| As the energy shortage and environmental problems caused by traditional fossil energy have attracted wide publicity,developing new clean energy is the inevitable choice of sustainable development for mankind.Nuclear power generation has led the world in clean energy.As one of the raw materials for nuclear energy,uranium is an important and valuable radioactive resource.Uranium resource is a scarce mineral on land;however,it is sufficient in the ocean.Therefore,the rational exploit and utilization of uranium resources in the ocean is of great strategic significance for the development of nuclear power in China.Human activities such as uranium mining and improper disposal of radioactive waste cause uranium to flow to the environment which endangers the human health.Therefore,the purification of uranium in the environment has important practical significance for the healthy development of human beings.In this paper,three kinds of composite adsorbents were synthesized,and their adsorption behaviors and the selectivity toward uranium were investigated.Furthermore,the adsorption process was evaluated by both kinetic models and isothermal models.Dendritic fiber nano-silica?DFNS?was first synthesized by template method and hydrothermal method,and then SiO2/Mg-Fe layered hydroxide composites?DFNS/Mg-Fe LDH?were prepared by coprecipitation.The optimum pH of the composite is 5.0.The adsorption process can be well fitted by pseudo-second-order and Langmuir model.The removal rate under low concentration can reach 97%.Based on the results of ion strength test and XPS,the adsorption process is controlled by the complexation of inner sphere surface,which indicates that the metal-oxygen on LDH lamella plays an important role in fixing uranium.Amino functionalized MOF materials were in situ grown on the surface of SiO2,to give composite DFNS/UiO-66-NH2.The adsorption properties of uranium were evaluated by batch adsorption experiments.The adsorption capacity is obviously increased by the introduction of MOF.The optimum pH value of the composite material is 8.0,which is close to the pH value of real seawater.Therefore,it can be applied to the extraction of uranium from seawater.In addition,the removal rate of uranium in simulated seawater is over 93%.Based on the XPS analysis,the good adsorption performance of uranium is mainly attributed to the coordination of metal-oxygen and amino groups in DFNS/UiO-66-NH2 with uranium.Considering the influence of algae and microbes on adsorption efficiency in real seawater,functional silica composite adsorbents NH2-DFNS/Ag were prepared by grafting amines and reducing silver ions.Silver particles endow the material with biofouling resistance.The removal rate of uranium in simulated seawater can reach more than 92%.At the same time,the introduction of amines also enhances the selectivity of DFNS to uranium.Based on the results of XPS,it can be inferred that amines play a significant role in the process of uranium adsorption. |
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