Characterization, decontamination and health effects of fly ash from wasteincinerators

The aims of the present work are a) to investigate the physical and chemica l properties of incinerator ash which are of importance for its utilization and environmental impact; b) the evaluate the occupational exposure of inc inerator workers to trace metals; and c) to develop a novel technology for the conversion of contaminated fly-ash from incinerators into a material wh ich can be disposed of cheaply or used in the construction industry. The di scussion is illustrated by results obtained through experiments. Morphologically, fly-ash consists of irregularly shaped material, of widely varying sizes. Some minerals are identified using powder X-ray diffraction , i.e. calcite, pyrite, halite and maghemite. The chemical composition of a sh samples examined consist of Ca, Al, Si, K, Ti, Mg, Fe, K, Na and Mn as t he major and minor elements. Trace elements such as Pb, Co, Cr, Ni, Cu, Se, Mo and Cd are also found. The samples tested are rich in Cl, Cr, Zn, Sn an d Pb, as compared to the earth's crust values. About 50% of the fly-ash par ticles are smaller than 5.5 mu m. These particles can play an important rol e in transferring toxic metals into the human blood stream by inhalation, d eposition and absorption. The ash is reported as having medium fusibility, with softening between 1220 degrees C and 1250 degrees C due to it's pyrite content. This is most likely to give clinker problems and affect the sinte ring process of fly-ash. The detoxification approach is based on the fact t hat sintering or melting of this ash results in the destruction of its toxi c organic components, including fixation of its heavy metal content to form an unleachable material which can be landfilled or used for building roads . A key aspect of this work is the technique used to ensure the energy effi ciency of the sintering/melting process which is based on the application o f a regeneration heating concept. The conclusions of the research are expec ted to have a major impact on future codes of practice and standards for de aling with contaminated fly-ash.