Chapter Two - Characterization and Recycling of Bottom Ash

Abstract

As one of the byproducts of municipal solid waste (MSW) incineration, abundant bottom ash is generated in MSW incinerators. Composition of bottom ash and distribution of components in terms of size, mass, material (ceramic, metal, glass, molten slag), physical and chemical properties, and mineral content are fully explored and presented. Generally, metal, glass, plastics, wood, and paper may be present. The constituents of bottom ash larger than 4mm in approximate diameter made up 60.3% and 58.3%, respectively; they can be screened and washed out easily and may be used as secondary materials in the construction industry. The metal objects taken from bottom ash include ferrous metal items such as iron sheeting, wire and nails, and nonferrous metal items such as aluminum pans and copper wire. Metal is distributed mainly in a particle size of 16–25mm. The main mineral content of ashes is found to be SiO2, CaCO3, CaSO4, 3Al2O3 2SiO2, and CaAl2Si2O8. Moreover, ratios of SiO2 in bottom ash are higher than those in fly ash, this possibly being ascribed to the glass in the waste. The evolution of iron-rich constituents in bottom ash and the mineralogical characterization of incineration bottom ash are fully discussed, with an emphasis on heavy metal-bearing phases.