Experimental Study On Electrokinetic Remediationof Lead Contaminated Soil

Because of poor permeability,cohesive soil is difficult to repair after heavy metal pollution.In this paper,the remediation of lead contaminated soil was studied by electrokinetic remediation,and the effects of various factors on the removal efficiency of heavy metals were discussed.The main work is as follows:（1）the effect of electrokinetic remediation on the restoration of lead contaminated saturated sand,mainly analyzed the effects of electrolyte,voltage,electrode and enhanced technology on the removal efficiency;（2）The adsorption characteristics and influence factors of calcareous sand on heavy metal ions;（3）the effect of PRB（calcareous sand and bone）and electrokinetic remediation technology used to repair lead contaminated kaolin.Through the analysis of the test results,the following conclusions are reached:（1）electrokinetic remediation can effectively remove lead from saturated sand.When KCl and KNO₃ are used as electrolyte,the removal rate of lead can reach98.37%when the titanium electrode is coated.The repair effect is influenced by electric potential gradient,electrolyte and electrode type.The acidity and alkali effect caused by the change of soil pH are the main factors affecting the electric repair.The removal rate of lead in the saturated sand is reduced when the citric acid buffer solution or the exchange electrode method is used.（2）pH₀ and solid-to-liquid ratio had more influence on the removal efficiency than the reaction temperature.Under the condition of T=30℃,r=1.0g/L,C₀=1000mg/L,the removal rate reached 97.6%,88.15%,and 65.72%.Experimental consequences of adsorption kinetics showed that the adsorption of Pb²⁺、Cu²⁺、Cd²⁺on calcareous sand was fast reaction.The adsorption quantity reached more than 80%of the maximum adsorption quantity Q_m within 60 minutes,and reached equilibrium within 120minutes.The pseudo-second-order kinetic model can describe the adsorption process of Pb²⁺、Cu²⁺、Cd²⁺on the calcareous sand,and isothermal adsorption process conforms to the Langmuir model.Calcareous sand has high adsorption capacity of heavy metal ions,Q_m of Pb²⁺、Cu²⁺、Cd²⁺was 1052.95mg/g,1329.84mg/g,and1050.56mg/g.Experimental results of thermodynamics showed that the adsorption process of Pb²⁺、Cu²⁺、Cd²⁺was spontaneous exothermic reaction,and low temperature benefit the adsorption.The main mineral composition of calcareous sand is aragonite,calcite and magnesite.Its adsorption mechanism for lead is the chemical reaction of carbonate ions in minerals and lead ions to produce Cerussite.（3）electrokinetic remediation has effect on lead contaminated kaolin,and prolonging the time of electrokinetic remediation is conducive to the improvement of removal rate.The position of PRB and filling material have significant influence on the repair effect.The PRB in the middle of the soil can improve the removal effect of the repair test.Calcareous sand has a better repair effect than bone carbon.