The Preparation And Application Of Novel High Performance Uranium Adsorbent

Uranium is one of the most important elements in the nuclear industry,which has been widely used in the nuclear plants and the nuclear weapons.The uranium resources of mining significance are relatively inadequate in China when compared with other countries.As the nuclear power industry enters the production stage,the contradiction between supply and demand of uranium resources will become more significant,and the competition for uranium ore will be fiercer in the world.Uranium in the ocean could support nuclear power for thousands of years.On the other hand,radioactive waste from uranium tailings is a potential hazard in the process of uranium mining.The release of uranium-containing radioactive waste water into the environment would cause great threat on human health and the whole ecosystem.Therefore,in view of the two aspects of resource utilization and environmental protection,uranium extraction from seawater and the removal of uranium from nuclear industry waste liquids are urgent tasks.In the process of uranium extraction,the biggest challenges are microbial contamination from the environment,competitive adsorption of co-existing ions,and removal of low-grade uranium.The purpose of this dissertation is to improve the antifouling,adsorption selectivity and efficiency of uranium removal.Ultra-high molecular weight polyethylene?UHMWPE?fiber and recycled polymeric membrane are selected as the substrate.Radiation technology and chemical modification,such as zinc-preloading,modification of quaternary ammonium groups,ion imprinting technology based on radiation-crosslinking and chemical grafting,were used on the functionalization of the base materials.A series of adsorbents were prepared to solve the challenges of uranium extraction.The chemical structure,chemical composition,morphology and spatial distribution of functional groups were analyzed and discussed.Eventually,the adsorption for uranium and removal of uranium were studied systematically by static adsorption,flow column adsorption and adsorption from natural seawater.The main results of the dissertation are as follows:?1?The preparation of Zn@AO fiber and investigation on its adsorption for uranium and antifouling properties.Amidoxime and carboxyl groups were modified onto UHMWPE fiber by radiation grafting and quaternization.Subsequently,UHMWPE fiber modified with amidoxime was preloaded with Zn²⁺.Synchrotron infrared spectroscopy shows that Zn²⁺mainly binds with carboxyl group on the fiber.The adsorption capacity of uranium increased by 37%and the adsorption rate constant increased by 67%after the loading of zinc ions.In addition,the antimicrobial properties of the adsorbents against Aspergillus niger,Bacillus subtilis and Vibrio alginolyticus were improved.Finally,the adsorption capacity for uranium from natural seawater was increased by more than 50%,and the amount of marine fouling on the surfaces of adsorbents was significantly reduced.?2?The preparation optimization of quaternary ammonium salt adsorption fiber and its adsorption of uraniumAcrylonitrile and dimethyl aminoethyl methacrylate were modified on UHMWPE fiber by radiation grafting.The preparation of amidoximated adsorbents modified with quaternary ammonium was regulated and optimized by changing the order of amidoximation and quaternization.The results from the screening adsorption experiments and the characterization of the spatial distribution of functional groups by SEM-EDS,show that when the quaternary ammonium groups are distributed in inner layer of the fiber,and the amidoxime groups are distributed in the outer layer of the fiber,the obtained adsorbent?Q-AO?has the enhanced adsorption performance for uranium.Compared with traditional amidoximated adsorbents,Q-AO fiber has higher adsorption capacity and adsorption rate.Moreover,the introduction of quaternary ammonium groups improved the utilization rate of amidoxime groups on uranium coordination.Besides,adsorption capacity of Q-AO fiber for uranium from natural seawater increased by seven times,and the selectivity was also significantly improved.The amount of marine fouling on the surfaces of adsorbents was significantly reduced.?3?The preparation of AO-Imp fiber and the investigation of adsorption selectivity for uranium4HB was modified on UHMWPE fiber by radiation grafting technology,with subsequent modification of amidoxime groups by ring-opening reaction,Mikel addition reaction and amidoximation to obtain amidoximated adsorbent.Then,ion imprinting technology based on radiation crosslinking was carried out.Micro-nanopores and sub-nanometer free-volume pores appear on the material surface.The results of adsorption experiments show that the adsorption selectivity of the fiber for uranium has been significantly improved after imprinting,and the adsorption capacity has been nearly doubled.?4?The preparation of AO-Membrane and the investigation of the removal of uraniumThe waste plastic was recycled as polymeric membrane substrate,and the hydroxyl group was modified on the substrate by radiation induced grafting,and then acrylonitrile and acrylic acid were modified by Cerium induced grafting.Finally,AO-Membrane was prepared by amidoximation.It was found that nano-holes and ordered nanoparticle structure appeared on the surface of the adsorbent,and the amidoxime groups was mainly distributed in the outer layer of membrane.The mechanical strength can be maintained at 14 MPa.The results of adsorption experiments show that the uranium concentration can be reduced from 100?g/L to less than 50?g/L at pH of 3 to8,meeting the national standard of uranium solution discharge.The adsorption performance of the adsorbent was enhanced with multiple cycles of adsorption and desorption.The results of the flow adsorption experiment show that 1 mg/L uranium-containing solution with 1250 times of AO-Membrane volume could be efficiently reduced to 50?g/L by AO-Membrane,and the adsorbed uranium can be can completely and rapidly desorbed by 0.5 mol/L hydrochloric acid solution.