Effect of gangue spontaneous combustion on reclaimed soil quality of large-scaled opencast mine in loess area

For researching the effect of gangue spontaneous combustion on reclaimed soil quality, soil physical and chemical properties, contents of heavy metals, soil microbe and enzyme activities were studied by taking soils having been reclaimed for 13 years as objects, which located in south refuse dump of Antaibao large-scaled opencast mine in Pingshuo County, Shanxi Province, and original geomorphologic soil was chosen as the references. The results showed that the physical properties of reclaimed soil were influenced by gangue spontaneous combustion significantly. Compared with normal platform and original geomorphologic soils, bulk density of gangue spontaneous reclaimed soil was lower and total porosity was higher. Non-capillary porosity in 0-20 cm and 20-40 cm layers of gangue spontaneous combustion reclaimed soil were up to 42.08% and 39.49%, respectively, which were much higher than that of normal platform and original geomorphologic soils. However, capillary porosity in 0-20 cm and 20-40 cm layers of gangue spontaneous combustion reclaimed soil were 16.41% and 15.60%, respectively. Field water-holding capacity in 0-20 cm and 20-40 cm layers of gangue spontaneous combustion reclaimed soil were only 14.92% and 13.11%, which were 47.76% and 39.95% of that of normal platform, respectively. Contents of organic matter, rapidly available phosphorus and soil pH value were decreased and content of readily available potassium was increased due to gangue spontaneous combustion. The mass fractions of Hg, Pb and Cr, especially Hg and Cr were increased significantly. Total microorganism in gangue spontaneous reclaimed soil was 0.82% less than that of normal platform reclaimed soil. The amount of bacteria, actinomycetes and fungi were 0.80%, 1.64%, 1.24% of that of normal platform reclaimed soil, respectively. The activities of catalase and invertase were decreased and urease was increased slightly in gangue spontaneous combustion reclaimed soil as compared to normal platform reclaimed soil. In a word, gangue spontaneous combustion caused reclaimed soil extreme deterioration and decreased reclaimed soil quality.