Leaching And Chelator-induced Phytoextraction Of Pb-and Tl-contaminated Soil By Zea Mays L.and The Impact On Underground Water

Chelator-induced phytoextraction of heavy metal contaminated soil is an important way of soil remediation technology.It is of great practical significance to study the leakage risk of heavy metal contaminated soil under rainfall conditions.Chelator-induced phytoextraction of Pb-and Tl-contaminated soil by Zea mays L.and associated leaching characteristics under rainfall conditions were investigated in this study.For this purpose,DTPA and oxalic acid were used as chelating agents,cultivation-leaching experiment was conducted.Furthermore,the adsorption and dispersion coefficients of chelate heavy metals were determined by experiments of adsorption of chelate heavy metals in the soil of the lower aeration zone and leaching experiments of the soil column that migrated in the soil of the lower aeration zone.A convection-dispersion mathematical model for the transport of complex heavy metals in the soil in the lower aeration zone was established.The migration behavior of the complex heavy metals in the soil was predicted and the risk of groundwater pollution was evaluated.Results showed that:(1)Pb and Tl concentrations in the leaching solution under acid rainfall condition were 1.8 and 1.5 times that of non-acid rain.(2)The amounts of Pb and Tl in the leaching solution were significantly enhanced by the addition of DTPA,and the effect was more pronounced in both Pb and Tl contaminated soil.(3)According to the linear decline rule,the Tl concentration of the leachate from Tl-contaminated soil treated by oxalic acid under acid rainfall condition was 65.0 times that of the drinking water standard.In addition,the available Pb and Tl in soil under other conditions are almost completely washed out.(4)Irrespective of the soil being single-or combined-contaminated,the bioconcentration factors(BCFs)of Z.mays for Pb and Tl,as well as translocation factors(TFs)for Pb were both significantly increased,with the addition of DTPA,while there was no significant effect after adding oxalic acid.Furthermore,there was a significant improvement in BCF(for Tl)in combined-contaminated soils.(5)The adsorption isotherms of Tl and Pb and its complexes on soil accord with the Langmuir equation,but in the range of low concentration,the adsorption isotherms of heavy metals are approximately in line with the linear law.(6)Based on the results of soil column leaching experiments and CDE model,the dispersion coefficients of heavy metals in the lower aeration zone under DTPA chelating conditions were determined,Tl: 0.000006145 and Pb:0.000006000.(7)Based on the CDE model,the migration of heavy metals in the down-aeration zone under DTPA chelating and Pb chelating conditions was predicted.The results showed that the migration distance of the heavy metals in the 15 repair cycles was 0.20 m and 0.30 m,and the migration distance at 30 cycles was 0.35 m and 0.50 m.The migration distance is much smaller than the groundwater depth of 5m,so the groundwater would not be polluted.