| With the continuous development of industry,agriculture and transportation,more and more harmful heavy metals have entered the soil environment through various channels,which in the long run has caused immeasurable pollution and harm to the environment.The Hanyuan area is located in the middle section of the Dadu River.The lead-zinc mine is rich in reserves and has a long mining history.Long-term lead-zinc mining has brought prominent heavy metal pollution problems to the local environment.Therefore,it is of great practical significance to study the distribution characteristics of soil heavy metals and the migration behavior of Cd and Zn in Hanyuan area.In this paper,46 soil samples from the Hanyuan lead-zinc mining area and surrounding areas were collected using environmental geochemistry and trace element geochemical methods and principles.The samples were analyzed and analyzed for the trace heavy metal elements and their occurrence patterns.The clean soil samples in the soil were tested by soil column experiments to simulate the migration behavior of exogenous pollutants Cd and Zn.The understandings and conclusions are as follows:1.The soil in Hanyuan area is polluted by heavy metals in different degrees.The average content of seven heavy metal elements such as As,Cd,Cr,Cu,Pb,V and Zn exceeds the soil background value of Sichuan Province.Among them,the four heavy metal elements such as As,Cd,Pb and Zn exceeded the standard,and the average content reached more than three times the background value.The average content of Cr,Cu and V only slightly exceeded the background value,and the pollution status was lighter.2.The heavy metal pollution situation in the lead-zinc mining area,the Dadu River area and the whole area is generally the same,and the comprehensive pollution degree from high to low is Cd>Pb>Zn>As>Cr>Cu>V.Heavy metal pollution shows a trend of radiation from the lead-zinc mining area,and the heavy metal pollution in the area along the Dadu River is lighter than that in the lead-zinc mining area.Among the seven heavy metal elements,except for Cr,Cu and V,there is no obvious artificial enrichment,and the other elements are disturbed by human factors,resulting in obvious enrichment,mainly in mining,smelting and vehicle transportation.3.The results of BCR continuous extraction method show that the extractable state of Cd,Pb and Zn is higher and the damage is higher,while the proportion of residual elements of As,Cr,Cu and V is higher and relatively stable.The overall bioavailability from high to low is Cd>Pb>Zn>Cr>V>Cu>As.4.The migration rate of Cd and Zn in soil is proportional to the ionic strength.Under the same ionic strength conditions,the migration speed of Cd is faster than Zn,and the peak of the outflow concentration is higher.5.Under the condition of a large amount of constant background solution,the concentration of Cd and Zn tends to be stable after a large decrease,showing a gentle and tailing phenomenon.However,in the late stable phase under the same ionic strength condition,the Cd concentration is higher than the Zn concentration.6.The penetration properties of Cd and Zn in soil systems are different.And the same species have different penetrating properties at different ionic strengths.At high ionic strength,Cd has a high upward penetration ability,and different ionic strengths do not hinder the Zn upward penetration. |
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