Properties and evaluation of amidoxime-based UHMWPE fibrous adsorbent for extraction of uranium from seawater

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.

Reactivity of a di(amidoxime) ligand in the presence of Cu(II)/Ni(II)

As the primary functional groups of amidoxime sorbents for uranium recovery from seawater, di(amidoxime) ligands can be cyclized in situ into different ligands in the presence of Cu(II)/Ni(II) at different pH values. Here we first found that a linear ligand glutardiamidoxime can be catalyzed into a cyclic ligand glutarimidedioxime by Ni(II) in acidic solution.

Efficient sequestration of boron from liquid phase by amidoxime-functionalized poly(acrylonitrile-co-acrylic acid): experimental and modelling analyses

This study aims to produce amidoxime-modified poly(acrylonitrile-co-acrylic acid) using an optimized method and to investigate the performance of amidoxime-modified poly(acrylonitrile-co-acrylic acid) on the adsorption of boron ions in batch operations. Batch adsorption was conducted at the physiochemical parameters of pH, adsorbent dosage, and initial boron concentration. The isotherms and kinetics of adsorption data were studied at various initial boron concentrations. The renewed synthesis process gave a production yield of 77%, and the conversion of nitrile group to amidoxime was 78%. The adsorption reached its optimum point at pH = 8, adsorbent dosage = 4 g·L^-1, and initial adsorbent concentration at 40 ppm. The best model fits for isotherm adsorption was the Sips model with heterogeneity factor (n) = 0.7611. In the kinetic study, the adsorption data fitted best with pseudo-second-order model. The synthesized polymeric adsorbent could be recycled with little decline in its boron entrapment capacities. Hence, amidoxime-modified poly(acrylonitrile-co-acrylic acid) exhibited high adsorption capacity and could be potentially explored as an alternative to commercial resin in the removal of boron from wastewater.

Complexation of uranyl(vi) with succinimidedioxime in comparison with glutarimidedioxime

Glutarimidedioxime favors 1 : 2 neutral uranyl complex species, whereas succinimidedioxime tends to form a cross-linked 2 : 2 binuclear complex with uranyl ions.

Development of a Fibrous Adsorbent Prepared Via Green Vapor-Phase Grafting Polymerization for Uranium Extraction

Owing to many problems of the detriment by large amount of organic reagents, high cost and difficulty of industrialization, development of high-efficiency economical technologies for uranium extraction is an irresistible trend to support steady supply of nuclear energy. Herein, a novel fibrous adsorbent, named as AO-HPE fibers, was prepared by introduction of amidoxime groups using the green vapor-phase grafting polymerization (VPGP) technology of monomer acrylonitrile (AN). Gaseous AN was grafted onto the ultra high molecular weight polyethylene (UHMWPE) fibers at 80 °C in the enclosed evaporation and condensation reflux system. The innovative technology not only endowed synthetic process high monomer utilization ratio but also excellent environmental friendliness. The AO-HPE fibers exhibited an appreciable calculated maximum adsorption capacity (Q _m) of 1144.94 mg·g^-1 in uranium solution and an adsorption capacity of 14.11 mg·g^-1 in simulated seawater. Meanwhile, the higher uranium selectivity than main competing ion vanadium (adsorption mass ratio was almost 5) was achieved. The adsorption process accorded closely with chemisorption mechanism. This work provided a novel idea for the synthetic method of adsorbents for uranium extraction, and inspired the sustainable technologies for grafting polymerization of monomer AN.

Theoretical insights into the possible applications of amidoxime-based adsorbents in neptunium and plutonium separation

Efficient separation of neptunium and plutonium from spent nuclear fuel is essential for advanced nuclear fuel cycles. At present, the development of effective actinide separation ligands has become a top priority. As common adsorbents for extracting uranium from seawater, amidoxime-based adsorbents may also be able to separate actinides from high-level liquid waste (HLLW). In this work, the complexation of Np(IV,V,VI) and Pu(IV) and alkyl chains (R = C₁₃H₂₆) modified with amidoximate (AO^-) and carboxyl (Ac^-) functional groups was systematically studied by quantum chemical calculations. For all the studied complexing species, the RAc^- and RAO^- ligands act as monodentate or bidentate ligands. Complexes with AO^- groups show higher covalency of the metal-ligand bonding than the analogues with Ac^- groups, in line with the binding energy analysis. Bonding analysis verifies that these amidoxime/carboxyl-based adsorbents possess higher coordination affinity toward Pu(IV) than toward Np(IV), and the Np(VI) complexes have stronger covalent interactions than Np(V). According to thermodynamic analysis, these adsorbents have the ability to separate Np(IV,V,VI) and Pu(IV), and also exhibit potential performance for partitioning Pu(IV) from Np(IV) under acidic conditions. This work can help to deeply understand the interaction between transuranium elements and amidoxime-based adsorbents, and provide a theoretical basis for the separation of actinides with amidoxime-based adsorbents.

Results of an Ocean Trial of the Symbiotic Machine for Ocean uRanium Extraction

Amidoxime-based adsorbents have become highly promising for seawater uranium extraction. However, current deployment schemes are stand-alone, intermittent operation systems that have significant practical and economic challenges. This paper presents two 1:10 scale prototypes of a Symbiotic Machine for Ocean uRanium Extraction (SMORE) which pairs with an existing offshore structure. This pairing reduces mooring and deployment costs while enabling continuous, autonomous uranium extraction. Utilizing a shell enclosure to decouple the mechanical and chemical requirements of the adsorbent, one design concept prototyped continuously moves the shells through the water while the other keeps them stationary. Water flow in the shells on each prototype was determined using the measurement of radium adsorbed by MnO₂ impregnated acrylic fibers contained within each enclosure. The results from a nine-week ocean trial show that while movement of the shells through the water may not have an effect on uranium adsorption by the fibers encased, it could help reduce biofouling if above a certain threshold speed (resulting in increased uptake), while also allowing for the incorporation of design elements to further mitigate biofouling such as bristle brushes and UV lamps. The trace metal uptake by the AI8 adsorbents in this trial also varied greatly from previous marine deployments, suggesting that uranium uptake may depend greatly upon the seawater concentrations of other elements such as vanadium and copper. The results from this study will be used to inform future work on the seawater uranium production cost from a full-scale SMORE system.

A novel ion-imprinted amidoxime-functionalized UHMWPE fiber based on radiation-induced crosslinking for selective adsorption of uranium

A novel uranium-imprinted adsorbent (AO-Imp fiber) was prepared by radiation-induced crosslinking of amidoxime-functionalized ultra-high molecular weight polyethylene fiber (AO fiber). The porous structure was characterized by scanning electron microscopy (SEM) and positron annihilation lifetime (PAL) spectroscopy after ion imprinting. This ion-imprinted fiber exhibited enhanced adsorption selectivity for uranium in the form of both UO₂²⁻ and [UO₂(CO₃)₃]⁴⁻ in batch experiments. Compared with AO fiber, the adsorption capacity of the AO-Imp(250) fiber for uranium increased from 0.36 mg g⁻¹ to 1.00 mg g⁻¹ in simulated seawater and from 5.02 mg g⁻¹ to 12.03 mg g⁻¹ in simulated acid effluent, while its adsorption capacities for other co-existing metal ions were particularly low. This study provides an approach to prepare ion-imprinted adsorbents without introducing crosslinking reagents, which may be a promising method for uranium extraction.

A novel uranium-imprinted adsorbent (AO-Imp fiber) was prepared by radiation-induced crosslinking of amidoxime-functionalized ultra-high molecular weight polyethylene fiber (AO fiber).

Phosphate-Functionalized Polyethylene with High Adsorption of Uranium(VI)

For uranium extraction from seawater, development of new stable and reusable sorbents with high affinity and good selectivity for U(VI) is required. Herein, a new phosphate-functionalized polyethylene (denoted PO₄/PE) was synthesized via a simple Ar-jet plasma treatment of PE in concentrated H₃PO₄ and was employed in U(VI) extraction from seawater. The prepared PO₄/PE shows superior performance in the extraction of trace U(VI) from seawater. The adsorption process followed the second-order kinetics model and the Langmuir model. The maximum adsorption capacity of PO₄/PE for U(VI) reaches 173.8 mg/g at pH 8.2 and 298 K. PO₄/PE can be effectively regenerated by 0.1 mol/L Na₂CO₃ and reused well even after eight cycles. Experimental results offer a new approach for U(VI) uptake from seawater.

Synergistic nanofibrous adsorbent for uranium extraction from seawater

A nanofibrous adsorbent containing dual-ligands with a synergistic effect of uranyl adsorption from simulated seawater was fabricated by a parallel-blend electrospinning method.

Bifunctional polymeric microspheres for efficient uranium sorption from aqueous solution: synergistic interaction of positive charge and amidoxime group

Polymeric microspheres with a positive charge and amidoxime group are synthesized for uranium capture, and the synergistic interaction leads to highly selective and fast adsorption.

Sequestering uranium from UO2(CO3)34− in seawater with amine ligands: density functional theory calculations

The stabilities of complexes of uranyls with primary amines and CO₃²⁻ groups decrease with increasing chain length of the amine.