Abstract
In situ ultrasonic monitoring system together with complementary conventional ex situ monitoring techniques was used in this study to understand the formation mechanism of zeolite A from coal fly ash. The results obtained gave more detailed information compared to previous studies that had been conducted to understand the fly ash zeolitization process. Understanding zeolite formation mechanism from coal fly ash is expected to enable rational design of the synthesis processes. [Display omitted]
► In situ ultrasonic monitoring of crystallization of zeolite A from coal fly ash was successfully conducted. ► Complementing ex situ analyses techniques were used to confirm the results of in situ ultrasonic monitoring process. ► A simulated synthesis mixture prepared from analytical grade sources of Si and Al was also monitored and used for comparison. ► The influence of ageing fly ash based precursors was studied using the in situ ultrasonic set up at room temperature.
In this study, high phase purity of zeolite A was prepared from coal fly ash precursors. The molar regime of both the clear solution extract and unseparated fly ash slurry was adjusted to achieve the right composition for zeolite A crystallization. The formation process for zeolite A from coal fly ash precursors was monitored in detail using an in situ ultrasonic system and was complemented by use of ex situ techniques such as XRD, FTIR, SEM and FTIR. The findings from both the in situ ultrasonic monitoring process and ex situ techniques clearly contributed significantly in unmasking the formation process of zeolite A from coal fly ash compared to previous studies reported in the literature. The study also enriches the existing body of literature by deeply investigating the gel–solution–crystal interactions starting from this complex feedstock. Comparable ultrasonic signals were generated when both clear and unseparated fly ash based precursor solutions were used during the zeolite synthesis process.