Characteristics of coal ashes in Yanzhou mining district and distribution of trace elements in them

Abstract

In the process of combustion of coal organic and inorganic materials in it will undergo a complex variation. Part of them will become volatiles and, together with coal smoke, enter into atmosphere, some will remain in micro-particulates such as ash and dust and find their way into atmosphere in the form of solid particles, and the rest will be retained in ash and slag. Coal ashes are the residues of organic and inorganic substances in coal left after coal combustion and the composition of coal ashes is dependent on that of minerals and organic matter in coal. This paper deals with the chemical composition of coal ashes, the distribution of trace elements in them and their petrological characteristics, and also studies the relationship between the yield of coal ashes and the distribution of trace elements. In addition, a preliminary study is also undertaken on the factors that affect the chemical composition of coal ashes. As viewed from the analyses of coal ash samples collected from the Yanzhou mining district, it can be seen clearly that coal ashes from the region studied are composed chiefly of crystalline materials, glassy materials and uncombusted organic matter and the major chemical compositions are SiO2, Al2O3, Fe2O3, and CaO, as well as minor amounts of SO3, P2O5, Na2O, K2O and TiO2. During the combustion of coal, its trace elements will be redistributed and most of them are enriched in coal ashes. At the same time, the concentrations of the trace elements in flying ash are much higher than those of bottom ash, i.e., with decreasing particle-size of coal ashes their concentrations will become higher and higher. So the contents of trace elements are negatively proportional to the particle-size of coal ashes. There has been found a positive correlation between the trace elements Th, V, Zn, Cu and Pb and the yield of coal ashes while a negative correlation between Cl and the yield of coal ashes.