Research On Soil Heavy Metal Pollution Characteristics And Ecological Restoration In A Lead-Zinc Mining Area

Mining activities not only bring us the economic benefits,but also bring many environmental and ecological issues.According to the Bulletin of the National Investigation on Soil Pollution by the Ministry of Environment Protection,China,there are large volume of heavy metal polluted soil in which the concentrations of lead（Pb）,cadmium（Cd）,copper（Cu）,zinc（Zn）,arsenic（As）and other metal elements far exceed the national standards.Aiming at the heavy metal pollution caused by the non-ferrous metal industry in Hunan,the typical lead-zinc mines tailings were selected in this study.The accumulation characteristics of Pb,Zn,Cu and Cd elements in mining area were analyzed through field investigation.The ecological risk were assessed by the conbation of the nemerow index,potential ecological risk index and geoaccumulation index to determin the distribution law and ecological risk of heavy metals in the lead-zinc mining area.Through field engineering experiments,the effect of biochar and organic compost on soil heavy metals,was studied and the mechanism of soil heavy metal stabilization was discussed.The main conclusions are as follows:（1）The content of lead（Pb）element ranged from 129.88 to 1880.88mg·kg^-1,with an average value of 715.93 mg·kg^-1.The content of Zinc（Zn）element ranged from 101.29 to 1644.61 mg·kg^-1,with an average value of 612.45 mg·kg^-1.The content of Copper（Cu）element ranged from 16.63 to 700.74 mg·kg^-1,with an average value of 246.47 mg·kg^-1.The content of cadmium（Cd）element ranged from 0.39 to 35.71 mg·kg^-1,with an average value of 12.61 mg·kg^-1.The average content of each element in the order is Pb>Zn>Cu>Cd.（2）The contents of Pb,Zn,Cu and Cd in soil of each functional area presented by the orders of mining area>tailing area>road area>living area.Through BCR morphological analysis,the occurrence forms of different heavy metals in the soil of mining area are quite different.The contents of different forms of heavy metal elements following the orders:Residue state>Oxidizable state>Reducible state>Exchangeable state.The contents of exchangeable state of Lead（Pb）,Zinc（Zn）,copper（Cu）and cadmium（Cd）are 113.74 mg·kg^-1,132.37 mg·kg^-1,34.09 mg·kg^-1and 2.67 mg·kg^-1,respectively.It is 3.79,1.57,1.36 and 18.8 times higher than that of soil background value in Hunan province.（3）The pollution indices of lead（Pb）,zinc（Zn）,copper（Cu）and cadmium（Cd）in mining areas are 2.05,2.04,2.46 and 21.02,respectively.Among which the Cadmium（Cd）is severely polluted,while lead（Pb）,zinc（Zn）and copper（Cu）are moderately polluted,indicating that the accumulation intensity of cadmium（Cd）in the mining area is the largest.The potential ecological damage index of heavy metal elements in soil of mining area is Cd（105.08）>Cu（73.94）>Pb（10.23）>Zn（2.04）,among which Cd（Cd）shows strong potential ecological damage,Copper（Cu）shows moderate potential ecological damage,lead（Pb）and Zinc（Zn）show slight potential ecological damage.The soil accumulation indexes of Pb,Zn,Cu and Cd are 3.72,1.97,2.30 and 5.16,respectively.Cadmium（Cd）is seriously polluted,lead（Pb）is heavily polluted,copper（Cu）is severely polluted,and zinc（Zn）is moderately polluted.（4）The results of single factor pollution index,potential ecological hazard index and ground accumulation index showed that Cd was the most serious element in the soil of this mining area,and should be treated first.The single factor pollution index of soil heavy metals in mining area and tailing area is Cadmium（Cd）>3.0>Copper（Cu）>lead（Pb）>Zinc（Zn）>2.0,indicating that the Cadmium（Cd）element is severely polluted,while the lead（Pb）and zinc（Zn）element are moderately polluted.The soil cadmium（Cd）pollution index of road traffic area and residential area was above 3.0,which was at the level of heavy pollution.Except for the living area,the comprehensive pollution index of soil in other functional areas is greater than 3.0,and the comprehensive pollution index of soil in tailing and mining areas is as high as 29,indicating that the soil in the study area is severely polluted,and the soil pollution in tailing and mining areas is the most serious,requiring priority treatment.（5）Both biochar and organic compost could effectively promote the growth of ryegrass and increase the aboveground and underground biomass of ryegrass,effectively.Among which the combination of biochar and compost had the best effect.The addition of biochar and compost significantly increased the contents of soil organic carbon,nitrogen,phosphorus and potassium and ensured the nutrient supply for plant growth.The effects of different remediation agents on soil heavy metal stabilization were as follows:biochar+compost>compost>biochar.The contents of soil organic carbon,total nitrogen,available phosphorus and available potassium in biochar+compost treatment were48.81 g·kg^-1,2.54 g·kg^-1,76.98 mg·kg^-1 and 317.33 mg·kg^-1,respectively,which increased by 189.3%,124.7%,84.6%and 304.4%compared with the control.Biochar and compost significantly reduced the contents of Pb,Zn,Cu and Cd in the extracted soil.The effects of different remediation agents on soil heavy metal stabilization were as follows:biochar+compost>compost>biochar.The contents of Pb,Zn,Cu and Cd extracted from NH₄NO₃ were 6.28 mg·kg^-1,23.84 mg·kg^-1,17.06 mg·kg^-1and 0.29 mg·kg^-1,respectively,under biochar+compost treatment.Compared with the control,it decreased by 50.59%,58.81%,71.79%,54.01%.Figures 18,Tables 15,References 120...