Adsorption behaviors and characteristics of methylene blue on fly ash in aqueous solutions

Fly ash (FA) was used as adsorbent to remove methylene blue (MB) in aqueous solutions, adsorption kinetics and isotherm equations were analyzed to reveal the characteristics, optimal operation conditions were attained through orthogonal experiments. The results revealed that FA was acceptable on MB removal. The process was a pseudo-second-order reaction and fit Langmuir isotherm equation better with correlation coefficients of R² 0.9989 and the maximum adsorption capacity 11.0865 mg/g, the reaction could proceed spontaneously and the reaction was endothermic. Orthogonal experiments indicated that of MB concentration 20 mg/L, dosage of FA 0.5 g and initial pH value 5 was optimal, the average removal efficiency was 98.77%. FA was appropriate to remove MB and Cr(III) together in aqueous solutions. With acceptable removal efficiency and lower cost, the reaction system with FA was potential in future utilization for wastewater purification.