Conjugated Microporous Functional Polymers For Adsorption Of U(Ⅵ) From Radioactive Liquid Waste

During the rapid development of nuclear energy,a large amount of spent fuel will be generated.This kind of fuel can no longer sustain the nuclear reaction and plenty of high-level liquid wastes will be produced during the post-processing,which contains 95% of 238 U,1% of 235 U,1% of Pu,0.1% of other lanthanides,3% of fission products and other radioactive elements.It is of strategic significance to realize the recycling of spent fuel.However,the coexistence of high acidity,strong radioactive and fissile nuclear elements is the main challenge in extracting uranium from high-level waste liquids.Meanwhile,the running of nuclear industry also can produce a large number of middle and low liquid wastes,which will cause water and soil pollution after entering the environment,and may enter the human body through various channels,causing harm to the environment and humans.In view of the above problems,it is particularly important to study the adsorption and separation of U(Ⅵ)in radioactive waste liquid with good radiation-resistant,high-selectivity and large-capacity adsorption materials.Specific studies of this paper are as follows:(1)Acetylcysteine-functionalized microporous conjugated polymers(MCPs)for potential separation of U(Ⅵ)from radioactive effluentsIn this study,a serial of radioresistant microporous conjugated polymers(MCPs)are prepared for potential separation of uranium from radioactive effluents.Specifically,1,3,5-triethynylbenzene based MCPs are prepared by Sonogashira-Hagihara reaction and post-functionalized with N-Acetylcysteine(NAC)moieties through thiol-yne click reaction.The NAC-modified MCPs possessing excellent radioresistance and a high surface area ~610 m2/g are then investigated for potential separation of uranium from radioactive effluents.The effects of NAC graft degree,surface area,p H value,sorbent dose,initial concentration,and competing ions on uranium sorption are studied.The modified MCPs demonstrate a rapid and selective uranium separation with a high sorption capacity of ~165 mg/g,furthermore,the chemical structure of the sorbents was well preserved after irradiation,even at the irradiation dose up to 200 k Gy,indicating that they could be a type of promising sorbents to effectively extract uranium from radioactive effluents.(2)Conjugated microporous polymers bearing phosphate ester ligands as an efficient sorbent for potential U(Ⅵ)extraction from high-level liquid wastesIn this work,a new approach for potential uranium extraction from HLWs using conjugated microporous polymers(CMPs)bearing ethylphosphate ester ligands(MCP-PE)as sorbent is reported.TEM and SEM characterization show that MCP-PE sheets possess an overlapping flaky morphology.MCP-PE exhibits excellent binding selectivity for U(Ⅵ)ions with a high sorption capability of 73 mg U/g in 6 M HNO3 solutions.Thanks to its rigid π-conjugated skeleton,the MCP-PE after γ-ray irradiation of 1,000 k Gy in 6 M HNO3 shows no dramatic changes in structure,sorption capacity and selectivity.MCP-PE possesses outstanding reusability for U(Ⅵ)adsorption when regenerated with alkaline solutions.The sorption mechanism was studied by XPS and FTIR measurements revealing that uranyl ions tend to form complexes as UO2(NO3)2 in 6 M HNO3,and then bind to P=O groups of phosphonate ligands.This work provides a new method for effective recovery of U(Ⅵ)from HLWs using functional CMPs as sorbent.