Influence Of Acid Rain On Release Characteristics Of Cr(?)?Cu And Cd From Soil By Dynamic Simulation

As filter area,the soil,among in four layers(the biosphere,hydrosphere lithosphere,atmosphere),connects the organic world to the inorganic world.Soil is the ultimate source of food for human and affects the health and life of human being.However, with the rapid development of the world,the soil environment has been suffered unprecedented pollution, especially,the heavy metal contamination that have now become the focal point of our society.As an important component of the earth's crust and an essential element of the organism,The content of heavy metals in soil exceeds natural background values,because human activities and natural processes lead to the release of heavy metals.As is known to all,industrial wastewater and sludge application in agricultural soils has become a common practice in developing countries.Excessive heavy metals in the soil may lead to the decrease of soil quality, crop yield and poor quality of agricultural products.Mining,as one of the main activities of human beings,causes heavy metal pollution, including arsenic, lead, cadmium, chromium, mercury.The heavy metal pollution is a direct threat to the quality of the surrounding environment, the safety of ecosystem and human health.The heavy metal in contaminated soil,not only can go into surface water with the surface runoff,but also can infiltrate into groundwater with rainfall,causing surface water and groundwater pollution.It can also spread to the atmosphere through the wind dust, cauing pollution of the atmospheric environment and other secondary environmental problems.The soil heavy metal pollution is elusive, hysteresis,refractory, irreversible and cumulative,which can not be found easily by physiological senses like water pollution and air pollution.And heavy metal in water or air can easily dilute or migrate in water or air.In short,the soil heavy metal pollution requires a great deal of time to found and a huge amount of money to disposal.As one of the most serious environmental problems,Acid rain,that usually happens in more and more cities, has an effect on migration and transformation of heavy metal in soil. Acid rain aggravated the harm of heavy metal pollution in soil, Soil acidification is caused by acid rain on soil heavily,Acid rain increases the mobility of heavy metals in soil, and the concentration of heavy metals in soil increases.These heavy metals migrate and spread in the soil gap, to the underground water after a period of time, causing pollution of groundwater.Groundwater pollution is not intuitive, easy to detect, groundwater pollution is more subtle and complex than surface water pollution.The methods to repair surface water pollution can not be used to repair groundwater pollution.Therefore, in order to repair the groundwater pollution, we must first study migration and transformation of heavy metals in the soil for simulation and forecast.Although it has been studied that the heavy metal pollution of soil has an important influence on water quality,the fraction of soil heavy metal which is soluble in water,stability of soil heavy metals in water, Relationship between soil heavy metal accumulation and its effect on water quality,Relationship between soil heavy metals release and soil properties,the interactive influence of soil contaminated by heavy metal and the proximity of water to the polluted soil are unknown.Therefore,developing contamination risk assessment of heavy metals in soil to surface water and groundwater,establishing the diagnostic criteria for heavy metal pollution in soil suitable for water quality safety is a very important issue in environmental pollution control and an important basic work of pollution prevention and control at present.The results can provide theoretical and technical support for improving the ecological environment of soil restoration.According to mean annual precipitation of Wuhan, The influence of acid rain on the release characteristics of heavy mental from soil is investigated to provide data support for forture research on relationship between the acid rain and soil heavy metal pollution, but also predict the effect of heavy mental migration on groundwater.The release characteristics of Cr(?)(Cu,Cd) from contaminated soil,spiked with inorganic salts of Cr(?)(Cu,Cd),were investigated by dynamic leaching experiment in soil column with simulated acid rain.The soil samples were divided into five groups(i.e.,A,B,C,D,E)and the contents of Cr(?)(Cu,Cd) in the contaminated soil decrease in the order of E>D>C>B>A.Conclusions were obtained as follows:In general,with the leaching time extension,the Cr(?)(Cu,Cd)concentration of leachate was declined obviously,The release of Cr(?)(Cu,Cd)from soil spiked by inorganic salts was much faster for the initial few days and then it became slower.The relationships of Cr(?)(Cu,Cd)concentration of leachate with contents in soil are the same.Initially,The more of Cr(?)(Cu,Cd) in soil,the higher concentration of leachate is.with the leaching time extension,the concentration of all leachate are roughly same.the release rate trends of three kinds of heavy metals are basically the same.the release rate of Cr(?)(Cu,Cd) was initially rapid and gradually declined after the fourth leaching.The release process of Cr(?)(Cu,Cd) in the soil were simulated by first-order kinetic equation,double constant velocity equation,parabola equation and amended Elovich equation.The results show that The release processes of Cr from soil were fitted with mathematical equations.the amended Elovich equation could better describe the release processes of Cr.The release processes of Cu and Cd from soil were fitted with double constant velocity equation.the double constant velocity equation could better describe the release processes of Cu and Cd.the release rate of Cr(?)(Cu,Cd) is influenced by the pH value of simulated acid rain. ed.When the pH value of the simulated acid rain is 3.8,the release rate of Cr(?)(Cu,Cd) reaches the maximum value respectively.the release rate of Cd and Cu increased with the decrease of pH value.The relationship of release rate of Cr with the pH value is complicated.The release rate of Cr was significantly influenced by the change of pH value most among the three kind of heavy mentals.With the decrease of pH value,the rlease rates of A,B,C,D,E have increased 1.39%,1.04%,2.23%,1.84%, respectively.the pH values of leachate is above the pH value of simulated acid rain and have nothing to do with Cr(?)(Cu,Cd) concentration in soil and the pH value of simulated acid rain which is 3.8,4.7 or 5.6. with the leaching time extension,the change of the pH values of leachate of Cr(?)(Cu,Cd) is different.The pH values of leachate of Cr,which are weak alkaline,remained stable, then increased sharply, and finally back to the stable.The pH values of leachate of Cu,which are neutral,first increased sharply, then remained stable for a period of time, and then increased sharply, finally return to stable.first increased sharply, and then decreased rapidly, then increased sharply, and finally return to stable.