Study On The Performance And Mechanism Of U(Ⅵ) Removal By Coated Nanoscale Zero-valent Iron

In recent years,nanoscale zero-valent iron（n ZVI）has attracted extensive attention due to its large specific surface area,many active sites and strong reducibility.It has been proved that n ZVI can be used to remove a variety of pollutants,such as chlorinated organics,inorganic anions,heavy metals and other pollutants with high oxidation state.However,due to its inherent magnetic interaction and van der Waals force,n ZVI is prone to agglomeration and oxidation,which limits the application of n ZVI in the remediation of pollutants.The data show that coating one or more substances on the surface of n ZVI can reduce the oxidation and agglomeration,and can improve the mobility of n ZVI.In this study,Mg（OH）₂with good adsorption performance and low environmental pollution was selected as the coating material,and the coated nanoscale zero-valent iron（n ZVI@Mg（OH）₂）was synthesized by liquid phase reduction method,and was used to remove uranium in the solution.The main research contents and results are as follows:（1）The effects of p H,contact time,material dosage and initial concentration of uranium on the removal of uranium in n ZVI@Mg（OH）₂solution were studied through batch experiments.The results showed that when the initial p H of solution was 3,contact time was 60 min,dosage was 0.4 g/L and initial concentration of uranium was 5 mg/L,the removal efficiency of uranium by n ZVI@Mg（OH）₂is the highest,which can reach99.36%,and is higher than that of n ZVI under the same conditions..（2）n ZVI@Mg（OH）₂was characterized by SEM,TEM,XRD,BET and other methods.The results showed that Mg（OH）₂was successfully coated on the surface of n ZVI.After coating,the distribution of n ZVI was uniform and chain-like.The dispersion of n ZVI was improved,and the specific surface area increased from 15.0 m²/g to 20.4 m²/g.（3）The results showed that the Pseudo-first-order kinetic model and Freundlich isothermal adsorption model could better describe the removal process of uranium by n ZVI@Mg（OH）₂.The n ZVI@Mg（OH）₂before and after reaction was analyzed and characterized by SEM,XRD and XPS,etc.According to the characterization results,the removal process and mechanism of uranium by n ZVI@Mg（OH）₂were analyzed,which mainly included adsorption,reduction and co-precipitation.（4）Through sedimentation experiments and column breakthrough experiments,the suspension stability and mobility of n ZVI before and after coating were explored,and the results showed that the suspension stability and mobility of n ZVI were improved after coating.