficiently long operation time. Furthermore, the PB/TA-M membrane displayed excellent radioactive ¹³⁷Cs removal performance, significantly exceeding those of commercial NF and RO PA membranes due to its higher radiation stability, indicating its viability for application in treating actual radioactive wastewater.

Collagen Fiber-Based Advanced Separation Materials: Recent Developments and Future Perspectives

Separation plays a critical role in a broad range of industrial applications. Developing advanced separation materials is of great significance for the future development of separation technology. Collagen fibers (CFs), the typical structural proteins, exhibit unique structural hierarchy, amphiphilic wettability, and versatile chemical reactivity. These distinctive properties provide infinite possibilities for the rational design of advanced separation materials. During the past 2 decades, many progressive achievements in the development of CFs-derived advanced separation materials have been witnessed already. Herein, the CFs-based separation materials are focused on and the recent progresses in this topic are reviewed. CFs widely existing in animal skins display unique hierarchically fibrous structure, amphiphilicity-enabled surface wetting behaviors, multi-functionality guaranteed covalent/non-covalent reaction versatility. These outstanding merits of CFs bring great opportunities for realizing rational design of a variety of advanced separation materials that were capable of achieving high-performance separations to diverse specific targets, including oily pollutants, natural products, metal ions, anionic contaminants and proteins, etc. Besides, the important issues for the further development of CFs-based advanced separation materials are also discussed.

Highly Selective Adsorption of 99TcO4-/ReO4- by a Novel Polyamide-Functionalized Polyacrylamide Polymer Material

The treatment of radioactive wastewater is one of the major problems in the current research. With the development of nuclear energy, the efficient removal of ⁹⁹TcO₄^- in radioactive wastewater has attracted the attention of countries all over the world. In this study, a novel functional polyamide polymer p-(Amide)-PAM was synthesized by the two-step method. The experimental results show that p-(Amide)-PAM has good adsorptive properties for ⁹⁹TcO₄^-/ReO₄^- and has good selectivity in the nitric acid system. The kinetics of the reaction of p-(Amide)-PAM with ⁹⁹TcO₄^-/ReO₄^- was studied. The results show that p-(Amide)-PAM has a fast adsorption rate for ⁹⁹TcO₄^-/ReO₄^-, the saturated adsorption capacity reaches 346.02 mg/g, and the material has good reusability. This new polyamide-functionalized polyacrylamide polymer material has good application prospects in the removal of ⁹⁹TcO₄^- from radioactive wastewater.

Electrodialysis for the volume reduction of the simulated radionuclides containing seawater

In this study, electrodialysis (ED) was performed to concentrate the radionuclides containing seawater for volume minimization. The concentration behaviors of the trace radioactive elements were also explored. Under the optimal voltage drop of 6 V and the volume ratio of 1:40, the concentration times of Cs⁺, Co²⁺, Sr²⁺ and I^- could reach 9.9, 9.5, 20.1 and 32.5, respectively. Furthermore, it enabled over 80% volume reduction and over 90% removal of all hazardous radionuclides. Hence, ED is a feasible and promising method to manage the radioactive wastewater due to its high concentration and decontamination performances. For identical ion contents, the concentration rate for the cations presented the order of Na⁺ > Cs⁺ > Sr²⁺ > Co²⁺; the hydration radius and hydration free energy played the dominant roles in ion concentration. In contrast, for the ED concentration of trace radioactive elements, of which the contents are several magnitudes lower than the predominant salt concentration, the concentration rate presented the order of Sr²⁺ > Cs⁺ > Co²⁺ > Na⁺; the specific charge began to play an important role when the predominant ion approached its saturated salt concentration. For the anions, I^- always migrated faster than Cl^- at diverse concentrations.

Adsorption of caesium and cobalt ions on the muscovite mica clay-graphene oxide-γ-Fe2O3-Fe3O4 composite

The muscovite mica clay-graphene oxide-maghemite-magnetite (γ-Fe₂O₃-Fe₃O₄) composite was first used for the adsorption of caesium(I) and cobalt(II). The presence of clay minerals, graphene oxide, maghemite, and magnetite was detected in the prepared composite by XRD, WD-XRF, Mössbauer spectroscopy, and ATR-FTIR. The SEM and TEM results show that the composite has a layered structure with irregularly shaped pores on the surface. It was found that the adsorption of ions depends on the initial concentration, pH (except for caesium), mass of adsorbent, temperature, and contact time. The maximum adsorption capacity for Cs(I) and Co(II) was 2286 mg/g and 652 mg/g, respectively, and was obtained at concentrations (Cs(I) = 12,630 mg/L; Co(II) = 3200 mg/L), adsorbent mass of 0.01 g, pH (Cs(I) = 7; Co(II) = 5), temperature of 20 ± 1 °C, and contact time of 24 h. The high adsorption capacity of the composite could be due to a diversity of functional groups, a large number of active sites or the multilayer adsorption of caesium and cobalt ions on the surface of the composite. The Freundlich, Langmuir isotherms, and the pseudo-second-order kinetic model better describe the adsorption of these ions on the composite. The adsorption was non-spontaneous endothermic for Cs(I) and spontaneous endothermic for Co(II). The proposed mechanism of adsorption of Cs and Co ions on the composite is complex and involves electrostatic interactions and ion exchange. The ANFIS model proved to be quite effective in predicting the adsorption of Cs(I) and Co(II), as shown by the obtained values of R², MSE, SSE, and ARE.

Fabrication of a porous polyacrylonitrile nanofiber adsorbent for removing radioactive 60Co

A Co2+ adsorbent was prepared using electrospun porous polyacrylonitrile (PAN) nanofibers, featuring easy recovery for reuse compared with a nanoparticle-based adsorbent. As an efficient ligand for Co2+, ethylenediaminetetraacetic acid (EDTA) was introduced on the surface of porous PAN nanofibers with the aid of a branched polyethyleneimine (PEI) linker to obtain an adsorbent with carboxylic acid groups. On the adsorbent surface, the carboxylic acid and amine groups from EDTA could adsorb Co2+ via ion exchange and chelation, and amine groups from PEI that remained after EDTA functionalization played a role in coordinating Co2+. The amine and carboxylic acid groups were simultaneously involved in the adsorption on the surface, making it possible to remove Co2+ over a wide pH range. An investigation of the adsorption isotherms and kinetics of the nanofibrous adsorbent indicated that monolayer chemisorption was achieved with a maximum Co2+ adsorption capacity of 8.32 mg/g. In addition, radioactive 60Co was efficiently removed by the adsorbent with a removal extent of more than 98%. Considering the easy separation from Co2+ solution and regeneration of the nanofibrous adsorbent and its availability in a wide pH range, the adsorbent has great advantages in practical applications.

Aqueous Strippable Polymer Coating for Highly Efficient Primary Radioactive Uranium Decontamination with Versatility on Diversified Surface

The decontamination of radioactive materials on the surfaces of nuclear facilities has generated large quantities of waste from the rapid development of the nuclear industry, posing a potential threat globally. Strippable coating has been employed for some time to remove radioactive contamination due to its high performance and removability, flexibility, and compatibility with various substrates. Herein, an aqueous strippable coating based on an adsorbent/polyvinyl alcohol (PVA) polymer was developed to remove radioactive uranium from stainless-steel surfaces that showed greater decontamination than that of DeconGel, with an efficiency of 87.2% for 5 g/L uranium and 95.5% for 22.5 g/L uranium, along with a high repeatability and better mechanical properties. Furthermore, the prepared coating was versatile and could be applied to a range of substrate surfaces (lacquered, aluminum, glass, plastic, and ceramic), with outstanding performance ranging from 79.2 to 95.4% for 1 g/L uranium. The prepared coating could also be applied through brushing or spraying to horizontal or vertical substrates. The exceptional performance could be due to the synergistic effect of the introduction of ethylene diamine tetra-acetic acid disodium salt (EDTA-2Na) as a chelating agent and the nano-adsorbent CaCO₃/TiO₂.

Rapid Determination of Gross Alpha/Beta Activity in Water Based on Reverse Osmosis Membrane Enrichment Pretreatment

Radioactivity of gross alpha/beta is an index of water quality detection, which can reflect the radioactivity intensity of water. However, the traditional detection method of these parameters, thick source method, has problems of cumbersome and time consumption in sample preparation and cannot realize the rapid detection on-site. Based on this, this paper studies the enrichment method based on reverse osmosis membrane to accurately and quickly determine the gross α and gross β in water by using the reverse osmosis membrane as the carrier and enriching the radionuclides in water to the high-pressure side of the reverse osmosis membrane to replace the sample preparation process in traditional thick source method, so as to shorten the sample processing time in the detection process and avoid the cumbersome sample preparation process. The reverse osmosis membrane enrichment method for the determination of gross in 241Am and 40KCl standard solutions was used to study gross alpha/beta radioactivity, and the results showed that the average recoveries of radioactivity of gross alpha/beta were 95.0% and 93.6%, respectively. At the same time, the results of the thick source method and the reverse osmosis membrane method on the gross alpha/beta of actual water samples in 5 different regions were compared. It showed that the thick source method and the reverse osmosis membrane method had a good consistency in the detection results of total α and total β radioactivity, and the reverse osmosis membrane method had better stability than the thick source method. The average relative standard deviations (RSD) of the gross alpha and gross beta activity obtained by the thick source method are 11.9% and 7.3%, respectively, while RSD of the gross alpha and gross beta radioactivity obtained by the reverse osmosis membrane method were 6.9% and 4.7%, respectively. The preparation time of single sample was reduced by 75.7%, and the overall detection cycle time was reduced by 68.1%.

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.

Characterization of bio-adsorptive removal performance of strontium through ureolysis-mediated bio-mineralization

The adsorptive removal performance of strontium (Sr) through bio-mineralization metabolism under various parameters was evaluated in this study. The primary mechanism of bio-mineralization used in this study was the urea hydrolysis process through bacterial enzymatic catalysis. Bacillus sp, which was isolated from river sediment, was used as a ureolytic bacteria. Various environmental conditions were set as different initial concentrations of Sr (10, 50, 100, 200, and 500 mg/L), and various ratios of Mg/Ca (4, 2, 1, 0.5, and 0.25). The concentrations of Sr²⁺, Ca²⁺, and Mg²⁺ in the solution of the batch experiment were measured to identify the bio-mineralization performance and the removal rate of Sr. In addition, the main Sr removal mechanism of ureolytic bacteria was identified. As a result, for Sr removal of bacteria, the bio-mineralization mechanism was more predominant than the adsorption of Sr. The rapid growth and high nucleation site production were observed when the initial concentration of Sr²⁺ increased and the Mg/Ca ratio was lowered, resulting in high biomineralization performance and Sr removal rate. The main phases of carbonate minerals formed in the presence of Sr, Ca, and Mg were SrCO₃ and SrCa(CO₃)₂. Mg²⁺ could retard the bacterial growth and participate in the formation of carbonate minerals, when a large amount of Mg²⁺ was present. Furthermore, the desorption rate of Sr²⁺ from bacterial pastes containing the carbonate minerals increased as the concentration of HCl increased, although the carbonate minerals were in a stable state.

Membrane Distillation for Wastewater Treatment: A Mini Review

Water serves as an indispensable part of human life and production. On account of the overexploitation of traditional water sources, the demand for wastewater recycling is expanding rapidly. As a promising water treatment process, membrane distillation (MD) has been utilized in various wastewater treatments, such as desalination brine, textile wastewater, radioactive wastewater, and oily wastewater. This review summarized the investigation work applying MD in wastewater treatment, and the performance was comprehensively introduced. Moreover, the obstructions of industrialization, such as membrane fouling, membrane wetting, and high energy consumption, were discussed with the practical investigation. To cope with these problems, various strategies have been adopted to enhance MD performance, including coupling membrane processes and developing membranes with specific surface characteristics. In addition, the significance of nutrient recovery and waste heat utilization was indicated.

Simultaneous decontamination of multi-pollutants: A promising approach for water remediation

Water remediation techniques have been extensively investigated due to the increasing threats of soluble pollutants posed on the human health, ecology and sustainability. Confronted with the complex composition matrix of wastewater, the simultaneous elimination of coexisting multi-pollutants remains a great challenge due to their different physicochemical properties. By integrating multi-contaminants elimination processes into one unit operation, simultaneous decontamination attracted more and more attention under the consideration of versatile applications and economical benefits. In this review, the state-of-art simultaneous decontamination methods were systematically summarized as chemical precipitation, adsorption, photocatalysis, oxidation-reduction, biological removal and membrane filtration. Their applications, mechanisms, mutual interactions, sustainability and recyclability were outlined and discussed in detail. Finally, the prospects and opportunities for future research were proposed for further development of simultaneous decontamination. This work could provide guidelines for the design and fabrication of well-organized simultaneous decontaminating system.

Enhancement of the heterogeneous adsorption and incorporation of uraniumVI caused by the intercalation of β-cyclodextrin into the green rust

The influence of intercalated anions on the structure and composition of green rusts supplies a theoretical possibility for the investigation of the structural modification of Fe^II/Fe^III (oxyhydr)oxide materials. β-Cyclodextrin was intercalated into the mixed-valent iron-based hydroxide layers to synthesize new green rust materials (β-CD GRs), pursuing high-capacity uranium^VI (U^VI) sorption. The molar ratios of Fe^II to Fe^III and the molar ratios of β-CD GR to Fe^II + Fe^III had a significant effect on the synthesis of β-CD GRs. The synthesis process was further optimized by the quadric predictor and desirability function in a central composite design in combination. Both strong acidity and alkalinity were harmful to the adsorption of β-CD GRs towards U^VI. The pseudo-first-order kinetic model and Langmuir isotherm model were appropriate in fitting the whole adsorption process. The maximum monolayer adsorption capacity of β-CD GRs was 2548.61 mg/g. The presence of mimic groundwater constituents explicitly deteriorated the interaction between β-CD GR and U^VI species. Nanoscale nodules and particles were formed on the β-CD GR after the adsorption experiments. The peaks at 1159 and 609 cm^-1 vanished with the band at 1103 cm^-1 being left-shifted to 1117 cm^-1 in the FTIR spectra of β-CD GR during the heterogeneous process. The intercalation of β-CD brought obvious enhancement of U^VI species sorption to the GR material, which was combinedly driven by several reaction pathways and different from the unmodified GRs.

A critical review of environmental and public health impacts from the activities of evaporation ponds

Evaporation ponds (EVPs) are among the most cost-effective, and simple wastewater treatment technologies used in many regions/countries with high solar radiation levels. However, its operational limitations, which include the overflow of wastewater, leakages via liners, and large surface area of the EVP that is exposed to atmosphere, creates a negative feedback to the environment. Therefore, the main aim of this review study of more than a hundred works published a little all over the continents is to provide a summary of various contaminations that are associated with EVPs activities through different environmental compartments. In addition, the impacts of EVP on fauna, human health including the current on-site sustainable mitigation strategies were also reviewed. The first conclusion from this study shows that the most commonly contaminants released into surface waters, groundwater, soil and sediments were heavy metals, pesticides, herbicides, selenium, including several major anions and cations. Non-methane hydrocarbons (NMHCs), volatile organic compounds (VOCs), and particulate matters (PMs) were the main air pollutants emitted from the surfaces of an EVP. Limited data is available about the emissions of atmospheric greenhouse gas (GHGs) especially carbon dioxide (CO₂) and methane (CH₄) from EVP surfaces. Migratory birds and aquatic organisms are the most vulnerable fauna as EVP wastewaters can cause obstruction of movements, affect diversity, and causes mortalities following the exposure to the toxic wastewater. The study revealed limited data about the potential health risk associated with occupational and environmental exposure to radiological hazards and contaminated drinking water from EVP activities. On-site EVP treatment strategies using bioremediation and electrochemical treatment technologies have shown to be a promising sustainable mitigation approach. Knowledge gaps in areas of GHGs monitoring/modeling, pollution exposure estimation and health risk assessments are urgently required to gain deeper understanding about the impact of EVP activities, and incorporate them into future EVP designs.

Removal of radioactive cesium from contaminated water by whey protein amyloids-carbon hybrid filters

We report on the application of an innovative whey protein amyloids–carbon hybrid filter for the removal and disposal of the long-lived radioactive fission product ¹³⁷Cs from aqueous samples. Test experiments revealed a reduction of ¹³⁷Cs radioactivity by a factor of 340 compared to the initial solution, with an efficiency as high as 99.7%. The adsorption capacity of the membrane was explored by performing several cycles of filtration, indicating a potential retention of more than 115 MBq per gram of filtering material at the applied experimental conditions. These results pave the way for further investigations on the applicability of this filter material to other nuclear fission products.

The efficient removal of the long-lived fission product ¹³⁷Cs from radioactive water by a filter material based on whey protein fibrils and activated carbon.

Copper Rich Composite Materials Based on Carboxylic Cation Exchangers and Their Thermal Transformation

The effect of a cupric deposit (Cu2+, CuO) on the thermal decomposition of carboxylic cation exchangers (CCEs) is not known, and such studies may have practical significance. CCEs have a very high ion exchange capacity, so an exceptionally large amount of CuO (which is a catalyst) can be precipitated inside them. Two CCEs, macroreticular (Amberlite IRC50) and gel-like (Amberlite IRC86), served as a polymeric support to obtain copper-rich hybrid ion exchangers. Composites with CuO particles inside a polyacrylic matrix (up to 35.0 wt% Cu) were obtained. Thermal analyses under air and under N2 were performed for CCEs in the H+ and Cu2+ form with and without a CuO deposit. The results of sixteen experiments are discussed based on the TG/DTG curves and XRD patterns of the solid residues. Under air, the cupric deposit shifted the particular transformations and the ultimate polymeric matter decomposition (combustion) toward lower temperatures (even about 100-150 °C). Under N2, the reduction of the cupric deposit to metallic copper took place. Unique composite materials enriched in carbonaceous matter were obtained, as the products of polymeric matrix decomposition (free radicals and hydrogen) created an additional amount of carbon char due to the utilization of a certain amount of hydrogen to reduce Cu (II) to Cu0.

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).

Integrated forward osmosis-adsorption process for strontium-containing water treatment: Pre-concentration and solidification

The volume reduction and subsequent solidification of soluble radionuclides have been known as the major challenges in global radioactive water management, with the urgent needs for new technology development. Thus, a novel forward osmosis (FO)-adsorption process was developed for decontamination of strontium-containing radioactive water. The FO filtration driven by the osmotic pressure difference across FO membrane was more cost- and energy-effective for pre-concentration and volume reduction of low-concentration radioactive water prior to solidification, whereas subsequent adsorption with a novel adsorbent offered an effective mean for high-efficiency fixation of soluble radioactive on adsorbent. Results showed that the FO unit in the proposed integrated process could lead to a concentration factor of 10, with 90% of water volume reduction. The concentrated stream with a smaller volume from FO was further treated through adsorption of Sr²⁺ by nanostructured layered sodium vanadosilicate which had an excellent adsorption capacity of 174.3 mg Sr²⁺/g. It was found that 96.8-99.9% of soluble Sr²⁺ in FO concentrate could be removed by adsorption within several seconds. As the result, an excellent solidification of Sr²⁺ with an ultimate concentration factor of 1000 was achieved in the proposed novel integrated FO-adsorption process. These clearly demonstrated that this process would offer an environmentally sustainable and economically viable engineering solution for high-efficiency decontamination of Sr²⁺-containing radioactive water.

Indigenous Fish-Based Assessment of Genotoxic Potentials of the Helong Reservoir in Guangzhou, China

The present study was conducted to assess the genotoxic potential of water from the Helong Reservoir, which was designated as a strategic drinking water source by the Guangdong Provincial Government of China in October 2016. Four kinds of common indigenous fish samples (Labeo rohita, Cirrhinus molitorella, red tilapia, and Oreochromis niloticus) were collected at 6 sampling sites during the period from July to November 2020. Fish from the clean drinking water source of the upper reaches of the Liuxihe Reservoir in Guangzhou were collected as the control. Both the alkaline single cell gel electrophoresis assay and the micronucleus test were used to detect DNA damage and the micronucleus rate in erythrocytes of fish samples, respectively. The results indicated that there was a significant increase in comet tail length, Olive tail moment, and micronucleus rates of all fish samples compared with those of the control (p < 0.05). The order of sensitivity to DNA damage and micronucleus formation was Labeo rohita > Cirrhinus molitorella > red tilapia > Oreochromis niloticus. The results of the 2 kinds of experiments were in perfect agreement with each other. We conclude that there are obvious genotoxic effects from the water in the Helong Reservoir. As a strategic drinking water source, the safety of the Reservoir water quality should be considered. The local government should put the restoration of the Helong Reservoir water quality on the agenda as soon as possible. Environ Toxicol Chem 2021;40:1919-1927. © 2021 SETAC.