Study of the Thermal Stability of Faujasite Zeolite Synthesized from Kaolin Waste from the Amazon

The waste from the processing of kaolin in the Amazonian region of Brazil was subjected to a calcination process at 700 degrees C for 2 h to obtain metakaolin, which, together with sodium hydroxide and sodium silicate, formed the reaction mixture. This mixture was subjected to an aging step (24 hat 60 rpm), and a subsequent hydrothermal process at 110 degrees C for 10 h. By means of X-ray diffraction (XRD), differential thermal and thermogravimetric analysis (DTA/TG) and scanning electron microscopy (SEM) techniques, the crystallization of a single phase, faujasite (FAU) zeolite, was observed. In the postsynthesis process, it was verified by means of XRD that the thermal stability of this structure persists up to a temperature of 600 degrees C. At 800 degrees C, the structure of FAU collapses. Beginning at 850 degrees C, new nepheline phases are formed, and at 1000 degrees C, nepheline and mullite phases are formed.