Dynamic Simulation Of Acid Rain On Heavy Metal Release And Enzyme Activity In Contaminated Soil

In recent years,with the acceleration of China's industrialization and the rapid development of China's industrialization and urbanization,soil heavy metal pollution has increasingly become a serious environmental problem.Meanwhile,China is the third largest acid rain area in the world,and the southwest acid rain area is the traditional acid rain precipitation area in China,which is listed as one of the four main acid rain distribution areas.And these areas happen to be where heavy metal pollution sites are relatively concentrated.In some contaminated sites,especially in the areas where heavy metal residues are stored,acid rain will not only lead to the leaching of heavy metals from waste residue,but also cause more serious harm by interacting with heavy metal ions.However,the existence forms,toxicity and migration capacity of heavy metal anions and heavy metal cations in soil vary a lot.In this study,hexavalent chromium and lead ion were selected as the typical representative of heavy metal ion of anions and cations,through dynamic simulation of the acid rain in different p H leaching hexavalent chromium and lead pollution of soil to study the performance of two kinds of heavy metal ion migration,and under the condition of different p H of the measured soil hexavalent chromium and lead ions adsorption performance parameters,use the Hydrus-2D,to simulate the process of heavy metal migration and in situ enzyme spectrum technology were used to detect the changes of enzyme activity during leaching,under the condition of acid leaching is established,hexavalent chromium and the migration of Pb in soil model and the response mechanism of enzyme activity.The main conclusions are as follows:(1)Under acid rain leaching conditions,leaching of hexavalent chromium and lead ions in the soil will be promoted,and the lower the p H of acid rain,the greater the leaching amount of heavy metal ions;Soil in low p H environment of hexavalent chromium ions have greater adsorption quantity,and to lead ions adsorption quantity smaller,affected by this reason,low p H value of acid leaching conditions can accelerate the migration process of lead ions,slow down the process of migration of hexavalent chromium,in spite of this,in a long time scales,low p H value of acid leaching hexavalent chromium contaminated soil cumulative leaching rate is higher.(2)The hexavalent chromium content in the soil and lead all can produce greater inhibitory effect on phosphatase activity,and the lower the p H,hexavalent chromium content and lead content is higher,the more obvious inhibitory effect,and hexavalent chromium on activity of phosphatase inhibitory effect far outweigh the inhibitory effect of lead on phosphatase activity,suggests that hexavalent chromium on soil has more strong toxic;Along with the continuous leaching process,pollution in the soil phosphatase activity will gradually recover,the recovery rate with the increase of acid rain eluviation p H and speed up,but because of lead ions in soil exist in a variety of forms,can exchange state of lead downward migration,other forms of lead is relatively stable,still abounds with soil,inhibit phosphatase activity,cause the phosphatase activity leaching compared to hexavalent chromium experimental group before and after the change is not obvious.Acid rain can also inhibit phosphatase activity,and the lower the p H,the more obvious the inhibition.(3)Hydrus-2D has a good simulation effect on the migration process of anions and cations in the soil profile.The REDOX reaction in the leaching process will make the simulated value slightly higher than the actual value.Since hexavalent chromium is more easily reduced to trivalent chromium at low p H,the lower the p H,the greater the deviation between the simulated value and the actual value.The difference between the simulated value and the measured value of lead ion is affected by the transformation from lead in carbonate binding state to lead in exchangeable state.(4)For the actual chromium contaminated site soil,the leaching process of hexavalent chromium caused by precipitation was mainly concentrated in the first 8 months,during which the contamination risk of hexavalent chromium to soil and groundwater was the greatest.However,the leaching process of lead in leadcontaminated sites is a slow and long-term process,and the leaching amount of rainwater in the early stage of leaching is the largest.Therefore,for the two contaminated sites,it is necessary to take waterproof and anti-seepage measures,complete treatment as soon as possible,and reduce the diffusion range of heavy metals in the soil.