Removal of ammonium ions from aqueous solutions using zeolite synthesized from red mud

Abstract

This study investigates the removal of ammonium from aqueous using zeolite synthesized from red mud. The zeolite was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), the specific surface area, and the cation exchange capacity (CEC). SEM and XRD indicated that most of the synthetic zeolite was crystalline, with zeolite P and Analcime as the major components. The CEC increased from 81.9 to 111 mmol/100 g during the synthesis process. The effects of adsorbent dosage, shaking time, initial pH, initial ammonium ion concentration, and competitive cations were investigated by batch experiments. The result shows that the parameters mentioned above have great influence on the ammonium removal by using the synthesized zeolite, and the effect of cations follows the order Na⁺> K⁺> Ca²⁺> Mg²⁺. To understand the exchange process of ammonium by the synthesized zeolite, the adsorption dynamics was described by Ho’s pseudo-second-order kinetic model. The Ho’s pseudo-second-order kinetic model was found to provide excellent kinetic data fitting. Five models including Langmuir, Freundlich, Koble–Corrigan, Tempkin and D–R were used in this experiment to fit with the equilibrium isotherm data, and the Koble–Corrigan model gave the best fit. The maximum ammonium adosorption capacity obtained is 17.5 mg/g. The results implies that the zeolites synthesized from red mud is an efficient adsorbent for the removal of ammonium ion.

Keywords:

• Ammonium
• Synthetic zeolite
• Red mud
• Adsorption

Acknowledgements

The authors are grateful for the financial support provided by the National Key Technology R&D Program (2012BAJ21B04), National Natural Science Funds for Distinguished Young Scholar (No. 51325804) and the National Natural Science Foundation of China (No. 51108436).