Synthesis of zeolites from coal fly ash: Application of a statistical experimental design

With the intention of decreasing the experimental test runs during the optimization of synthesis of zeolites from fly ash, a 2 ⁴ full-factorial experimental design was applied in this study. The preparation parameters that had showed significant influence on the synthesis of pure phase zeolite Na-P1 using one-step-ata- time experimental approach were included, but extended also to those parameters of importance identified in the literature. At the same time, it was important that the levels of variation of parameters not be restricted to the conditions where a pure phase of zeolite Na-P1 was formed. The four synthesis variables investigated were; NaOH concentration (NaOH:SiO ₂ molar ratio ranged between 0.35 and 0.71), ageing temperature (35-55°C), hydrothermal treatment time (36-60 h) and temperature (130-150°C). The results obtained were assessed by the improvement in the cation exchange capacity (CEC) of the obtained zeolite, which showed that the phase purity is strictly controlled by the synthesis conditions. In the end, this approach provided sufficient understanding of the relationship between product properties and the four synthesis parameters, which took into account the individual effects as well as linear and nonlinear interacting phenomena. From the analysis, it was found that the main effects were ageing temperature and hydrothermal treatment time and temperature, which showed some interactions among each other.