*Leaching Mechanisms of Trace Elements from Coal and Host Rock Using Method of Data Mining DOI: http://dx.doi.org/10.5772/intechopen.100498*

When the host rock is leaching with water, As, Hg, and Se were originated from oxidation and dissolution of sulfur-mineral; especially for pyrite, Cr was mainly controlled by the transformation of clay minerals. When the coal is leaching with water, As and Hg showed high affinity of sulfur-minerals, and Se and Cr seemed to be controlled by the water-rock interaction of clay minerals. It suggested that Se exist in sulfide mineral, clay minerals, and also organic matters. Therefore, the leaching mechanism of Se is not unique, and multiple mechanisms may control or influence the leaching behaviors. Cd and Pb showed apparent differences between the solid samples and liquid samples. The mechanism leading to this result was probably explained not only the releasing process, but also the adsorption process. These elements are typical metal elements. They can be easily adsorbed in the alkaline and neutral environment. Therefore, the released metal elements were adsorbed by clay minerals and organic matters. The immigration mechanism and long-term environmental impact need further studies.
