Physico-chemical characteristics of fly ash samples from thermal power plants of Orissa

Abstract

Some physico-chemical characteristics of three fly ash samples have been studied with an objective to create a data base for different fly ash samples in the country. It has been observed that relevant physical properties of the samples show systematic variation with particle size distribution. Thus, while apparent density and optical or geometrical area increase with fineness of the particles from sample 1 to 3, true density, voidage and void volume exhibit opposite behaviour. Batch leaching studies indicate that whereas for samples 1 and 2 most of the trace metals (except Cu) leach out rapidly from the surface of the ash particles in the <i>p</i>H range 6.4-7.5, under acidic conditions (pH ~ 4.5) the rates of leaching of most trace metals, except Co and Cd, are relatively slow for sample 3. The <i>p</i>H values of zero charge of the three major oxide constituents namely, SiO₂, Fe₂O₃ and Al₂O₃ as determined by the solid addition method, conform more or less to the literature values of 2.5, 7.0 and 9.5 respectively. Viscosity a measurement of aqueous suspension indicates that sample 3 is least hydrated in water and therefore shows low viscosity value even at high concentration of slurry.