Water-endurable intercalated graphene oxide adsorbent with highly efficient uranium capture from acidic wastewater

Carboxymethyl cellulose and metal-organic frameworks immobilized into polyacrylamide hydrogel for ultrahigh efficient and selective adsorption U(VI) from seawater

Metal-organic frameworks (MOF)-polymer hybrid hydrogel solves the processable forming of MOF powder and energy consumption of uranium extraction. However, the hybrid hydrogel by conventional synthesis methods inevitably lead to MOF agglomeration, poor filler-polymer interfacial compatibility and slowly adsorption. Herein, we designed that ZIF-67 was implanted into the carboxymethyl cellulose/polyacrylamide (CMC/PAM) by network-repairing strategy. The carboxyl and amino groups on the surface of CMC/PAM drive the uniform growth of ZIF-67 inside the CMC/PAM, which form an array of oriented and penetrating microchannels through coordination bonds. Our strategy eliminate the ZIF-67 agglomeration, increase the interfacial compatibility between MOF and polymer. The method also improve the free and fast diffusion of uranium in CMC/PAM/ZIF-67 hydrogel. According to the experimental, these enhancements synergistically enabled the CMC/PAM/ZIF-67 have a maximum adsorption capacity of 952 mg g-1. The adsorption process of CMC/PAM/ZIF-67 fits well with pseudo-second-order model and Langmuir isotherm. Meanwhile, the CMC/PAM/ZIF-67 maintain a high removal rate (87.3 %) and chemical stability even during ten adsorption-desorption cycles. It is worth noting that the adsorption amount of CMC/PAM/ZIF-67 in real seawater is 9.95 mg g-1 after 20 days, which is an ideal candidate adsorbent for uranium extraction from seawater.

Utilization of nickel-graphite electrode as an electron donor for high-efficient microbial removal of solved U(VI) mediated by Leifsonia sp

Enzymatically catalyzed reduction of metals by bacteria has potential application value to uranium-mine wastewater. However, its practical implementation has long been restricted by its intrinsic drawbacks such as low efficiency and long treatment-time. This study aims to explore the effect of electrodes on U (VI) removal efficiency by a purified indigenous bacteria isolated from a uranium mining waste pile in China. The effects of current intensity, pH, initial U (Ⅵ) concentration, initial dosage of bacteria and contact time on U (Ⅵ) removal efficiency were investigated via static experiments. The results show that U(VI) removal rate was stabilized above 90% and the contact time sharply shortened within 1 h when utilized nickel-graphite electrode as an electron donor. Over the treatment ranges investigated maximum removal of U (Ⅵ) was 96.04% when the direct current was 10 mA, pH was 5, initial U (Ⅵ) concentration was 10 mg/L, and dosage of Leifsonia sp. was 0.25 g/L. In addition, it is demonstrated that U (VI) adsorption by Leifsonia sp. is mainly chemisorption and/or reduction as the quasi-secondary kinetics is more suitable for fitting the process. FTIR results indicated that amino, amide, aldehyde and phosphate -containing groups played a role in the immobilization of U (VI) more or less. SEM and EDS measurements revealed that U appeared to be more obviously aggregated on the surface of cells. A plausible explanation for this, supported by XPS, is that U (VI) was partially reduced to U (IV) by direct current then precipitated on the cells surface. These observations reveal that Nickel-graphite electrode exhibited good electro-chemical properties and synergistic capacity with Leifsonia sp. which potentially provides a new avenue for uranium enhanced removal/immobilization by indigenous bacteria.

Biomimetic synthesis of polydopamine-graphene oxide/hydroxyapatite for efficient and fast uranium(VI) capture from aqueous solution

A novel and efficient mesoporous nano-absorbent for U(VI) removal was developed through an environment-friendly route by inducing the biomimetic mineralization of hydroxyapatite (HAP) on the bioinspired surface of polydopamine-graphene oxide (PDA-GO). PDA-GO/HAP exhibited the greatly rapid and efficient U(VI) removal within 2 min, and much higher U(VI) adsorption capacity of 433.07 mg·g-1 than that of GO and PDA-GO. The enhanced adsorption capacity was mainly attributed to the synergistic effect of O-H, -C=N-, and PO43- functional groups and the incorporation of uranyl ions by the formation of a new phase (chernikovite, H2(UO2)2(PO4)2·8H2O). The adsorption process of U(VI) fitted well with pseudo-second-order kinetic and Langmuir isotherm model. Moreover, PDA-GO/HAP showed a high U(VI) adsorption capacity in a broad range of pH values and owned good thermal stability. PDA-GO/HAP with various excellent properties made it a greatly promising adsorbent for extracting uranium. Our work developed a good strategy for constructing fast and efficient uranium-adsorptive biomimetic materials.

Graphitic N-doped biochar for superefficient uranium recycling from nuclear wastewater

N-doped biochar (AL-N/BC) prepared by pyrolyzing lignin in various temperatures manifested superefficient performance for uranium (U) recycling from nuclear wastewater. The optimist AL-N/BC-700 showed higher adsorption capacity of 25,000 mg/g and faster kinetics of 4100 g·min^-1·mg^-1 than the most of reported adsorbents, and excellent adsorption-desorption capability (adsorption rate > 90 % and desorption rate > 70 % after 12 cycles). Moreover, the high applicability of AL-N/BC-700 was verified by its superefficient U(VI) adsorption performance in a broad working pH range, various water matrices, and high irradiation stability. Furthermore, the adsorption mechanism discloses the significant role of graphitic N, rather than pyridinic N or pyrrolic N, for U(VI) adsorption. Overall, this work not only presents an applicable approach to alleviate the increasingly serious energy crisis via recycling U(VI) from nuclear wastewater, but also enriches the method of synthesizing N-doped materials for U(VI) adsorption.

MOF-implanted poly (acrylamide-co-acrylic acid)/chitosan organic hydrogel for uranium extraction from seawater

In this study, a composite hydrogel with a low swelling ratio, excellent mechanical properties, and good U (VI) adsorption capacity was developed by incorporating a metal-organic framework (MOF) with a poly (acrylamide-co-acrylic acid)/chitosan (P(AM-co-AA)/CS) composite. The CS chain, which contains NH₂, reduces the swelling ratio of the hydrogel to 4.17 after 5 h of immersion in water. The coordinate bond between the MOF and carboxyl group on the surface of P(AM-co-AA)/CS improves the mechanical properties and stability of P(AM-co-AA)/CS. The U(VI) adsorption capacity of P(AM-co-AA)/CS/MOF-808 is 159.56 mg g^-1 at C₀ = 99.47 mg L^-1 and pH = 8.0. The adsorption process is well fitted by the Langmuir isotherm and pseudo-second-order model. The P(AM-co-AA)/CS/MOF-808 also exhibits good repeatability and stability after five adsorption-desorption cycles. The uranium adsorption capacity of the developed adsorbent after one month in natural seawater is 6.2 mg g^-1, and the rate of uranium adsorption on the hydrogel is 0.21 mg g^-1 day^-1.

Highly selective extraction of uranium from wastewater using amine-bridged diacetamide-functionalized silica

A major environmental concern related to nuclear energy is wastewater contaminated with uranium, thus necessitating the development of pollutant-reducing materials with efficiency and effectiveness. Herein, highly selective mesoporous silicas functionalized with amine-bridged diacetamide ligands SBA-15-ABDMA were prepared. Different spectroscopy techniques were used to probe the chemical environment and reactivity of the chelating ligands before and after sorption. The results showed that the functionalized SBA-15-ABDMA had a strong affinity for uranium at low pH (pH = 3) with desirable sorption capacity (68.82 mg/g) and good reusability (> 5). It showed excellent separation performance with a high distribution coefficient (K_d,U > 10⁵ mL/g) and separation factors SF_U/Ln > 1000 at a pH of 3.5 in the presence of lanthanide nuclides, alkaline earth metal and transition metal ions. In particular, SiO₂spheres-ABDMA was used as a column material, which achieved excellent recovery of U(VI) (> 98%) and good reusability for samples of simulated mining and nuclear industries wastewater. XPS and crystallography studies clearly illustrated the tridentate coordination mode of U(VI)/PEABDMA and the mechanism and origin behind the high selectivity for U.

Electrochemical removal and recovery of uranium: Effects of operation conditions, mechanisms, and implications

Removing and recovering uranium (U) from U-mining wastewater would be appealing, which simultaneously reduces the adverse environmental impact of U mining activities and mitigates the depletion of conventional U resources. In this study, we demonstrate the application of a constant-voltage electrochemical (CVE) method for the removal and recovery of U from U-mining wastewater, in an ambient atmosphere. The effects of operation conditions were elucidated in synthetic U-bearing water experiments, and the cell voltage and the ionic strength were found to play important roles in both the U extraction kinetics and the operation cost. The mechanistic studies show that, in synthetic U-bearing water, the CVE U extraction proceeds exclusively via a single-step one-electron reduction mechanism, where pentavalent U is the end product. In real U-mining wastewater, the interference of water matrices led to the disproportionation of the pentavalent U, resulting in the formation of tetravalent and hexavalent U in the extraction products. The U extraction efficacy of the CVE method was evaluated in real U-mining wastewater, and results show that the CVE U extraction method can be efficient with operation costs ranging from $0.55/kgU ~ $64.65/kgU, with varying cell voltages from 1.0 V to 4.0 V, implying its feasibility from the economic perspective.

Oil-Water Separation Polypropylene Foam with Advanced Solvent-Evaporation Induced Coexistence of Microspheres and Microporous Structure

For decades, crude oil spills and oil wastewater have become the most problematic environmental pollution and damage to public health. Therefore, it is considerable to develop superhydrophobic polymer foam for separating oil from water with high selectivity and sorption capacity. Here, a new type of environmentally friendly pure polypropylene (PP) foam with superhydrophobicity is first time proposed with a particular coexistence of microspheres and microporous structure fabricated via an advanced solvent-evaporation method. The PP foam exhibits exceptional superhydrophobic with a water contact angle of 151° and the maximum saturated adsorption capacity of 26 g/g. After more than 15 h of cyclic continuous oil-water pumping experiment, it still maintains a high oil absorption efficiency of 98%, providing the basis for practical commercial applications. More importantly, the variation of hydrophobic properties is described by Flory-Huggins polymer solution theory and Huggins interaction parameters, and the optimal solution ratio range is predicted which providing a relevant theoretical basis for actual industrial production. This article is protected by copyright. All rights reserved.

Ultra-high flexibility amidoximated ethylene acrylic acid copolymer film synthesized by the mixed melting method for uranium adsorption from simulated seawater

If U(VI) in seawater (unconventional uranium resource) can be extracted efficiently, it can provide important supplies and guarantees for the stable development of nuclear power. In this study, a mixing melting method without condensation agent was proposed to prepare ultra-high flexibility and different proportions DAMN modified EAA resin film (EAA-DAMN) through the condensation reaction between -COOH and -NH₂ and the uniform mixing of liquid EAA and DAMN. In addition, the dense film structure and -CN of EAA-DAMN were transformed into multiple pores structure and amidoxime groups of the amidoximated EAA (AO-EAA) by amidoxime reaction. The AO-EAA-3 showed the most excellent adsorption performance (q_e=146.40 mg g^-1) at pH = 5, which was 2.33 times that of EAA. Moreover, a hypothesis was proposed for the first time that -NH₂ in the material could combine with H⁺ ionized by water to form -NH₃⁺, and then adsorbed NO₃^- in the solution through electrostatic attraction, and O element from NO₃^- adsorbed on the surface and N-O from amidoxime groups of material as the adsorption active sites performed coordination with U(VI), thereby improving the adsorption performance of AO-EAA.

Graphene-based materials for the adsorptive removal of uranium in aqueous solutions

Ground water contamination by radioactive elements has become a critical issue that can pose significant threats to human health. Adsorption is the most promising approach for the removal of radioactive elements owing to its simplicity, effectiveness, and easy operation. Among the plethora of functional adsorbents, graphene oxide and its derivatives are recognized for their excellent potential as adsorbent with the unique 2D structure, high surface area, and intercalated functional groups. To learn more about their practical applicability, the procedures involved in their preparation and functionalization are described with the microscopic removal mechanism by GO functionalities across varying solution pH. The performance of these adsorbents is assessed further in terms of the basic performance metrics such as partition coefficient. Overall, this article is expected to provide valuable insights into the current status of graphene-based adsorbents developed for uranium removal with a guidance for the future directions in this research field.