Uranium-containing Wastewater Research Articles

Phytic acid-functionalized polyamidoxime/alginate hydrogel for targeted uranium extraction from acidic wastewater

Efficient removal of uranium from radioactive wastewater is crucial for both environmental protection and sustainable development of nuclear energy. However, selectively extracting uranium from acidic wastewater remains a significant challenge. Here we present a phytic acid-functionalized polyamidoxime/alginate hydrogel (PAG) via a facile one-step hydrothermal reaction. The PAG, leveraging the robust binding affinity of phytic acid and the selective coordination of amidoxime for U(VI), exhibited high efficiency and selectivity in adsorbing U(VI) from acidic uranium-containing wastewater. At pH 2.50, U(VI) adsorption equilibrium was achieved within 60 min, showcasing a maximum theoretical adsorption capacity of 218.34 mg/g. Additionally, the PAG demonstrated excellent reusability, maintaining a uranium removal rate exceeding 90 % over five adsorption-desorption cycles. Remarkably, the as-synthesized PAG removed 94.1 % of U(VI) from actual acidic uranium-contaminated groundwater with excellent anti-interference performance, reducing U(VI) concentration from 272.0 μg/L to 16.1 μg/L and making it meet the WHO drinking water standards (30 μg/L). The adsorption mechanism was elucidated through XPS and DFT calculation, revealing that the uranyl ion primarily coordinated with phosphate and amidoxime groups on phytic acid and polyamidoxime, respectively. These findings underscore the promising potential of PAG hydrogel for addressing acidic uranium-containing wastewater from uranium mining and metallurgy.

Construction of three-dimensional polyethyleneimine incorporated graphene oxide aerogels as high-capacity electrode for enhanced uranium(VI) electrosorption performance

Electrosorption technique is paid more attention in recovery of uranium(VI) due to its low energy consumption, green process and easy regeneration, but still is hindered by the limited accessible active sites on the electrode material, poor surface wettability and inherent ion exclusion effects. Herein, novel there dimensional porous polyethyleneimine/graphene oxide aerogel (PEI/GOA) electrode was constructed by incorporating polyethyleneimine into graphene oxide and using chitosan as binder for uranium(VI) electrosorption. The synthesized PEI/GOA had a stable three-dimensional porous structure, high specific capacitance (54.06F/G) and good charge–discharge stability. The electrosorption process of uranium(VI) by PEI/GOA electrode was affected by applied voltage and pH, fitted by the pesuo-second-order kinetics and Langmuir model. The maximum theoretical electrosorption capacity of uranium(VI) by PEI/GOA electrode at − 1.2 V was 419.71 mg/g, which was 2.2 times higher than that of pure graphene oxide electrode. PEI/GOA electrode exhibited less than 20 % loss after five cycles using 0.1 M NaHCO3 as the eluent. The efficient U(VI) electrosorption by PEI/GOA electrode was not only attributed to the formation of the electric double layer, but also due to the interaction and synergy of the –NH2, –CONH- and –OH on the PEI/GOA electrode. This research offers a new approach for the efficient removal of uranium (VI) from uranium-containing wastewater.

Extraction of Uranium by a Pyrazole-Based Porous Organic Polymer.

In this work, we report a pyrazole-based porous organic polymer (namely, ECUT-POP-2) for extraction of uranium. ECUT-POP-2 affords a high uranium extraction capacity of up to 1851 mg/g, excellent selectivity, and good reusability, suggesting its superior application in treating uranium-containing wastewater and acquring nuclear fuel.

Nano-Fe3O4/polymerize aniline/carbon cathode based microbial fuel cell for efficient power generation and uranium separation

Microbial fuel cells (MFCs) have gained increasing attention in the field of uranium-containing wastewater (UCW) treatment as a self-powered bioelectrochemical system (BES) due to its advantages of recovering uranium resources and generating electricity. However, the lack of catalytic active sites on the carbon fiber cathode significantly hinders the reaction performance of surface electrons with uranium ions in solution, thereby limiting the application of MFC. In this study, we propose a carbon brush (CB) cathode modification process that utilizes cyclic voltammetry synthesis technique (CVS) to polymerize aniline (PA) on the surface of carbon fibers and uniformly load nano-Fe3O4 particles (nFe3O4). The loading of PA/nFe3O4 not only significantly improve the catalytic active sites but also enhance the synergistic effect of adsorption and conductivity of CB cathode. Consequently, the nFe3O4/PA/CB-MFC showed excellent ability to continuous power generation and uranium separation. Over eight cycles of uranium separation, the nFe3O4/PA/CB-MFC exhibited an average maximum power density of 15.17 mW/m2 and a uranium separation efficiency of 95.52 %, showcasing substantial enhancements by 2.10-fold and 1.44-fold compared to the CB-MFC, respectively. Our study presents an efficient approach to enhance the efficiency of uranium separation and boost power density of MFC by increase catalytic active sites on carbon-based cathode.

Adsorptive removal of uranium from aqueous solution using magnetic hydroxyapatite

High efficiency and easy separation adsorbents are important for the treatment of uranium-containing wastewater, but still face challenges. In this paper, a new effective adsorbent for uranium removal from wastewater, i.e., PEG-β-CD-nHA@Fe3O4 composite, was synthesized by hydrothermal reaction using iron doping and in-situ co-precipitation method, in which polyethylene glycol (PEG) and beta-cyclodextrin (β-CD) were used as double templates to mediate the synthesis process. The results showed that the morphology and magnetic property of the composite were significantly improved. The adsorption capacity reached 928.46 mg/g, and the composite could be quickly magnetically separated after U(Ⅵ) adsorption. U(Ⅵ) adsorption performance was obviously affected by adsorbent dosage, pH, contact time and U(VI) concentration. Pseudo-second-order (PSO) and Sips models could accurately fit adsorption experimental data, indicating that it was chemisorption, in which –OH and PO43- played an important role. U(VI) ions were adsorbed and fixed through complexation, precipitation and ion exchange. The results indicated that PEG-β-CD-nHA@Fe3O4 composite was a green, efficient and easily separated adsorbent for U(VI) removal.

Magnetic alginate supported potassium manganese ferrocyanide for the recovery of uranium from acidic wastewater

Abstract With the rapid development of the atomic energy industry, the demand for nuclear fuel has risen, while the limited resources of uranium mines make it difficult to meet the needs of the future development of nuclear energy. Expanding sources of uranium acquisition is necessary, and the enrichment and recovery of precious uranium from uranium-containing wastewater is invaluable. By synthesizing alginate supported potassium manganese ferrocyanide nanocomposites with magnetic response (KMnFC/MA/Fe3O4), the high efficiency adsorption and separation of uranium in acidic uranium-containing wastewater can be realized conveniently and quickly. The magnetic composite was characterized by a variety of technical means, and the adsorption behavior of the magnetic material on uranium was studied by static adsorption experiments under different environmental conditions. The adsorption kinetics and isotherm of uranium by KMnFC/MA/Fe3O4 were studied by using some common linear adsorption models. The results show that the adsorption rate of KMnFC/MA/Fe3O4 on uranium is fast, and the adsorption equilibrium can be reached within 90 min. The adsorption process conforms to a pseudo-secondary kinetic model and is dominated by chemisorption. The adsorption of uranium by KMnFC/MA/Fe3O4 magnetic material is single molecular layer adsorption, and the maximum adsorption capacity is 425.5 mg g−1 at 35 °C. KMnFC/MA/Fe3O4 is a promising adsorbent in the field of acidic low-concentration uranium wastewater treatment because of its good effect on the treatment of low concentration uranium wastewater, the concentration of uranium in the wastewater reaches the emission standard after treatment and it is easy to be separated magnetically after adsorption.

Dipole Moment and Built-In Polarization Electric Field Induced by Oxygen Vacancies in BiOX for Boosting Piezoelectric-Photocatalytic Removal of Uranium(VI).

Piezoelectric-photocatalysis is distinguished by its piezoelectricity as an external force that induces deformation within the catalyst to engender a polarized electric field compared to conventional photocatalysis. Herein, the piezoelectric photocatalyst BiOBr has been expertly synthesized via a plasma process and applied for piezoelectric-photocatalysis removal of uranium(VI) for the first time. The abundant surface oxygen vacancies (OVs) could induce a dipole moment and built-in electric field, which endows BiOBr with excellent separation and transport efficiency of photogenerated charges to actuate more charges to participate in the piezoelectric-photocatalytic reduction process. Consequently, under visible light and ultrasound (150 W and 40 kHz), the removal rate constant of OVs-BiOBr-30 (0.0306 min-1) was 2.4, 30.6, and 6 times higher than those of BiOBr (0.01273 min-1), ultrasound, or photocatalysis, respectively. The piezoelectric-photocatalytic synergy is also universal for BiOX (X = Cl, Br, or I) to accelerate the reduction rate of uranium(VI). This work highlights the role of piezoelectric-photocatalysis in the treatment of uranium-containing wastewater, which is of great significance for resource conservation and environmental remediation.

Solvent-regulated self-assembled carbon nitride for photocatalytic reduction of U(VI) in water.

Manufacturing high-performance and reusable materials from radioactive uranium-containing wastewater remains a significant challenge. Herein, a supramolecular self-assembly strategy was proposed, using melamine and cyanuric acid as precursors and using intermolecular hydrogen bond force to form carbon nitride (CN-D) in different solvents through a single thermal polymerization strategy. Supramolecular self-assembly method is a promising strategy to synthesize a novel carbon nitride with molecular regulatory properties. In addition, 98% of U(VI) in wastewater can be removed by using CN-D for 60min under visible light. After five cycles of recycling, more than 95% of U(VI) can still be reduced, indicating that it has good recyclability and reusability. This study not only provides an efficient photocatalytic method of uranium reduction, but also provides a new method for self-assembly synthesis.

One-step synthesis of phospho-rich, silica-enhanced chitosan aerogel for the efficient adsorption of uranium(VI)

In this study, an amorphous silica reinforced, phosphoric-crosslinked chitosan foam (P-CTS@SixOy) was prepared. The introduction of amorphous silica not only increased the affinity of the adsorbent for uranium, but also improved the stability of the material. The number of active sites of P-CTS@SixOy was increased by the introduction of phosphate groups. The material exhibited excellent uranium adsorption performance with the removal capacity and efficiency of 850.5 mg g−1 and 98.1 %, respectively. After regenerations, the morphology of P-CTS@SixOy still maintained, and the uranium adsorption efficiency remained above 90 %, manifesting the excellent cycle performance of P-CTS@SixOy. In the dynamic adsorption experiment, P-CTS@SixOy successfully concentrated the volume of uranium-containing solution, and exhibited excellent uranium adsorption performance. The analysis of kinetics, isotherms, and thermodynamics manifested that the uranium adsorption behavior of P-CTS@SixOy was a spontaneous, endothermic, monolayer chemical adsorption process. X-ray photoelectron spectroscopy, Scanning Electron Microscope, and Fourier Transform Infrared Spectrometer were used to characterized the P-CTS@SixOy before and after adsorption, which demonstrated that the main interaction mechanism between uranium and P-CTS@SixOy was the complexation. These studies indicated the huge application prospect of P-CTS@SixOy in the treatment of large-scale uranium-containing wastewater.

Efficient purification of low-level uranium-containing wastewater by polyamine/amidoxime synergistically reinforced fiber

The removal and recovery of uranium [U(VI)] from organic containing wastewater has been a challenging in radioactive wastewater purification. Here, we designed a polyamine/amidoxime polyacrylonitrile fiber (PAN-AO-A) with high removal efficiency, excellent selectivity, excellent organic resistance and low cost by combining the anti-organic properties of amidoxime polyacrylonitrile fiber (PAN-AO-A) with the high adsorption capacity of polyamine polyacrylonitrile fiber, which is used to extract U(VI) from low-level uranium-containing wastewater with high ammonia nitrogen and organic content. PAN-AO-A adsorbent with high grafting rate (86.52%), high adsorption capacity (qe = 618.8 mg g−1), and strong resistance to organics and impurity interference is achieved. The adsorption rate of U(VI) in both real organic and laundry wastewater containing uranium is as high as 99.7%, and the partition coefficients (Kd) are 7.61 × 105 mL g−1 and 9.16 × 106 mL g−1, respectively. The saturated adsorption capacity of PAN-AO-A in the continuous system solution can reach up to 505.5 mg g−1, and the concentration of U(VI) in the effluent is as low as 1 μg L−1. XPS analysis and Density functional theory (DFT) studies the coordination form between U(VI) and PAN-AO-A, where the most stable structure is η2-AO(UO2)(CO3)2. The –NH–/-NH2 and –C(NH2)N–OH groups of PAN-AO-A exhibit a synergistic complex effect in the U(VI) adsorption process. PAN-AO-A is a material with profound influence and limitless potential that can be used for wastewater containing U(VI) and organic matter.

Engineering layered double hydroxide with enzyme-mimicking antibiofouling ability for uranium capture

Materials capable of capturing environmentally mobile uranium from various sources, including nuclear waste and bio-aggressive seawater, are critical for energy and environmental sustainability. Unfortunately, the stability and reusability of existing absorbents is limited in seawater due to the ubiquitous and notorious biofouling, and therefore, developing high-performance materials with antibiofouling activity is of great importance for uranium capture. Here we report a tungstate exchanged layered double hydroxide composite (MgAl-LDH-NO3--WO42-) that exhibits a significant uranium removal efficiency of 98.8 % in 240 ppm uranium-containing wastewater and a maximum uptake capacity of 409.6 mg g−1. More importantly, MgAl-LDH-NO3--WO42- displays an excellent antibiofouling ability in bio-aggressive seawater by mimicking natural haloperoxidase in marine algae, enabling the excellent cyclic stability for uranium capture from seawater. This work provides an effective strategy to develop highly efficient LDH-based materials for uranium capture.

Facile synthesis of robust polyethyleneimine incorporated chitosan composite hydrogel for efficient enrichment of uranium(VI) in aqueous solution

The development of polymer hydrogel with abundant ion diffusion paths is needed to address sustainable energy supply and ecological security. Herein, a robust chitosan-based polymer hydrogel with superior structural stability and sufficient active sites was fabricated by incorporating polyethyleneimine into chitosan for efficient enrichment of uranium(VI). The as-prepared chitosan-based polymer hydrogel has a maximum uranium adsorption capacity of 291.75 mg-U/g at pH= 6, together with relatively good selectivity to uranium(VI). The adsorption process was described well with the pseudo-second-order kinetic model and Langmuir isotherm model. The main adsorption mechanism was related to the complexation of uranyl ions with the amino and hydroxyl groups. The chitosan-based polymer hydrogel, with the merits of facile preparation, easy solid-liquid separation, eco-friendliness and cyclic utilization highlights its promising application in uranium removal and recovery from uranium-containing wastewater.

A convenient functionalization strategy of polyimide covalent organic frameworks for uranium-containing wastewater treatment and uranium recovery

The purpose of this research was to design and synthesize an adsorbent based on polyimide covalent organic frameworks (PICOFs) for uranium-containing wastewater treatment and uranium recovery. A modified solvothermal method was innovatively proposed to synthesize PICOFs with high specific surface area (1998.5 m2 g−1) and regular pore structure. Additionally, a convenient functionalization strategy of PICOFs was designed through polydopamine (PDA) and a well-dispersed polymer (MPC-co-AO) containing multiple functional groups, forming stable composite (PMCA-TPPICOFs) in which the hydrogen bonding and cation-π interactions between PDA and MPC-co-AO played a key role. The obtained PMCA-TPPICOFs as an adsorbent exhibited strong selectivity for uranyl ions (maximum adsorption capacity was 538 mg g−1). In simulated wastewater with low uranium concentrations, the removal rate reached 98.3%, and the concentration of treated simulated wastewater met discharge standards. Moreover, PMCA-TPPICOFs was suitable for fixed-bed column adsorption because of its favorable structure. According to the research about adsorption mechanism, the adsorption primarily relied on electrostatic interaction and complexation. In summary, PMCA-TPPICOFs exhibited good potential for uranium-containing wastewater treatment, expanding the application of PICOFs. And the proposed functionalization strategy and modified solvothermal method may promote research in the fields of material functionalization and COFs synthesis. Environmental ImplicationUranium is a raw material for nuclear energy applications, which is toxic and radioactive. If uranium is discharged with wastewater, it would not only pose a threat to the environmental protection and life safety, but also cause the loss of precious nuclear raw materials. Although adsorption was considered to be an effective way to remove uranium, many of the developed adsorbents were difficult to apply due to the harsh wastewater environment and complex preparation processes. This study reported a novel adsorbent and a new functionalization strategy, which was expected to solve the problem of uranium recovery in wastewater.

Electrodeposition nanofabrication of carboxylated carbon nanotubes/α-MnO2 nanorods/ polypyrrole composites as high hybrid capacitance electrodes for efficient U(VI) electrosorption

The uranium-containing wastewater resourced from the nuclear fuel cycle presents serious harm to human health and ecological environment. Herein, carboxylated carbon nanotubes/α-MnO2 nanorods/polypyrrole (CMP) composite as high hybrid capacitance (EDL and pseudocapacitance) electrodes with good electrosorption performance for U(VI) were nanofabricated by the electrodeposition of polypyrrole (PPy) on the surface of carboxylated carbon nanotubes/α-MnO2 nanorods composites using potentiostatic method. The morphology and structure characteristics, electrochemical properties and electrosorption U(VI) properties of the CNT/α-MnO2/PPy composites were systematically investigated. The results show that among the CMP composites obtained at different pyrrole concentrations, CMP-0.10 has the highest specific capacitance (366.97F/g), and its electrosorption performance is also the best, which is due to its well balanced porous structure and high hybrid capacitance which favors U(VI) ions transfer and storage. Cyclic voltammetry (CV) curves with obvious redox peaks were observed at low sweep speeds, indicating its hybrid capacitance behavior of CMP composites in which the capacitance contribution can be quantified. The electrosorption experiments were performed in a capacitive deionaiztion (CDI) system in which different factors (voltage, pH, U(VI) concentration and contact time, etc.) on the electrosorption of U(VI) were investigated, which shows that high U(VI) removal could be achieved at a wide pH range. The theoretical simulation using different models shows the best fit of the Langmuir model for the electrosorption isotherms and PFO model for the kinetics. The U(VI) electrosorption capacity reaches 339.45 mg/g at 0.9 V and pH 4.5 for CMP-0.10, which is much higher that achieved at 0.0 V. The facile fabrication, excellent electrochemical and electrosorption performance as well as good cycling stability for the CMP composites highlight their potential application in radioactive wastewater treatment.

Efficient removal of U(VI) from aqueous solution by hydroxyapatite/graphene oxide composite microspheres

Abstract Effective treatment of uranium-containing wastewater is of great significance to the sustainable development of nuclear power and the protection of ecological environment. In this study, a highly efficient uranium adsorbent, graphene oxide (GO)/nano-hydroxyapatite (nHA) composite microspheres (nHA@rGO) was synthesized, which could effectively remove uranium from aqueous solution. Under the condition of pH = 3.5, T = 298 K, the maximum adsorption capacity reached 1672.96 mg/g. The results of batch experiments showed that the adsorption capacity of nHA@rGO microspheres was higher than that of nHA microspheres, indicating the enhancement of GO. The adsorption kinetics conformed to the pseudo second-order model. The changes of nHA@rGO microspheres before and after uranium adsorption were analyzed by FT-IR, XPS and XRD. The mechanisms of U(VI) ions adsorption onto nHA@rGO microspheres involved precipitation, surface complexation and ion exchange, in which the hydroxyl and phosphoric acid groups played important roles. The results showed that the prepared nHA@rGO microspheres can be used as an efficient and promising adsorbent for the treatment of uranium-containing wastewater.

Electrodeposition nanofabrication of graphene oxide/polypyrrole electrodes with high hybrid specific capacitance for enhancing U(VI) electrosorption

The uranium-containing wastewater generated in the nuclear fuel cycle poses a serious threat to the environmental ecosystem, and electrosorption can be an effective method for U(VI) removal. Herein, the electrodeposition nanofabrication of a novel composite electrode (GO/PPy) with high hybrid specific capacitance for U(VI) electrosorption. The results showed that the combination of GO with PPy significantly improved the specific capacitance, conductivity and cycling ability, thereby enhancing U(VI) electrosorption. Among various GO/PPy composites, GO/PPy-0.2 presented the highest specific capacitance, and its electrosorption capacity of U(VI) was also the highest, owing to its high specific capacitance and open interlayer channels for ion storage. The cyclic voltammetry characteristic of GO/PPy-0.2 is characterized by capacitive control, which highlights the contribution of PPy pseudocapacitance to electrosorption. The isotherms and kinetics of U(VI) electrosorption were found to be well-simulated by the Langmuir model and the PFO model, respectively. The maximum U(VI) electrosorption capacity reached 246.5 mg/g at pH 4.0 and 0.9 V. This work provides a feasible strategy for the electrodeposition nanofabrication of high-performance GO/PPy electrodes by incorporating a EDL capacitance material (GO) with a pseudo-capacitance material (PPy) to improve the specific capacitance and stability of the electrodes. Meanwhile, it also provides insights into electrosorption mechanism based on hybrid capacitance (double layer capacitance and pseudo capacitance) and N/O complexation, which was confirmed by XPS and FTIR characterization. Overall, the excellent electrochemical electrosorptive performance of GO/PPy-2 endows its promising application in CDI for efficient separation of U(VI) from radioactive wastewater.

Synthesis and fabrication of segregative and durable MnO2@chitosan composite aerogel beads for uranium(VI) removal from wastewater

To address the imperative need for efficient removal of uranium-containing wastewater and mitigate radioactive contamination risks associated with nuclear energy, the development of materials with high removal efficiency and facile separation is crucial. This study designed and synthesised MnO2@chitosan (CTS) composite aerogel beads by in-situ growing δ-MnO2 on porous CTS aerogel beads. This approach not only mitigates the agglomeration of MnO2 nanospheres but also significantly enhances the porous structure and surface area of MnO2@CTS. These cost-effective and eco-friendly millimeter-scale spherical aerogels exhibited convenient separation properties after adsorption. These characteristics help mitigate the risk of equipment seam blockage and secondary pollution that are often associated with powdered adsorbents. Additionally, MnO2@CTS exhibited remarkable mechanical strength (stress approximately 0.55 MPa at 60 % strain), enabling rapid separation and easy regeneration while maintaining high adsorption performance even after five cycles. Significantly, MnO2@CTS exhibited a maximum adsorption capacity of 410.7 mg/g at pH 6 and 298 K, surpassing reported values for most CTS/MnO2-based adsorbents. The chemisorption process of U(VI) on MnO2@CTS followed the pseudo-second-order kinetic and Dubinin-Radushkevish models. X-ray photoelectron spectroscopy analysis further confirmed the reduction of U(VI) to U(V/IV). These findings highlight the substantial potential of MnO2@CTS aerogel beads for U(VI) removal from aqueous solutions, positioning them as a promising solution for addressing U(VI) contamination in wastewater.

Highly efficient and selective adsorption of uranium (VI) in acidic solution by TOPO impregnated PAN capsules

The adsorption capacity and adsorption rate of most adsorbents for U (VI) are maximum in the pH value range of 5 ∼ 9. However, uranium-containing wastewater produced during uranium mining is usually highly acidic. Therefore, it is of great significance to prepare adsorbents suitable for the separation and enrichment of U(VI) ions from strongly acidic solutions. PAN capsules were synthesized by phase transformation method, and then impregnated TOPO in PAN capsules by impregnation method. TOPO/PAN has good morphology and higher adsorption capacity for U(VI) under acidic conditions. The effects of time, solid–liquid ratio, pH and ionic strength on TOPO/PAN adsorption of U(VI) were studied. The experimental results showed that the pseudo-second-order kinetic model and Langmuir model well described the kinetic and equilibrium data of adsorption process. The capsules have fast adsorption rate, good adsorption capacity and good ion selectivity in highly acidic solutions. After 5 cycles, the adsorption rate of TOPO/PAN is still above 96 % and the adsorption rate decreases by 1.2 %, which indicate that TOPO/PAN has good reusability. The research shows that TOPO/PAN has good practical application value.

Two-dimensional sp2 carbon-conjugated COFs electrode for efficient electro-adsorption of uranium

Electro-adsorption has been shown great potential for radionuclides separation from aqueous solution benefit from its advantages, such as energy conservation, environmental protection. Herein, a 2 D sp2 carbon-conjugated COFs was obtained by the Knoevenagel reaction between 1,4-phenylenediacetonitrile and 1,3,5-tris(p-formylphenyl)benzene, and then amidoximated by treatment with hydroxylamine, the sp2 carbon-conjugated COFs functionalized carbon felts achieved efficient electro-adsorption for uranium(VI). A variety of characterization techniques were used to determine the chemical structure and morphology of the prepared sp2 carbon-conjugated COFs. The adsorption equilibrium of the sp2 carbon-conjugated COFs for uranium(VI) can be reached within 10 min at pH 6.0 and 1.2 V, more than twice faster than physicochemical adsorption according to the kinetic constants (K2). The maximum electro-adsorption capacity was calculated to be 478.5 mg/g fitted by Langmuir isotherm model, which was much higher than 294.1 mg/g obtained by physicochemical adsorption. Meanwhile, the distribution coefficient Kd of the electrode for uranium was 1.07 × 105 mL/g, indicating the sp2 carbon-conjugated COFs possessed excellent selectivity for uranium(VI) against co-existing cations. XPS studies confirmed that both hydroxyl and amino groups of amidoxime in COFs-AO are involved in the coordination of uranium(VI). Most importantly, the electrode showed good reusability, which makes it possible to remove uranium(VI) from uranium-containing wastewater. This work could allow sp2 carbon-conjugated COFs to be expanded to efficiently cleanup other contaminants by rational topology construction and ligands design.

Effective separation of U(VI) in acidic uranium-containing wastewater by potassium manganese ferrocyanide and carbon nanotube encapsulated calcium alginate beads

The separation and enrichment of uranium from uranium containing wastewater is important for the sustainable development of nuclear energy. Therefore, there is an urgent need to develop a low-cost, readily available, simple preparation process and environmentally friendly adsorbent. In this study, potassium manganese ferrocyanide and carbon nanotube encapsulated calcium alginate beads (KMnFC/CNT@SA) for uranium adsorption was prepared by a simple method using the inexpensive natural polymer material sodium alginate and the ion exchange material potassium manganese ferricyanide as well as carbon nanotubes capable of enhancing the spatial structure. Static adsorption experiments show that the adsorption capacity of KMnFC/CNT@SA for uranium is significantly affected by pH, contact time, U(VI) concentration and temperature, but is not affected by sodium ion concentration in solution. Furthermore, desorption and cycling tests demonstrate that KMnFC/CNT@SA has good reusability, with the adsorption capacity remaining above 89.83% of the maximum adsorption capacity after 10 adsorption-desorption cycles. It is worth noting that KMnFC/CNT@SA can adsorb uranium well under acidic conditions, and is easy to solid-liquid separation and recovery. This work provides an effective strategy for the development of high-quality, inexpensive, practical and durable adsorbents for uranium extraction from acidic uranium-containing wastewater.