Environmental aspects of trace elements in coal combustion

During coal formation, many trace elements are accumulated with respect to mean crust and mean soil, which may impose environmental hazards in coal combustion. This review tries to combine available data from chemical technology, geochemistry and analytical chemistry in order to overlook the fate of trace elements in the coal combustion process and their pathways to various ash fractions. Volatilization techniques which have been used in microchemistry for several decades to achieve decomposition and separation from main elements of the crust simultaneously, are briefly outlined. A compilation of data of trace element contents of coals, coal ashes and slags is given, as well as tables of boiling points, to indicate possible volatilization reactions in reducing, oxidizing, or halogenide containing gas streams. Particle size and depletion temperature influence the composition of ash. Data from selective leaching of coal and coal ash help to estimate environmental impacts as well as to stimulate strategies for future regain of valuable trace elements. Magnetometric profiling is suggested as a new tool to detect accumulations of particles emitted by combustion processes into the environment, in order to find suitable sites for immission sampling.