Leaching Removal And Mechanism Of Heavy Metals From Fine Particles Polluted Soil

This research takes a compound heavy metal contaminated site as the research object.For the fine particles soil with the size of less than 0.075 mm,this reserch has screened out the optimal leaching conditions for different heavy metals by oscillating washing and obtained the leaching agent compound plan.Then analyze the leaching effect,leaching characteristics and mechanism of the fine particles soil.In order to research a reference basis for the remediation of compound heavy metal contaminated soil,the main results are as follows:（1）This study used EDTA,NTA,CA,KHSO₄,KH₂PO₄as the eluents,and the leaching process can be divided rapid reaction stage,slow reaction stage and leaching equilibrium stage.The experiment data are fitted by 4 models and the results show that the leaching process could be better described with Elvioch model than with others.NTA has the highest removal effect on Pb when the concentration is 0.75mol/L.But as for EDTA,the elution rate decreases with the increase of concentration,and the removal effect is the best at the concentration is 0.05mol/L.KHSO₄has the best elution effect on Zn and as the concentration increases the leaching rate increases continuously.The removal effect of NTA and CA on Zn is the second.At 0.5mol/L,the Cd removal rate of 5 kinds of eluents is above 74%,KHSO₄and EDTA have the best removal effect.As the concentration of KH₂PO₄increases,the leaching rate of heavy metals increase,but the leaching efficiency is always lower than the other leaching eluents.Furthermore,the leaching efficiency of the eluents for Pb and Zn increases with the increase of temperature（5℃-45℃）,the removal effect of Cd changes little with temperature.When the solid-liquid ratio is 1:20,the eluent has the best leaching effect.As the number of leaching increases,the leaching rate of single heavy metals decrease,meanwhile,the total leaching volume increase.After 5 times leaching with NTA,CA and KHSO₄,the leaching amount of Pb is close to that of EDTA.After 2times leaching with KHSO₄,the Zn content has reached the risk screening values for soil contamination,One time leaching of Cd has achieved the purpose of repairing.（2）Eluent compounding results shows that using NTA-CA or EDTA-KHSO₄as the eluent,the best effect is obtained in 12 hours and when the concentrations is 0.5mol/L,the solid-liquid ratio of is 1:10,the temperature is 35℃,time leaching to the fine particles soil,it can reach the restoration goal.（3）Although EDTA and NTA have the best Pb removal effects,they significantly increase the acid extractable of Pb.After NTA,CA,KHSO₄and KH₂PO₄leaching,the proportion of Zn residual state in the fine-grained soil increased.Represents that four eluents can promote other forms of Zn transform to stable forms.Before leaching,the active form of Cd in the soil accounts for a large proportion and has high bioavailability.After leaching,the content of inactive form increases.All five leaching agents can reduce its migration ability and biological toxicity.XRD and FTIR spectra shows that the leaching eluents have no obvious effect on the mineral composition of the soil.The leaching eluents can effectively removal of heavy metals,but there are small amount of residual EDTA and NTA.