| In order to understand the ecological destruction situation of the open mining, an field investigation and sampling of soil were conducted in Guiping manganese mining area in Guangxi. The soil nutrient status and heavy metal concentrations were determined, and using The pollution index, Nemerow index, Geoaccumulation index and The potential ecological risk index to evaluate the heavy metal pollution status; Discussing heavy metal elements existence forms in diggings soil have the effects to plants. Combining the soil research and local geography, climate and the regional vegetation situation, propose the ecological restoration model for this manganese mine. The main conclusions are as follows:(1) The mining soil is general strongly acidic, the mean pH is 3.63～4.77. EC is very low, with an average range is 0.02～0.09ds·m-1. TN in tailing pond, eucalypt forest and cassava land were in the lower levels, the remaining samples were reached the level gradeâ…¡above of the grading index of soil fertility. TP in 1# tailing pond and peanut land (mineable part) were in higher levels than other samples, but overall still low, and it has become a limiting factor for plant growth. TOM of peanut land(mineable part) was the highest, eucalypt forest and tailing pond were lower,lowed than 10 g·kg-1. C/N of the mine soil are 9-13.(2)The total concentrations of Mn, Pb, Zn, Cr, Cu and Cd in the mine soils all exceeded the relevant soil background values for Guangxi. The total concentrations of Pb, Cu and Cr in the mine soil does not exceed the standard, Zn and Cd were over the classâ…¡of the national environmental quality standard for soil.The content of Mn in soil greatly exceeded the upper limit standard of the 170～1200mg·kg-1, Mn and Cd were heavy metal pollution elements in the mine soil. Available contents of the soil of the 6 measured elements did not exceed the classâ…¡of the national environmental quality standard for soil.(3) Using The pollution index, Nemerow index, Geoaccumulation index and The potential ecological risk index to evaluate heavy metal pollution status in manganese mine abandoned soil. pollution index indicated that mine soils were not polluted by Pb, Cu and Cr, but slightly polluted by Zn and seriously polluted by Cd. All I-geos showed slight to moderate contamination for Pb and Cu; moderate severe contamination for Zn, never to slight contamination for Cr; severe to extreme contamination for Cd and Mn.When Ei was concerned, the results showed slight for Pb,Zn, Cu and Cr, severe for Cd.Evaluation of three methods are basically the same results, but slightly different. The results showed that the total pollution level of mining reached the heavy level.(4) According to the sequential extraction, Mn,Znå'ŒCu were dominated by iron-manganese oxides and residual fraction. Pb was dominated by exchangeable fraction, residual fraction and iron-manganese oxide. Cr was dominated by residual fraction, Cd was dominated by exchangeable, carbonate and residual fraction.(5)From the bioavailability of different forms of heavy metals, available and potentially available parts of Mn can be very high proportion, was 88.01%, and potentially available parts was 87.77%, available part was very small,only 0.24%; available and potential available parts of Pb have a small difference, they were 36%; For Zn and Cr, they were dominated by inert fraction,the proportion was 71.65% and 75.27%; Cr was seriously dominated by inert fraction in the 6 elements, reached 81.80%, available part was 7.69%. Available and potentially available parts of Cd were 33.06% and 39.57%; inert fraction was small.(6)According to the actual situation,ecological restoration measures can be proposed:suiting local conditions, planing purposes and methods of ecological restoration rationally; renovating and improving the soil matrix; resuming mine vegetation to improve the ecological landscape; using tailings resources fully. |
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