Assessment of hydrothermal parameters on alkaline activation of fly ashes using a central composite design

Abstract

Coal fly ash (CFA) is a powder generated during combustion of coal; its improper disposal constitutes an environmental issue. To minimize this problem, one of the uses of CFA is as feedstock for production of zeolite. Different studies have shown that zeolites may be easily obtained from CFA by relatively cheap and fast conversion processes. Most of these studies have been focused on the study of the zeolite synthesis using classical methods through changing one factor per time and fixing the other factors, where it illustrates the impact of each variable individually via a huge number of experiments, however it doesn’t consider the effect of the interaction between different factors under study. This study aims to evaluate the effects of hydrothermal synthesis parameters, time of activation (t), temperature of synthesis (T) and concentration of alkaline activator ([NaOH]), on the formation of zeolite. Morphological and structural properties were determined through scanning electron microscopy and X-ray diffraction. The experiments were designed through a central composite design. The results revealed that 4M NaOH, 90℃ and time synthesis of 36 h were the conditions for a higher conversion of CFA into sodalite, furthermore, it was obtained P1-Na and losod as zeolite phases.