Enhancing the removal efficiency of methylene blue in water by fly ash via a modified adsorbent with alkaline thermal hydrolysis treatment.

An effective adsorbent of methylene blue was synthesized from coal fly ash (FA; waste material from a coal power plant) by a denaturing process with an alkaline solution at 90 °C. The denatured fly ash (D-FA) has a surface area and pore volume of 66.39 m 2 g -1 and 15.33 cm 3 g -1 , respectively, whereas the values of the original FA are negligible, i.e. , 3.55 m 2 g -1 and 0.02 cm 3 g -1 . The removal of methylene blue (MB) in aqueous solution by D-FA was increased in the range of initial MB concentration (10-20 mg L -1 ); contact time (0-120 min); pH (2-8); D-FA dosage (1-4 g L -1 ). However, a larger value of those operational parameters would not improve the removal activity. Furthermore, the methylene blue adsorption on the denatured FA was fitted with the Langmuir model with R 2 = 0.9991; the maximum adsorption capacity was determined as 28.65 mg g -1 from the model. Overall, the highest removal efficiency of MB using D-FA with the dosage of 4 g L -1 was 97.1% in 30 mg L -1 solution of methylene blue at pH = 7. The alkaline hydrothermal denaturation of waste FA is a promising approach to produce an adsorbent with beneficial environmental engineering applications.