Study On Remediation Of Heavy Metal Contaminated Soil With Electrokinetic Theory Combined Chemical Reaction

In recent years,the remediation of heavy metal contaminated soil is a thorny problem in environmental control,especially the soil near the industrial areas such as tailings,tanning and electroplating.electrokinetic remediation technology can realize the directional movement of ions in the soil,and has the advantages of simple operation and fast repair speed,which has been widely studied.However,focusing effect,uneven distribution of heavy metal removal rate and other defects are the key problems to be solved in the practical application of electric method.In this paper,the chemical coupling based on electrokinetic principle is proposed to improve the defects of electrokinetic remediation technology.Firstly,the changes of voltage gradient,current,electrolyte concentration,heavy metal residual concentration of soil and electricity consumption in the process of remediation of the single heavy metal contaminated soil of chromium,cadmium,copper,nickel and lead,and mixed heavy metal contaminated soil by electrokinetic remediation technology were defined.Then,to solve the problems of poor effect and focusing effect caused by the high concentration of heavy metals in the electrolyte,electrochemical reduction and chemical precipitation were used to reduce the concentration of heavy metals in the electrolyte during the repair process,so as to optimize the effect of electrokinetic remediation technology.Finally,it is emphasized to verify the effect of single and mixed contaminated soil under the combined treatment from the perspective of removal rate,energy conservation and other aspects,and further optimize the technical parameters of remediation.The research results can provide theoretical basis and data support for electrokinetic remediation technology of heavy metal contaminated soil.The research conclusions are as follows:（1）In the process of electrokinetic remediation technology repair,the current first increases and then decreases,and the peak value appears between 10 and 40 h,then gradually decreases and tends to be stable.The concentration of heavy metals in the electrolyte increases continuously with time,and basically reaches saturation after 4 d of remediation,and the migration guiding force for heavy metal ions in the soil decreases or even loses its capacity.At this point,simply increasing the remediate time does not contribute much to the repair effect.Under the action of electrokinetic remediation,the removal rate of heavy metal pollutants in the soil was unevenly distributed.For chrome-contaminated soil,the removal rate of pollutants near the cathode and anode was82.16%and 0.24%,respectively.Serious pollutant focusing effect occurred near the anode.（2）Electrolysis of water by sacrificial iron anode helps to reduce chromium（Ⅵ）to chromium（Ⅲ）and adjust the pH from 5 to 6.5 to achieve the separation and removal of its precipitation.The optimum precipitation parameters of heavy metal chromium:the voltage gradient is 0.8 V·cm^-1,the current density is greater than 6.67 m A·cm^-2,the electrode area is 90 cm²,and the electrode distance is 15 cm.The combination of Na OH+Ca（OH）₂ can achieve the optimal precipitation effect of cadmium,copper,nickel and lead,and the optimal purification parameter of cathode electrolyte is:p H is 10～11,and the precipitation time is 15 min.（3）In the experimental study,it was confirmed that the concentration of heavy metals in the electrolyte in the chemical coupling was significantly lower than that in the electrokinetic remediation method,which was basically maintained at 200～300 mg·L^-1.The removal rates of single heavy metal contaminated soil increased by 3.53%,19.50%,7.80%,36.50%and 24.79%,respectively,compared with the electrokinetic remediation method.The removal rate of mixed heavy metal contaminated soil was 12.08%,22.10%,26%,32.30 and 29.28%higher than that of electrokinetic remediation method.At the same time,the current of the chemical coupling was significantly lower than that of the electrokinetic remediation method.In the 5 d repair cycle,the power consumption of the chemical coupling was 0.53 k W·h lower than that of the other.The chemical coupling is not only helpful to improve the remediation effect of mixed heavy metal contaminated soil,but also to enhance the economy of energy saving,and can transfer the pollutants into recyclable sediments.The chemical coupling is more suitable for practical engineering applications.