Reductive Dechlorination Of Carbon Tetrachloride And By-products By Electrochemical Process

In recent years,carbon tetrachloride?CT?has been frequently detected in the groundwater due to the its wide application in the fields such as chemical industry and medical treatment,It has anesthetic effect on the central nervous system and severely harm the liver and kidney of human body.Its existence in the environment draws wide attention.The chlorinated hydrocarbon pollution in groundwater is mainly removed by the reductive dechlorination of zero-valent iron PRB.However,the DCM produced by CT after reductive dechlorination cannot be dechlorinated by zero-valent iron.Therefore,the removal process of zero-valent iron reducing the accumulation of DCM within the CT process becomes a technical blind area of zero-valent iron PRB.In this research,the environmental friendly electrochemical reduction method is selected in the removal of CT and its intermediate products in the custom-made electrolyzer,then the reaction mechanism of reductive degradation is discussed so as to provide theoretical basis for groundwater contaminated with CT.The main research results are as follows:1)Selecting the electrode and optimizing the method of electrochemical removal of CT:in the condition of 40 mA electric current?electric current density of 2.13mA/cm²?,choosing Fe as anode,Cu as cathode,and CT can be completely removed in 5 hours.After 3 hours,the CT removal rate of the Cu electrode is up to 98%,which was 20-25%higher than that of the mixed metal oxide?MMO?electrode,and the use of Cu electrode is more economical and convenient.2)Adding vitamin B₁₂ can effectively degrade the intermediate products:the single electrochemical system can not effectively remove DCM.With vitamin B₁₂ as the electronic media,combined with the electrochemical method,it is found that not only the removal rates of the CF and CT are improved,but also the DCM is effectively degraded.Adding 0.1mM vitamin B₁₂ into the electrochemical system,the resulting DCM can be removed completely within 3 hours.In the experiment,the method of adding vitamin C the reductant to remove the pollutants is tried,only found that it can accelerate the degradation of CT and CF,but not of DCM.3)Using scanning electron microscope?SEM?and X-ray diffraction?XRD?characterization methods to characterize the electrode and precipitation of the reaction,the production of iron oxide is found on the Fe electrode surface and there is no obvious change on the Cu electrode.The precipitation is mainly composed of goethite,iron oxide,and magnetite,proving that the reduction of organic matter mainly is the process of hydrodechlorination near the corrosive cathode.4)When SO₄^2-?Cl^-?HCO₃^-?Na⁺?Ca²⁺are at low concentrations,respectively corresponding to 50 mg/L,50 mg/L,183 mg/L,100 mg/L,60 mg/L,they all can promote the degradation of CT.The reason is that the ion introduced into the experiment increases the electrolyte concentration and promotes the electrochemical reaction.However,with the increase of ion concentration,the degradation of CT is inhibited.Cl^-and Ca²⁺have significant effect on the intermediate degradation,mainly because Ca²⁺is easy to form complex and precipitation,adhering on the electrode surface which influences the activity of the electrode;and the existence of Cl^-inhibits the positive processing of the reaction equilibrium.