Design And Synthesis Of Magnetic Ammonium Phosphomolybdate Composites And Study On The Mechanism Of Synergistic Removal Of Cesium And Uranium

The development and use of clean energy produced by nuclear power plants is becoming a major trend in world development,but this will inevitably lead to the problem of radioactive nuclide pollution.To achieve sustainable development of the ecological environment,it is necessary to remove ¹³⁷Cs and ²³⁸U nuclides from radioactive nuclides,as they are stable in solution,have high fluidity,have extremely long half-lives,and the harm of continuous decay to humans and the environment is incalculable.Research has shown that ammonium phosphomolybdate（AMP）has a good removal effect on Cesium,but microcrystalline particles limit its practical application.Combining AMP microcrystals with Fe₃O₄large particle microspheres makes the material magnetic and easy to separate from water,breaking through the size limit of AMP.By utilizing the characteristic that dopamine can establish a membrane structure on any material surface,this paper designs and synthesizes AMP composite material.AMP is embedded in polydopamine（PDA）,and a hydrophilic functional structural film is established on the surface of Fe₃O₄.At the same time,PDA also has a good chelating effect on Uranium.The composite material can be used to synergistically remove Cs and U from radioactive seawater.The magnetic AMP composite material is represented as AMP@PDA@Fe₃O₄（named X-Y APF,where X and Y represent the doping mass ratios of AMP and PDA,respectively）.The specific content mainly includes the following four parts:（1）This article used dopamine to establish a functional membrane structure on the surface of a substance through self-polymerization reaction at room temperature.AMP was successfully combined with Fe₃O₄,and the successful synthesis of the material was verified by XRD,SEM,TEM,etc.The characterization method indicated that the size of the synthesized APF particles was about 100 nm and the crystal structure was well preserved.The VSM result indicated that the material has magnetism and can be used for magnetic recovery.（2）The adsorption performance of the series of APF composite materials for Cs（I）was tested.During the process of APF adsorption,the adsorption performance of the materials were investigatedunder different conditions such as p H,time,temperature,dosage,and coexisting ions.The optimal p H range for adsorbing Cs（I）in APF was 6.0～8.0,with an optimal adsorption amount of 35.26 mg/g at p H=6.0.The effects of common cations on the adsorption were studied,and it was found that the adsorption was sensitive to the presence of K⁺.The adsorption reaction of Cs（I）followed the pseudo second-order adsorption kinetics and Langmuir isotherm adsorption model.At the same time,increasing temperature was beneficial for the forward direction of the reaction to explore the adsorption mechanism.It was found that the adsorption process mainly involves ion exchange between Cs（I）and NH₄⁺in the APF composite material.（3）In order to enhance the adsorption capacity for U（VI）,increase the proportion of polydopamine doping in the composite material.The adsorption effect of 40-10 APF on U（VI）was explored.By increasing the dosage of 40-10 APF from 0.1 to 1.0 g/L,the adsorption efficiency also increased from 24.95%to 97.51%.At a dosage of 0.5 g/L,the performance of the material in adsorbing U（VI）was tested at p H 3.0～9.0,and the best adsorption effect for U（VI）was found at p H 7.0（85.86%）.The kinetics,isothermal adsorption model,and adsorption thermodynamic model of APF material were studied,and it was found that the adsorption process of U（VI）by the material was more in line with the pseudo second-order adsorption kinetics and Langmuir isothermal adsorption model.In thermodynamic modelsΔS⁰>0 andΔG⁰<0 indicate that the adsorption of U（VI）by 40-10 APF was spontaneous,and heating was beneficial for the forward reaction.The mechanism of U（VI）adsorption on composite materials was studied,and the results showed that the adsorption process of U（VI）was mainly dominated by C-O complexation,while the complexation effect of-HN-/=N-on U（VI）played an auxiliary role.（4）In order to verify the ability of APF composite materials to adsorb Cs（I）and U（VI）simultaneously,TEM electron microscopy analysis showed that Cs（I）and U（VI）could be adsorbed.When APF was added into natural seawater containing Cs（I）and U（VI）,it still had high selectivity for Cs（I）and U（VI）,and the adsorption efficiency could reach 97.65%and84.63%,respectively.These results provide a reference for the removal of radioactive contaminants from radioactive seawater.