Removal of Dyes from Aqueous Solution by Sorption with Coal Fly Ash

The use of coal fly ash (FA), a massive byproduct of coal-fired power plants, for removal of dyes, methylene blue (MB) and rhodamine B (RB), from aqueous solution has been studied. Eight different types of FAs obtained from power plants utilizing Australian, Chinese, Colombian (3 types), Indonesian, Philippine and Thailand coals were employed as adsorbent materials of the dyes. Batch experiments were performed by contacting 1.0 g of FA and 50 mL of MB or RB aqueous solution of desired concentration with continuous stirring at various pH and temperature of 25 oC. The effects of reaction time, pH of solution, and initial concentration of dye on the adsorption of MB and RB were studied. The adsorption equilibrium was established within a few minutes in both MB and RB adsorption with a Colombian FA. Some of other FAs require 30 -60 min to attain the adsorption equilibrium for both dyes and more than 20 hrs required with Thailand FA. The adsorption of MB increased slightly and linearly with increasing the solution pH. In the RB adsorption, the maximum adsorption was observed between pH 2.8 and 4.5. The adsorption capacity depends significantly on the chemical and/or physical characteristics of individual FA. The adsorption capacity of MB was found more than 2.0 x 10 -5 mol/g and 1.6 x 10 -6 mol/g for a Colombian FA and Thailand FA, respectively. The adsorption capacity of RB was smaller than that of MB for all the FAs studied. This study demonstrates that FA is an effective adsorbent for the removal of dyes from aqueous solution and the possibility of using FAs for a simple and inexpensive method of removal of color from wastewaters.