Degradation Of Polychlorinated Biphenyls In Soil By Fe-based Fenton Reaction System

Polychlorinated biphenyls are recognized globally as persistent,strong carcinogenic pollutants.The treatment of PCB contaminated sites has become an urgent need to improve the ecological environment.In this study,Fenton-like reaction system consisted of montmorillonite loading nano-zero-valent and hydrogen peroxide,which was used to degrade polychlorinated biphenyls(PCB67)in soil.Firstly,the nano zero-valent iron was loaded into the montmorillonite matrix by impregnation method.The average iron content of the material was 25.3mg·g-1.Through a series of characterization methods,the nano-zero-valent iron particles were dispersed evenly in the clay matrix layer.The diameter is mostly between 40?90nm.The stability of the material and the iron ion leaching experiment show that about a small amount of the iron will be leached from the iron-carrying material during the reaction.The degradation rate of polychlorinated biphenyl after 3 times repeated use of the material has decreased,but the removal rate is still above 63%.Secondly,the effects of iron-loaded materials,hydrogen peroxide,initial pH,ratio of water to soil,and dosing method on the degradation of PCBs in the Fenton-like system were investigated one by one,and the amount of iron-carrying material added was 29.88 g kg-1,.The dosage of hydrogen peroxide(30%aqueous solution)is 45.35 g kg-1,the initial pH is 3.5,and the ratio of water to soil is 2.5:1.Adding all the hydrogen peroxide by mixing the material and soil after adding dosing method,the average removal rate can be achieved more than 76%.Influencing factor experiment investigate the dosage of iron-carrying material,hydrogen peroxide,the initial pH and the ratio of water to soil.Then,the optimization of the degradation conditions was carried out to obtain 31.21 g kg-1 of iron-containing material,45.99 g kg-1 of hydrogen peroxide(30%aqueous solution),initial pH of 3.04,and water-soil ratio at 2.32,the best removal rate of polychlorinated biphenyls reached 79.44%,and the reliability of the system prediction was confirmed by verification experiment.Finally,the mechanism of the reaction system was studied,The degradation kinetics equation was determined:(?)The degradation process follows a pseudo first-order kinetic model.The main degradation mechanism is the oxidation of active oxygen groups and dechlorination of zero-valent iron.Degradation products of PCB67 were mostly consisted by lipids and ketones.