Synergistic Remediation Of Contaminated Soils Through Immersion-desorption And Elctrokinetic Method

Heavy metal contaminated soil is very common and highly harmful,and has attracted widespread attention from the whole society in recent years.Electric kinetic mediation（EKR）is an effective in-situ repair technology with the advantages of short repair cycle and wide applicability.However,the electric remediation of heavy metal contaminated soil is influenced by various factors such as voltage gradient,electrode form,electrolyte type,and remediation cycle.At the same time,due to the frequent occurrence of the"focusing effect"in the traditional electric repair process,the repair efficiency is uneven,the overall electricity consumption is large,and the physical and mechanical indicators of the soil after repair are less considered,which restricts its development.In order to reveal the adsorption desorption process and mechanism between heavy metals and soil particles,the Taihu Lake sludge was selected to remodel copper(Cu²⁺)contaminated soil,and the effects of key factors such as the type of desorption reagent,concentration,time and soil water ratio on the desorption efficiency were studied.The adsorption of Cu²⁺on the Taihu Lake sludge is mainly chemical adsorption,supplemented by physical adsorption.The adsorption process can be described by quasi first order dynamic reaction.Freundlich isotherm adsorption model is more suitable for describing the adsorption process of the Taihu Lake sludge to Cu²⁺.The adsorption of the Taihu Lake sludge to Cu²⁺is neutral adsorption,and belongs to single-layer heterogeneous adsorption.The Cu²⁺desorption efficiency by low molecular weight organic acids is ranked as follows:citric acid>tartaric acid>lactic acid>oxalic acid.Among them,citric acid exhibits the optimal desorption effect at a concentration of0.2mol/kg,and reaches a peak desorption rate of about 60%at 25℃.The desorption efficiency of Cu²⁺shows a trend of first increasing and then decreasing with the increase of time,and the option desorption was obtained at around 25 minutes.It can provide theoretical guidance for the electric remediation of heavy metal contaminated soil by revealing the adsorption desorption process and mechanism between heavy metals and soil particles.On the basis of revealing the adsorption desorption mechanism between heavy metals and soil particles,a method of immersion desorption synergistic electric remediation of heavy metal contaminated soil is proposed.Using a self-made organic glass repair tank,investigate the effects of different low molecular weight organic acids and different concentrations of citric acid on the electric repair effect.By comparing the acid cycle electric repair test with the immersion desorption electric repair test,the effects of different methods on heavy metal removal rate,electrical energy consumption,and mechanical properties were studied.The removal rate of heavy metals is highest at a concentration of 0.1mol/kg citric acid,and the soil strength increases most significantly after restoration.Under the conditions of 30V voltage and 0.1mol/L citric acid concentration for 48 hours of repair,the energy consumption of immersion desorption synergistic electric repair decreased by 12.6%compared to acid cycling enhanced electric repair,and the soil shear strength increased by 38-120k Pa.Soaking desorption combined with electric remediation not only removes heavy metal contaminated ions but also improves the shear strength of soil,which is beneficial for the secondary utilization of contaminated soil after remediation.The synergistic effect of immersion desorption and electric remediation leads to the separation of electrode plates and soil,reducing the efficiency of electric remediation.This article develops a new type of probe extended anode.At a concentration of 0.1mol/kg citric acid,the drainage capacity of the new extended electrode increased by 27.9%compared to the traditional electrode,the interface energy consumption decreased by 61.5%,the unit drainage energy consumption decreased by27%,the average removal rate of heavy metals increased by 17.7%,and the average shear strength of soil increased by 32.8%.Intermittent power on mode is adopted to further solve the problems of uneven distribution of soil moisture content and strength and high energy consumption after immersion desorption and electric repair.Under the optimal on-off ratio of 36:2,the difference in water content between the cathode and anode regions decreases by 12%and the difference in shear strength decreases by 18.6%after intermittent electrification.Compared to continuous electrification,the unit drainage energy consumption is reduced by 2.4%.Intermittent electrification improves soil uniformity,but instead reduces unit drainage energy consumption.Electric energy is more converted into drainage kinetic energy,which has certain reference value for practical engineering applications.