Crystallization mechanism of zeolite A from coal kaolin using a two-step method: Fid-Bau Portal

Crystallization mechanism of zeolite A from coal kaolin using a two-step method

Zhou, Zhihui / Jin, Ge / Liu, Hong / Wu, Jianxiong / Mei, Jinfeng

Abstract Zeolite A was synthesized from coal kaolin using a two-step method. The crystallization mechanism was studied. The synthesis was composed of pre-crystallization at a low temperature and crystallization at a high temperature. The influence factors on crystallinity were investigated, including calcination temperature of kaolin, crystallization time, pre-crystallization temperature and time, and composition of synthetic liquid. X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR) were used to characterize the nucleation and crystal growth processes. The results indicate that abundant nuclei were formed during the pre-crystallization period, whereas crystallization process during the first h in crystallization period was still a nucleation stage. Also, metakaolin had dissolved thoroughly after the synthesis liquid crystallized for 3h, and the nuclei were rapidly grown into zeolite A crystals at this time. An excess crystallization time results in a dissolution of as-synthesized crystals and a decrease of crystallinity as well as a too high concentration of OH⁻.

Graphical abstract Zeolite A was synthesized from coal kaolin using a two-step method which is composed of pre-crystallization at a low temperature and crystallization at a high temperature. The influence factors on crystallinity were investigated, including calcination temperature of kaolin, crystallization time, pre-crystallization temperature and time, and synthesis liquid composition. X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR) were used to characterize the nucleation and crystal growth processes. The results indicate that abundant nuclei were formed during the pre-crystallization period, whereas crystallization process during the first 2h in crystallization period was still a nucleation stage. Also, metakaolin was dissolved thoroughly after the synthesis liquid crystallized for 3h, and the nuclei were rapidly grown into zeolite A crystals at this time. An excess crystallization time leads to the dissolution of as-synthesized crystals together with the decrease of crystallinity, so does a too high concentration of OH⁻. Display Omitted

Highlights • Zeolite A was synthesized from coal kaolin using a two-step method. • The influence factors on crystallinity were investigated. • The first 2h during crystallization period is still a nuclei stage. • Metakaolin is dissolved thoroughly after the synthesis liquid crystallized for 3h. • A relatively high n(Na2O/SiO2) is beneficial to the crystallization stage.