More than 1000× uranium exists in the oceans than exists in terrestrial ores. With nuclear power generation expected to increase over the coming decades, access to this unconventional reserve is a matter of energy security. With origins in the mid-1950s, materials have been developed for the selective recovery of seawater uranium for more than six decades, with a renewed interest in particular since 2010. This review comprehensively surveys materials developed from 2000–2016 for recovery of seawater uranium, in particular including recent developments in inorganic materials; polymer adsorbents and related research pertaining to amidoxime; and nanostructured materials such as metal–organic frameworks, porous-organic polymers, and mesoporous carbons. Challenges of performing reliable and reproducible uranium adsorption studies are also discussed, as well as the standardization of parameters necessary to ensure valid comparisons between different adsorbents.

Materials for the Recovery of Uranium from Seawater

Brine management methods: Recent innovations and current status

This study identifies how the amidoximate anion, AO, interacts with the uranyl cation, UO(2)(2+). Density functional theory calculations have been used to evaluate possible binding motifs in a series of [UO(2)(AO)(x)(OH(2))(y)](2-x) (x = 1-3) complexes. These motifs include monodentate binding to either the oxygen or the nitrogen atom of the oxime group, bidentate chelation involving the oxime oxygen atom and the amide nitrogen atom, and η(2) binding with the N-O bond. The theoretical results establish the η(2) motif to be the most stable form. This prediction is confirmed by single-crystal X-ray diffraction of UO(2)(2+) complexes with acetamidoxime and benzamidoxime anions.

How amidoximate binds the uranyl cation.

Magnetically modified hydroxyapatite nanoparticles for the removal of uranium (VI): Preparation, characterization and adsorption optimization

A novel amidoxime-based adsorbent of titanium-molybdopyrophosphate-g-amidoxime (TMP-g-AO) was prepared by chemical coprecipitation and subsequent chemical modifications. The successful grafting of acrylonitrile group and the subsequent conversion of acrylonitrile group to amidoxime groups were characterized by scanning electron microscopy-energy dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N2–BET, and thermal analysis. The adsorption behavior of uranium(VI) on TMP-g-AO was investigated for low concentration uranium solution by batch experiments at a fixed pH of 8.2 ± 0.1. It is found that the adsorption rate of uranium from solution was 99.77% when the uranium concentration was 42.3 μg/L, pH = 8.2 ± 0.1, temperature = 298.15 K, and the adsorbent dosage = 0.05 g. The kinetic data follow the pseudo-second-order model, and adsorption equilibrium data fit the Langmuir model well. The thermodynamics parameters (ΔS, ΔH, and ΔG) indicate that the adsorption ...

New Amidoxime-Based Material TMP-g-AO for Uranium Adsorption under Seawater Conditions

Crosslinked polyacrylamides were synthesized by solution polymerization using benzoyl peroxide as the radical initiator. The water–insoluble polymer obtained was functionalized by reacting with hydroxylamine to convert the amide group into hydroxamic acid group. The resultant functionalized polymer was characterized in terms of moisture uptake, elemental composition, IR spectra, thermal stability, exchange capacity and heavy metal sorption. The sorbent, obtained in particulate form, was investigated for its sorption properties with respect to uranium from uranyl nitrate solutions under unstirred batch conditions. This paper will concentrate on preparation, characterization and performance evaluation with respect to uranium sorption as a function of concentration, time, solution pH and temperature. The potential of this sorbent for uranium and other heavy metal ion recovery from sea water is ascertained.

Polyhydroxamic Acid Sorbents for Uranium Recovery

A novel sorbent, poly-acryl hydroxamic acid was prepared in-house from acrylamide monomer by solution polymerization method. Surface morphology and energy dispersive X-ray spectroscopy revealed that the sorbent was capable of encaging uranium from aqueous solution. Sorption potentials of uranium ions were investigated using the sorbent in dilute alkaline aqueous solution by varying pH of solution, sorbent quantities, contact time, initial uranium ion concentration and temperature of solution. Results from batch sorption experiment with simulated nuclear plant effluent showed the sorbent could remove uranium(VI) ions efficiently in presence of competitive ions such as Ca(II), Mg(II), Mn(II), Cu(II), Fe(III) and nitrate. Sorption characteristics were studied using Langmuir and Freundlich isotherms. The evaluated thermodynamic parameters indicated the present sorption process was endothermic and spontaneous. This work provided a promising and new sorbent for removing hazardous material like uranium from industrial wastewater.

Removal of uranium(VI) from dilute aqueous solutions using novel sequestering sorbent poly-acryl hydroxamic acid

Solid-phase extraction process using chelating sorbent is a novel technique due to its high separation efficiency and simplicity. A designed three-dimensional cross-linked hydrophilic chelating polymeric sorbent, polyacrylhydroxamic acid, was developed for enhanced uptake of uranium from waste solution (pH 6–9) by complexation between the sorbent’s active functional group and uranium. The sorbent was synthesized by polymerization of acrylamide with cross-linking agent, followed by conversion and functionalization with hydroxylamine hydrochloride. In this paper, removal and recovery of uranium from effluent of uranium material processing plant in the presence of competitive ions such as sodium, calcium and magnesium were studied using the sorbent. Uranium uptake property of the developed sorbent was also investigated with respect to sorbent’s physical characteristics such as bead size distribution and bead swelling, in batch experiments. Distribution coefficient of uranium in the sorbent was substantially high (1,250 mL of effluent/g of sorbent), and immobilization factor was 0.028. The results showed that more than 90 % recovery of uranium is viable from nuclear effluent without preconditioning. Breakthrough profiles of column operation were successfully described for effective removal of uranium in continuous mode. The novel sorbent has been used for polishing the nuclear wastewater and hence to mitigate the environmental issues.

Extraction of uranium from nuclear industrial effluent using polyacrylhydroxamic acid sorbent

Research and technological developments are being pursued vigorously all over the world to reduce the cost of desalinated water. Thermal and membrane-based desalination processes are very well known and plants are being operated to augment the demand of fresh water essential for drinking in water-scarce countries and to sustain the industrial processes. Any further improvement in energy reduction can only be marginal considering the complexity of the desalination system. The alternative approach is to add value by recovering edible salt, rare and valuable metals, such as caesium, titanium, uranium and vanadium, from the reject brine streams. In this regard, a novel polymeric chelating resin was designed and developed in Desalination Division, BARC laboratory with significant potential for this achievement. In this paper, the characteristics and potential of the resin have been described for the recovery of valuable elements based on experimental findings.

Strategy of deriving 'wealth from waste' from concentrated brine of desalination plant

The act of enrichment or improving the quality of product concentration, i.e. 'pre-concentration', has been studied with respect to uranium plant effluent, which contains uranium in 10?30 ppm level intermingled with a huge number of interfering ions, such as magnesium, in percent level. The effects of different operating conditions, such as concentration of uranium in the effluent, pH, the time required for uptake of uranium and the effect of the presence of other elements in the effluent, in batch experiments have been investigated. Using this in-house novel resin for preferential uranium uptake, the sorbed matrix has been eluted with different eluant concentration for further enrichment of radionuclides in the elute. High uptake values for uranium ions prove its selectivity, and fractional elution ensures further reuse of sorbent and significant improvement in uranium enrichment.

Sangita Pal

Papers

Polyhydroxamic Acid Sorbents for Uranium Recovery

Removal of uranium(VI) from dilute aqueous solutions using novel sequestering sorbent poly-acryl hydroxamic acid

Extraction of uranium from nuclear industrial effluent using polyacrylhydroxamic acid sorbent

Strategy of deriving 'wealth from waste' from concentrated brine of desalination plant

Recovery and pre-concentration of uranium from secondary effluent using novel resin