Radioactive Wastewater Research Articles

High efficiency removal of Cs+ by Fe-Co framework PBAs from radioactive wastewater

The widespread application of nuclear energy has increased the risk of contamination by radionuclide 137Cs. Prussian blue analogues are considered to be excellent materials for the removal of 137Cs from wastewater due to their unique structure. In this work, Cs+ adsorbent for PBAs with Fe-Co framework, potassium iron hexacyanocobaltate (PBAFe), was synthesized by room temperature precipitation method. Systematic structural characterization and performance results of PBAFe showed that it has a specific surface area of 452.8 m2/g and an average pore size of 8.6nm, providing more active sites for Cs+. The adsorption of Cs+ on PBAFe exhibited fast reaction kinetics (within 10min) and high adsorption capacity (82.90mg/g), and the removal rate of Cs+ reached 98.57%. The efficient removal of Cs+ by PBAFe in various real water environments showed its excellent selectivity and potential for practical application. In addition, adsorption mechanism studies showed that the adsorption of Cs+ was achieved by ion exchange with K+ in the PBAFe lattice. PBAFe has the advantages of simple synthesis and good selectivity, and has potential application in the harmless treatment of Cs+ in radioactive wastewater.

Fabrication of novel adsorptive photocatalyst GQDs/Sn3O4 for highly efficient synergistic removal of U(Ⅵ)

Developing economically efficient adsorption-photocatalysis bifunctional uranium-containing wastewater treatment agents is significant for environmental remediation and governance. In this study, a novel adsorptive photocatalyst based on low-cost hybrid GQDs/Sn3O4 nanocomposite (GSO) was fabricated using a one-step hydrothermal method for highly efficient synergistic uranium removal. The batch adsorption experiments revealed that the adsorption process of GSO-15 on U(VI) matched the pseudo-second-order model and Langmuir isotherm, with a maximum Langmuir adsorption capacity (qmax) of 226.51mg·g−1 at pH 6.0. In addition, U(VI) reduction by GSO-15 under visible light irradiation demonstrated excellent photocatalytic performance, while the optimal removal rate of U(VI) by synergistic adsorption-photoreduction was up to 99.67%, which was significantly higher than that of physicochemical adsorption. Furthermore, the mechanism of GSO-15 photoreduction of U(VI) was explored through various methods, indicating that the photocatalytic performance was primarily attributed to its strong visible light absorbability, narrow bandgap, and efficient separation and transfer of photoinduced electron-hole pairs. After five cycles of photocatalytic reduction desorption, the removal rate remained above 95%, indicating excellent structural stability and considerable recyclability. The decrease in the removal rate was negligible in the presence of coexisting metal ions. This study provides novel insights into the design and fabrication of efficient adsorptive photocatalytic materials for treating radioactive uranium-containing wastewater.

Metagenomic analysis of the dichotomous role of uranium in regulating intracellular and extracellular antibiotic resistance genes in activated sludge

Antibiotic resistance genes (ARGs) in activated sludge include intracellular ARGs (iARGs) and extracellular ARGs (eARGs), both of which are recognized as emerging pollutants. While the activated sludge process has been commonly considered for treating wastewater contaminated with radionuclide, the effects and mechanisms of radioactive heavy metals on the fate of iARGs and eARGs (i/e-ARGs) in activated sludge are largely elusive. Here, the distribution, mobility, and hosts of i/e-ARGs in activated sludge during environmental concentrations (50 μg/L and 5000 μg/L) of radioactive uranium (U) stress were explored via metagenomics. The results revealed that the total relative abundance of iARGs and eARGs decreased by 11.62% and 10.41%, respectively, after 90 days of 50 μg/L of U treatment. In contrast, both i/e-multi- and tetracycline ARGs remarkably increased after being exposed to 5000 μg/L of U. Additionally, exposure to 5000 μg/L of U triggered notable decrease in i/e-insertion sequences and plasmids abundance, but significantly enriched i/e-integrons (p < 0.05). Partial least squares pathway modelling indicated that the prevalence of iARGs and eARGs in activated sludge was primarily driven by bacterial hosts and functional genes, respectively. Our findings revealed the dichotomous variation landscape and mechanisms of i/e-ARGs dynamics in activated sludge during U exposure, offering valuable insights for controlling ARGs risk during radioactive wastewater treatment.

Highly-selective and well-effective removal of cesium ions by segregative titanium-ferrocyanide/chitosan melamine sponge composite

Selectively and efficiently removing Cs is of great urgency and challenge for the treatment of radioactive wastewater. In this work, titanium-ferrocyanide/chitosan melamine sponge composite (TFCM) was synthesized by cross-linking and titanium-doping strategy, and employed to remove Cs+ from water. The obtained TFCM exhibited excellent adsorption performance for Cs+, due to its porous and 3D skeleton structure. The TFCM demonstrated a broad range of pH (pH = 3–11) suitability and high removal ratio of Cs+. The adsorption behavior of TFCM on Cs+ conformed to the Langmuir adsorption process and pseudo-second-order kinetics model. Remarkably, TFCM displayed a high selectivity in Cs+ adsorption with the presence of other cationic (K+, Na+, Ca2+, Mg2+). TFCM could easily be separated from water because of loading on the melamine sponges. Besides, the TFCM could maintain more than 78.1 % removal ratio of Cs+ after five adsorption-desorption cycles. Furthermore, the concentration of Cs+ could decrease to 10 μg/L from 20 mg/L with a prominent removal ratio of 99.95 %. Characterization results revealed that the adsorption process of Cs+ by TFCM was dominated by ion-exchange. In summary, the TFCM is a high selectivity, efficiently and easily separable adsorbent with excellent application prospects for removing Cs from radioactive wastewater.

Comparative study of silica-based porous materials in the purification of radioactive wastewater

A significant challenge in the treatment of low-level radioactive wastewater is the effective purification of low-concentration radionuclides. Silica-based adsorbents are advantageous for the deep-purification of low-concentration metal ions. This study investigates three primary types of silica-based adsorbents: functionalized mesoporous silica, various modified zeolites, and mesoporous calcium silicate hydrate (C-S-H). These adsorbents were synthesized and their deep-purification effects on heavy metals and radionuclides were compared. The results indicated that mesoporous silica showed relatively poor adsorption for most metal ions. Zeolites outperformed mesoporous silica, with Zn framework-modified zeolites showing enhanced adsorption for several metal ions. Notably, C-S-H displayed superior adsorption performance, achieving high adsorption capacities for various metal ions and radionuclides. Specifically, at a dose of 0.5 g/L, the adsorption efficiency of C-S-H for numerous radionuclides in nuclear power plant wastewater exceeded 92–99 %, highlighting its potential for practical applications. An in-depth analysis of the physical and chemical structure and the adsorption mechanisms of C-S-H revealed its large mesoporous structure and electrostatic attraction to cations across a wide pH range. Multivalent cations were removed through exchange with Ca2+ in C-S-H, whereas monovalent cations were removed through exchange with Na+ in C-S-H. The cyclic structure of silica-oxygen tetrahedra in C-S-H, which promotes large pore formation and provides abundant ion exchange sites, underpins its excellent adsorption properties. This study offers valuable insights for the selection and application of silica-based materials in radioactive wastewater treatment.

Interface-Confined nanocatalysts at hollow porous nanofibers for High-Performance cascaded remediation of radioactive wastewater

The evolution of efficient remediation technologies for radioactive wastewater is crucial for the sustainable development of nuclear energy. The cascade strategy that combines adsorption and photocatalysis has emerged as one of the most ground-breaking approaches. However, the current composite materials are undesirable in practical applications due to the low interface exposures of nanocatalysts with limited light utilization, undesirable mass transfer as well as long free radical diffusion distances from photocatalytic sites to adsorption sites. Herein, we present the fabrication of hollow porous composite nanofibers (HPN) with high interface exposures of nanocatalysts and reduced mass transfer resistances via the interface-confined engineering by integrating coaxial electrospinning with non-solvent-induced phase separation. The hollow porous architecture effectively diminishes mass transfer resistance, leading to rapid adsorption and providing sufficient uranyl ions for the subsequent cascade photoreduction. Meanwhile, the high interface exposure of the nanocatalysts enables efficient uranium reduction, which serves to regenerate the adsorption sites for higher adsorption capacity as well as durable stability. Such an elegant architecture allows the HPN to achieve an over 2-fold improvement in removal rates than that of conventional composite nanofibers and removal ratios as high as 98.86 % within 270 min. The design concept and outstanding performance make it a promising and practical technology for the remediation of radioactive wastewater.

U(Ⅵ) sorption by porous sodium zirconium phosphate pellets from aqueous solution

Zirconium phosphate is the first artificially produced layered phosphate that can sorb a variety of nuclides from solutions. Sodium zirconium phosphate (NZP) was a type of α-zirconium phosphate (α-ZrP). The porous sodium zirconium phosphate pellets (p-NZP-P) with a diameter of more than ∼3 mm were prepared and used for uranium sorption. The p-NZP-P could be immersed in solutions for more than 5 days without dissolving and structurally collapsing. The sorption properties of U(Ⅵ) on p-NZP-P in solutions were investigated by both static and dynamic sorption tests. Synthetic p-NZP-P was analyzed in detail using various characterizations to investigate their character and structural changes. In the static sorption experiment, the equilibrium sorption capacity reached the 77.5 ± 1.5 mg·g−1 when the initial concentration of U(Ⅵ) was 100 mg/L, pHinitial = 4.5, T = 25 ℃. Uranium sorption increased by ∼69 % and ∼215 %, respectively, when the initial uranium concentration was increased from 100 to 300 mg·L−1 and the temperature was increased from 15 to 55 °C. Furthermore, uranium sorption increased by ∼541 % when the initial pH increased from 2.5 to 4.5, while it decreased by ∼39 % when the initial pH increased from 4.5 to 7.0. The sorption data corresponded to the pseudo-second-order kinetic model and the Langmuir isotherm model, as well as the theoretically predicted value of sorption capacity (∼199.9 mg·g−1). The results of the dynamic sorption experiment showed that decreasing the quality, increasing the flow rate and the initial U(Ⅵ) concentration would shorten the breakthrough time. The dynamic sorption data agreed well with the Thomas model. The characterization confirmed the porous properties, while the U(Ⅵ) sorption mechanisms relate to –OH coordination and ion exchange. A radioactive rare earth wastewater treatment test suggested that p-NZP-P could be the potential uranium sorbent due to its good stability and efficiency. This paper opened opportunities for the development of practical materials for treating radioactive wastewater in the application of actual scenarios.

Foam separation of radio-molybdenum oxyanions (99MoO42−) incorporated into Co(II)/Al(III) layered double hydroxide using anionic surfactant

Foam separation of radio-molybdenum oxyanions (99MoO42−) incorporated into in-situ formed Co(II)/Al(III) layered double hydroxide (LDH) particles was applied for recovery of these anionic species from aqueous solutions. The results showed that Co(II)/Al(III) molar ratios of 2 and 2.5 resulted into not only high recovery values for 99MoO42− (R > 0.97), but also high decontamination factor (DF = 33 and 36, respectively). Almost complete recovery was achieved for 99MoO42− coprecipitated with Co(II)/Al(III) LDH in the pH range 9.9–10.5. Ageing time of 5 min was sufficient to completely coprecipitate the concerned anionic species. Sodium dodecyl sulfate (SDS) concentrations in the range 1.5 × 10−3 - 3 × 10−3 mol/L had the ability to efficiently form hydrophobic 99MoO42--Co(II)/Al(III)-LDH particles, where recovery values of about 0.96 were achieved with high DF values. The influence of the coexistence of different foreign anions (Cl−, NO3−, HCO3−, CO32− and SO42−) during coprecipitation process of 99MoO42− and foam separation of the resultant particles was investigated. The suggested strategy in the present study was effectively applied for recovery of 99MoO42− anions from ground water (R ≈ 0.98 and enrichment ratio (ER ≈ 7172) and radioactive process wastewater (R ≈ 0.96 and ER = 3887). Based on characterization of Co(II)/Al(III) LDH using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) before and after foam separation process using SDS and the obtained data, the recovery mechanism of 99MoO42− was proposed.

Removal of 4-(2-pyridylazo) resorcinol and Arsenazo-III from liquid waste solutions using Penicillium oxalicum: Gamma irradiation studies

The current investigation involved the isolation of a fungal strain from liquid radioactive wastewater, which was then identified as Penicillium oxalicum and was employed to remove 4-(2-pyridylazo) Resorcinol (PAR) and Arsenazo-III (Ar-III) from liquid waste solutions. The physicochemical properties of the biosorbent fungi were analyzed using SEM and FT-IR. The biosorption effectiveness of PAR and Ar-III was investigated under several experimental settings, including pH values, adsorption times, biosorbent weight, initial dye concentrations, and reaction temperatures. The Langmuir isotherm model describes the adsorption isotherms well, with capacities of 10.88 and 11.96mgg-1 for PAR and Ar-III, respectively. The sorption of PAR and Ar-III exhibited E values of 19.84 and 17.84kJ/mol, respectively, indicating that the process is chemical adsorption. The pseudo-second-order kinetic model was determined as the most accurate representation of the biosorption kinetics. Both film diffusion and intra-particle diffusion describe the diffusion of coloring reagents through the biosorbent material. The thermodynamic analysis showed that chemical adsorption regulated the biosorption of the coloring reagent on the biosorbent material, while exothermic and spontaneous biosorption of PAR and Ar-III was observed. The extensive decolorization and easy operating circumstances demonstrated the promise of Penicillium oxalicum for the biological treatment of textile dyes.

Synthetic and natural antibacterial carbon adsorbents for clinical nuclear waste management

Patients undergoing high-dose radioiodine ablation (RAI) therapy in Nuclear Medicine Department need to be isolated in a special designed ward for a few days. Large amount of clinical radioactive wastewater from patient body is produced during high-activity RAI therapy. The radioactive wastewater needs to store in a delay tank until the radioactivity decayed below acceptable limit before being discharged and indirectly limit the patient admission and treatment. This study is to propose an alternative antibacterial adsorbent for I-131 extraction from clinical radioactive wastewater at the nuclear medicine department using graphene oxide silver (GOAg) and bamboo activated carbon (BAC). The synthesised adsorbents and their sediments (filtered sample) were analysed using field emission scanning electron microscopy (FESEM) for morphological analysis and analysed using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and X-ray diffraction (XRD). XPS spectra for C 1s adsorbents show intensity peaks at 284.45 eV (C=C) and 285.3 eV (C–C) for GOAg and its sediments, and 284.35 eV (C–C), 287.00 eV (C=O), and 290.07 eV (π–π∗ transitions) for BAC and its sediments. FTIR spectra reveal various functional groups of adsorbents: C=C (1637.50772 cm−1), C=O (1340.48041 cm−1), and C–O–C (1031.88060 cm−1) for GOAg and its sediments, and C=C (1635.57897 cm−1), C–C (1257.54421 cm−1), and C–O (1188.10925 cm−1) for BAC and its sediments. XRD patterns exhibit peaks at 2θ = 27.82°, 29.39°, 32.24°, and 46.22°, which can be attributed to the (002) diffraction plane, (220) crystallographic plane, (111) plane of Ag2O, and (200) crystallographic plane, respectively, for GOAg and its sediments. Meanwhile, the peaks at 2θ = 26.56° and 42.41°, which correspond to (002) and (100) planes, respectively, for BAC and its sediments. The d-spacing and the crystallinity index of each adsorbent were also determined. The estimation of the remaining β− particles during the adsorption of I-131 was carried out using PHITS. The finding of this study is beneficial for alternative radionuclide extractions technique from clinical radioactive wastewater in nuclear medicine.

Assessment of electrochemical removal mechanisms of diverse transition metal dichalcogenides for caesium ion removal in wastewater treatment

Abstract Effective treatment of radioactive wastewater is crucial for broader nuclear energy adoption, with caesium radionuclides (most exist in the form of caesium chloride) presenting challenges due to their long half-life and biological hazards. Conventional adsorbents like zeolites and carbon-based materials, including graphene, face limitations in adsorption capacity due to the formation of electric double layers (EDL). This has led to the investigation of alternatives such as transition metal dichalcogenides (TMDs) e.g., MoS2, MoSe2, and WSe2, which offer promising galleries for caesium ion removal. Aside from extensively studied MoS2, there is limited research on the adsorption mechanisms and capacities of other TMDs like MoSe2 and WSe2. Here, we conduct a comparative study examining the removal mechanisms and capacities of exfoliated MoS2, MoSe2, and WSe2 nanosheets, alongside an evaluation of these properties in relation to graphene. Our investigation reveals distinct removal mechanisms and capacities among these three materials for capturing caesium ions in a variety of mechanisms. MoS2 nanosheets primarily utilise a pseudocapacitive charge storage mechanism via intercalation, as evidenced by a total charge storage of 0.78 C g1, with only 2.6% stored via EDL formation. In contrast, MoSe2 predominantly relies on EDL formation, with almost 60% of the total 0.54 C g1 charge storage attributed to this mechanism. Lastly, WSe2 exhibits a combination of both charge storage behaviours, with a total charge storage of 0.77 C g1, of which 14% is due to EDL formation. This research highlights the potential efficacy of TMDs as viable materials for caesium removal, offering an appealing alternative to conventional adsorbents and likely fostering advancements in water treatment technologies.

Photoinduction of Pt single atoms decorated on UiO-66-NH2 for photocatalytic extraction of uranium under open system

The photocatalytic method has been proven as one of the effective methods for uranium removal from radioactive wastewater. Herein, a photocatalyst UiO-66-NH2-Pt was prepared using the adsorption-photoinduction method. Pt was first adsorbed on the substrate and then photo-reduced under light irradiation to be doped into the structure of UiO-66-NH2. The characterization results implied the formation and atomic dispersion of Pt with a loading content of 1.90 wt%. The loading of Pt has promoted the effective separation and transfer of photogenerated electron-hole pairs, broadened the visible light adsorption range and narrowed down the bandgap, thus to enhance the photocatalytic activity. Then they were applied for the photo-removal of uranium under air atmosphere. The reaction rate of UiO-66-NH2-Pt was about 7 times that of pure UiO-66, confirming the higher photocatalytic activity after the loading of Pt. It showed good reusability and was also universal for different water matrix. The detection of hydroxyl radicals with EPR method indicated the formation of H2O2, which could react with uranyl ions to form metastudtite under air. This work further verified the feasibility of photoinduced synthesis of Pt single atom and provided a novel material for photocatalytic removal of uranyl ion under air.

Enhanced visible light photocatalytic activity of Pt cluster modified carbon nitrides for U(VI) removal

Photocatalysis has been regarded as one of the effective methods of removing U(VI) from radioactive wastewater in recent years, due to the benefits of being environmentally friendly and efficient. In this work, a Pt cluster modified carbon nitride photocatalyst (Pt-CN) was synthesized in zinc chloride molten salt. The photocatalysts were characterized by XRD, IR, XPS, UV–vis, PL and EIS. The result demonstrated that the doping of Pt makes Pt-CN show higher electronic conductivity and better charge separation and migration, leading to an enhanced photocatalytic activity and faster kinetics compared with bulk graphitic carbon nitride (g-C3N4). Moreover, for uranium contained solution photocatalytic treatment, Pt-CN reached 94.6 % removal efficiency after 300 min of illumination with Xe light, and the kinetics improved by a factor of three compared to that of g-C3N4. Furthermore, the good reusability and photostability of the Pt-CN was confirmed as the removal efficiency remained at 83.7 % even after being recycled and reused five times. The photocatalytic reaction product was characterized as (UO2)O2·2 H2O, and the mechanism was deduced as uranium species reacting with H2O2 generated by light illumination in an open system. This molten salt one-step synthesis and Pt doping method and the performance of U(VI) extraction in air showed a promising potential for the application of Pt-CN for U(VI) extraction and removal from water.

Uranium extraction from wastewater by heteroatom-doped carbon microspheres derived from polyphosphazene loading with zinc oxide

The effective management of uranium-contaminated wastewater is crucial for environmental protection and public health safety. In this context, a novel composite was synthesized involving the intergration of zinc oxide into heteroatom-doped polyphosphazene carbon microspheres (TAC/ZnO) by hydrothermal method. The incorporation of ZnO into TAC significantly enhanced the porosity, offering more adsorption sites and improving the uranium adsorption performance. The optimal adsorption experiment achieved a remarkable adsorption capacity of 513.9 mg.g−1 for U(VI) at a pH of 5.5 within just 80 min. Additionally, the adsorption process was found to be endothermic and spontaneous, following both the Langmuir isothermal adsorption model and the pseudo-second-order kinetic model. Moreover, the TAC/ZnO presented higher selectivity for U(VI) in the presence of other cations. Even after 8 cycles, TAC/ZnO maintained a good removal rate for U(VI), decreasing from 97.54 % to 81.95 %. Furthermore, the findings from X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations indicated that the adsorption mechanism of U(VI) on TAC/ZnO may involve the coordinated interaction between oxygen atoms in Zn-O and nitrogen atoms in pyridinie-N-oxide with uranyl ions. Overall, this study presents an easily prepared, cost-effective, and highly efficient adsorbent that offers potential for large-scale production and practical application in purifying radioactive wastewater.

Construction of MIL-100(Fe)-DMA material for efficient adsorption of Sr and Cs ions from radioactive wastewater

A novel metal-organic framework (MOF) material, MIL-100(Fe)-DMA, was synthesized using the solvothermal method. The structure of the MOF was characterized using scanning electron microscopy-energy dispersive X-ray spectroscopy, N2 adsorption–desorption isotherms, X-ray diffraction analysis, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy. Batch adsorption experiments were performed to investigate the effects of initial Sr2+ and Cs+ concentrations, adsorption time, pH, and coexisting cations on the adsorption performance of the material. The adsorption mechanism was further elucidated using adsorption kinetics and isotherm models. The results indicated that the adsorption of Sr2+ and Cs+ does not significantly affect the MOF material structure. As reaction time and initial ion concentration increased, the adsorption capacity of MIL-100(Fe)-DMA for Sr2+ and Cs+ increased rapidly and then gradually reached equilibrium. Optimal adsorption occurred under alkaline conditions, with maximum adsorption capacity observed at pH = 8. The adsorption process for Sr2+ and Cs+ was well described by the pseudo-second-order kinetic model, the Weber–Morris model, and the Langmuir adsorption isothermal model. The adsorption process was mainly identified as monolayer chemical adsorption, influenced by multiple factors. Characterization combined with density functional theory calculations revealed that the unsaturated carboxylic acid groups on the surface of the MOFs play a crucial role in the interaction with Sr2+ and Cs+.

Enhanced cesium removal from wastewater using a potassium hexacyanoferrate/gelatin aerogel composite

In the wake of the 2011 Fukushima nuclear disaster, the presence of radioactive cesium (137Cs) in nuclear wastewater has posed a critical and enduring health risk. Addressing this challenge, we have synthesized a gelatin aerogel, denoted as KCuFC/GA, immobilized with potassium cupric ferrocyanide (KCuFC) through an in situ approach, aiming for the efficient extraction of 137Cs from aqueous environments. This novel aerogel's rich porous structure enhances the accessibility of adsorption sites, thereby significantly promoting the capture of Cs+. The adsorption of cesium onto KCuFC/GA was investigated under various experimental conditions, including initial solution pH, contact time, initial cesium concentration, and the presence of coexisting ions (K+, Na+, Ca2+, Mg2+, Sr2+). The results indicated that the adsorption performance was largely independent of pH, achieving a high cesium removal rate of 93.4 % within the first 5 minutes. The cesium adsorption data were well-described by the Langmuir adsorption model, indicating a maximum adsorption capacity of 222.22 mg·L−1. Furthermore, in the presence of various competing ions, KCuFC/GA has demonstrated unparalleled selectivity for Cs+, with a partition coefficient (Kd) of 2.49 × 105 mL·g−1, and has sustained its adsorptive properties across five cycles of use. Through systematic investigation, including X-ray photoelectron spectroscopy (XPS) analysis, we have elucidated the adsorption mechanism, highlighting the pivotal role of ion exchange between lattice K+ and Cs+. The straightforward fabrication process and the aerogel's robust cesium removal capabilities from complex solutions indicate that KCuFC/GA is a promising candidate for real-world applications in the treatment of radioactive wastewater.

Anchoring nanoscale zero-valent iron within bacterial cellulose particles for boosting efficient adsorption of Co(II) and Sr(II) from seawater: Dual system and varying adsorption mechanisms

Increasing attention has been paid to radioactive wastewater to direct discharge in Japan or accidental leaks. Strontium-90 (90Sr) and Cobalt-60 (60Co) are the most hazardous nuclides in waste discharged form nuclear reactors. Because of their high solubility and long half-lives, these radioisotopes can persist for hundreds of years before decaying to negligible levels. Herein, a green and biodegradable material nanoscale zero-valent iron (nZVI) supported by bacterial cellulose particles (BCP-nZVI) is constructed for the first time to adsorb Co2+ and Sr2+ in single and binary systems. BCP-nZVI shows superior adsorption capacities of Co2+ and Sr2+in a single system within a wide range of pH values from 5 to7, while the coexistence of Co2+ adsorption inhibits the Sr2+ in binary system. Pseudo-second-order dynamics model and Langmuir isothermal model can be indicated the BCP-nZVI adsorption progress with 107.10 mg/g (Co2+) and 64.96 mg/g (Sr2+) maximum adsorption capacity. BCP-nZVI has outstanding stability, allowing it to be stored for more than one month with compromising its performance. More importantly, BCP-nZVI exhibits exceptional removal efficiency of Co2+(92.53%) and Sr2+(58.62%) removal in natural seawater systems. The mechanism investigation illustrates the high adsorption capacity of BCP-nZVI for Co2+ is controlled by redox and hydroxyl complexation. While Sr2+ is controlled by hydroxyl complexed adsorption, thus it has weak against interference by cations like Na+, Ca2+, etc. BCP-nZVI exhibits the advantages of high adsorption capacity, wide pH range, strong stability, and good applicability in natural seawater, which has excellent potential for application in radioactive ions removal.

Rapid vitrification of Sr-loaded zeolite by microwave sintering for disposal of secondary radioactive wastes: Mechanism and performance

The rapid solidification of Sr-loaded zeolite, a potential secondary solid waste, is highly urgent for nuclear post-accident remediation. Microwave heating is first employed to dispose of spent Sr-loaded adsorbent. The adsorption kinetics and isotherm model of zeolite NaX for Sr(Ⅱ) was reported. Meanwhile, the effect of B2O3 additive on the phase evolution, microstructure, and chemical durability was systemically investigated. The results showed that the B2O3 addition could effectively lower the sintering temperature from 1200 ℃ to 1000 ℃ via microwave heating. The stable glass form was successfully obtained with sintering temperature of 1000 ℃, B2O3-doped amount of 25 wt.%, and dwell time of 40 min. The Sr was homogeneously distributed in the sintered matrix without substantial enrichment. Moreover, the leaching rate of Sr in the solidified form was about 1.19 × 10-5 g·m−2·d−1 after 42 days, demonstrating its excellent chemical stability. This study indicated rapid low-temperature vitrification of Sr-loaded zeolite by microwave heating was a promising approach for removal and immobilization of Sr in radioactive wastewater.

Study and characterization of zeolites for the removal of artificial radionuclides in wastewater samples from nuclear power plants

4A, 13X, phillipsite and chabazite zeolites have been characterized regarding their capacity to remove Cs+ and Co2+ ions from aqueous solutions. The aim is to simulate the decontamination process of radioactive wastewater, originating from the former Garigliano nuclear plant in Italy, which is contaminated with 137Cs and 60Co. The four zeolites, in powder state, have been tested with solutions containing cesium nitrate and cobalt nitrate hexahydrate, in both individual and combined configurations, at different solid/liquid ratios. The Cs+ and Co2+ concentrations have been monitored over time by inductively coupled plasma (ICP) spectrometry. The results demonstrate the high efficacy of 13X zeolite providing almost 100 % of removal of both elements in a relatively short time (20–30 min). These findings are the basis for the kinetic characterization of the zeolite using radioactive solutions and, hence, for the setup of an in-situ pre-pilot plant to carry out tests with contaminated wastewater at the Garigliano facility. 13X zeolite presents a promising alternative for decommissioning radioactive wastewater.

Effect of operating variables on selective radiostrontium separation from aqueous waste matrices using a novel crown ether-based amino-modified mesoporous silica sorbent

A new sorbent, DFDB18C6@SBA-NH2, created by grafting diformal dibenzo-18-crown-6-ether (DFDB18C6) onto amino-modified mesoporous silica (SBA-NH2) has been used for the selective removal of radiostrontium (r-Sr: 90Sr) from aqueous waste. The Sr-sorption behavior was investigated at various operating conditions, including pH, contact time, initial Sr2+ concentration, temperature, and the presence of competing ions (e.g., Li, Na, K, Rb, Ca, Mg, and Ba). Kinetic investigations showed that the sorption process followed pseudo-second order kinetics, whereas isotherm modeling demonstrated that the Langmuir model provided the most excellent fit, implying monolayer sorption. The thermodynamic study indicated that the sorption process is endothermic. The sorbent effectively removed 90Sr (∼99.67 %) from Chornobyl-derived radioactive wastewater in the presence of other ions. These findings suggest the potential of DFDB18C6@SBA-NH2 as an effective tool for 90Sr separation from aqueous waste matrices.