Elution of Uranium and Transition Metals from Amidoxime-Based Polymer Adsorbents for Sequestering Uranium from Seawater

Nano-tentacled interconnected channels organic gel for rapid uranium extraction from seawater

Due to dwindling terrestrial uranium resources and escalating ecological pressures, the long-term viability of uranium supply has become a critical concern. The immense uranium reserves in seawater present a potential solution, yet extraction technology faces dual challenges of efficiency and adaptability to complex marine environments. Current interconnected porous adsorbents, despite their high flux properties, are limited by low specific surface area and weak mechanical strength, which constrain their effectiveness. Here, inspired by the unique hierarchical structures of marine organisms, we describe an organic gel adsorbent with supermacroporous and interconnected channels (10 ∼ 100 µm) adorned with "nano-tentacle" structures. This design significantly enhances the specific surface area by 18 times, increasing adsorption sites and imparting antibacterial properties. Notably, this adsorbent maintains structural integrity and superior mechanical strength (1.32 MPa tensile and 2.44 MPa compressive strength) even when fully saturated. During a 23-day trial in natural seawater, a uranium adsorption rate of 0.332 mg g⁻¹ day⁻¹ was achieved. This work offers a pioneering approach for the design and fabrication of hierarchical structured adsorbents, highlighting the immense potential of extracting uranium from seawater for sustainable energy production.

High mechanical property and hydrophilic electrospun poly amidoxime/poly acrylonitrile composite nanofibrous mats for extraction uranium from seawater

Seawater reserves about 4.5 billion tons of uranium, if properly extracted, could be a sustainable green energy resource for hundreds of years, alternating its limited terrestrial ore and reducing the CO2 emitted from fossil fuels. The current seawater uranium adsorbents suffer neither economically viable nor adsorption efficiency, requiring more development to harvest satisfactorily uranium from seawater. Amidoxime-based fibrous adsorbents are the most promising adsorbents of seawater uranium due to abundant chelating sites. However, they suffer from severe shrinkage and stiffness once they dry, losing porous architecture and mechanical properties. Herein, an economical and scalable two-nozzle electrospinning technology was applied to produce poly amidoxime nanofibers (PAO NFs) supported by Poly acrylonitrile nanofibers (PAN NFs) as composite PAO/PAN nanofibrous mats with high structure stability. These PAO/PAN mats, with rapid wettability and excellent mechanical strength, show promising uranium adsorption capacities of 369.8 mg/g at seawater pH level, much higher than PAO and PAN NFs. The uranium adsorption capacity of the PAO/PAN mat reached 5.16 mg/g after 7 days of circulating (10 ppm uranium) spiked natural seawater. Importantly, the composite mat maintained its fibrous structure after five adsorption-desorption cycles with more than 80 % of its adsorption capacity, confirming its recyclability and stability. Therefore, the composite PAO/PAN mat fulfills the basic requirements for effectively and economically trapping uranium from seawater, which could be a matrix for further development.

Bifunctional solid-state ionic liquid supported amidoxime chitosan adsorbents for Th(IV) and U(VI): Enhanced adsorption capacity from the synergistic effect

Uranium and thorium of symbiotic relationship commonly appear in one kind of raw or spent ore. The simultaneous enrichment toward both metals in the first step is essential during many hydrometallurgy processing. Therefore bifunctional solid-state ionic liquid supported amidoxime chitosan (ACS) adsorbents were developed to simultaneously adsorb the two metal from the aqueous solution. The adsorption capacity of the bifunctional adsorbents toward uranium and thorium were significantly superior to the ionic liquid-free amidoxime chitosan, obviously proving the synergistic effect. For both uranium and thorium, the adsorption capacity in the consequence of ACS-[N4444][DEHP], ACS-[N4444][EHEHP], ACS-[N1888][DEHP] and ACS-[N1888][EHEHP] prove the steric effect and PO bonding played important roles in the adsorption. Study on isotherms and kinetics demonstrated the adsorption of ionic liquid-ACS adopted monolayer and chemical way. The ΔGo of very small negative values highlighted ionic liquid-ACS were prone to adsorb uranium and thorium. The study showed feasibility of bifunctional solid-state ionic liquid supported amidoxime chitosan adsorbents for Th(IV) and U(VI).

Uranium extraction from seawater: material design, emerging technologies and marine engineering

Uranium extraction from seawater (UES), a potential approach to securing the long-term uranium supply and sustainability of nuclear energy, has experienced significant progress in the past decade. Promising adsorbents with record-high capacities have been developed by diverse innovative synthetic strategies, and scale-up marine field tests have been put forward by several countries. However, significant challenges remain in terms of the adsorbents' properties in complex marine environments, deployment methods, and the economic viability of current UES systems. This review presents an up-to-date overview of the latest advancements in the UES field, highlighting new insights into the mechanistic basis of UES and the methodologies towards the function-oriented development of uranium adsorbents with high adsorption capacity, selectivity, biofouling resistance, and durability. A distinctive emphasis is placed on emerging electrochemical and photochemical strategies that have been employed to develop efficient UES systems. The most recent achievements in marine tests by the major countries are summarized. Challenges and perspectives related to the fundamental, technical, and engineering aspects of UES are discussed. This review is envisaged to inspire innovative ideas and bring technical solutions towards the development of technically and economically viable UES systems.

Application of poly(amidoxime)/scrap facemasks in extraction of uranium from seawater: from dangerous waste to nuclear power

To effectively kill microorganisms on scrap facemasks (FMs) surface and provide new material for extracting uranium (U(VI)) from seawater, scrap FMs was treated by N2 capacitance coupled (CCP) plasma and modified with polyamidoxime (PAO). The obtained PAO/FMs was well characterized and applied as an adsorbent in the extraction of U(VI) from seawater. The effects of environmental conditions on the adsorption capability of PAO/FMs for U(VI) were briefly studied. Results showed that plasma technique can synchronously kill microorganisms and induce acrylonitrile (AN) polymerization on FMs surface. The prepared PAO/FMs presented excellent adsorption capability for U(VI). The experimental results highlighted the application of plasma technique in the management of scrap FMs, and PAO/FMs in the extraction of U(VI) from seawater.

Amidoxime functionalized chitosan for uranium sequestration in vivo

Amidoxime functionalized chitosan (AC) was recommended as a chelator for uranium sequestration in vivo in this study, and the structure-activity relationship was also explored. Compared with ZnNa₃-DTPA, which was a commercial uranium mobilization drug, AC exhibited excellent biocompatibility and uranium removal efficiency, whether by injection or orally, which could reduce the amounts of uranium deposited in kidneys and femurs by up to 43.6% and 32.3%. In particular, ACs still possessed the ability to mobilize uranium in vivo even if administration was delayed for 72 h.

Polyamidoxime grafting on ultrahigh-strength cellulose-based jute fabrics for effectively extracting uranium from seawater

Ultrahigh-strength cellulose-based jute fabric (jute–TMC–PAO) for the highly effective extraction of uranium from seawater.

Extremely stable amidoxime functionalized covalent organic frameworks for uranium extraction from seawater with high efficiency and selectivity

Uranium extraction from seawater is of strategic significance for nuclear power generation. Amidoxime-based functional adsorbents play indispensable roles in the recovery of seawater uranium with high efficiency. Nevertheless, balancing the adsorption capacity and selectivity is challenging in the presence of complicated interfering ions especially vanadium. Herein, a polyarylether-based covalent organic framework functionalized with open-chain amidoxime (COF-HHTF-AO) was synthesized with remarkable chemical stability and excellent crystallinity. Impressively, the adsorption capacity of COF-HHTF-AO towards uranium in natural seawater reached up to 5.12 mg/g, which is 1.61 times higher than that for vanadium. Detailed computational calculations revealed that the higher selectivity for uranium over vanadium originated from the specific bonding nature and coordination pattern with amidoxime. Combining enhanced adsorption capacity, excellent selectivity and ultrahigh stability, COF-HHTF-AO serves as a promising adsorbent for uranium extraction from the natural seawater.

A highly efficient uranium grabber derived from acrylic fiber for extracting uranium from seawater

An amidoxime and carboxylate containing chelating adsorbent derived from acrylic fiber shows a fast adsorption rate and high uranium and low vanadium adsorption capacities in real seawater tests.

Ultra-High Performance of Hyper-Crosslinked Phosphate-Based Polymer for Uranium and Rare Earth Element Adsorption in Aqueous Solution

In this work, a new type of hyper-crosslinked phosphate-based polymer (HCPP) polymerized by bis(2-methacryloxyethyl)phosphate has been developed for uranium and rare earth element (REE) extraction in an aqueous solution. The influence of the pH value, contact time, initial concentration, temperature, and competing ions on uranium adsorption of HCPP is investigated in detail. HCPP exhibits a maximum uranium adsorption capacity of up to 800 mg g^-1 at pH = 6.0 and excellent selectivity toward uranium adsorption over coexisting ions, because of the high affinity between HCPP and uranium ions and dense phosphate groups on the backbone. It also demonstrates high adsorption performance in both simulated seawater with a high salt concentration and a real nuclear industrial effluent. Besides, the crosslinked network structure of HCPP endows this polymer with high chemical stability and reusability. Furthermore, the adsorption mechanism is probed by energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared measurements. It is confirmed that the adsorption of uranium on the adsorbent originates from the interaction between phosphate groups and uranium ions. Meanwhile, HCPP also displays high REE adsorption capacities. This work indicates that the phosphate-based HCPP could be utilized as a promising adsorbent for the effective removal of uranium and REEs from aqueous solution.

Siderophore-inspired chelator hijacks uranium from aqueous medium

Over millennia, nature has evolved an ability to selectively recognize and sequester specific metal ions by employing a wide variety of supramolecular chelators. Iron-specific molecular carriers—siderophores—are noteworthy for their structural elegance, while exhibiting some of the strongest and most selective binding towards a specific metal ion. Development of simple uranyl (UO₂²⁺) recognition motifs possessing siderophore-like selectivity, however, presents a challenge. Herein we report a comprehensive theoretical, crystallographic and spectroscopic studies on the UO₂²⁺ binding with a non-toxic siderophore-inspired chelator, 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H₂BHT). The optimal pK_a values and structural preorganization endow H₂BHT with one of the highest uranyl binding affinity and selectivity among molecular chelators. The results of small-molecule standards are validated by a proof-of-principle development of the H₂BHT-functionalized polymeric adsorbent material that affords high uranium uptake capacity even in the presence of competing vanadium (V) ions in aqueous medium.

Development of simple uranyl recognition motifs possessing siderophore-like binding strength and selectivity presents a challenge. Here the authors show a comprehensive theoretical and experimental study on uranyl binding with a polymeric adsorbent material decorated with a non-toxic siderophore inspired small molecule chelator.

An anionic manganese(ii) metal–organic framework for uranyl adsorption

A robust MOF that can rapidly and selectively adsorb uranyl in a seawater system is reported.

Interactions of vanadium(iv) with amidoxime ligands: redox reactivity

The use of amidoxime-functionalized polymer fibers as a sorbent for uranium has attracted recent interest for the extraction of uranium from seawater. Vanadium is one of the main competing ions for uranium sorption as V(v) species, however, vanadium is also present as V(iv) in seawater. In the present study, the interactions of V(iv) with amidoxime and similar ligands were explored. Attempts were made to synthesize V(iv) complexes of glutaroimide-dioxime, a molecular analogue of polymer sorbents. However, V(iv) was found to react irreversibly with glutaroimide-dioxime and other oxime groups, oxidizing to the V(v) oxidation state. We have explored the reactions and propose mechanisms, as well as characterized the redox behavior of the vanadium-glutaroimide-dioxime complex.

An overview and recent progress in the chemistry of uranium extraction from seawater

This review provides a brief background on the extraction of uranium from seawater as well as recent work by the United States Department of Energy on this project. The world's oceans contain uranium at 3 parts per billion, and despite this low concentration, there has been historical interest in harvesting it, mainly in Japan in the 1980s and the United States in this decade. Improvements in materials, chemistry, and deployment methods have all been made, with the ultimate goal of lower cost. This has been partially realized, dropping from approximately $2000 per kg U₃O₈ extracted in 1984 to $500 per kg today, although this is not yet competitive with terrestrial uranium. This technology may become cost-competitive if the cost of land-based uranium rises, especially if seawater extraction technology is improved further. The coordination chemistry aspects of the project are described in more detail, exploring the functional groups that are present on typical polymer sorbents as well as small-molecule analogues of these ligands. Selectivity for uranium over other metals, particularly vanadium, remains problematic, and techniques to both quantify binding strength and selectivity in order to overcome this issue are essential for future cost improvements.

Highly Efficient Interception and Precipitation of Uranium(VI) from Aqueous Solution by Iron-Electrocoagulation Combined with Cooperative Chelation by Organic Ligands

A new strategy combining iron-electrocoagulation and organic ligands (OGLs) cooperative chelation was proposed to screen and precipitate low concentrations (0-18.52 μmol/L) of uranium contaminant in aqueous solution. We hypothesized that OGLs with amino, hydroxyl, and carboxyl groups hydrophobically/hydrophilically would realize precuring of uranyl ion at pH < 3.0, and the following iron-electrocoagulation would achieve faster and more efficient uranium precipitation. Experimentally, the strategy demonstrated highly efficient uranium(VI) precipitation efficiency, especially with hydrophilic macromolecular OGLs. The uranium removal efficiency at optimized experimental condition reached 99.65%. The decrease of zeta potential and the lattice enwrapping between U-OGLs chelates and flocculation precursor were ascribed to the enhanced uranium precipitation activity. Uranium was precipitated as oxides of U(VI) or higher valences that were easily captured in aggregated micelles under low operation current potential. The actual uranium tailing wastewater was treated, and a satisfied uranium removal efficiency of 99.02% was discovered. After elution of the precipitated flocs, a concentrated uranium solution (up to 106.52 μmol/L) with very few other metallic impurities was obtained. Therefore, the proposed strategy could remove uranium and concentrate it concurrently. This work could provide new insights into the purification and recovery of uranium from aqueous solutions in a cost-effective and environmentally friendly process.

Origin of the unusually strong and selective binding of vanadium by polyamidoximes in seawater

Amidoxime-functionalized polymeric adsorbents are the current state-of-the-art materials for collecting uranium (U) from seawater. However, marine tests show that vanadium (V) is preferentially extracted over U and many other cations. Herein, we report a complementary and comprehensive investigation integrating ab initio simulations with thermochemical titrations and XAFS spectroscopy to understand the unusually strong and selective binding of V by polyamidoximes. While the open-chain amidoxime functionalities do not bind V, the cyclic imide-dioxime group of the adsorbent forms a peculiar non-oxido V⁵⁺ complex, exhibiting the highest stability constant value ever observed for the V⁵⁺ species. XAFS analysis of adsorbents following deployment in environmental seawater confirms V binding solely by the imide-dioximes. Our fundamental findings offer not only guidance for future optimization of selectivity in amidoxime-based sorbent materials, but may also afford insight to understanding the extensive accumulation of V in some marine organisms.

Successful Coupling of a Bis-Amidoxime Uranophile with a Hydrophilic Backbone for Selective Uranium Sequestration

The amidoxime group (-RNH₂NOH) has long been used to extract uranium from seawater on account of its high affinity toward uranium. The development of tunable sorbent materials for uranium sequestration remains a research priority as well as a significant challenge. Herein, we report the design, synthesis, and uranium sorption properties of bis-amidoxime-functionalized polymeric materials (BAP 1-3). Bifunctional amidoxime monomers were copolymerized with an acrylamide cross-linker to obtain bis-amidoxime incorporation as high as 2 mmol g^-1 after five synthetic steps. The resulting sorbents were able to uptake nearly 600 mg of uranium per gram of polymer after 37 days of contact with a seawater simulant containing 8 ppm uranium. Moreover, the polymeric materials exhibited low vanadium uptake with a maximum capacity of 128 mg of vanadium per gram of polymer. This computationally predicted and experimentally realized selectivity of uranium over vanadium, nearly 5 to 1 w/w, is one of the highest reported to date and represents an advancement in the rational design of sorbent materials with high uptake capacity and selectivity.

Kinetics of complexation of V(v), U(vi), and Fe(iii) with glutaroimide-dioxime: studies by stopped-flow and conventional absorption spectroscopy

Stopped-flow and conventional kinetic experiments were conducted to compare the rates of complexation of glutaroimide-dioxime with V(v), U(vi), and Fe(iii) to support efficient seawater recovery of uranium.