Study On Mechanism Of Oxidative Degradation Of Organic Pollutants By Hydroxyl Radical During Iron Electrocoagulation

Iron electrocoagulation（EC）technology is widely used in the field of wastewater treatment because of its simple structure,low cost and wide range of treatment.At present,EC is mainly considered as a separation technology,and its main mechanism of action is adsorption and precipitation.However,the transformation phenomenon of pollutants exists in EC.According to different types of pollutants,the mechanism of action is explained as the oxidation transformation caused by the reduction of inorganic valence pollutants by Fe（II）or the activation of Fe（II）to generate Fe（IV）,while the organic pollutants are oxidized by anodic chlorine or directly oxidized by anodes.Compared with inorganic pollutants,the degradation mechanism of organic pollutants in EC is more complex.Based on the process of Fe（II）activating oxygen to produce active oxides under neutral conditions,this study proposed the mechanism of EC to produce hydroxyl radical oxidation.The main research contents and conclusions of this paper are as follows:（1）Using aniline as the probe compound,it was verified that the removal mechanism of aniline in EC was not the traditional adsorption,precipitation,anodic chlorine evolution oxidation and direct anodic oxidation,but the oxidation degradation caused by the interaction between Fe（II）generated by electrolysis and dissolved oxygen.In addition,·OH/HCO₃^-reaction in bicarbonate system also contributed to the formation of CO₃^-·.（2）In this paper,the factors affecting hydroxyl free radical oxidation degradation of aniline produced by EC were studied.It was found that in the system of sodium bicarbonate,the increase of solution pH value（6.5⁸.5）was beneficial to the oxidative degradation of aniline,while in the system of sodium chloride and sodium sulfate,the trend was opposite.Fe（II）-carbonate complex helps Fe（II）to activate O₂ to produce active oxide,and improving the concentration of sodium bicarbonate(10⁵0mmol?L^-1)has little effect on the improvement of aniline oxidation efficiency.The degradation efficiency of aniline increased with the increase of current intensity（10⁹0 mA）.The increase of initial aniline concentration(0.1¹ mg?L^-1)promotes more aniline to be oxidized and degraded,but the degradation rate of aniline decreases accordingly.The addition of organic ligands to the electrocoagulation system may affect the generation of active oxides by Fe（II）activated O₂.（3）By studying the degradation of organic pollutants by EC in typical environment,the same oxidation mechanism and rule were found in the simulated sulfonamide polluted groundwater and the simulated phenol wastewater.In the study of EC process simulation As（III）and sulfonamide pollution of groundwater,found in EC hydroxyl free radical oxidation degradation of sulfonamide and at the same time be able to generate Fe（Ⅳ）oxide removal of As（III）.In the EC treatment of simulated phenol wastewater,adding sodium oxalate and EDTA can significantly improve the degradation rate of phenol.The results show that hydroxyl radical can be produced by EC under neutral conditions,and the existence of Fe（II）-carbonate complex can promote the production of hydroxyl radical.This study provides new theoretical evidence for explaining the transformation or degradation behavior of pollutants in EC system,which is helpful to improve the theoretical cognition of EC.This study shows that EC can generate hydroxyl radicals under neutral conditions,leading to oxidative degradation of organic pollutants,and the presence of Fe（II）-carbonate complex can promote the production of hydroxyl radicals.This study provides new theoretical evidence to explain the transformation or degradation of pollutants in EC system,which is helpful to improve people’s theoretical cognition of EC.