Fly Ash

Fly ash is a Coal Combustion Product (CCP) from coal-burning electric generating plants. This finely divided material exhibits cementitious and pozzolanic properties. 

Chemically, FA was silica to an extent of 55-70 %, followed by alumina 10-18 %, iro oxide 6-20 %, and lime magnesia and alkalis varied between 1 and 5 % each. It was reported that FA generally contains elements like Cu, Pb, Cd, Ag, Mn, Fe, Ti, Na, Mo, S, P, Zn, and Cl in different concentrations depending upon the type of coal used (Kaw et al., 1990; Valcovic et al., 1992; Karwas et al., 1995).

Besides natural ash, there are two types of fly ash:

1.       Class F normally from bituminous coal (low and high contents of Fe with 80-85 % of silica and alumina)

2.       Class C normally from sub-bituminous coal (high content of CaO )

3.     Either class can come fro, lignite or bituminous or sub bitumonous.

It is commonly used as a 20 – 30 % cement replacement in concrete; in catalyst application; utilization as an absorbent; ion-exchanger; and desiccant trough zeolitization, desulfurization agent, antirust, agricultural purpose, and application such as into admixture and filler of polymeric materials (including rubber and plastic).

There are four products from CCP; fly ash, bottom ash, flue gas desulfurization material, and boiler slag. The image below is a typical coal-fired steam generating system.

References : Karwas C P 1995 J. Environ. Sci. Hlth. 30 1223

       Kaw J L, Khanna A K and Waseem W 1990 Expt. Pathol. 39 49 

       Valkovic O, Jaksic M, Caridi A, Cereda E, Haque A M I, Cherubini R, Maschini G and Menapace E 1992 
                       Nucl. Instrum. Meth. Phys. Res. B69 479