Study On Separation Properties Of Amino Modified Chitosan-based Adsorbent With Different Morphology For U（Ⅵ）

With the increase of human demand for energy and the decrease of existing resources,we must pay attention to the development of clean energy,such as nuclear energy.However,a series of uranium pollution problems may be caused serious threats for human beings and the ecological environment during the utilization of nuclear energy.Therefore,the problem which was solved urgently is the treatment of uranium-containing wastewater.Chitosan is the second largest natural polymer except cellulose.It is a kind of renewable resource,and its structure contains a lot of amino and hydroxyl groups,which was easy to modify.Therefore,the research focused on the concept of green,environmental protection and regeneration,we prepared two kinds of efficient adsorbents by grafting modification and freeze-drying method.The adsorption performance and adsorption mechanism of the adsorbent were explored through a series of experiments and characterization methods.The specific research contents are as follows:1.The chitosan microsphere with excellent morphology and uniform particle size was successfully synthesized by emulsification crosslinking method using chitosan as matrix and glutaraldehyde as crosslinking agent.Subsequently,the polyethyleneimine was grafted onto the surface of the chitosan microspheres,we successfully prepared polyethyleneimine-chitosan composite microspheres,which named as n-PEI/ECH-CTS.The particle size distribution of n-PEI/ECH-CTS ranges from 90μm to 110μm.The adsorption experiment results showed that the amount of polyethyleneimine was 0.4 g,the adsorbent has the best adsorption performance for U（VI）.The Langmuir model was used to fit the experimental data,and the maximum adsorption capacity of 0.4-PEI/ECH-CTS for U（VI）was 374.37 mg·g^-1.The adsorption kinetics and isotherm experimental data showed that the adsorption of U（VI）on 0.4-PEI/ECH-CTS reached equilibrium within 4 h,and its adsorption process was a spontaneous and endothermic process.In addition,0.4-PEI/ECH-CTS has high selectivity for U（VI）in simulated nuclear waste.The removal efficiency of0.4-PEI/ECH-CTS for U（VI）was 100%from the six-element mixed system（Ni（II）,Co（II）,Gd（III）,Pr（III）,Ce（III）,La（III））.The HNO₃(1.0 mol·L^-1)could elute about99.35%U（VI）from 0.4-PEI/ECH-CTS-U（VI）.It was found that the adsorption efficiency remained above 90%after seven recycles.In order to verify the adsorption mechanism of 0.4-PEI/ECH-CTS for U（VI）,the chelation mode of U（VI）and0.4-PEI/ECH-CTS was discussed by XPS and DFT theoretical calculation.The results showed that the adsorption mechanism of 0.4 PEI/ECH-CTS for U（VI）was mainly the ratio of 0.4-PEI/ECH-CTS to UO₂²⁺was 2:1,and two N atoms of0.4-PEI/ECH-CTS coordinated with UO₂²⁺.In conclusion,0.4-PEI/ECH-CTS has a high removal efficiency for U（VI）,which was easier to recover than powder,and was more suitable for practical industrial applications.2.In order to further improve the adsorption performance and adsorption efficiency of adsorbent for U（VI）,a novel polyvinyl polyamine modified chitosan aerogel was synthesized by freeze-drying method.And the PEPAx/PDAy-CMCSm-n was applied to enrich and recover U（VI）in radioactive wastewater.The optimum concentration of four materials（polyvinyl polyamine,polydopamine,carboxylated chitosan and glutaraldehyde）was investigated by orthogonal experiment.The results showed that concentration of CMCS was 3.5%,the concentration of PDA was 0.7mg·m L^-1,the concentration of PEPA was 2.0%,the volume of GLA was 250μL.The saturated adsorption capacity of the aerogel for UO₂²⁺is 467.73 mg·g^-1,which corresponded to Langmuir isothermal model.The results of adsorption kinetic experiments showed that PEPA/PDA-CMCS can quickly adsorb U（VI）,and the equilibrium time was 1 h.The adsorption kinetics corresponded to the pseudo-second-order kinetic model.Compared with 0.4-PEI/ECH-CTS composite microspheres,the adsorption performance and adsorption rate of PEPA/PDA-CMCS were greatly improved.At the same time,the adsorption of UO₂²⁺by PEPA/PDA-CMCS was a spontaneous and endothermic process,and the increase of temperature was beneficial to the adsorption reaction.The selectivity experiment results showed that PEPA/PDA-CMCS can selectively recover U（VI）from the seven-element mixed system（Ni（II）,Co（II）,Gd（III）,Pr（III）,Ce（III）,La（III））.In addition,the adsorption efficiency of UO₂²⁺by PEPA/PDA-CMCS was still above90%after 4 cycles of elution experiments.In order to verify the adsorption mechanism of PEPA/PDA-CMCS for U（VI）,the chelation mode of U（VI）and PEPA/PDA-CMCS was discussed by XPS and DFT theoretical calculation.The results showed that the adsorption mechanism of PEPA/PDA-CMCS for U（VI）was mainly amino of adsorbent coordinated with U（VI）.And the carboxyl of PEPA/PDA-CMCS coordinated with U（VI）was secondary.In summary,the polyvinyl polyamine modified chitosan aerogel has good adsorption performance and fast adsorption rate for U（VI）.It is an efficient adsorbent for uranium removal in radioactive wastewater.