Removal Of Uranium Research Articles

Sonochemical synthesis of guar gum - Zirconium phosphate composite for efficient capture of uranium from water

The increasing presence of uranium as a radionuclide contaminant in water is a threat to human health and the environment. Sonication-assisted crosslinking of guar gum, a biopolymer, is carried out with zirconium phosphate to form an adsorbent (GG@ZrP) for the removal of uranium from water. The surface characteristics, functionalities, and thermal stability of the composite were established using various analytical and spectral tools. Langmuir, Freundlich, and Sips models were used to evaluate the batch adsorption parameters. The adsorbent exhibited an excellent Langmuir adsorption capacity of 500 mg g−1 towards adsorption of uranium at pH 6. The adsorption was endothermic (ΔH, 22.63 kJ mol−1) and followed pseudo-second order kinetics. The synergistic influence of hydroxyl-rich guar gum and phosphate moieties resulted in efficient binding of uranium. With a high selectivity towards interfering cations and anions and applicability over a good range of pH, this adsorbent is a promising candidate for uranium remediation from water.

Development and characterization of kaolin-based PVA/alginate polymer composite (KPA) for removal of uranium and strontium from aqueous solutions

The present study used low-cost, abundant, and nontoxic kaolin and kaolin-based PVA/alginate composite (KPA) as adsorbents to remove U(VI) and Sr(II) ions from aqueous solutions. The characterization of the adsorbents was performed by several techniques. The results showed that PVA/alginate enhanced the functional groups and changed the surface morphology. Adsorption isotherm parameters were determined through both linear and non-linear regression analyses, from which it was inferred that the Langmuir model provides a better fit than other ones. The uranium removal capacity of KPA significantly improved as compared to that of kaolin, reaching 104.17 mg/g under the conditions of 30 min, pH 4.0, 298 K, and a solid-to-liquid ratio of 1.2 g/L. The strontium removal capacity of kaolin was significantly high as compared to that of KPA, reaching 68.96 mg/g under the optimum conditions. Removal of the radionuclides on both adsorbents was better described by the pseudo-second-order kinetic model, showing the ions to be immobilized on the adsorbents through chemical adsorption. Kaolin was not affected by interfering metals for U(VI) and Sr(II) adsorption, but KPA composite was influenced by the other metals. The adsorbents display potential as candidates to remove uranium and strontium from wastewater.

Uranium removal from contaminated groundwater using goethite-loaded composite microporous membrane

In this study, we have coupled adsorption and membrane separation for the removal of uranium from contaminated groundwater in environmentally relevant conditions at low energy requirements. This study mainly focuses on elucidating uranium, U(VI), adsorption mechanisms using surface complexation modeling approach in a novel goethite-loaded composite microfiltration membrane (GLM). This experiment involved immobilizing goethite nanorods in a microporous (0.22 μm pore size) poly (vinylidene fluoride) (PVDF) membrane. The effect of varying goethite loading and hydraulic residence time on U(VI) removal was investigated at field-relevant pH (i.e. pH 8.5). U(VI) adsorption (i.e. 4.95 μg·mg−1) was optimum at a goethite loading 1.20 mg·cm−2. The effect of varying hydraulic residence time had no impact on U(VI) removal which was also confirmed via performing batch adsorption kinetic experiments. GLM membrane loaded at 1.2 mg·cm−2 could treat 275 L of U(VI) contaminated water having 200 μg of U L−1 below WHO drinking water limit (i.e. 30 μg of U L−1) with 1 m2 of membrane surface area with a adsorption capacity of 6.12 μg·mg−1. Varying the pH of aqueous solution, containing U(VI) from pH 4.0 to pH 10.0, showed a significant impact on uranium uptake ranging from 0.7 μg·mg−1 to 2.63 μg·mg−1 by the composite membrane. The adsorption mechanism of uranium onto goethite was explained via the formation of bidentate surface complexes using the Surface Complexation Model (SCM). The results of batch pH edge experiments and SCM have been compared with pH experiments performed using GLM. The results of SCM predicted the batch pH edge experiment within a RMSE of 0.055. The trend of U(VI) removal in membrane experiments was observed to be similar to that of batch pH edge experiments and was well predicted SCM model. Our results showed that the novel goethite-loaded membrane has the potential for the effective removal of uranium with a lower specific energy consumption.

Constructing Stable Nitrogen-Rich Core-Shell CdS@MC for Photocatalytic Reduction of U(VI) in Air without Sacrificial Agent.

Photocatalytic reduction of uranium from U(VI) to U(IV) has been recognized as an effective treatment method for uranium wastewater. However, most photocatalysts have to be reduced under inert gas and sacrificial agent. Here, a class of nitrogen-rich core-shell photocatalysts (CdS@MC) with high stability was successfully prepared by modifying CdS with melamine and cyanuric chloride condensation. When the initial concentration of U(VI) was 100 mg/L and the solid-liquid ratio was 0.2 g/L, the removal of U(VI) by CdS@MC without sacrificial agent under air could reached 95%. The removal rate was still above 80% after five cycles with good stability and good removal rate of U(VI) at high salt concentration. CdS@MC not only efficiently generates electrons for photocatalytic reduction of U(VI), but also generates H2O2 from O2, which then reacts with uranyl ions to produce metastudtite. This study provides a new direction for the study of efficient uranium removal photocatalysts without sacrificial agent in air environment.

Highly efficient removal of uranium (VI) from aqueous solutions by APTES/ATP

Uranium-containing wastewater poses a significant threat to both the ecological environment and human health. Adsorption is a crucial method for purifying uranium wastewater. Using 3-Aminopropyltriethoxysilane (APTES) to modify attapulgite (ATP), we successfully prepared a cost-effective and high-performance adsorbent material, APTES-modified attapulgite (APTES/ATP). This material was utilized for the purification of uranium-containing wastewater. Characterization techniques were employed to study the structure and surface properties of the material. The adsorption performance of the material was investigated using single-factor experiments. The adsorption isotherms, kinetics, and thermodynamics were also studied and discussed. The results indicated that APTES/ATP exhibited an adsorption capacity of 382.13 mg·g−1 for uranium at room temperature. The adsorption process followed the Langmuir adsorption model and pseudo-second-order kinetics, indicating that the adsorption of uranium by the material was a monolayer chemisorption. Adsorption thermodynamics revealed that the process was endothermic and spontaneous. The adsorption mechanism primarily involved electrostatic attraction and interactions between −NH2, Si-O, and −OH groups with uranium. In summary, the prepared APTES/ATP demonstrated excellent adsorption capacity for uranium and shows promise for the purification of uranium-containing wastewater.

Constructing Ce–OH groups on CeO2 for enhancing removal and recovery of uranium from wastewater and seawater

Efficient recovery of uranium from wastewater and seawater provides an important guarantee for the sustainable growth of nuclear energy. Herein, we skillfully use the alkali etching method to construct CeO2 hollow spheres rich in Ce–OH groups for the removal and recovery of uranium from water matrixes. It is found that the CeO2 exhibits fast adsorption kinetics (equilibrium time within 10 min) and moderate adsorption capacity (143.1 mg/g), and the removal efficiency of low concentration uranium (0.1 g/L and 1 g/L) reaches 100% within 1 min of adsorption. Moreover, the adsorption of uranium by CeO2 is almost unaffected by common anions and cations in the environment, even if the concentration of anions is 1000 times that of uranium. More importantly, the CeO2 can enrich uranium concentration in seawater by 167.9 times and the recovery rate reaches 83.9%. Mechanistic studies reveal that the adsorption of uranium by CeO2 is mainly attributed to the rich Ce–OH groups on the surface of CeO2, resulting in the rapid adsorption of U(VI) and mainly forms a single-bridge model. The findings of this study provide a green and efficient path for the removal and recovery of uranium from wastewater and seawater.

Efficient Uranium Removal from Aqueous Solutions Using Silica-Based Adsorbents Functionalized with Various Polyamines.

With the rapid development of nuclear energy, the contamination of environmental water systems by uranium has become a significant threat to human health. To efficiently remove uranium from these systems, three types of silica-based polyamine resins-SiPMA-DETA (SiPMA: silica/poly methyl acrylate; DETA: diethylenetriamine), SiPMA-TETA (TETA: triethylenetetramine), and SiPMA-TEPA (TEPA: tetraethylenepentamine)-were successfully prepared, characterized, and evaluated in batch experiments. Characterization results showed that the silica-based polyamine resins were successfully prepared, and they exhibited a uniform shape and high specific surface area. SiPMA-DETA, SiPMA-TETA, and SiPMA-TEPA had nitrogen contents of 4.08%, 3.72%, and 4.26%, respectively. Batch experiments indicated that these adsorbents could efficiently remove uranium from aqueous solutions with a pH of 5-9. The adsorption kinetics of U(VI) were consistent with the pseudo-second-order model, indicating that the adsorption process was chemisorption and that adsorption equilibrium was achieved within 10 min. SiPMA-TEPA, with the longest polyamine chain, exhibited the highest adsorption capacity (>198.95 mg/g), while SiPMA-DETA, with the shortest polyamine chain, demonstrated the highest U(VI) adsorption efficiency (83%) with 100 mM Na2SO4. SiPMA-TEPA still removed over 90% of U(VI) from river water and tap water. The spectral analysis revealed that the N-containing functional groups on the ligand were bound to anionic uranium-carbonate species and possibly contributed to the adsorption efficiency. In general, this work presents three effective adsorbents for removing uranium from environmental water systems and thus significantly contributes to the field of environmental protection.

Synthesis of magnetic S-nZVI nanoparticle and its application for the effective removal of radioactive uranium from seawater

Synthesis of magnetic S-nZVI nanoparticle and its application for the effective removal of radioactive uranium from seawater

Synthesis of Quinone‐Amine‐Linked Covalent Organic Frameworks for Boosting the Photocatalytic Removal of Uranium

AbstractCompared to imine covalent organic frameworks (COFs), the superior stability of amine‐linked COFs renders them more suitable for long‐term harsh real‐world environments. Their numerous amine sites can serve as functional groups or be subjected to post‐modification to further enhance the performance of the material. However, the assortment and abundance of amine‐linked COFs via currently lacking due to restricted monomer varieties and synthetic methods. Herein, this study presents an innovative approach for synthesizing quinone‐amine‐linked COFs by directly combining 2,5‐dihydroxy‐1,4‐benzoquinone (DHBQ) with various amine monomers and introduce a novel photocatalyst, DHBQ‐TAPP‐COF, specifically tailored to efficiently reduce uranium in harsh environments. DHBQ‐TAPP‐COF features a unique donor–acceptor structure, with the DHBQ units serving as acceptors because they contain abundant oxygen atoms that facilitate metal ion coordination, thereby enhancing charge carrier separation, carrier utilization, and uranium reduction efficiency. The quinone‐amine linkages offer improved stability, extended π‐conjugation, heightened local polarity, and conductivity, which enable efficient carrier transfer within the material and thus enhance the overall performance of the uranium photocatalyst. The proposed photocatalyst can efficiently reduce U(VI) without sacrificial agents or decomposition to precipitate UO2 at a recovery rate exceeding 98%. This catalyst provides an efficient and convenient strategy for the stable and high‐performance photocatalytic reduction of uranium.

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.

Performance and mechanism of amino-functionalized hydroxyapatite for uranium removal from strong acidity uranium wastewater

The extraction of uranium generates substantial volumes of acidic wastewater loaded with uranium, thereby posing imminent threats to ecological systems and human wellbeing. Consequently, the development of highly effective adsorbent materials for uranium sequestration under strong acidic conditions has become paramount. The amino group contains a lone pair of electrons and is a highly reactive nucleophilic group with a strong affinity for uranium. Herein, we report the amino-functionalized materials (HAP-L-1NH2, HAP-L-2NH2, and HAP-L-3NH2) derived from sodium citrate-modified hydroxyapatite (HAP-L) through a combination of ultrasonic heating and grafting with varying concentrations of 2-amino-1,3-propanediol. The study delved into their performance and underlying mechanisms for uranium removal from acidic wastewater. The findings indicate that an optimal pH of 3.0 favors uranium adsorption for all the materials, with adsorption equilibrium achieved within 30 min. Their respective maximum uranium adsorption capacities stand at 826.44, 990.09, 1060.21, and 884.95 mg g−1, significantly enhancing the adsorptive prowess of amino-functionalized HAP-L materials. The kinetics and thermodynamics manifest that spontaneous endothermic chemisorption occurs on a homogenous monolayer during the adsorption process. Notably, HAP-L-2NH2 robust resilience to interfering ions and exceptional recyclability. After eight cycles of adsorption-desorption, HAP-L-2NH2 retains a uranium adsorption rate of 93.96 % with a stable chemical structure. Application of HAP-L-2NH2 in treating real-world acidic uranium wastewater led to a notable increase in pH from 2.87 to 3.92 and a substantial reduction in uranium concentration from 0.883 mg L−1 to 0.0104 mg L−1. Uranium removal by HAP-L-2NH2 is primarily governed by ion exchange, electrostatic interaction, and co-precipitation reactions.

Influence of dissolved organic matter on U(VI) removal at varying hydrogeochemical scenarios in ultrafiltration process

Uranium (U) is a chemical and radioactive groundwater contaminant that needs to be regulated in drinking water to avoid health hazards. In this study, we have investigated the mechanisms underlying ultrafiltration (UF) process, a low energy-intensive technology, for the removal of uranium from contaminated groundwater, in the presence of dissolved organic matter (i.e. Humic Acid [HA]) under environmentally-relevant conditions representative of regional scenario of Punjab, India. Stirred cell UF experiments with aqueous solutions containing uranium were performed with five different UF membranes with molecular weight cut off (MWCO) ranging from 1 kDa to 30 kDa at a pH of 8.5 that represented ambient groundwater scenario. In the absence of HA, the U(VI) removal was highest for the UF membrane with the lowest MWCO (i.e. 1 kDa) and vice-versa. Further, the effect of various solution parameters viz. pH, concentration of HA, and salinity have been studied using three different UF membranes viz. 5 kDa, 10 kDa, and 30 kDa. Uranium rejection was found to be maximum at pH 5.5 with ca. 97 %, 94 %, and 87 % rejection for 5 kDa, 10 kDa, and 30 kDa membranes, respectively. Further, U(VI) speciation results of the hydrogeochemical model corroborated that the removal of U(VI) in the presence of HA was highly dependent on feed solution pH. Moreover, U(VI) removal increased significantly with an increase in HA concentration, indicating the dominant role of U(VI)-HA complexes. Further, it was observed that increasing the salinity levels to 100 mM in the feed solution (i.e. semi-brackish water scenario) decreased U(VI) rejection primarily due to the charge screening effect. Our results show that using the UF separation process, the World Health Organization’s drinking water guideline value of 30 µg of U L−1 could be achieved in U(VI) contaminated groundwater that contains significant HA levels.

Enhanced sorbent properties by synergistic effect of biomass extract functional groups for effective uranium uptake from aqueous system

Adsorption for uranium removal from aqueous systems has been extensively studied, due to its many advantages. However, the great costs and complexity of many sorbent preparation methods are still restricting the progress. Hence, this research aimed to introduce a novel, simple and green method for enhancing Amberlite IR-120 properties for U(VI) removal. Adsorption process parameters were evaluated by batch method and sorbent was characterized before and after uranium adsorption by FTIR, SEM and EDS analysis. The results demonstrated that sorbent was effective for U(VI) removal at pH 5, 100 mg dose with 60 mg/L of U(VI) concentration within 40 min at higher temperatures. The removal efficiency was 87.7% and process was found feasible according to thermodynamic data. Kinetic modelling showed best correlation with pseudo-second order model (r2 = 0.999) and applied isotherms could all describe investigated process suggesting a complex mechanism of U(VI) uptake. Effect of interfering ions (Pb(II), Ni(II) and Co(II)) in a concentration of 45 and 60 mg/L decreased U(VI) removal to 45%. Additionally, AAS method confirmed that used sorbent has significant affinity towards Pb(II). Desorption study revealed successful uranium recovery in up to 3 cycles of sorption/desorption. The EDS analysis revealed the uranium presence with 4.7% and FTIR analysis revealed bands characteristic for stretching vibrations of O=U=O. Proposed mechanism involved U(VI) uptake via non-covalent interactions, inter/intra-molecular hydrogen bonding and intraparticle diffusion. Techno-economic analysis showed that with used preparation method 1 g of ASP costs 0.022 $. Hence, this study offers a novel method for sorbents properties enhancements.

Encapsulation of Bamboosa vulgaris culms derived activated biochar into hierarchical permeable, phosphate rich and functionalized alginate aerogel composites and its contribution in U(VI) adsorption

In this study, a facile methodology was designed to encapsulate Bamboosa vulgaris culms derived activated biochar (BVC) in a variable mass ratio, into a three-dimensional hierarchical porous and permeable and amino-thiocarbamated alginate (TSC) to prepare hybrid biosorbents (BVC-MSA). These ultralight and lyophilized phosphate rich macroporous sorbents were rationally characterized through FTIR, XRD, BET, SEM-EDS, elemental mapping, XPS techniques and employed for efficient UO22+ adsorption from aqueous solutions. The phytic acid (PA) was found to be a suitable hydrophilic and phosphorylating agent for the TSC matrix through hydrogen-bonded crosslinking when employed in a correct mass ratio (1:3). The SEM-EDS and XPS analyses confirmed the UO22+ sorption onto BVC-MSA-3 (the most suitable composite with a BVC/TSC mass ratio of 30.0 % w/w) and provided evidence of heteroatom involvement in developing the physico-chemical interactions. The BCV-MSA-3 exhibited the best response as a sorbent during kinetics/sorption process, therefore, it was selected to study the equilibrium sorption studies. The BCV-MSA-3 removal efficiency increased from 12.1 to 94.2 % using 0.2 to 1.8 g/L sorbent dose at pH (4.5). The mentioned sorbent displayed a significant maximum sorption capacity qm (309.55 mg/g at 35 °C) calculated through the best-fitted Langmuir and Temkin models (R2 ≈ 0.99). The sorption kinetics followed the pseudo-second-order (PSORE) model and exhibited fast sorption rate teq (180 min). Thermodynamic parameters clarified that the sorption process is feasible ΔGo (−25.3 to −27.6 kJ/mol kJ/mol), endothermic ΔHo (27.17 kJ/mol), and proceeds with a positive entropy (0.176 kJ/mol.K). The study shows that BCV-MSA-3 could be an alternative and auspicious sorbent for uranium removal from aqueous solution.

Effects of Detoxifying Substances on Uranium Removal by Bacteria Isolated from Mine Soils: Performance, Mechanisms, and Bacterial Communities

In this study, we investigated the effect of detoxifying substances on U(VI) removal by bacteria isolated from mine soil. The results demonstrated that the highest U(VI) removal efficiency (85.6%) was achieved at pH 6.0 and a temperature of 35 °C, with an initial U(VI) concentration of 10 mg/L. For detoxifying substances, signaling molecules acyl homoserine lactone (AHLs, 0.1 µmol/L), anthraquinone-2, 6-disulfonic acid (AQDS, 1 mmol/L), reduced glutathione (GSH, 0.1 mmol/L), selenium (Se, 1 mg/L), montmorillonite (MT, 1 g/L), and ethylenediaminetetraacetic acid (EDTA, 0.1 mmol/L) substantially enhanced the bacterial U(VI) removal by 34.9%, 37.4%, 54.5%, 35.1%, 32.8%, and 47.8% after 12 h, respectively. This was due to the alleviation of U(VI) toxicity in bacteria through detoxifying substances, as evidenced by lower malondialdehyde (MDA) content and higher superoxide dismutase (SOD) and catalase (CAT) activities for bacteria exposed to U(VI) and detoxifying substances, compared to those exposed to U(VI) alone. FTIR results showed that hydroxyl, carboxyl, phosphorus, and amide groups participated in the U(VI) removal. After exposure to U(VI), the relative abundances of Chryseobacterium and Stenotrophomonas increased by 48.5% and 12.5%, respectively, suggesting their tolerance ability to U(VI). Gene function prediction further demonstrated that the detoxifying substances AHLs alleviate U(VI) toxicity by influencing bacterial metabolism. This study suggests the potential application of detoxifying substances in the U(VI)-containing wastewater treatment through bioremediation.

A synergistic bioelectrochemical-photocatalytic system for efficient uranium removal and recovery

Bioelectrochemical system (BES) is a promising technology for uranium recovery, which also enables simultaneous electricity generation. However, the bioelectrochemical recovery of uranium is hindered by its slow process due to the low reduction potential provided by microorganisms. Herein, we developed an innovative bioelectrochemical-photocatalytic system (BEPS) that combines the advantages of BES and photocatalysis, achieving enhanced uranium removal and recovery. The photogenerated electrons in BEPS possess a more negative reduction potential and stronger reduction capability than microbial electrons in BES, significantly accelerating uranium reduction and deposition on the electrode surface. Moreover, the electrons from the bioanode combine with photogenerated holes through the external circuit, effectively inhibiting the recombination of charge carriers. The BEPS significantly enhances uranium removal efficiency, kinetic, and electricity generation through a synergistic coupling mechanism between the bioanode and photocathode. Notably, the UO2 deposited on the electrode surface exhibited a recovery efficiency of 98.21 ± 1.37%, and the regenerated electrode sustained its photoelectric response and uranium removal capabilities. Our findings highlight the potential of the BEPS as an effective technology for uranium recovery and electricity generation.

The insight into behavior and mechanism of chitosan-embedded hydroxyapatite gel spheres used for efficient solidification of uranium in wastewater

In this work, hydroxyapatite (HAP), an environmentally friendly material was prepared with Phosphogypsum (PG) as calcium source, and uranium immobilization gel spheres were prepared by chitosan (CS) embedding, which would reduce HAP agglomeration while providing an abundance of uranium-loving groups, realizing “treating waste for waste”. The optimum pH for U(VI) removal was determined to be 4, the optimum dosage was 0.2 g/L, and qmax = 350.88 mg/g through batch experiments. When C0 = 10 mg/L, it was found that the removal rate of U(VI) by HAP-CS could be up to 99.92 %, and the residual uranium concentration was 0.008 mg/L, which meets the national emission standard. The removal rate of uranium can reach 95.92 % by applying it to high concentration uranium ore wastewater. CS was found to have good biocompatibility with HAP by SEM, FTIR, XRD, and XPS characterization. Meanwhile, we found that Ca, –OH, and P-O play a dominant role in the uranium removal process, and the main mechanism of uranium removal by Hydroxyapatite-Chitosan gel spheres (HAP-CS) is surface complexation, ion exchange, and dissolution–precipitation binding. The HAP-CS has high uranium removal efficiency, simple solid–liquid separation, and good biocompatibility, and can be used to treat actual uranium-containing wastewater.

Regulatory roles of extracellular polymeric substances in uranium reduction via extracellular electron transfer by Desulfovibrio vulgaris UR1

The pathway of reducing U(VI) to insoluble U(IV) using electroactive bacteria has become an effective and promising approach to address uranium-contaminated water caused by human activities. However, knowledge regarding the roles of extracellular polymeric substances (EPS) in the uranium reduction process involving in extracellular electron transfer (EET) mechanisms is limited. Here, this study isolated a novel U(VI)-reducing strain, Desulfovibrio vulgaris UR1, with a high uranium removal capacity of 2.75 mM/(g dry cell). Based on a reliable EPS extraction method (45 °C heating), manipulation of EPS in D. vulgaris UR1 suspensions (removal or addition of EPS) highlighted its critical role in facilitating uranium reduction efficiency. On the second day, U(VI) removal rates varied significantly across systems with different EPS contents: 60.8% in the EPS-added system, 48.5% in the pristine system, and 22.2% in the EPS-removed system. Characterization of biogenic solids confirmed the reduction of U(VI) by D. vulgaris UR1, and the main products were uraninite and UO2 (2.88–4.32 nm in diameter). As EPS formed a permeable barrier, these nanoparticles were primarily immobilized within the EPS in EPS-retained/EPS-added cells, and within the periplasm in EPS-removed cells. Multiple electroactive substances, such as tyrosine/tryptophan aromatic compounds, flavins, and quinone-like substances, were identified in EPS, which might be the reason for enhancement of uranium reduction via providing more electron shuttles. Furthermore, proteomics revealed that a large number of proteins in EPS were enriched in the subcategories of catalytic activity and electron transfer activity. Among these, iron-sulfur proteins, such as hydroxylamine reductase (P31101), pyruvate: ferredoxin oxidoreductase (A0A0H3A501), and sulfite reductase (P45574), played the most critical role in regulating EET in D. vulgaris UR1. This work highlighted the importance of EPS in the uranium reduction by D. vulgaris UR1, indicating that EPS functioned as both a reducing agent and a permeation barrier for access to heavy metal uranium.

Enhancing the uranium (VI) adsorption performance of phosphoric acid functionalized porous silica by controlled introduction of phosphoric acid group

The post-grafting of porous silica with organic group is a common method for the synthesis of organo-functionalized silica adsorbent. However, this method usually produces adsorbents with limited adsorption performances due to the pore blocking caused by the irregular introduction of organic group. In this work, we report the controllable synthesis of phosphoric acid functionalized porous silica adsorbent based on the co-condensation method for uranium (VI) adsorptive removal with enhanced adsorption performance. Characterizations of the obtained silica verify its porous structure and confirm the homogeneous distribution of phosphoric acid groups inside the silica. This silica is able to efficiently remove 98 % of uranium from a 100 mg/L uranium (VI) solution within 10 min at a dosage of 0.6 g/L and the maximum uranium (VI) adsorption amount reaches 509 mg/g. Both adsorption capacity and adsorption rate of this silica are superior than that of the silica synthesized based on conventional post-grafting method. Moreover, this silica can be reused for five times with uranium (VI) removal efficiency above 95 % and it is well applied in adsorption column for dynamically adsorptive removal of uranium (VI) from real nuclear wastewater. Mechanism-related investigations reveal that uranium (VI) adsorption on this silica proceeds by effective ion exchange of uranium (VI) ion with either phosphoric acid or silanol group and the formation of uranyl phosphonate or uranyl silicate complex. This work provides a feasible strategy to synthesize functionalized porous silica without significant pore blocking, and demonstrates the enhancement effect of regulating surface adsorption groups on the adsorption performances of porous silica. Besides, this work offers a promising adsorbent for efficient treatment of uranium-containing nuclear wastewater and reveals the mechanism of uranium adsorption on those silica adsorbent containing phosphoric acid, thiol or thioether group.

Photocatalytic high-effective removal and recovery of uranium induced by benzyl alcohol with low cost and environment-kind

Photocatalysis, one of the environment-friendly and efficient technology, showed application prospects on uranium removal and recovery in spite of the expensive photocatalysts. Herein, we reported a novel strategy induced by benzyl alcohol for photo-autocatalytic removal and recovery of uranium, which achieved excellent removal rate and avoided the dependence on photocatalysts. The results showed that, in slightly acidic environments, the uranium removal rate could achieve over 99 % under air within an hour illumination via the redox reaction of radical ion pair [UO2+, Ph·CHOH], which can be produced by the photoactivation of benzyl alcohol for the active benzylic C(sp3) − H bonds. At the same time, benzyl alcohol was selectively oxidized to benzaldehyde, an important industrial feed stock of significance in fine and chemical industries. Moreover, uranium could be removed to 186 ppb within 4 h of illumination, which was up to the emission standard proposed in GB 23727–2020. This strategy exhibited excellent removal performance upon solar illumination and recovered uranium with 99.08 % removal rate in the existence of heteroions, which indicated that our strategy has important application potential.