Fly ash for colour removal from synthetic dye solutions

my ash was investigated for its ability to adsorb dyes from aqueous solutio ns. Batch pH, kinetic and isotherm studies were performed on a laboratory s cale with synthetic dye solutions made up of four different commercial grad e dyes. Fly ash samples with differing compositions and particle sizes were employed to understand the effect of fly ash composition and particle size on their dye removal capacity. The first-order rate equation by Lagergren was tested on the kinetic data, and isotherm data was analyzed for possible agreement with the Langmuir and Freundlich adsorption isotherm equations. The removal capacity of fly ash for the different dyes was compared with th at of granular activated carbon under identical conditions. Results showed that fly ash exhibited reasonably good dye removals for Basic Blue 9, Acid Blue 29 and Acid Red 91 while the removals by fly ash exceeded that of gran ular activated carbon for Disperse Red 1. Lime content in fly ash seemed to influence dye adsorption to a significant degree - better adsorption was o bserved at lower particle sizes because of the increased external surface a rea available for adsorption. Acid Blue 29 adsorption by fly ash provided t he best fit for the Lagergren first-order plot. Because high pH and heavy m etals (leached from fly ash) in the treated wastewater may exceed the limit s set in municipal sewer-use bylaws, engineering and economic feasibility a ssessment should include these aspects when considering fly ash for colour removal.