Synthesis and characterization of pure phase zeolite 4A from coal fly ash

Abstract

This study was aimed at the synthesis of pure phase zeolite 4A from coal fly ash sourced from Nishat power plant in the Punjab province of Pakistan. Analysis of fly ash (FA) demonstrated that it can be used to produce low silicate type zeolites specifically zeolite 4A due to its Si/Al molar ratio of ∼2. The current investigation emphasized on the addition of induction time (before and after crystallization) to the fly ash extract of Si-Al-Na species that was extracted from fly ash. The induction time helped in catalysing primary and secondary gel formation during the synthesis leading to controlled formation of single phase with high crystallinity and small crystallite size. The physiochemical investigations of synthetic zeolite 4A by using various analytical techniques made the proposed process justified on comparison with commercial zeolite 4A. The X-Ray Diffraction (XRD) analysis for synthesize zeolite 4A confirmed only one crystallographic phase and small crystallite size with 82% crystallinity compared to reference zeolite with 75% crystallinity. Fourier-Transform Infrared spectroscopy (FTIR) spectra revealed the structural aspects of synthesis and reference zeolite by indicating the presence of identical structural units with same height and width of peaks. Morphological analysis by Scanning Electron Microscope (SEM) showed a well-defined cubic shape of synthesis zeolitic crystals. Surface area analyses by Brunauer–Emmett–Teller (BET) showed that synthesized zeolite possessed 122 m2/g surface area that is 3 times higher than reference zeolite of 36.3 m2/g. The synthesized zeolite was also found to have smaller particle size than reference zeolite. Thermal stability comparison of both zeolites was studied by non-isothermal Thermo Gravimetric Analysis-Differential Thermal Analysis (TGA-DTA) thermograms from 25 to 800 °C temperature and both the samples were found to be stable at 800 °C.