Removal of Phosphate from Aqueous Solution Using Zeolite Synthesized from Fly Ash by Alkaline Fusion Followed by Hydrothermal Treatment

Abstract

The removal of phosphate from aqueous solution by the adsorption process using zeolite synthesized from fly ash was investigated in this study. The XRD patterns revealed that the major crystalline phase of the synthesized zeolite was gismondine. The phosphate immobilization capacity (PIC) increased significantly from 52.7 mg/g of fly ash to 102.9 mg/g of synthesized zeolite after conversion. The batch experiments were conducted to investigate the effect of pH, initial phosphate concentration, and adsorbent amount. The maximum adsorption capacity was obtained at the pH value of 7.0. The adsorption process followed Ho' pseudo-second-order model, and both liquid film and intra-particle diffusion were the rate-controlling step for the process. The adsorption equilibrium data had been analyzed by Langmuir, Freundlich, Radlich-Peterson, Koble-Corrigan, Tempkin, Dubinin-Radushkevich, and Generalized models. The results showed that the Langmuir model gave the best fit. The process was also found to be endothermic. The maximum phosphate adsorption capacity obtained was 132.02 mg/g (30°C), 156.36 mg/g (40°C) and 184.17 mg/g (50°C), respectively, suggesting that the synthesized zeolite is a promising material and can be used to remove phosphate from wastewater.

Keywords:

• adsorption isotherm
• alkaline fusion followed by hydrothermal method
• fly ash
• kinetic model
• phosphate removal
• synthesized zeolite

ACKNOWLEDGEMENTS

This work was supported by the National Water Special Project (2009ZX07210-009-02), the National Science and Technology Support Project (2006BAC10B03) and the National High Technology R&D Program (2008AA06Z301).