Study on mechanism and properties of methylene blue adsorption on different compositions coal fly ash

Three kinds of coal fly ashes were collected from three thermal power plants. Kinetics, mechanism and other influencing factors of methylene blue adsorption by coal fly ashes have been studied. The results showed that the most important factor influencing adsorption is the particle size other than the C content of coal fly ash. The kinetics of methylene blue adsorption on the Weihe coal fly ash, Xijiao coal fly ash and Baqiao coal fly ash all follow the second-order kinetic equation, their second-order adsorption rate constants being 5.80, 4.149 and 1.204 × 10-2 g·mg-1·min-1 respectively. The adsorption process is controlled by intra-particle diffusion. The intraparticle diffusion rate constants of methylene blue adsorption onto Weihe, Xijiao and Baqiao coal fly ashes are 0.067, 0.109 and 0.160 mg·g-1·min-1/2 respectively. The adsorbed amount increases with the initial concentration of methylene blue decreasing and increases with the dosage of coal fly ashes increasing. The adsorbed amount of methylene blue increases first and then decreases slightly with the initial pH increasing.