Characterization of phase transformation from low grade kaolin to zeolite LTA in fusion technique: Focus on quartz melting and crystallization in presence of NaAlO2

The presence of clay and non-clay impurities, mainly quartz, in the processed kaolin is the inherent problem in the formation of zeolite LTA due to scarcity of aluminum. Therefore; in the current investigation the phase transformation from low-grade kaolin to LTA structure was studied in the fusion technique to achieve the appropriate frame. The quartz reaction with alkali solution and zeolite crystallization were related to starting material composition, temperature, NaOH/kaolin, NaAlO2/kaolin, and ageing time. The obtained products were characterized via X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller textural measurements. The quartz reaction was accompanied by partial crystallization of hydrosodalite in the hydrothermal stage. The conversion of hydrosodalite to LTA frame was governed by aluminum ion content in which the relative crystallinity depends on starting kaolin composition. The presence of illite and pyrophyllite in the starting material composition results in the formation of amorphous phase while the absence of illite and pyrophyllite is the most efficient in the crystallization of nano-porous zeolite LTA, 10-12 nm, with the highest relative crystallinity, 100%, in comparison to reference manufactured commercially. Furthermore, the ageing time should be controlled within 24 h otherwise, the more extended ageing leads to lower relative crystallinity. A simplified method based on methylene blue adsorption was suggested for evaluating the change in the textural characteristics of synthesized materials. Hydrosodalite represented superior adsorption behavior compared to zeolite LTA. According to the presented pathway, the well-crystallized zeolite LTA can be produced from lowgrade kaolin.