Study On Pollution Characteristics And Effectiveness Control Of Heavy Metals In Site Soil

In recent years,due to the adjustment of industrial structure and the transformation of land use methods,industrial enterprises in various places have relocated and shut down,resulting in a large number of polluted land plots.Due to the company’s previous weak technology and environmental protection awareness,the large pollutants discharged during the production process leaked into the soil and other environmental media,causing pollution,especially heavy metal pollution.The problem of heavy metal pollution is becoming more and more serious,seriously threatening ecological security and human health.According to statistics,there are 10 million hectares of existing heavy metal contaminated sites in my country,mainly including industrial leak sites,solid waste sites,and mining contaminated sites.Among them,industrial waste sites account for about 34.9% of pollution exceeding standards.To date,researchers have made significant progress on the adsorption,transportation,speciation transformation and stabilization of heavy metals in farmland soils,however,these studies usually neglected the influence of real environmental factors in the contaminated site on the behavior of heavy metals,such as site soil spatial structure variation,acid rain leaching,moisture conditions.Based on sufficiently summarizing previous research results and aiming at compensating the weakness of present studies,this research studied the industrial characteristics,regional distribution characteristics and hydrological distribution characteristics of heavy metal pollution in the site soil,by investigating the pollution characteristics of heavy metals in contaminated sites in Zhejiang Province.The column acid rain leaching experiment studied the characteristics of the migration,release and morphological changes of heavy metals in the site;the actual contaminated soil of the electroplating plant was used as the research object,and the hydrological conditions coupled with stabilizer stabilization experiments were conducted to study the effects of the site hydrological conditions coupled stabilizers on the soil the stabilizing effect of heavy metals.The main conclusions of this study are follows:(1)Contaminated sites in Zhejiang Province are mainly concentrated in more developed cities such as Hangzhou,Ningbo,Shaoxing,Huzhou and Wenzhou,and most of them are compound pollution.The types of heavy metals are Cu,Ni,Pb,Cd,Zn,Cr,As,etc.;The highest concentration of heavy metals in 41% of the plots is distributed in the 0-0.5 m miscellaneous fill layer,the buried depth of groundwater is less than 2m,and the concentration of heavy metals decreases with the increase of soil depth.The concentration of heavy metals decreases with the increase of soil depth;the pollution of Pb,Ni and As is more serious,and the Cu,Zn,Cd pollution is mainly concentrated in the chemical industry,Pb pollution is mainly concentrated in the manufacturing of lead batteries and non-ferrous metal smelting industries,Ni pollution is mainly concentrated in the electroplating and non-ferrous metal smelting industries,As pollution is concentrated in the chemical and non-ferrous metal smelting industries,and Cr pollution is mainly concentrated in the Leather industry.(2)The experimental results of the migration of heavy metals in the site under simulated acid rain leaching conditions show that the heavy metals Cu,Pb,Ni,and Cd mainly accumulate in the surface soil after entering the soil.The migration rate of heavy metals in the same soil layer is different,and Cd The soil has the highest mobility,namely Cd>Pb>Cu>Ni.After acid rain leaching begins,Cu,Pb,Ni,and Cd in the soil increase in the silt and clay layers.Acid rain can promote their migration.The migration of heavy metals in the soil is mainly controlled by the adsorption characteristics of the soil;The horizontal migration of Pb,Ni,and Cd is affected by the heterogeneity of the soil,with greater uncertainty,and a dominant flow phenomenon appears in the vertical direction;during the acid rain leaching process,the upper soil that migrates with water flow The medium heavy metals are not completely adsorbed by the soil,and a part of them will enter the groundwater;the miscellaneous fill layer acid can extract Cu and Cd,and the reducible form Pb and Zn have a higher ratio,indicating that the four heavy metals have high activity in the miscellaneous fill soil layer.,High mobility;Cu,Pb,Ni,Cd residues in the silt layer and clay layer soil after acid rain leaching are significantly higher than the miscellaneous fill layer,so their mobility in the silt layer and clay layer is lower than Miscellaneous fill soil layer.(3)Taking the actual soil contaminated by the electroplating plant as the research object,the hydrological conditions(aeration zone,interaction zone,saturation zone)coupled with stabilizing materials(biochar and phosphate)to stabilize the soil heavy metals are studied,and the results show that,Compared with the control,the stabilization effect of biochar on Cu and Ni is better than that of phosphate;under the conditions of saturation zone,the addition of biochar has obvious stabilization effect on Cu,Ni,Pb;under the alternate zone,biochar can reduce the exchangeable state The content of Cu and Ni.Phosphate in the saturation zone can reduce the content of exchangeable Zn;the use of stable materials can convert heavy metals in the soil into components that are more tightly bound to the soil matrix.Under the conditions of the saturation zone,phosphate stabilizes Zn.The effect is obvious;phosphate stabilizes Ni in the soil with a particle size of less than 0.075 mm under the saturated zone condition more obviously,and biochar stabilizes the Pb in the soil with a particle size of0.15-0.075 mm under the saturated zone condition more obviously;With the decrease of soil particle size,Ni and Pb in soil S1 and S2 gradually transform to stable forms.