Study On Electrokinetics Remediation Of Radioactive Uranium Contaminated Soil With Kaolin And Zero-valent Iron

The wastes generated by uranium mining and metallurgy activities are usually stored in uranium tailings ponds.After a long period of accumulation,radioactive nuclides may be released into the surrounding environment,affecting the living environment of human beings,animals and plants.Therefore,it is very necessary to remediation of uranium contaminated soil.The object of this study is uranium contaminated soil.After optimizing the response surface experimental conditions of electrokinetic remediation and combining with the measures of material characterization analysis,the mechanism of kaolin-zero-valence iron strengthening electrokinetic remediation of uranium tailings pond soil was revealed:Firstly,the optimum experimental design was carried out with uranium removal rate η as the index,and a mathematical model was established,which could fit the influence of voltage gradient,electrolyte concentration and time on the electric repair process.The voltage gradient and electrolyte concentration should not be too high or too low in order to obtain better repair effect.The optimal experimental parameters obtained by response surface fitting were voltage gradient 1.1V/cm,repair time 6.9d and citric acid concentration 0.11mol/L.Under these conditions,the average removal rate of uranium in the soil was 50.12%±0.76%.The accumulation of uranium in the central part has been reduced but still exists;Secondly,under different p H values and different proportions of kaolin and zero-valent iron mixture,uranium aqueous solution was adsorbated,and the adding mass ratio of kaolin and zero-valent iron mixture under acidic conditions was 3:1,which could reduce the corrosion of zero-valent iron in anaerobic environment and improve the adsorption effect of uranium solution.Finally,different kaolin-zero-valent iron PRB media were added to the S2 and S3 soil regions near the anode in the electrodynamic repair device designed with the optimal experimental parameters obtained from the response surface experimental group to obtain the migration of uranium within the experimental period.The experimental results show that the addition of PRB medium can effectively alleviate the accumulation of uranium in the horizontal equipment,but this phenomenon cannot be completely eliminated.Moreover,the electrical repair device placed in S2 region with PRB medium has the best repair effect,and its overall removal efficiency can reach the highest of 71.16 ± 0.89%.By analyzing the XPS and EDS spectra of PRB,it was found that the kaolinite-zero-valent iron mixture mainly removed uranium from soil through reductive precipitation and adsorption mechanism.