Coal fly ash: From waste to industrial product

Coal fly ash is a beautiful material in the sense of being mainly composed of nearly perfect spheres of Al-silicate glass that - disserves applications making use of such properties, rather than to be used as an inert filler. However, leaching of mobile components restricts applications to bound form in which the leachable components are immobilized, as for example in cement and concrete products. Therefore, research has been undertaken to improve the technical and environmental quality of this material by applying forced leaching methods. Results show that quality can be improved but that new environmental problems are likely to appear and that the economics of the proposed process seems at the moment not favorable. However, some examples of successful application of fly ash as fillers in the polymer industry are given. Further, fly ash is a major source of Si and Al for the synthesis of industrial minerals. Using this line, zeolites and geopolymers are possible products to be synthesized. Finally, in order to assist the promotion of fly ash in other applications than cement and concrete, a scheme for developing specifications is given.