Study On The Enhanced Electro-Kinetic Remediation Of Heavy Metals Contaminated Soil

The electrokinetic remediation technology enriches and removes heavy metals by the principle of directional movement of heavy metal ions in a DC electric field.The DC electric field is formed by inserting electrodes on both sides of the soil to be repaired and applying DC voltage.This soil remediation technology has the advantages of in-situ repair,simultaneous removal of multiple heavy metals,and low cost.However,it also has shortcomings,such as"focus effect","polarization effect",etc,and ought to be strengthened by combined with other technologies or adding enhancers.Furthermore,since EK is mainly applied to theoretical and laboratory research,lacking of relevant data and experience in site application,more site application of EK is needed.This paper first used arsenic-contaminated soil as the research object,set four experiments,traditional electrokinetic remediation(EK),electrokinetic remediation using permeable reactive barrier(EK/PRB),electrokinetic remediation using approaching cathode(EK//M)and electrokinetic remediation using permeable reactive barrier and approaching cathode(EK/PRB/M)to explore the effect and practical value of PRB,approaching cathode on electrokinetic remediation.The results showed that:the average removal efficiency of soil arsenic by EK/PRB/M was 44.55%,at the initial voltage gradient of 1 V/cm and restoration time of 4 days.Compared with EK,EK/M,EK/PRB,the average removal efficiency of EK/PRB/M increased by 40.32%,24.25%and 23.38%respectively.The initial current density of each experiment was about 3.5 m A/cm~2.Soil p H and conductivity in EK/PRB/M was higher than other experiments,so more arsenic dissolved into soil liquids and moved to the cathode and anode respectively under the action of electroosmotic current and electromigration,and adsorbed by PRB once go through PRB,eliminating of the"focusing effect"of arsenic.Compared with EK,EK/M,the power consumption of EK/PRB/M was61.4 Wh and reduced by 27.1 Wh,65.3 Wh respectively,so EK/PRB/M can improve arsenic recovery efficiency on the basis of reducing energy consumption.Then the cadmium-contaminated soil was taken as the research object,set electrokinetic remediation experiments enhanced with different polarity exchange,EK1(fixed electrodes),EK2(electrodes exchanging every 4 days),EK3(electrodes exchanging every 2 days)in the laboratory,to explore the influence of switching frequency on electrokinetic remediation.The results showed that:the average removal efficiency of cadmium in EK3 was 40.29%after 8 days of remediation with 1 V/cm voltage gradient.Under the same voltage gradient and repair time,the removal rates of EK3 increased by 39.42%and 7.41%respectively,compared with EK1 and EK2.The initial current density of each experiment was about 1.2m A/cm~2.With the increase of exchange frequency,the overall p H range of the electric repair system was concentrated in the acidic range,so cadmium migration was easier and removal efficiency was higher.At last,applied electrokinetic remediation on site to cadmium-contaminated soil to explore the influencing factors and repair effects of repairing heavy metal cadmium.The results showed that:the total cadmium and plant available cadmium removal rates were up to48.75%and 91.43%,respectively,at the initial voltage gradient of 1 V/m and restoration time of 14 days.The current density of the electric repair systems were range at 0.75?3.25m A/cm~2and,larger,changed more frequently than that of the laboratory.Soil p H and electrical conductivity did not change much before and after remediation as the site belonged to the open system,the regulation of soil itself was stronger.Soil points with high content of total cadmium or plant available cadmium had the higher removal rate of total cadmium and plant available cadmium.The results showed that electric remediation had better effect on soil with high concentration of heavy metals.