Ligand And Charge-functionalized Sorbents For High Efficient Uranium Sorption

Nowadays increasing energy demands and uncertainty in fossil fuel promote the development of nuclear energy. Uranium supply has received more and more attention for nuclear energy before uranium resource becomes scarce on land. Uranium in oceans is found about 4.5 billion tons, which is about 1,000 times of uranium on land. Therefore, the development of new sorbents for uranium seawater extraction is critical for guaranteeing nuclear development in future. However, the concentration of uranium in seawater is very low(~ 3.3 ppb), and there are large amount of coexisting ions, which all restrict the efficiency and cost of uranium extraction from seawater. Considering uranium(VI) in seawater presents principally as uranyl tricarbonate complex([UO2(CO3)3]4-), we took advantage of the synergistic effect of charges and ligands to design two kinds of functional polymer. It is expected that the obtained sorbents could extract uranium with fast rate and high selectivity.Specific studies of this paper are as follows:(1) Cationically Charged Poly(amidoxime)-Grafted Polypropylene Nonwoven Fabric for Potential Uranium Extraction from SeawaterA new sorbent, cationically charged poly(amidoxime)-grafted polypropylene nonwoven fabric was prepared for potential uranium extraction from seawater. Specifically, poly(1-vinylimidazole)(PVIm) was grafted onto polypropylene nonwoven fabric under γ-ray irradiation, and was then quaternized with 4-bromobutyronitrile and followed by amidoximation to give the fibrous sorbent. The sorption could reach equilibrium with a capacity of 119.76 mg U/g within 50 h at pH 8.0 and 298.15 K. Compared with the uncharged sorbent, PP-g-PVIm+Br-AO showed faster kinetics, higher selectivity and larger sorption capacity for uranium extraction. Even at low uranium concentration(1.7 ppb), the cationic sorbent also shows higher sorption capacity and higher sorption rate in comparison with uncharged sorbent. Therefore, the cationically charged amidoxime-based sorbent was expected to extract uranium from seawater.(2) Phosphonate-Functionalized Polystyrene Microspheres with Controlled Zeta Potential for Efficient Uranium SorptionPhosphonate-functionalized polystyrene microspheres with controlled Zeta potential for efficient sorption of uranium(VI) were reported here. Specifically, the microspheres were prepared by emulsion polymerization with diethyl-(4-vinylbenzyl) phosphonate(DEVBP) as comonomer and emulsifier, and Zeta potentials could be controlled with different kinds of initiators. The sorbents with high positive zeta potentials showed faster rate and higher selectivity than the negative ones. The process followed second-order kinetics model, and could reach equilibrium with a capacity of 83.4 mg U/g within 200 min at pH 8.0 and 298.15 K. There were relatively larger capacities for the sorbents with high zeta potential than the neutral ones. Furthermore, the sorbents could be efficiently regenerated and reused well after five cycles. This work may provide a new approach to highly efficient sorption of uranium(VI) from aqueous solution.