Characteristic Pollutant Soil

China is the world's largest producer of coke,more than half of the world's coke is exported by China,China is the global coke production and supply center.As a result of the rapid demand for coke,the production process caused great pressure of environmental pollution.With the requirement of the sustainable development strategy,the adjustment of industrial structure and urbanization development puts forward new requirements,some heavily polluting enterprises such as coking industrial relocation,after a lot of pollution sites have been left,left,part of the pollution is very complexed,there are lots of various pollutants,polluted soil and groundwater.In the process of redeveloping the contaminated site,workers' health may be damaged due to inadequate protection measures and inadequate safety protection.At the same time,the construction of residential buildings on the polluted site may bring health risks,and a large number of abandoned and idle polluted sites,so it is very necessary to investigate and evaluate the pollution status of coking sites,soil and groundwater which are seriously polluted for a long time.This paper,taking a waste coking plant in southern Shanxi Province as the research object,the pollution area of soil heavy metal pollution characteristics and risk assessment are studied,analyzed the types and content of heavy metals,using the single factor pollution index,inside,the comprehensive index method,potential ecological risk index method,analysis of 8 kinds of heavy metal content in soil,pollution and environmental risks,screening may affect the characteristics of the groundwater pollution;Leaching is one of the important ways that heavy metals in soil may cause groundwater pollution.The pollutant moves down the vertical profile of soil along with the leached action of permeated water,which makes the complex behavior of adsorption,desorption or distribution of pollutants between water-soil particles.Leaching experiments can be more true to the release of the heavy metal elements in soil on the surrounding environment simulation,experimental simulation in rainfall leaching contact,under different pH leaching solution,the soil drenchfiltrate pH,electrical conductivity(EC)and the characteristics of pollutants,heavy metals in the soil release characteristics,for the screen is easy to the characteristics of the pollution of groundwater pollutant release of heavy metals in soil,the regularity of foundation.The results are as follows:(1)the evaluation of heavy metal pollution in the soil of the coking plant shows that the heavy metal Hg and Zn pollution is the most serious in the soil of the contaminated site.Both Hg and Zn are in the level of heavy pollution,while Cu and Ni are in the level of light pollution while Cr is at the warning limit of pollution,which requires special attention.Overall,the site is at a mild risk level.Through the evaluation,it can be screened that the most serious risk levels of polluted sites are the heavy metals Hg,Zn,Cu,Cr and other heavy metals with the same risk levels,which are in the light pollution level.(2)through dynamic leaching experiments,it was found that the leaching capacity of the leaching solution with pH=3.1 was significantly higher than that of other pH value solutions.With the increase of pH value,the leached filtrate concentration of each heavy metal element decreased,indicating that the pH is an important factor affecting the migration of the characteristic pollutant-heavy metal.During the leaching experiment,the pH of the leached filtrate was significantly different from that of EC in five leached solutions with different pH values.The change trend of pH and conductivity(EC)of leached filtrate is just opposite,that is,the greater the pH,the smaller the EC.Drench filtrate obviously had a similar change law of heavy metal concentration showed that four kinds of heavy metal elements with the increment of leaching,leaching filtrate diminishing from high to low concentration and gradually tend to be balanced,the leaching process is roughly divided into two stages,the early stage of the heavy metals in the soil by the eluviation,drench filtrate concentration significantly reduced with the increase of the amount of leaching,the late release of heavy metals presents a trend of more gently.Among them,the dividing point of heavy metals Cr,Cu and Pb is about 1000 mL,and that of Zn is about 1500 mL.According to the groundwater standards in China,the impacts of four heavy metals on the groundwater environment were analyzed and compared.The experimental results showed that the environmental risk of Zn was the smallest,the environmental risk of Cr was the largest,and the risk of Cu and Pb was in the middle.(3)analyze the migration changes of heavy metal elements in the soil before and after leaching of contaminated soil.As the distance moves down,the overall concentration ofheavy metal elements decreases.The greater the migration distance,the lower the concentration.At the later stage,the concentration of heavy metal elements tends to be the same in each soil layer.The content of Zn and Pb decreased rapidly in the early stage of leaching,while that of Cu was relatively slow,while that of Cr decreased slowly with the increase of leaching.After leaching,the morphology of the four heavy metals in the soil also changed greatly,the residue state became the dominant state obviously,and the proportion of the weak acid extraction state decreased greatly.In the early stage of leaching,except for the heavy metal Pb,the cumulative release of the other three elements increased rapidly.During this period,the smaller the pH value of the leaching solution is,the more it can promote the release amount and release rate of Zn,Pb and Cu.However,the difference between the release amount and release rate of Cr is weak under the action of the leaching solution with different pH values.At the later stage of leaching,the cumulative release of heavy metal elements showed a trend of slow growth.By analyzing and comparing the migration risks of the four heavy metals in the soil,it can be seen that Cu has the greatest migration risks in the soil and is easy to be leached out.