Studies on synthesis and characteristics of zeolite prepared from Indian fly ash

Abstract

In the present study, samples of coal fly ash were obtained from seven major Indian thermal power plants. These samples were transformed into fly ash zeolite (FAZ) using hydrothermal activation by treatment with NaOH. All experiments were carried out at 100 °C, but with different solid:liquid ratios, different concentrations of alkali and different incubation times. The chemical composition, mineralogy and morphology of the fly ash and FAZ were determined by wet chemical method after Na₂CO₃ fusion, x-ray diffraction and scanning electron microscopy. The cation exchange capacity of fly ash and FAZ was determined using the ammonium acetate method (IS:2720). The ammonium exchange capacity was determined by the titrimetric method. The experiments demonstrate that zeolite can be synthesized at 100 °C using alkali. The cation exchange capacity and ammonium adsorption capacity of FAZ (up to 250 meq/100 g and 22.93 mg NH₄ ⁺/g respectively) indicate that the FAZ may be potentially useful to reduce heavy metals and other pollutants from contaminated environments. Therefore, zeolitization at low temperature potentially allows waste fly ash to be used in an economically advantageous way.

Keywords:

• fly ash
• fly ash zeolite
• cation exchange capacity
• ammonium adsorption capacity
• solid waste management

Acknowledgements

The authors are grateful to the Ministry of Coal, Government of India, for funding the grant-in-aid project for carrying out the investigation. Thanks are due to Dr. Amelendu Sinha, Director of the Central Institute of Mining and Fuel Research, Dhanbad, India, for the support during the investigation period. Thanks are also due to Dr. Eric Condliffe, School of Earth and Environment, University of Leeds, for carrying out the SEM analysis of the fly ash and fly ash zeolite.