Experimental Study On Electrokinetic Adsorption Remediation Of Cadmium Contaminated Soil

Along with human activities such as agriculture,industry and military,a large amount of soil is polluted by heavy metals.Due to the toxicity of heavy metals,it may have adverse effects on soil organisms and plants,threatening soil ecology and agricultural production.Unlike organic pollutants,heavy metals in soil cannot be biodegradable.They will exist in the soil for a long time or migrate to the aquifer,so they will remain in the soil for a long time and cannot be degraded.Therefore,it is urgent to develop effective separation technologies to permanently remove inorganic pollutants from the soil.In recent years,a number of techniques have been developed to treat soils contaminated by heavy metals,such as leaching,vegetative enrichment,thermal desorption,and electrokinetic remediation.Among them,electrokinetic remediation technology is an emerging technology that can be used to clean sites contaminated by organic and inorganic pollutants,and is recognized as the most suitable for low permeability porous matrix remediation technology.Based on the artificial simulation configuration of cadmium contaminated soil as experiment object,build a homemade device test,using electric repair technology,combined with the optimal electrode arrangement,the response surface method for optimizing the repair and composite modification biochar characterization methods,the current value change,soil physical and chemical properties,heavy metal removal rate,and discusses and analyzes the distribution form of heavy metals before and after repair.The main conclusions are as follows:（1）The influence of triangle（2-E-1）,rectangle（2-E-2）and hexagon（2-E-3）three different two-dimensional electrode arrangement modes on electrokinetic remediation of cadmium contaminated soil was investigated.The results show that in the 2-E-3 group,the p H value of the sampling point closest to the cathode S5 is 8.98,and the p H value of S4 is 8.13.The current decline rate is high,and the p H is in a weakly alkaline environment.The cadmium removal efficiency of the sampling points（S1,S2）near the anode is as high as 95.54%.Compared with the 2-E-1 and 2-E-2 groups,the electromechanical remediation efficiency of heavy metal Cd in soil was increased by 25.63%,and the comprehensive removal rate of Cd at each sampling point was up to 89.6%.The pollutant removal was uniform and efficient.（2）The response surface（RSM）method was used to optimize theinfluencing factors of electrokinetic remediation.The Central Composite（CCD）experimental design method was used to provide a polynomial regression mathematical model for electrokinetic remediation of Cd pollution in soil and optimize the reaction conditions.The F value of the simulation equation is 15.67,the correlation coefficient R² is 0.9338,and the adjusted correlation coefficient R_adj² is 0.9042,indicating that the equation has good regression and strong significance.The model results showed that the optimal electric field intensity was 2.25 V·cm^-1,the repair time was 120.79 h,and the water content was 17.06%.The removal rate of cadmium in soil was increased by 3.17%,2.86%and 2.43%,respectively,and the electric energy consumption was reduced by 10.54%,11.28%and9.97%,respectively.（3）Through the screening experiment of biochar modificationconditions,the final modification time was 48h,the solid-liquid ratio was1:10,and the iron ion concentration in FeCl₃ solution was 1 mol·L^-1 as the modification conditions of biochar.After modification,the morphology and structure of FeCl₃-MBC changed,the carbon pore structure was clean and clear,and iron ions were uniformly loaded on the surface of modified biochar,showing a multi-micropore structure.Both FeCl₃-MBC and BC have characteristic diffraction peaks of crystalline carbon fibers and graphite crystals.The peaks of FeCl₃-MBC are wider and lower than that of BC.The crystallinity of FeCl₃-MBC is reduced after modification,and the specific surface area of grains is increased,and the adsorption capacity is stronger.At the same time,the number of hydroxyl groups in the modified FeCl₃-MBC increased,indicating that the modified FeCl₃-MBC was rich in iron-containing oxides,which improved the cation exchange capacity of FeCl₃-MBC and further improved the adsorption capacity of heavy metal ions.（4）With electric-FeCl₃-MBC composite modified biochar method to repair of cadmium contaminated soil,the electric field intensity of 2 V·cm^-1,0.1 mol·L^-1citric acid as the electrolyte,repair the reaction time of 120 h,under the condition of current cycle fluctuation change appears along with the time to repair,Cd²⁺from the soil surface in the soil solution from migration,cathode area compound modification biochar addition,influence of heavy metals Cd²⁺ion hydrolysis equilibrium,maintain soil p H value in the lower range change.The experimental sampling points showed that the exchangeable Cd content was high near the cathode area,and the organic Cd area was evenly distributed.The average removal rate of heavy metal contaminated soil containing 50 mg·kg^-1 Cd coulds reach 90.95%.