Experimental Study On The Vertical Migration Of Typical Heavy Metals From The Saturated Zone To Unsaturated Zone

With the rapid development of economic life,the pollution of heavy metals in soil and groundwater caused by industrial production has become increasingly serious.To carry out soil and groundwater treatment and restoration work,it is necessary to study the transport characteristics of heavy metals in it.In the past,most studies focused on the transport of heavy metals under leaching tests,and there were few studies on the effects of capillary.In this paper,an indoor soil column capillary water rise test is conducted to study the transport of five typical heavy metals(Pb,Cu,Cr,Cd,Ni)between the saturated zone and the unsaturated zone.Based on the testing of the basic physical and chemical properties of soil,the effects of heavy metal concentrations in saturated zones and soil textures on soil water content,capillary water rise height and time,and heavy metal content were studied.The test results were analyzed from the geological environment of the sampling site,mineral composition,particle size distribution,gravity and capillary water,and other interactions between water,soil and heavy metals.The main conclusions are as follows:(1)Within 48 hours,with the increase of capillarity rising height,the soil moisture content decreased gradually,and the rising rate of capillarity slowed down,the longer the time was taken.In the test group with lead nitrate concentration of 10mg/L,the maximum capillary rise height was 35.7cm.In the test group with lead nitrate concentration of 50mg/L,the capillary rise height was the lowest(28.8cm).In the experimental groups with different soil textures(all lead nitrate concentrations in the saturated zone were 10mg/L),the capillary rise rate of clay was faster than that of sand at the beginning,and after 8 hours,the capillary rise rate of sand was faster than that of clay.At the end of the experiment(48h),the height of capillary rise in sand was higher than that of clay.(2)The concentration of lead nitrate in the saturated zone and the soil texture in the vadose zone can influence the migration of heavy metals.In the experimental groups with different concentrations of lead nitrate,the higher the concentration of lead nitrate in the saturated zone,the stronger the heavy metal migration in the vadose zone.It is concluded that the thickness of electric double layer,the change of clay content and ionic strength all affect the migration of heavy metals.In the soil test group with different texture,the content change of typical heavy metals in sand soil is significantly greater than that of clay.Analysis shows that sand soil particle size distribution is wide,non-uniformity coefficient is large,and capillary tube diameter is small.The adsorption capacity between heavy metals and soil particles is weak by hydrogen bond.Therefore,the migration ability is stronger than that of clay,which has concentrated particle size distribution,small non-uniformity coefficient and large capillary tube diameter.The cation adsorption between heavy metals and soil particles is strong,so the migration ability in soil is weak.(3)The heavy metal concentration in the saturation zone was tested and found that several heavy metals appeared in the saturation zone after the test.It is further demonstrated that capillarity promotes the migration of heavy metals between the saturation zone and the vapor zone.