Removal of anionic dyes from wastewater using fly ash based adsorbent

Facing the great challenge of increasing solid waste and huge amount of wastewater, "treating the wastes with wastes" seems to be a proper and sustainable development method. Fly ash, a typical solid waste, has attracted much attention for its high-value applications. In this study, three types of fly ash were sampled from different power stations in China and used for multiple anionic dyes wastewater adsorption. According to the static adsorption, fly ash sourced from Chifeng (CF) was identified as Class C with a total amount of SiO2, Al2O3, and Fe2O3 of 67.65% via chemical composition analysis, and presented best adsorption performance on Reactive Brilliant Red K-2BP, Congo Red 4BS, and Acid Brilliant Red KN. Moreover, the pseudo-second-order kinetic fitted the adsorption processes of KN and 4BS with the theoretic adsorption capacity of 39.35 and 39.85 mg/g, respectively. However, the pseudo-first-order kinetic better described the adsorption process of K-2BP with the theoretical adsorption capacity of 43.24 mg/g. For the dynamic adsorption, the decolorization rate of K-2BP on CF increased from 82.6% to 96.5% as the flow velocity increased from 10 to 70 rpm. The metal cations on CF, such as Fe3+ and Al3+, could hydrolyze and work as flocculants and coagulants to remove dye molecules from wastewater. This study provides a research case and an application potential for the resource reutilization of fly ash to treat printing and dyeing wastewater.