Study On Improving The Washing Efficiency Of Heavy Metal-Contaminated Clayey Soil Based On Repeated Ice Segregation

Based on the National Natural Science Foundation "Research on the migration and purification technology of specific heavy metal pollutants under the effects of freeze-thaw",to improve the removal efficiency of heavy metal contaminated clayey soil and shorten remediation cycle by freeze-thaw and washing technology,the theory of repeated ice segregation was applied to increase the migration amount of eluent and improve the removal efficiency.Taking the local soil contaminated by Cd and Pb as the research object.Firstly,the laboratory batch washing tests were carried out,comparing the removal effect of heavy metals with EDTA+ citric acid and EDTA+ tartaric acid under different liquidsoild ratio conditions.The appropriate eluent combination and concentration were determined.Secondly,the freeze-thaw and washing tests with the selected eluent under different temperature gradient were carried out.The removal efficiency of heavy metals under different working(type and concentration of eluent,replenishment method of eluent,freeze-thaw conditions)and the changes in the speciation of heavy metals were analyzed.Draw the following conclusions:(1)In the batch washing test,the effect of EDTA and tartaric acid compound washing is better than that of EDTA and citric acid compound washing.(2)By controlling the thawing rate can increase liquid–soild ratios compared with the freeze-thaw and washing test without repeated ice segregation,the water intake amount is increased by about 20%.Compared with FTW1-2,the removal rate of heavy metals Cd and Pb in FTW1-1 increased by 43.95% and 171.74%.(3)Under the action of repeated ice segregation,it is one or there freeze–thaw cycles,but for a specific area in the soil column,the freeze–thaw front fluctuates up and down repeatedly,forming several freeze–thaw cycles.This phenomenon increases eluent intake and helps the eluent to fully contact and react with heavy metals in the soil.Therefore,the removal rate of heavy metal increased and the remediation cycle of contaminated soil is shortened.(4)Freeze–thaw and washing effectively remove the acid extractable,reducible,oxidizable Cd and acid extractable and reducible Pb under repeated ice segregation.The paper has 45 pictures,10 tables,and 64 references.