Characteristics of the distribution of typical heavy metals in the soils of underground coal fire

In the present paper,the authors conducted some experiments on the samples of the soils of Daquanhu coal fire for analyzing the characteristics of the heavy metals distribution in this fire zone,such as the Hg,As,Cu,Pb,Cr and the Zn,which is relevant to the soil properties of the sampling sites. Results show that the temperature increases with the depth increase of the sampling site in both normal and abnormal area,and the variation of temperature in- crease in the normal area is less than that of the abnormal area. The content of organic matter of soils decreases with the depth increase of the sampling site in both the normal area and the abnormal area. And the layer one,the layer two,the layer three and the layer four of the normal area soil contains more organic matter than that of the abnormal ar- ea soils. The contents of some heavy metals in the layer one of normal area soil,such as the Cu,Pb,Cr,Zn and the Ni, are less than that of the layer one of the abnormal soil. In the layer two of the abnormal area soil,the content of these heavy metals shows a trend of increase. In both the normal area and the abnormal area soils,the contents of the Hg, As,Cu and the Ni fluctuate little along the increase of the depth of sampling site. But the contents of the Pb,Cr and the Zn in abnormal area soil fluctuate more than that of the normal area soil. Results also show that the heat effect of the coal fire,the topography of the fire zone,the properties of the soil and the local climate parameters are the main factors to impact the spatial distribution of the heavy metals in the soil of underground coal fires. An analysis of the As speciation shows that the content of the residual As speciation is the highest,and that of the water soluble As specia- tion is the lowest. Contents contour maps show that the accumulating characteristics of the water soluble As speciation within the soil of the layer one to layer four consequently has the same trend of the accumulation of CaCO3 in this are- a. In the normal area of the fire zone,the contents of the residual As speciation and the iron As speciation have the same trend of change as the change of CaCO3 following the sampling depth increase. However,in the abnormal area of the fire zone,the content of the residual As fluctuates with a similar trend of the content of the organic matter following the increase of sampling depth. The mean content of the water soluble As in both the normal area and the abnormal ar- ea stays stable,which indicates that no close relationship exists between the As content and the soil temperature as well as the soil properties.