Application Potential And Remediation Of Heavy Metal Contaminated Soil In Tongguan Of Shaanxi

Mining and metallurgical process formed abandoned fields,such as open-pit mining,tailings,and resulted in a large number of solid wastes.Heavy metals in the tailings slag gradually spreaded to surroundings under the action of rainfall and wind erosion,which destroyed the ecological environment and caused serious pollution to the water and soil.Therefore,it is very important to repair the heavy metal contaminated soil and restore vegetation function.In this study,the demonstration projects of soil remediation in Tongguan of Shaanxi were taken as the cases.The contaminated status of heavy metals in the study areaswere discussed,which was resulted from artisanal gold mining and lead-zinc tailings.Additionally,the strategies of remediation technique and the evaluation of remediation results included the safety of agricultural products were also emphasized.Soil replacement and in-situ stabilization techniqueswere so far proven to be effective methods in theremediation of contaminated soils.Lime,calcium phosphate,fly ash and Na₂Swere added to immobilize the heavy metals in contaminated soils.The long-term application potential of these techniqueswere evaluated scientifically.The results were as follows.?1?Artisanal gold miningand lead-zinc smelting caused serious pollution to the surrounding soil.Soil in Xijiezi was seriously contaminated in the studied area for Cd,Pb and Hg,and the residue mining waste was the main source.The contents were 25.1?1116mg·kg^-1,2.30?5.20mg·kg^-1,0.15?20.Omg·kg^-1,which exceeded the national standard.Soil in Xinxin was seriously contaminated in the studied area for Zn,Cd,Pb and Hg,and the waste piles,piling and smelting areas waste were the main sources.The contents were 89.2?742mg·kg^-1,1.59?362mg·kg^-1,88.4?7622mg·kg^-1,0.21?35.0mg·kg^-1.?2?The contents of heavy metals showed a decreasing trend from the pollution source to the surrounding farmland soil and decreased gradually with the increase of the depth of the pollution source.Some soil profiles were contaminated seriously.Heavy metal contents exceeded the national standard in the 0?120cm range.?3?Pollution assessment results of surface soil in Xijiezi:All soil samples were contaminated,and 97.1%of the soil samples were severely polluted.The potential ecological risk index was applied to assess and the result indicated that potential ecological risk index ranged from 668 to 10969,and all the samples had very strong ecological hazard by Cd,Hg,Pb.The Igcoshowed that the degree of heavy metal pollution from strong to weak order:Cd>Pb>Hg>Zn>Cu.?4?Pollution assessment results of surface soil in Xinxin:The proportion of soil samples contaminated by light,medium and severe pollution was 5.88%,35.3%and 58.8%respectively.The potential ecological risk index was applied to assess,Cd was the most potential ecological hazard of metal elements,and all the samples had very strong ecological hazard.?5?Acceptable remediation methods decreased total heavy metal contents?except Cd?and availableheavy metal contents.There was a significant correlation between the available heavy metalcontentsin soil and pH,organic matter and total heavy metals in soil.With the increase of repair time,the content of soil available state had a tendency to increase.?6?The contents of Cd,Pb,Hg in agricultural products were higher than the permissible value according to GB 2762-2012,which means a risk exists for agricultural practices on the remediated soils.Therefore,all the agricultural products were not permittedto enter the market circulation.?7?In order to explore the most suitable planting mode,some common vegetables were planted in the soil after remediation.It was found that there were differences in the accumulation ability of heavy metals in different vegetables.Leafy vegetables usually had highermetal accumulations than non-leafy vegetables.?8?The contents of heavy metals in crops were not significantly correlated with the contents of total and available heavy metals in soil.The TF values of Cd,Pb and Hg in agricultural products were very small.That means the migration of heavy metals in soil-crop system was small.The TFof heavy metals in corn was the highest,so there was a certain risk to continue planting.?9?Food production was not recommended immediately after heavy metal polluted soil remediation.A consecutive investigation should be conducted for the assurance of food safety.