Synthesis of ZSM-5 zeolites from biomass power plant ash for removal of ionic dyes from aqueous solution: equilibrium isotherm, kinetic and thermodynamic analysis

Abstract

In this work, industrial biomass power plant ash was used to synthesize the ZSM-5 zeolites for the first time with the original intention to turn value-added material into wealth, and then committed to adsorption performance testing. Typical chemical structure and morphology of ZSM-5 zeolite were identified by comprehensive technologies. Uniquely, it was found that there was a low pressure hysteresis loop which was caused by crossed 10-membered rings in the N₂ adsorption–desorption isotherm. To investigate the adsorption performance for dyes, the zeolite samples were used to remove cationic (MB) and anionic (CR) dyes from aqueous. The results demonstrated that when it came to adsorbing MB, the isotherm was in line with the Redlich–Peterson model (R² > 0.99), whereas it was matched up with the Sips model (R² > 0.99) for adsorbing CR. Kinetic models were assigned to the pseudo-second order equation (R² ≥ 0.99) along with remarkable intraparticle diffusion. In the end, thermodynamic parameters were ΔG⁰ < 0, and E_a > 0. Especially, adsorbing MB was ΔS⁰ > 0, and ΔH⁰ > 0, whilst adsorbing CR was ΔS⁰ < 0, and ΔH⁰ < 0, which indicates that electrostatic interaction plays a significant role in the whole process. All in all, this work might encourage novel attempts to dispose of industrial biomass ash.