Radioactive waste treatments by using zeolites. A short review

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.

Highly efficient uranium uptake by the eco-designed cocamidopropyl betaine-decorated Na-P1 coal fly-ash zeolite

In some locations around the globe, the U concentrations may exceed WHO standards by 2-folds therefore, effective yet environmentally wise solutions to purify radioactive waters are of significant importance. Here, the optimized and fully controlled coal-fly-ash based Na-P1 zeolite functionalization by employing novel, biodegradable biosurfactant molecule - cocamidopropyl betaine (CAPB) is showcased. The zeolite's surface decoration renders three composites with varying amounts of introduced CAPB molecule (Na-P1 @ CAPB), with 0.44, 0.88, and 1.59-times External Cation Exchange Capacity (ECEC). Wet-chemistry experiments revealed extremely high U adsorption capacity (qmax = 137.1 mg U/g) unveiling preferential interactions of uranyl dimers with CAPB molecules coupled with ion-exchange between Na+ ions. Multimodal spectroscopic analyses, including Fourier-Transformed Infra-Red (FT-IR), X-ray Photoelectron (XPS), and X-ray Absorption Fine Structure (XAFS), showed the hexavalent oxidation state of U, and no secondary release of the CAPB molecule from the composite. The EXAFS signals fingerprint changes in the interatomic distances of adsorbed U, showing the impact of the O and N, heteroatoms present in the CAPB molecule on U binding mechanism. The presented research outcomes showcase the easy, scalable, optimized, and environmentally friendly synthesis of biofunctional zeolite effectively purifying the real-life U-bearing wastewaters from the vicinity of the Pribram deposit (Czech Republic).

Monte Carlo Simulations of Water Pollutant Adsorption at Parts-per-Billion Concentration: A Study on 1,4-Dioxane

1,4-dioxane, an emerging water pollutant with high production volumes, is a probable human carcinogen. The inadequacy of conventional treatment processes demonstrates the need for an effective remediation strategy. Crystalline nanoporous materials are cost-effective adsorbents due to their high capacity and selective separation in mixtures. This study explores the potential of all-silica zeolites for the separation of 1,4-dioxane from water. These zeolites are highly hydrophobic and can preferentially adsorb nonpolar molecules from mixtures. We investigated six zeolite frameworks (BEA, EUO, FER, IFR, MFI, and MOR) using Monte Carlo simulations in the Gibbs ensemble. The simulations indicate high selectivity by FER and EUO, especially at low pressures, which we attribute to pore sizes and shapes with a greater affinity to 1,4-dioxane. We also demonstrate a Monte Carlo simulation workflow using gauge cells to model the adsorption of an aqueous solution of 1,4-dioxane at a 0.35 ppb concentration. We quantify 1,4-dioxane and water coadsorption and observe selectivities ranging from 1.1 × 105 in MOR to 8.7 × 106 in FER. We also demonstrate that 1,4-dioxane is in the infinite dilution regime in the aqueous phase at this concentration. This simulation technique can be extended to model other emerging water contaminants such as perfluoroalkyl and polyfluoroalkyl substances (PFAS), chlorofluorocarbons, and others, which are also found in extremely low concentrations.

Unraveling the nuclear isotope tapestry: Applications, challenges, and future horizons in a dynamic landscape

Nuclear isotopes, distinct atoms characterized by varying neutron counts, have profoundly influenced a myriad of sectors, spanning from medical diagnostics and therapeutic interventions to energy production and defense strategies. Their multifaceted applications have been celebrated for catalyzing revolutionary breakthroughs, yet these advancements simultaneously introduce intricate challenges that warrant thorough investigation. These challenges encompass safety protocols, potential environmental detriments, and the complex geopolitical landscape surrounding nuclear proliferation and disarmament. This comprehensive review embarks on a deep exploration of nuclear isotopes, elucidating their nuanced classifications, wide-ranging applications, intricate governing policies, and the multifaceted impacts of their unintended emissions or leaks. Furthermore, the study meticulously examines the cutting-edge remediation techniques currently employed to counteract nuclear contamination while projecting future innovations in this domain. By weaving together historical context, current applications, and forward-looking perspectives, this review offers a panoramic view of the nuclear isotope landscape. In conclusion, the significance of nuclear isotopes cannot be understated. As we stand at the crossroads of technological advancement and ethical responsibility, this review underscores the paramount importance of harnessing nuclear isotopes' potential in a manner that prioritizes safety, sustainability, and the greater good of humanity.

Design and Construction of the Uranyl Coordination Polymer with Multifunction Stimulus Response: Fluorescent Sensors for Halide Ions and Photochromism

It can provide ideas for the use of uranium elements in the treatment of spent fuel from nuclear wastewater to explore the application potential of uranium element. Thus, it is necessary to research the structure and properties of a novel uranyl coordination polymer (CP) for uranium recovery and reuse. Herein, we designed and prepared a new uranyl CP U-CMNDI based on UO22+ and H2CMNDI (H2CMNDI = N, N'-bis(carboxymethyl)-1,4,5,8-naphthalenediimide). Structural analysis shows that two uranyl ions are connected by two parallel deprotonated CMNDI ligands to form a discrete uranyl dimer structure. U-CMNDI can act as a potential stimulus-responsive halide ion sensor by a fluorescence "turn on" response in water. The limit of detection for fluoride (F-), bromide (Br-), iodide (I-), and chloride (Cl-) is 5.00, 5.32, 5.49, and 5.73 μM, respectively. The fluorescence "turn on" behavior is based on the photoinduced electron transfer (PET) mechanism between halide ions and electron-deficient NDI cores. In addition, U-CMNDI demonstrates a color response to ultraviolet light, exhibiting reversible photochromic behavior with a notable color change. The color change mechanism can contribute to the PET process and the radical process.

Fundamental properties and sustainable applications of the natural zeolite clinoptilolite

This review explores a set of sustainable applications of clinoptilolite, a natural zeolite abundant around the world in different localities. Thanks to its physico-chemical properties this material is extremely versatile for several applications, ranging from environmental catalysis and CO2 removal to industrial and agricultural wastewater purification, aquaculture, animal feeding, and food industry but also medical applications and energy storage systems. Due to the presence of cations in its framework, it is possible to tune the material's features making it suitable for adsorbing specific compounds. Thus, this review aims to provide insight into developing new technologies based on the use of this material that is sustainable, not harmful for humans and animals, naturally abundant, and above all cost-effective. Furthermore, it is intended to promote the use of natural materials in various areas with a view to sustainability and to reduce as far as possible the use of chemicals or other materials whose synthesis process can have a polluting effect on the environment.

Exploring zeolite-based composites in adsorption and photocatalysis for toxic wastewater treatment: Preparation, mechanisms, and future perspectives

Water scarcity has become a critical global concern exacerbated by population growth, globalization, and industrial expansion, resulting in the production of wastewater containing a wide array of contaminants. Tackling this challenge necessitates the adoption of innovative materials and technologies for effective wastewater treatment. This review article provides a comprehensive exploration of the preparation, applications, mechanisms, and economic environmental analysis of zeolite-based composites in wastewater treatment. Zeolite, renowned for its versatility and porous nature, is of paramount importance due to its exceptional properties, including high surface area, ion exchange capability, and adsorption capacity. Various synthetic methods for zeolite-based composites are discussed. The utilization of zeolites in wastewater treatment, particularly in adsorption and photocatalysis, is thoroughly investigated. The significance of zeolite in adsorption and its role in the photocatalytic degradation of pollutants are examined, along with its applications in treating volatile organic compounds (VOCs), dye wastewater, oil-field wastewater, and radioactive waste. Mechanisms underlying zeolite-based adsorption and photocatalysis, including physical and chemical adsorption, ion exchange, and surface modification, are elucidated. Additionally, the role of micropores in the adsorption process is explored. Furthermore, the review delves into regeneration and desorption studies of zeolite-based composites, crucial for sustainable wastewater treatment practices. Economic and environmental analyses are conducted to assess the feasibility and sustainability of employing zeolite-based composites in wastewater treatment applications. Future recommendations are provided to guide further research and development in the field of zeolite-based composites, aiming to enhance wastewater treatment efficiency and environmental sustainability. By exploring the latest advancements and insights into zeolite-based nanocomposites, this paper aims to contribute to the development of more efficient and sustainable wastewater treatment strategies. The integration of zeolite-based materials in wastewater treatment processes shows promise for mitigating water pollution and addressing water scarcity challenges, ultimately contributing to environmental preservation and public health protection.

Optimization of Selective Hydrometallurgical Tantalum Recovery from E-Waste Using Zeolites

To protect future high-tech metal demand, a selective and efficient recovery method for tantalum from a tantalum-rich e-waste component sample was developed. Ultrasound-assisted digestion of the component sample was optimized, and the highest dissolution rate was achieved using a mixture of 8 mol/L H2SO4 and HF at a temperature of 60 °C. The determined amount of tantalum was as high as 11 000 ± 1000 mg/kg, which results in a high potential for recyclable tantalum. The other major elements of this complex e-waste fraction were silicon, iron, aluminum, and tin. Efficient recovery of tantalum from the leachate was performed using the zeolite material ZSM-5. Extremely high selectivity and a recovery rate of over 98% were obtained. In terms of adsorption efficiency, selectivity, and durability of the material, optimal adsorption was obtained using the diluted sample at 0.5 mol/L of H2SO4. The adsorption capacity of ZSM-5 for tantalum was determined to be 10.5 ± 0.6 mg/g, and tantalum was selectively eluted with 1:4 diluted ethanolamine with a yield of 87.2 ± 1.5%.

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.

The potential of zeolite nanocomposites in removing microplastics, ammonia, and trace metals from wastewater and their role in phytoremediation

Nanocomposites are emerging as a new generation of materials that can be used to combat water pollution. Zeolite-based nanocomposites consisting of combinations of metals, metal oxides, carbon materials, and polymers are particularly effective for separating and adsorbing multiple contaminants from water. This review presents the potential of zeolite-based nanocomposites for eliminating a range of toxic organic and inorganic substances, dyes, heavy metals, microplastics, and ammonia from water. The review emphasizes that nanocomposites offer enhanced mechanical, catalytic, adsorptive, and porosity properties necessary for sustainable water purification techniques compared to individual composite materials. The adsorption potential of several zeolite-metal/metal oxide/polymer-based composites for heavy metals, anionic/cationic dyes, microplastics, ammonia, and other organic contaminants ranges between approximately 81 and over 99%. However, zeolite substrates or zeolite-amended soil have limited benefits for hyperaccumulators, which have been utilized for phytoremediation. Further research is needed to evaluate the potential of zeolite-based composites for phytoremediation. Additionally, the development of nanocomposites with enhanced adsorption capacity would be necessary for more effective removal of pollutants.

Eco-friendly and cost-effective adsorbent derived from blast furnace slag with black liquor waste for hazardous remediation

The current investigation concerns with preparation eco-friendly and cost-effective adsorbent (mesoporous silica nanoparticles (SBL)) based on black liquor (BL) containing lignin derived from sugarcane bagasse and combining it with sodium silicate derived from blast furnace slag (BFS) for thorium adsorption. Thorium ions were adsorbed from an aqueous solution using the synthesized bio-sorbent (SBL), which was then assessed by X-ray diffraction, BET surface area analysis, scanning electron microscopy with energy dispersive X-ray spectroscopy (EDX), and Fourier transforms infrared spectroscopy (FTIR). Th(IV) sorption properties, including the pH effect, uptake rate, and sorption isotherms across various temperatures were investigated. The maximum sorption capacity of Th(IV) on SBL is 158.88 mg/L at pH value of 4328 K, and 60 min contact time. We demonstrated that the adsorption processes comport well with pseudo-second-order and Langmuir adsorption models considering the kinetics and equilibrium data. According to thermodynamic inspections results, the Th(IV) adsorption process exhibited endothermic and random behavior suggested by positive ΔH° and ΔS° values, while the negative ΔG° values indicated a spontaneous sorption process. The maximum Th(IV) desorption from the loaded SBL (Th/SBL) was carried out at 0.25 M of NaHCO3 and 60 min of contact. Sorption/desorption processes have five successive cycles. Finally, this study suggests that the recycling of BFS and BL can be exploited for the procurement of a promising Th(IV) adsorbents.

A comprehensive study for the potential removal of 152+154Eu radionuclides using a promising modified strontium-based MOF

A facile modification of a strontium-based MOF using oxalic acid was carried out to prepare MTSr-OX MOF, which was used as a potential substance for eliminating 152+154Eu radioisotopes. Various analytical techniques were used to characterize MTSr-OX-MOF. The prepared MOF had a rod-like structure with a BET surface area of 101.55 m2 g-1. Batch sorption experiments were used to investigate the sorption performance of MTSr-OX-MOF towards 152+154Eu radionuclides where different parameters like pH, contact time, initial 152+154Eu concentration, ionic strength, and temperature were scrutinized to determine the optimum conditions for 152+154Eu removal. MTSr-OX-MOF showed superior effectiveness in the elimination of 152+154Eu with a maximum sorption capacity of 234.72 mg g-1 at pH 3.5. Kinetics fitted with the pseudo-second-order model and the Langmuir model correctly described the sorption mechanism. The thermodynamic variables were carefully examined, demonstrating that the 152+154Eu sorption was endothermic as well as spontaneous. The MTSr-OX-MOF has been found to be a significantly more effective sorbent towards 152+154Eu than that of many other adsorbents. When applied to real active waste, MTSr-OX-MOF demonstrated excellent removal performance for a wide range of radionuclides. As a result, the MTSr-OX-MOF can be recognized as an attractive solution for the 152+154Eu purification from active waste.

Transition Metal Catalysts for Atmospheric Heavy Metal Removal: A Review of Current Innovations and Advances

Atmospheric heavy metal pollution presents a severe threat to public health and environmental stability. Transition metal catalysts have emerged as a potent solution for the selective capture and removal of these pollutants. This review provides a comprehensive summary of current advancements in the field, emphasizing the efficiency and specificity of nanostructured transition metals, including manganese, iron, cobalt, nickel, copper, and zinc. Looking forward, we delve into the prospective trajectory of catalyst development, underscoring the need for materials with enhanced stability, regenerability, and environmental compatibility. We project that advancements in computational materials science, nanotechnology, and green chemistry will be pivotal in discovering innovative catalysts that are economically and environmentally sustainable. The integration of smart technologies for real-time monitoring and adaptive control is anticipated to revolutionize heavy metal remediation, ensuring efficient and responsive pollution abatement strategies in the face of evolving industrial scenarios and regulatory landscapes.

Fly Ash-Based Na-X Zeolite Application in Separation Process of Bovine Serum Albumin from Aqueous Solution in the Presence of Organic Substances with Anionic Character

The main purpose of the investigations was to explore the protein adsorption on porous materials, as well as to identify the mechanisms of protein attachment without and with other common environmental contaminants, such as drugs, polymers or surfactants. This study applied the Na-X zeolite for the adsorption of bovine serum albumin (BSA) from solutions with various pH values. Electrophoretic mobility measurements and potentiometric titrations were conducted in systems containing both protein and/or PAA (poly(acrylic acid) polymer/DCF (diclofenac) drug/SDS (sodium dodecyl sulfate) surfactant to investigate the protein binding mechanisms in the complex adsorbate systems. In addition, aggregate size and stability measurements were performed in the investigated systems. Based on the research results, it was possible to conclude that the protein adsorbed most preferably on the zeolite surface at a pH value close to its isoelectric point (pI) (102.15 mg/g), and protein adsorption was the lowest in the solutions with strongly alkaline (29.61 mg/g) or acidic (77.45 mg/g) pH values. Thus, the examined zeolitic material can be considered an effective adsorbent for protein removal from an aqueous solution.

Open-framework hybrid zinc/tin selenide as an ultrafast adsorbent for Cs+, Ba2+, Co2+, and Ni2

Efficient adsorption of radioactive ¹³⁷Cs⁺ and ⁶⁰Co²⁺ and their decay products ¹³⁷Ba²⁺ and ⁶⁰Ni²⁺ bears significance for hazard elimination in case of nuclear emergency, which relies on the adsorption rate enhancement that takes advantages of compositional and structural optimization. Herein, we report a zinc-doped selenidostannate constructed from T2-supertetrahedral clusters, namely K_3.4(CH₃NH₃)_0.45(NH₄)_0.15Zn₂Sn₃Se₁₀·3.4 H₂O (ZnSnSe-1K). The soft Se and micro-porosity synergistically endow this material with a binding affinity to Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺ ions and ultrafast kinetics with R > 97.6% in 2-60 min. In particular, ZnSnSe-1K can remove 99.34% of Cs⁺ in 2 min ⁽K_d^Cs > 1.5 × 10⁵ mL g^-1), contributing to a record rate constant k₂ of 9.240 g mg^-1 min^-1 that surpasses all metal chalcogenide adsorbents. ZnSnSe-1K exhibits good acid/base tolerance (pH = 0-12), and the adsorption capacities at neutral are 253.61 ± 9.15, 108.94 ± 25.32, 45.76 ± 14.19 and 38.49 ± 2.99 mg g^-1 for Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺, respectively. The adsorption performances resist well co-existing cations and anions, and the removal rates can keep above or close to 90% even in sea water. ZnSnSe-1K is employed in continuous column and membrane filtration, both of which shows excellent elimination efficiency (R > 99%) for mixed Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺. Especially, the membrane with an ultrathin (70 µm) ZnSnSe-1K layer can remove 97-100% Cs⁺ in suction filtration with a short contact time of 0.33 s. Combined with the simple synthesis, facile elution and great irradiation resistance, ZnSnSe-1K emerges as a selenide adsorbent candidate for use in environmental remediation especially that involving nuclear waste disposal.

Adsorption of heavy metals on natural zeolites: A review

Water pollution has jeopardized human health, and a safe supply of drinking water has been recognized as a worldwide issue. The increase in the accumulation of heavy metals in water from different sources has led to the search for efficient and environmentally friendly treatment methods and materials for their removal. Natural zeolites are promising materials for removing heavy metals from different sources contaminating the water. It is important to know the structure, chemistry, and performance of the removal of heavy metals from water, of the natural zeolites to design water treatment processes. This review focuses on critical analyses of the application of distinct natural zeolites for the adsorption of heavy metals from water, specifically, arsenic (As(III), As(V)), cadmium (Cd(II)), chromium (Cr(III), Cr(VI)), lead (Pb(II)), mercury(Hg(II)) and nickel (Ni(II)). The reported results of heavy-metal removal by natural zeolites are summarized, and the chemical modification of natural zeolites by acid/base/salt reagent, surfactants, and metallic reagents has been analyzed, compared, and described. Furthermore, the adsorption/desorption capacity, systems, operating parameters, isotherms, and kinetics for natural zeolites were described and compared. According to the analysis, clinoptilolite is the most applied natural zeolite to remove heavy metals. It is effective in removing As, Cd, Cr, Pb, Hg, and Ni. Additionally, an interesting fact is a variation between the natural zeolites from different geological origins regarding the sorption properties and capacities for heavy metals suggesting that natural zeolites from different regions of the world are unique.

Ultra-effective modified clinoptilolite adsorbent for selective thorium removal from radioactive residue

This study investigated the efficacy of using phosphate-modified zeolite (PZ) as an adsorbent for removing thorium from aqueous solutions. The effects of various factors such as contact time, adsorbent mass, initial thorium concentration, and pH value of the solution on the removal efficiency were analyzed using the batch technique to obtain optimum adsorption condition. The results revealed that the optimal conditions for thorium adsorption were a contact time of 24 h, 0.03 g of PZ adsorbent, pH 3, and a temperature of 25 °C. Isotherm and kinetics parameters of the thorium adsorption on PZ were also determined, with equilibrium studies showing that the experimental data followed the Langmuir isotherm model. The maximum adsorption capacity (Q_o) for thorium was found to be 17.3 mg/g with the Langmuir isotherm coefficient of 0.09 L/mg. Using phosphate anions to modify natural zeolite increased its adsorption capacity. Furthermore, adsorption kinetics studies demonstrated that the adsorption of thorium onto PZ adsorbent fitted well with the pseudo-second-order model. The applicability of the PZ adsorbent in removing thorium from real radioactive waste was also investigated, and nearly complete thorium removal was achieved (> 99%) from the leached solution obtained from cracking and leaching processes of rare earth industrial residue under optimized conditions. This study elucidates the potential of PZ adsorbent for efficient removal of thorium from rare earth residue via adsorption, leading to a reduction in waste volume for ultimate disposition.

Impact of silver-doped alumina nanocomposite on water decontamination by remodeling of biogenic waste

The main cause of various fatal diseases in humans and animals is environmental pollution. Ag-doped alumina nanocomposite was prepared using coffee husk extract with a large BET surface area of 126.58 m² g^-1 and investigated for its antibacterial potential against both bacterial strains Escherichia coli and Salmonella typhimurium, and observed as an effective sorbent for removing the water pollution dye indigo carmine (IGC). The lowest concentration of the nanocomposite and the maximum contact time required to achieve complete inhibition of bacteria present in the contaminated water, as well as the capacity of sorption of IGC, were investigated. The results showed that the minimum inhibitory concentration of the Ag-doped alumina nanocomposite was 12 µg mL^-1 for both bacterial strains, with the highest inhibition occurring in E. coli. Moreover, the nanocomposite exhibited an experimental qt of 462.7 mg g^-1 from 160 mg L^-1 IGC solution at 50 °C and followed the Langmuir model. The thermodynamic results showed that the process was endothermic, spontaneous, and physisorptive. The nanocomposite was used to fully treat water samples contaminated with 10 mg L^-1 concentrations of IGC. For six consecutive cycles, the reuse research showed an average efficiency of 95.72 ± 3.6%. Consequently, the synthesized Ag-doped alumina nanocomposite is suitable for treatments of contaminated water.

The effect of irradiation on the Cs, Co and Eu-removal from aqueous solutions using Greek minerals

Sorption properties of Greek bentonites and zeolites were investigated in raw form and after irradiation for removal of Cs, Co and Eu from aqueous solutions using 137Cs, 60Co and 152Eu as tracers and γ-spectroscopy. The sorption experiments were undertaken under different conditions (pH, concentration, competitive ions and temperature). The structural changes of the sorbents due to irradiation and metal sorption were examined through XRD, FTIR and SEM/EDS. Sorption isotherms were reproduced by mathematical models and thermodynamic parameters were derived. The results showed that the sorption capacity was slightly affected by irradiation. The environmental compatibility tests proved the safe disposal of the investigated materials.

Greenly synthesized zeolites as sustainable materials for corrosion protection: Design, technology and application

The progress and use of effective and economic anticorrosive resources are in high mandate due to huge safety and economic concerns about corrosion. Significant advancements have already been achieved that help in minimizing corrosion costs up to US $375 to US $875 billion annually. The use of zeolites in anticorrosive and self-healing coatings is well-studied and documented in many reports. The self-healing property of zeolite-based coatings is attributed to their ability to provide anticorrosive protection in the defected areas through forming protective oxide films i.e. passivation. The synthesis of zeolites from the traditional hydrothermal method is associated with several drawbacks including their high cost and discharge of harmful gases such as oxides of nitrogen (NO_x) and greenhouse gases (CO₂ and CO). In view of this, some green approaches such as solvent-free, organotemplate-free, use of safer organic templates, green solvents (e.g. ILs) and energy efficient (MW and US) heating, one-step reactions (OSRs) etc. are adopted in the green synthesis of zeolites. Recently, the self-healing properties of greenly synthesized zeolites are documented along with their mechanism of corrosion inhibition.

A strategy for bioremediation of nuclear contaminants in the environment

Radionuclides released from nuclear contamination harm the environment and human health. Nuclear pollution spread over large areas and the costs associated with decontamination is high. Traditional remediation methods include both chemical and physical, however, these are expensive and unsuitable for large-scale restoration. Bioremediation is the use of plants or microorganisms to remove pollutants from the environment having a lower cost and can be upscaled to eliminate contamination from soil, water and air. It is a cheap, efficient, ecologically, and friendly restoration technology. Here we review the sources of radionuclides, bioremediation methods, mechanisms of plant resistance to radionuclides and the effects on the efficiency of biological adsorption. Uptake of radionuclides by plants can be facilitated by the addition of appropriate chemical accelerators and agronomic management, such as citric acid and intercropping. Future research should accelerate the use of genetic engineering and breeding techniques to screen high-enrichment plants. In addition, field experiments should be carried out to ensure that this technology can be applied to the remediation of nuclear contaminated sites as soon as possible.

Additive manufacturing of geopolymers with hierarchical porosity for highly efficient removal of Cs. JOURNAL OF HAZARDOUS MATERIALS 2023;443:130161. [PMID: 36327833 DOI: 10.1016/j.jhazmat.2022.130161]

Geopolymers (GPs) have emerged as promising adsorbents for wastewater treatment due to their superior adsorption stability, tunable porosity, high adsorption capacity, and low-energy production. Despite their great promise, developing GPs with well-controlled hierarchical structures and high porosity remains challenging, and the mechanism underlying the ion adsorption process remains elusive. Here we report a cost-effective and universal approach to fabricate Na or K GPs with sophisticated architectures, high porosity, and arbitrary cation species exchange by means of additive manufacturing and a surfactant. The introduction of sodium lauryl sulfate (SLS) enhanced the porosity of the GP adsorbents, yielding NaGP-lattice-10%SLS adsorbent with a high total porosity of 80.8 vol%. Combining static and dynamic adsorption tests, the effects of morphology, surfactant content, and cation species on Cs⁺ adsorption performance were systemically investigated. With an initial Cs⁺ concentration of 900 mg/L, the printed NaGP exhibited a maximum Cs⁺ adsorption capacity of 80.1 mg/g, outperforming other adsorbents reported so far. The quasi-second-order fit of the NaGP adsorbent showed overall higher R² values than the quasi-first-order fit, indicating that the adsorption process was dominated by ion exchange. Combined with first-principles calculations, we verified that the content of water in the GP sod cages also affected the ion-exchange process between Na⁺ and Cs⁺.

New Approach To Understanding the Experimental 133Cs NMR Chemical Shift of Clay Minerals via Machine Learning and DFT-GIPAW Calculations

Structural determination of adsorbed atoms on layered structures such as clay minerals is a complex subject. Radioactive cesium (Cs) is an important element for environmental conservation, so it is vital to understand its adsorption structure on clay. The nuclear magnetic resonance (NMR) parameters of ¹³³Cs, which can be determined from solid-state NMR experiments, are sensitive to the local neighboring structures of adsorbed Cs. However, determining the Cs positions from NMR data alone is difficult. This paper describes an approach for identifying the expected atomic positions on clay minerals by combining machine learning (ML) with experimentally observed chemical shifts. A linear ridge regression model for ML is constructed from the smooth overlap of atomic position descriptor and gauge-including projector augmented wave (GIPAW) ab initio data. The constructed ML model predicts the GIPAW data to within a 3 ppm root-mean-squared error. At this stage, the ¹³³Cs chemical shifts can be instantaneously calculated from the Cs positions on any clay layers using ML. The inverse analysis, which derives the atomic positions from experimentally observed chemical shifts, is developed from the ML model. The input data for the inverse analysis are the layer structure and the experimentally observed chemical shifts. The Cs positions for the targeted chemical shifts are then output. Inverse analysis is applied to montmorillonite, and the resultant Cs positions are found to be consistent with previous results (Ohkubo, T.; et al. J. Phys. Chem. A 2018, 122, 9326-9337). The Cs positions on saponite clay are also clarified from experimentally observed chemical shifts and inverse analysis.

Rapid growth of MXene-based membranes for sustainable environmental pollution remediation

Water consumption has grown in recent years due to rising urbanization and industry. As a result, global water stocks are steadily depleting. As a result, it is critical to seek strategies for removing harmful elements from wastewater once it has been cleaned. In recent years, many studies have been conducted to develop new materials and innovative pathways for water purification and environmental remediation. Due to low energy consumption, low operating cost, and integrated facilities, membrane separation has gained significant attention as a potential technique for water treatment. In these directions, MXene which is the advanced 2D material has been explored and many applications were reported. However, research on MXene-based membranes is still in its early stages and reported applications are scatter. This review provides a broad overview of MXenes and their perspectives, including their synthesis, surface chemistry, interlayer tuning, membrane construction, and uses for water purification. Application of MXene based membrane for extracting pollutants such as heavy metals, organic contaminants, and radionuclides from the aqueous water bodies were briefly discussed. Furthermore, the performance of MXene-based separation membranes is compared to that of other nano-based membranes, and outcomes are very promising. In order to shed more light on the advancement of MXene-based membranes and their operational separation applications, significant advances in the fabrication of MXene-based membranes is also encapsulated. Finally, future prospects of MXene-based materials for diverse applications were discussed.

Impact of the Syn/Anti Relative Configuration of Cryptophane-222 on the Binding Affinity of Cesium and Thallium

We report in this article the synthesis, the X-ray crystal structure of compound syn-2, and its binding properties with cesium and thallium in aqueous solution under basic conditions. Compound syn-2 is the diastereomeric compound of anti-1 that shows very high affinity for cesium and thallium in aqueous solution under the same conditions. Despite the close structural similarities that exist between the syn-2 and anti-1 compounds, they show large discrepancy in their ability to bind cesium and thallium cations in the same conditions. Indeed, the syn-2 derivative has a lower affinity for these two cationic species and the binding constants are several orders of magnitude lower than those found for its congener. The large differences in affinity observed with these two compounds can be explained by the relative position of the six hydroxyl groups to each other.

Hydrothermal synthesis and sorption performance to Cs(I) and Sr(II) of zirconia-analcime composites derived from coal fly ash cenospheres

The paper is concerned with (i) the hydrothermal synthesis of hydrous zirconium dioxide (HZD) bearing analcime (HZD-ANA, zirconia-analcime) and (ii) its sorption properties with respect to Cs+ and Sr2+. The HZD-ANA particles were synthesized from coal fly ash cenospheres composed of aluminosilicate glass with (SiO2/Al2O3)wt.=3.1 and characterized by PXRD, SEM-EDS, STA, and low-temperature N2 adsorption. The non-radioactive simulant solutions of different acidity (pH=2–10) and Cs+/Sr2+ content (0.5–50.0 mg/L) were used in the work. The effect of synthesis conditions on the HZD-ANA particle size, zirconia content and localization as well as the sorption behavior with respect to Cs+ and Sr2+ (capacity, KD) were clarified. It was found that the small-sized HZD-ANA composites surpasses the Zr free analcime and large-sized HZD-ANA material in the Cs+ and Sr2+ sorption parameters (KD ~104–106 mL/g). The conditions to synthesize the zirconia-analcime composite of the highly enhanced sorption ability with respect to Sr2+ (KD ~106 mL/g) were determined. The high-temperature solid-phase re-crystallization of Cs+/Sr2+-exchanged HZD-ANA composites was shown to occur at 1000 °C resulting in a polyphase system based on nepheline, tetragonal ZrO2, and glass phase.

Modification of Clinoptilolite as a Robust Adsorbent for Highly-Efficient Removal of Thorium (IV) from Aqueous Solutions

The natural zeolite has been modified with sulphate and phosphate. The adsorption of thorium from the aqueous solutions by using the natural and modified zeolites has been investigated via a batch method. The adsorbent samples were characterized by X-ray Diffraction (XRD), N₂ adsorption-desorption (BET), Fourier transform infrared (FTIR), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDX). Modification of natural zeolite with sulphate and phosphate was found to increase its adsorption capacity of thorium but reduced its specific surface area (S_BET). The adsorption experiments were expressed by Langmuir, Freundlich and Dubinin-Radushkevitch (D-R) isotherm models and the results of adsorption demonstrated that the adsorption of thorium onto the natural and modified zeolites correlated better with the Langmuir isotherm model than with the Freundlich isotherm model. The maximum adsorption capacity (Qo) was determined using the Langmuir isotherm model at 25 °C and was found to be 17.27, 13.83, and 10.21 mg/g for phosphate-modified zeolite, sulfate-modified zeolite, and natural zeolite, respectively. The findings of this study indicate that phosphate-modified zeolite can be utilized as an effective and low-cost adsorbent material for the removal of thorium from aqueous solutions.

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.

Sulfur-modified zeolite A as a low-cost strontium remover with improved selectivity for radioactive strontium

Selective removal of radioactive strontium (⁹⁰Sr) from the environment is important, and selective adsorption/ion exchange is appropriate for removal of trace amounts of ⁹⁰Sr from large volumes of ⁹⁰Sr-contaminated water. Although various inorganic ion-exchange materials, including zeolites, have been investigated intensively for removal of Sr²⁺ due to their excellent resistance to radiation and high ion-exchange capacity, their ion-exchange selectivity for Sr²⁺ is poor in the presence of competing ions such as Ca²⁺ and Mg²⁺. Here, sulfur-modified NaA zeolite (S-NaA) was prepared for low-cost, selective ⁹⁰Sr removal because the elemental sulfur encapsulated in micropores provides additional Lewis acid-base interactions with Sr²⁺ during the Sr²⁺ ion-exchange. Our ion-exchange experiments revealed that S-NaA with 3 wt% sulfur (3 S-NaA) showed the highest Sr²⁺ selectivity among various S-NaAs containing up to 10 wt% sulfur because ion exchange involving bulky hydrated Sr²⁺ depends on the reduced micropore volume of S-NaA after sulfur loading. Most importantly, 3 S-NaA effectively and efficiently (>99.4%) removed ⁹⁰Sr from groundwater containing 8.4 ppt ⁹⁰Sr, demonstrating its excellent potential for practical application in the treatment of ⁹⁰Sr-contaminated water.

MXenes as emerging nanomaterials in water purification and environmental remediation

Environmental pollution has accelerated and intensified because of the acceleration of industrialization, therefore fabricating excellent materials to remove hazardous pollutants has become inevitable. MXenes as emerging transition metal nitrides, carbides or carbonitrides with high conductivity, hydrophilicity, excellent structural stability, and versatile surface chemistry, become ideal candidates for water purification and environmental remediation. Particularly, MXenes reveal excellent sorption capability and efficient reduction performance for various contaminants of wastewater. In this regard, a comprehensive understanding of the removal behaviors of MXene-based nanomaterials is necessary to explain how they remove various pollutants in water. The eliminate process of MXene-based nanomaterials is collectively influenced by the physicochemical properties of the materials themselves and the chemical properties of different contaminants. Therefore, in this review paper, the synthesis strategies and properties of MXene-based nanomaterials are briefly introduced. Then, the chemical properties, removal behaviors and interaction mechanisms of heavy metal ions, radionuclides, and organic pollutants by MXene-based nanomaterials are highlighted. The overview also emphasizes associated toxicity, secondary contamination, the challenges, and prospects of the MXene-based nanomaterials in the applications of water treatment. This review can supply valuable ideas for fabricating versatile MXene nanomaterials in eliminating water pollution.

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.

Design and construction of an electrochemical sensor for the determination of cerium(iii) ions in petroleum water samples based on a Schiff base-carbon nanotube as an ionophore

A carbon paste sensor (CPE) and screen-printed sensor (SPE) for Ce(iii)-selective determination were prepared using a 2,6-pyridine dicarbomethine-triethylene tetraamine macrocyclic Schiff base ligand (PDCTETA) and multi-walled carbon nanotubes (MWCNTs) as good sensing materials. With respect to most common cations, such as alkali, alkaline earth, transition, and heavy metal ions, the electrodes display high selectivity for the Ce(iii) ion. The sensors respond to Ce(iii) ions in a linear range of 1 × 10-7 to 1 × 10-1 and 1 × 10-8 to 1 × 10-1 mol L-1 with a slope of 18.96 ± 0.73 and 19.63 ± 0.51 mV per decade change in concentration with a detection limit of 1.10 × 10-8 and 5.24 × 10-9 mol L-1 for CPE (sensor IV) and SPE (sensor VIII), respectively. The sensors were found to have a lifetime of 102 and 200 days. The suggested electrodes performed well throughout the pH ranges of 3.5-8.0 and 3.0-8.5, with response times of 8 and 6 seconds for sensor IV and sensor VIII, respectively. The sensors have been used to measure Ce(iii) ions in water samples from several petroleum wells. They have also been utilized as indicator electrodes in Ce(iii) ion potentiometric titrations with EDTA. The results were quite similar to those obtained by employing atomic absorption spectrometry (AAS).

Adsorption properties and mechanism of uranium by three biomass materials

Wood fibers, bamboo fibers and rice husk were applied to the adsorption of uranium from aqueous solution to understand the uranium adsorption behavior and mechanism by these natural sorbents. The effects of time, adsorbent particle size, pH, adsorbent dosage, temperature and initial concentration were studied using batch technique. The adsorption mechanism was discussed by isothermal adsorption models, adsorption kinetic models. The results suggested that the three biomass adsorbents showed great efficiency of adsorption for uranium. The adsorption capacity of biosorbents of comparatively small particle size and large dosage is quite high. Uranium adsorption achieved a maximum adsorption amount at around pH 3 for wood fibers and bamboo fibers, and around pH 5 for rice husk. All isotherms fitted well to the Langmuir Freundlich and D-R equation, indicating that the adsorption process is favorable and dominated by ion exchange. Rice husk had a highest adsorption capacity, followed by bamboo fibers, while wood fibers had little uranium adsorption under the studied conditions, and the adsorption capacity was 12.22, 11.27 and 11.04 mg/g, respectively. The equilibrium data was well represented by the pseudo-second-order kinetics, indicating that the adsorption rate was controlled by chemical adsorption. Ion exchange was the main adsorption mechanism, and the exchange ions were mainly Na+ and K+.

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.