Leaching of Trace Elements from Coal Solid Waste

摘要

In the present work leaching of ash from coal-fired power plants is described. It concerns precipitator ash from powder-coal fired utilities, desulfurization ash from a dry-scrubbing process and fabric filter ash from a fluidized-bed boiler. Reproducibility of shake tests and column leaching has been studied. In the shake tests a wide range of solid to liquid ratios is applied, which allows extrapolation to column conditions. Column experiments carried out in upflow at a fixed flow-rate of approx. 1 cm per day showed good column performance and proved that equilibrium is reached fairly rapidly. A classification of precipitator ashes with respect to leaching behavior is given, which allows an estimate of leaching characteristics beforehand. In relation to this, the variability in coal and ash compositions has been studied. If we assume that, except for the extremely volatile (e.g. Hg, Br, Cl, F, B, (Se)), all elements including the chalacophile group elements are nearly completely retained in/on the ash collected by electrostatic precipitators, it should then be possible to relate coal composition for these elements to ash composition by means of the ash content of the coal. This assumption was verified; over the entire concentration range the agreement between predicted and measured ash composition is good. For most elements the deviation falls well within the uncertainty quoted. A large discrepancy is noted for Cr. (ERA citation 07:062630)