Study On Characteristics Of Heavy Metal Migration In The Farmland Area Of Xiba Town,Wutongqiao

Heavy metals in soil are important environmental pollutants,which are harmful to human health and have long-term effects.The migration process,risk control and remediation of heavy metal pollutants in soil have been widely concerned by the whole society.Taking the farmland soil of Xiba town Wutongqiao as the research object,using statistical methods,adsorption experiment,indoor soil column leaching experiment and field profiles comprehensive research method,this paper discusses the geological background,in the study area of farmland area spatial distribution characteristics of heavy metals and soil on the adsorption characteristics of heavy metal contaminated soil under different conditions and in the process of vertical migration accumulation of heavy metals in the soil profile and its distribution characteristics,obtained the following results:1.Basic characteristics of heavy metals in soilExcept for the local enrichment of As in the soil of the study area,the heavy metal contents of Cr,Cu,Zn,Cd and Pb were all higher than the local soil background value,and the accumulation of this 5 heavy metals in the soil was universal.The highest exceeding standard rate of Cd content is as high as 100%,and the excess rate of Cr,Cu,Zn and Pb content is not more than 15%.The distribution of pollution sources in the study area has a great influence on the spatial distribution characteristics of heavy metals.The statistics analysis indicated that Cu,Cr and Zn are from the same pollution source and Pb?As and Cd are from the same source.2.Adsorption characteristics of heavy metals in different soil typesThe apparent adsorption capacities of Cd²⁺,Cu²⁺and Zn²⁺on sandy soil and yellow cinnamon soil are linearly related to time,In addition,the apparent adsorption capacity gradually increased with time.The adsorption capacity of the three kinds of ions on the yellow cinnamon soil was higher than that on the sandy soil.The adsorption of heavy metal ions on the soil in the study area was simulated by the Langumir model,Freundlich model and Temkin model.Both the Langumir model and the Freundlich model could well simulate the isothermal adsorption of Cd²⁺,Cu²⁺and Zn²⁺in the soil.Results of the Langumir model showed that,except for Cu²⁺,the yellow cinnamon soil to Cd²⁺and Zn²⁺was morer than that of the sandy soil.The Freundlich model shows that the adsorption of heavy metal ions is a nonlinear adsorption.The adsorption rate of Cd²⁺in yellow cinnamon soil was in an inverted"S"shape with pH,and the adsorption in sandy soil increased slowly with pH.The adsorption of Zn²⁺and Cu²⁺increased rapidly at pH between 3 and 4.After pH is 4,the adsorption increased slowly with increasing pH.3.Leaching characteristics of heavy metals under indoor leaching conditionsIn the profiles of seasonal saturated zone and perennial unsaturated zone,the release processes of Cu,Zn and Cd are mainly divided into two stages.The first stage is the rapid release period of heavy metal.During this period,the heavy metal concentration in the leachate is high,and the release rate is constantly reduced,and the release process is rapid.In the second stage,the concentration of heavy metals in the leachate is very low and the cumulative release fluctuates regularly.The stronger the adsorption capacity of soil to heavy metals,the lower the release rate of the heavy metals.4.Vertical distribution characteristics of heavy metals in indoor soil column leaching and field profile experimentsIn the field profile test,the content of heavy metals in the profile was affected by the physical and chemical properties of the soil,and the change of Cu content in the profile was affected by the pH,organic matter and bulk density of the soil.There was a significant correlation between Zn content and powder content,but no significant correlation between Cd content and soil properties.Indoor soil column leaching test:in the perennial unsaturated zone,Cu and Zn have no significant migration and accumulation,Cd is released in the surface layer?0²0 cm?soil,and the heavy metal accumulates after the leaching liquid enters 40 cm.In the seasonal saturated zone,Cu migrates at 0²0cm and accumulates at 20⁴0 cm,but no significant changes are observed in other depths.Zn accumulates at 20⁴0 cm and 40⁶0cm,Cd accumulates at 20⁴0 cm after release at 0²0cm,and no significant changes are observed at40cm.Field profile test:in the perennial unsaturated zone,Cu migrates at 0²0cm and20⁴0 cm,and there is no significant change after 40cm.Zn migrates at 0²0cm,and accumulates at 40⁶0 cm and 60⁸0 cm.Cd migrates at 0²0cm,and accumulates at20⁴0 cm and 60⁸0 cm.In the seasonal saturated zone,Cu was enriched in different parts below 20 cm after surface migration,and Zn profile distribution was similar to indoor leaching test.Cd was enriched in 40⁶0 cm and 60⁸0 cm after surface metal migration.