Fabrication of granular three-dimensional graphene oxide/UiO-66 adsorbent for high uranium adsorption: Density functional theory and fixed bed column studies.

This study presents a thorough investigation of the novel application of graphene oxide (GO) modified with melamine formaldehyde to fabricate granular three-dimensional GO (3D-GO), followed by the introduction of UiO-66 doping (3D-GO/U) for high uranium (U) adsorption. The U(VI) adsorption isotherms revealed that 3D-GO/U-10 with 10 % UiO-66 incorporation exhibited an impressive adsorption capacity of 375.5 mg g-1 and remained high U(VI) sorption performance in wide pH range. The introduction of UiO-66 to 3D-GO (3D-GO/U-10) led to the deagglomeration of the UiO-66 particles. The in situ surface-enhanced-Raman-spectroscopy-analysis and density-functional-theory simulations showed the symmetric metal center site Zr-O2 on UiO-66 was discovered to exhibit the highest adsorption energy (-3.21 eV) for U(VI) species due to the electrons transfer from the oxygen atom to U(VI) drives the covalent bonding between the symmetric metal center sites Zr-O2 and U(VI) on 3D-GO/U-10. The 3D-GO/U-10 was regenerated using a 0.1 M Na2CO3/0.01 M H2O2 solution and achieved up to 89.7 % U(VI) removal in the 5th cycle. The continuous flow column experiments results revealed 3D-GO/U-10 can regenerate and maintain a U(VI) removal capacity of ∼76 % for up to 4 cycles column experiments. Therefore, 3D-GO/U-10 exhibits great potential for removing U(VI) from water bodies.

Statistically and visually analyzing the latest advancements and future trends of uranium removal.

Uranium contamination and remediation is a very important environmental research area. Removing radioactive and toxic uranium from contaminated media requires fundamental knowledge of targets and materials. To explore the-State-of-the-Art in uranium contamination control, we employed a statistical tool called CiteSpace to visualize and statistically analyze 4203 peer-reviewed papers on uranium treatment published between 2008 and 2022. The primary content presentations of visual analysis were co-authorships, co-citations, keyword co-occurrence analysis with cluster analysis, which could offer purposeful information of research hots and trends in the field of uranium removal. The statistical analysis results indicated that studies on uranium removal have focused on adsorption of uranium from aqueous solution. From 2008 to 2022, biochar and biological treatment were firstly used to sequester uranium, then adsorption for uranium removal dominates with adsorbents of graphene oxide, primary nanofiber magnetic polymers and metal-organic frameworks (MOFs). In recent years, photocatalysts and metal-organic frameworks are expected to be two of the most popular research topics. In addition, we further highlighted the characteristics and applications of MOFs and GOs in uranium removal. Overall, a statistical review was proposed to visualize and summarize the knowledge and research trends regarding uranium treatment.

Treatment of Uranium-Contaminated Ground Water Using Adsorption Technology via Novel Mesoporous Silica Nanoparticles.

Contamination of underground water by uranium (U) and other heavy metals is a growing concern. Mesoporous silica nanoparticles (MSNs) have shown great potential as an adsorbent material for heavy metal removal. This study synthesized a novel MSN using surface-initiated atom transfer radical polymerization (SI-ATRP) and evaluated its effectiveness for removing uranium from aqueous solutions under different conditions. The particle size was reduced to 150-240 nm to enhance adsorption. Fourier transform infrared characterization and thermogravimetric analysis confirmed successful synthesis and modification. Results showed that the MSN adsorbent was highly effective in removing U, with a removal rate of 85.35% at 120 min. Temperature had a significant impact, with the highest removal rate of 96.7% achieved at 25 °C and a U concentration of 10 ppm. The highest removal rate of 91.89% was achieved at a pH of 6 and a U concentration of 50 ppm. The highest removal rate of 95.16% was achieved at 25 mg and a U concentration of 50 ppm at room temperature for 60 min. The MSNs also showed a 58.27% removal rate in a mixture solution at room temperature for 60 min. This study demonstrates the effectiveness of the MSN adsorbent for removing U under different conditions.

Efficacy and mechanisms of δ-MnO2 modified biochar with enhanced porous structure for uranium(VI) separation from wastewater.

Even though uranium (U) is considered to be an essential strategic resource with vital significance to nuclear power development and climate change mitigation, U exposure to human and ecological environment has received growing concerns due to its both highly chemically toxic and radioactively hazardous property. In this study, a composite (M-BC) based on Ficus macrocarpa (banyan tree) aerial roots biochar (BC) modified by δ-MnO2 was designed to separate U(VI) from synthetic wastewater. The results showed that the separation capacity of M-BC was 61.53 mg/g under the solid - liquid ratio of 1 g/L, which was significantly higher than that of BC (12.39 mg/g). The separation behavior of U(VI) both by BC and M-BC fitted well with Freundlich isothermal models, indicating multilayer adsorption occurring on heterogeneous surfaces. The reaction process was consistent with the pseudo-second-order kinetic model and the main rate-limiting step was particle diffusion process. It is worthy to note that the removal of U(VI) by M-BC was maintained at 94.56% even after five cycles, indicating excellent reusability and promising application potential. Multiple characterization techniques (e.g. Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Brunauer-Emmett-Teller (BET) and X-ray Photoelectron Spectroscopy (XPS)) uncovered that U(VI) complexation with oxygen-containing functional groups (e.g. O-CO and Mn-O) and cation exchange with protonated ≡MnOH were the dominant mechanisms for U(VI) removal. Application in real uranium wastewater treatment showed that 96% removal of U was achieved by M-BC and more than 92% of co-existing (potentially) toxic metals such as Tl, Co, Pb, Cu and Zn were simultaneously removed. The work verified a feasible candidate of banyan tree aerial roots biowaste based δ-MnO2-modified porous BC composites for efficient separation of U(VI) from uranium wastewater, which are beneficial to help address the dilemma between sustainability of nuclear power and subsequent hazard elimination.

Comparative Study of the U(VI) Adsorption by Hybrid Silica-Hyperbranched Poly(ethylene imine) Nanoparticles and Xerogels.

Two different silica conformations (xerogels and nanoparticles), both formed by the mediation of dendritic poly (ethylene imine), were tested at low pHs for problematic uranyl cation sorption. The effect of crucial factors, i.e., temperature, electrostatic forces, adsorbent composition, accessibility of the pollutant to the dendritic cavities, and MW of the organic matrix, was investigated to determine the optimum formulation for water purification under these conditions. This was attained with the aid of UV-visible and FTIR spectroscopy, dynamic light scattering (DLS), ζ-potential, liquid nitrogen (LN2) porosimetry, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Results highlighted that both adsorbents have extraordinary sorption capacities. Xerogels are cost-effective since they approximate the performance of nanoparticles with much less organic content. Both adsorbents could be used in the form of dispersions. The xerogels, though, are more practicable materials since they may penetrate the pores of a metal or ceramic solid substrate in the form of a precursor gel-forming solution, producing composite purification devices.

High efficiency electrochemical separation of uranium(VI) from uranium-containing wastewater by microbial fuel cells with different cathodes.

As an emerging versatile technology for separating uranium from uranium-containing wastewater (UCW), microbial fuel cell (MFC) offers a novel approach to UCW treatment. Its cathode is essential for the treatment of UCW. To thoroughly investigate the efficacy of MFC in treating UCW, investigations were conducted using MFCs with five materials (containing iron sheet (IP), stainless steel mesh (SSM), carbon cloth (CC), carbon brush (CB), and nickel foam (NF)) as cathodes. The results revealed that each MFC system performed differently in terms of carbon source degradation, uranium removal, and electricity production. In terms of carbon source degradation, CB-MFC showed the best performance. The best uranium removal method was NF-MFC, and the best electricity production method was carbon-based cathode MFC. Five MFC systems demonstrated stable performance and consistent difference over five cycles, with CC-MFC outperforming the others. Furthermore, SEM and XPS characterization of the cathode materials before and after the experiment revealed that a significant amount of U(IV) was generated during the uranium removal process, indicating that uranium ions were primarily removed by electrochemical reduction precipitation. This study confirmed that abiotic cathode MFC had a high UCW removal potential and served as a good guideline for obtaining the best cathode for MFC.

Sustainable removal of uranium from acidic wastewater using various mineral raw materials.

Various types of plutonic and volcanic rocks and their alteration products from Greece (serpentinite, magnesite and andesite), have been used for sustainable removal of Uranium (U) from the acidic drainage of Kirki mine, as well as for the pH increase of the polluted solutions. In this light, this study aims at the further understanding and improvement of the ecofriendly reuse of sterile, natural raw materials (including those remaining through industrial processing and engineering testing of aggregate rocks), for remediation of acid mine drainage. The selected rocks constitute such residues of sterile materials were used as filters in experimental continuous flow devices in the form of batch-type columns, in order to investigate acidic remediation properties with special focus on U removal. The initial pH of the wastewater was 2.90 and increased after seven (7) days of experimental application and more specifically from the fourth day onwards. Uranium removal became quantitatively significant once pH reached the value of 5.09. The volcanic rocks appeared to be more effective for U removal than the plutonic ones because of microtextural differences. However, optimum U removal was mainly achieved by serpentinite: while the raw materials rich in Mg strongly reacted and remediated the pH of the drainage water waste. Furthermore, the increase of pH values due to the presence of mineral raw materials, provided increased oxidation potential which deactivated the toxic load of metals, particularly U. Consequently, batch-type serpentinite reaction with the tailing fluid caused a drop in U concentration from an initial value of 254 ppb to the one of 8 ppb, which corresponds to 97% of removal. Andesite presented the second best reactant for experimental remediation, especially when it was mixed with magnetically separated mineral fractions. Despite the fact that the proposed methodology is currently at a relatively low Technology Readiness Level (TRL), it carries the potential to become an extremely effective and low-cost alternative to conventional environmental restoration technologies.

Functionalization of clay surface for the removal of uranium from water.

A modification method of clay mineral surface was developed to improve its adsorption capacity of uranium. Uranium is a radionuclide with high toxicity and extremely long half-life, which can pollute the environment and endanger human health. This study proposes a new method of activation of clay mineral surface with phosphoric acid for rapid adsorption of uranium from aqueous solution. Compared with other modification methods, this method has the advantages of availability of raw materials, simple operation and good adsorption effects. It provides a cost-effective material to capture uranium ions from water. The essences of this new development are as following: • Activation and changes of clay minerals' surface functionalities with the treatment of phosphoric acid • Controlled modifications of the surface properties of the clay towards the enhancement of U adsorption capacity • Rapid removal of uranium from water.

The removal of uranium using novel temperature sensitive urea-formaldehyde resin: adsorption and fast regeneration.

A novel adsorbent of temperature sensitive urea-formaldehyde (TS-UF) resin was synthesized by base/acid two-step synthetic strategy with low formaldehyde/urea mole ratio of 0.8. The sorption kinetics of TS-UF resin obeys the pseudo-second-order model, and the adsorption is an endothermic process. The Langmuir model can well describe the sorption isotherms, through which the Qmax is calculated to be 99.2 mg/g for uranium (VI) at pH 6.0 and T = 298 K. The characterized results show that the functional groups -NH- and -CH2OH in TS-UF resin have been involved in uranium sorption via chemical interaction. The temperature sensitive property of TS-UF resin significantly accelerates the regeneration of TS-UF resin, which can be fast regenerated within 15 min at its low critical solution temperature 333 K and exhibits high removal efficiency of uranium (VI) (>90%) over 5 cycles. Therefore, TS-UF resin can be as a promising sorbent for the uranium (VI) removal from wastewater due to its low-cost, easy-fabrication, high-efficiency and fast regeneration. This work can not only boost the exploration of novel adsorbent materials, but also promote the investigations of the regeneration and reusability of adsorbents.

Radioactive Uranium Preconcentration via Self-Propelled Autonomous Microrobots Based on Metal-Organic Frameworks.

Self-propelled micromachines have recently attracted attention for environmental remediation, yet their use for radioactive waste management has not been addressed. Engineered micromotors that are able to combine highly adsorptive capabilities together with fast autonomous motion in liquid media are promising tools for the removal of nuclear waste, which is one of the most difficult types to manage. Herein, we fabricate self-propelled micromotors based on metal-organic frameworks (MOFs) via template-based interfacial synthesis and show their potential for efficient removal of radioactive uranium. A crucial challenge of the MOF-based motors is their stability in the presence of fuel (hydrogen peroxide) and acidic media. We have ensured their structural stability by Fe doping of zeolitic imidazolate framework-8 (ZIF-8). The implementation of magnetic ferroferric oxide nanoparticles (Fe3O4 NPs) and catalytic platinum nanoparticles (Pt NPs) results in the magnetically responsive and bubble-propelled micromotors. In the presence of 5 wt % H2O2, these micromotors are propelled at a high speed of ca. 860 ± 230 µm·s-1 (i.e., >60 body lengths per second), which is significantly faster than that of other microrod-based motors in the literature. These micromotors demonstrate a highly efficient removal of uranium (96%) from aqueous solution within 1 h, with the subsequent recovery under magnetic control, as well as stable recycling ability and high selectivity. Such self-propelled magnetically recoverable micromotors could find a role in the management and remediation of radioactive waste.

Characterization of arsenic oxidation and uranium bioremediation potential of arsenic resistant bacteria isolated from uranium ore.

Arsenic (As) is often found naturally as the co-contaminant in the uranium (U)-contaminated area, obstructing the bioremediation process. Although the U-contaminated environment harbors microorganisms capable of interacting with U which could be exploited in bioremediation. However, they might be unable to perform with their full potential due to As toxicity. Therefore, potential in arsenic resistance and oxidation is greatly desired among the microorganisms for a continued bioremediation process. In this study, arsenic-resistant bacteria were isolated from U ore collected from Bundugurang U mine, characterized and their As oxidation and U removal potentials were determined. 16S rRNA gene sequencing and phylogenetic analysis showed the affiliation of isolated bacteria with Microbacterium, Micrococcus, Shinella, and Bacillus. Except Bacillus sp. EIKU7, Microbacterium sp. EIKU5, Shinella sp. EIKU6, and Micrococcus sp. EIKU8 were found to resist more than 400 mM As(V); however, all the isolates could survive in 8 mM As(III). The isolates were found to readily oxidize As under different culture conditions and are also resistant towards Cd, Cr, Co, Ni, and Zn. All the isolates could remove more than 350 mg U/g dry cells within 48 h which were found to be highly dependent upon the concentration of U, biomass added initially, and on the time of exposure. Ability of the isolates to grow in nitrogen-free medium indicated that they can flourish in the nutrition deprived environment. Therefore, the recovery of isolates with the potent ability to resist and oxidize As from U ore might play an important role in toxic metal bioremediation including U.

Analysis of uranium removal capacity of anaerobic granular sludge bacterial communities under different initial pH conditions.

The bacterial community of an anaerobic granular sludge associated with uranium depletion was investigated following its exposure to uranium under different initial pH conditions (pH 4.5, 5.5, and 6.5). The highest uranium removal efficiency (98.1%) was obtained for the sample with an initial pH of 6.5, which also supported the highest bacterial community richness and diversity. Venn diagrams visualized the decrease in the number of genera present in both the inoculum and the uranium-exposed biomass as the initial pH decreased from 6.5 to 4.5. Compared with the inoculum, a significant increase in the abundances of the phyla Chloroflexi and Proteobacteria was observed following uranium exposure. At initial pH conditions of 6.5 to 4.5, the proportions of the taxa Anaerolineaceae, Chryseobacterium, Acinetobacter, Pseudomonas, and Sulfurovum increased significantly, likely contributing to the observed uranium removal. Uranium exposure induced a greater level of dynamic diversification of bacterial abundances than did the initial pH difference.

Functionalized magnetic mesoporous silica nanoparticles for U removal from low and high pH groundwater.

U(VI) species display limited adsorption onto sediment minerals and synthetic sorbents in pH <4 or pH >8 groundwater. In this work, magnetic mesoporous silica nanoparticles (MMSNs) with magnetite nanoparticle cores were functionalized with various organic molecules using post-synthetic methods. The functionalized MMSNs were characterized using N2 adsorption-desorption isotherms, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), (13)C cross polarization and magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy, and powder X-ray diffraction (XRD), which indicated that mesoporous silica (MCM-41) particles of 100-200nm formed around a core of magnetic iron oxide, and the functional groups were primarily grafted into the mesopores of ∼3.0nm in size. The functionalized MMSNs were effective for U removal from pH 3.5 and 9.6 artificial groundwater (AGW). Functionalized MMSNs removed U from the pH 3.5 AGW by as much as 6 orders of magnitude more than unfunctionalized nanoparticles or silica and had adsorption capacities as high as 38mg/g. They removed U from the pH 9.6 AGW as much as 4 orders of magnitude greater than silica and 2 orders of magnitude greater than the unfunctionalized nanoparticles with adsorption capacities as high as 133mg/g. These results provide an applied solution for treating U contamination that occurs at extreme pH environments and a scientific foundation for solving critical industrial issues related to environmental stewardship and nuclear power production.

Efficient removal of uranium from aqueous solution by zero-valent iron nanoparticle and its graphene composite.

Zero-valent iron nanoparticle (ZVI-np) and its graphene composites were prepared and applied in the removal of uranium under anoxic conditions. It was found that solutions containing 24 ppm U(VI) could be completely cleaned up by ZVI-nps, regardless of the presence of NaHCO3, humic acid, mimic groundwater constituents or the change of solution pH from 5 to 9, manifesting the promising potential of this reactive material in permeable reactive barrier (PRB) to remediate uranium-contaminated groundwater. In the measurement of maximum sorption capacity, removal efficiency of uranium kept at 100% until C0(U) = 643 ppm, and the saturation sorption of 8173 mg U/g ZVI-nps was achieved at C0(U) = 714 ppm. In addition, reaction mechanisms were clarified based on the results of SEM, XRD, XANES, and chemical leaching in (NH4)2CO3 solution. Partially reductive precipitation of U(VI) as U3O7 was prevalent when sufficient iron was available; nevertheless, hydrolysis precipitation of U(VI) on surface would be predominant as iron got insufficient, characterized by releases of Fe(2+) ions. The dissolution of Fe(0) cores was assigned to be the driving force of continuous formation of U(VI) (hydr)oxide. The incorporation of graphene supporting matrix was found to facilitate faster removal rate and higher U(VI) reduction ratio, thus benefitting the long-term immobilization of uranium in geochemical environment.

Glutamic acid containing supermacroporous poly(hydroxyethyl methacrylate) cryogel disks for UO22+ removal.

Supermacroporous cryogel with an average pore size of 10-200µm in diameter was prepared by cryopolymerization of N-methacryloyl-(l)-glutamic acid (MAGA) and 2-hydroxyethyl methacrylate (HEMA). The poly(HEMA-MAGA) cryogel was characterized by surface area measurements, FTIR, swelling studies, elemental analysis and SEM. The poly(HEMA-MAGA) cryogel had a specific surface area of 23.2m2/g. The equilibrium swelling ratio of the cryogel is 9.68g H2O/g for poly(HEMA-MAGA) and 8.56g H2O/g cryogel for PHEMA. The poly(HEMA-MAGA) cryogel disks with a pore volume of 71.6% containing 878µmol MAGA/g were used in the removal of UO22+ from aqueous solutions. Adsorption equilibrium of UO22+ was obtained in about 30min. The adsorption of UO22+ ions onto the PHEMA cryogel disks was negligible (0.78mg/g). The MAGA incorporation significantly increased the UO22+ adsorption capacity (92.5mg/g). The adsorption process is found to be a function of pH of the UO22+ solution, with the optimum value being pH 6.0. Adsorption capacity of MAGA contained PHEMA based cryogel disks increased significantly with pH and then reached the maximum at pH 6.0. Consecutive adsorption and elution cycles showed the feasibility of repeated use for poly(HEMA-MAGA) cryogel disks.