Pollution of agricultural soils resulting from a tailing spill at a Pb-Zn mine:A case study in Huanjiang,Guangxi Province
广西环江铅锌矿尾砂坝坍塌对农田土壤的污染及其特征

The collapse of the tailing dam in the Beishan Pb/Zn Mine of Huanjiang, Guangxi Province led to the spread of mining waste on the farmland along the Huanjiang River. Samples of polluted soil, unpolluted soil, mine tailing and river sediments were analyzed for pH, S content, heavy metals and rare earth elements in surface soil and soil depth profiles to assess the level of soil pollution. The results show that the polluted soils had increased concentrations of As, Pb, Zn and S and decreased pH, La, Ce and Nd. The maximum concentration of total soil S increased up to 2.29 % and the initial oxidation of metal sulphides from pyrite residues reduced the soil pH to extremely acidic (pH=2.5). Five years after the spill, there were still high concentrations of FeS2 in the soils, as identified by X-ray diffraction. The lower concentrations of La, Ce and Nd in the polluted soils than in the unpolluted soils resulted from leaching to deeper layers of the soil profile under the acidic conditions. The elevated concentrations of As, Pb, Zn were only found in the upper soil layer, up to 30 cm deep, indicating that the leaching of heavy metals was minimal under the local subtropical conditions. The maximum depth of decreased soil pH, resulting from spills of tailings containing pyrite, was in the upper 70 cm of the polluted soils.