Conversion of fly ash into zeolite: Effect of reaction temperature

The conversion of fly ash into zeolites has become an important waste management issue in recent years. Zeolites may be easily obtained from fly ash by the relatively cheap and fast hydrothermal conversion process. Raw fly ash is pretreated with hydrochloric acid at the determined optimum pre-treatment temperature, time and ratio of 80°C, 1 hour and 25∶5 (ml/g), respectively. Zeolite was then synthesized by mixing the pretreated fly ash with sodium hydroxide solution in a ratio of 150 g∶ 300 ml at various reaction temperatures: 90, 150, 210 and 350°C. XRD analysis of the fly ash with treatment and the structure of the as-synthesized zeolite indicates little change in the crystalline structure of the fly ash, although peak intensities of most components appear to decrease with increasing synthesis temperature. Evaluation of the particle size distribution of the zeolite material indicates that at higher temperatures a bimodal distribution and improved particle size uniformity manifest. In conclusion, the best zeolite material was obtained at 350°C.