Adsorption Behaviors And Mechanism Of Funtionalized Materials Towards Uranium

As the global energy structure changes,many countries are accelerating the development of nuclear power.Using nuclear energy to generate electricity can not only aliieviate global warming,but also maintain sustainable supplies of energy.For many types of reactors,uranium is an important element of nuclear fuel.The development of nuclear power requires a large demand for limited uranium resources.On the other hand,due to the increase in nuclear activities,the amount of uranium-containing nuclear waste generated in various processes related to nuclear activitieshas also increased.Because uranium has radioactivity,chemical and biological toxicity,as well as a longer half-life.The release of uranium-containing nuclear to the environment withouttreatment will lead to serious pollution to the ecosystem.However,the proper disposal of this kind of liquid waste can help protect the environment and increase the utilization of limited uranium resources.In summary,developing a reasonable and efficient method to adsorb uranium in uranium-containing nuclear liquid waste has become a research hotspot in recent years.For the adsorption method,the preparation of the adsorbent is the core technology.At present,researchers tend to prepare adsorbents with large specific surface area and specific functional groups.Large specific surface area means more adsorption sites,while specific functional groups usually have higher affinity and selectivity for uranium,and thus the utilization of the adsorbent can achieve the efficient adsorption of uranium.In this dissertation,the adsorption behavior,adsorption mechanism and desorption method of uranium onto the funcionalized materials in uranium-containing solutions were studied.The research contents and conclusions are as follows:?1?Amidoxime-functionalized ultra-high molecular weight polyethylene fibers?UHMWPEF-AO?was used as an adsorbent to adsorb uranium.The effects of pH value,contact time,initial uranium concentration,and temperature on the adsorption process were investigated.The experimental results showed that the adsorption process is highly correlated with pH and is a spontaneous endothermic reaction.The adsorption process can be described by the pseudo-second-order kinetics model and Langmuir isotherm model.The adsorption mechanism is monolayer chemisorption.The maximum adsorption capacity calculated by the Langmuir isotherm model is176.99 mg/g.The absorbed uranium can eventually be recovered as a uranium oxide mixture by sintering;?2?The carbon foam was firstly prepared and then followed by a strong acid oxidation treatment.The product obtained was labeled as oxidized CF and used to adsorb uranium in aqueous solution.The effects of pH,contact time,initial uranium concentration,and temperature were examined.Experimental results show that the oxidation treatment significantly improves the uranium adsorption capacity of oxidized CF.The adsorption process is highly correlated with the pH value.It is a spontaneous endothermic reaction.The adsorption process can be described by the pseudo-second-order kinetic model and the Langmuir isotherm adsorption model.The mechanism is a monolayer chemical adsorption,and the maximum adsorption capacity calculated by the Langmuir isotherm model is 305.77 mg/g.The absorbed uranium can eventually be recovered as U3O8 or Na2U2O7 by sintering.The adsorption process is expressed as:2RCOOH+UO₂²⁺?2?RCOO?UO₂+2H⁺;?3?Covalent organic polymer?COP?was prepared and used to adsorb uranium in aqueous solution.The effects of pH value,time,initial uranium concentration,temperature and coexisting metal ions on the adsorption process were investigated.The experimental results showed that the adsorption process is highly correlated with pH and is an endothermic reaction.The adsorption process can be described by the pseudo-second-order kinetic model and Langmuir isotherm model.The adsorption mechanism is monolayer chemical adsorption.The maximum adsorption capacity calculated by the Langmuir isotherm model is 145.56 mg/g.When applying in mixed solution containing multipal ions to absorb uranium,COP exhibits obvious selectivity towards uranium.