Abstract
The waste from the processing of kaolin in the Amazonian region of Brazil was subjected to a calcination process at 700°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 h at 60 rpm), and a subsequent hydrothermal process at 110°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°C. At 800°C, the structure of FAU collapses. Beginning at 850°C, new nepheline phases are formed, and at 1000°C, nepheline and mullite phases are formed.
Highlights
Transformations in the environment have been frequently occurring since the Industrial Revolution, and in recent decades, they have presented damage and environmental changes, causing risks and raising warnings about the quality of life of future generations[1]
The kaolinite waste was initially submitted to a drying process at a temperature of 100°C for 4 h in an oven, and soon after, it was subjected to a treatment for the reduction of its granulometry by spraying in a mortar to obtain a material with particles of the ideal size for the zeolite synthesis process
Based on the work done by Valtchev et al.[21], Cundy and Cox[22] and Maia et al.[12], to accelerate the synthesis time, the reaction mixture passed through an aging step, which occurred in an orbital-type agitator for 24 h at room temperature and at a rotation of 60 rpm
Summary
Transformations in the environment have been frequently occurring since the Industrial Revolution, and in recent decades, they have presented damage and environmental changes, causing risks and raising warnings about the quality of life of future generations[1]. A number of studies have been presented as means to minimize the impacts generated by the kaolin processing industry by using the wastes to produce new materials, such as ceramics and especially zeolites[3,4,5,6,7,8,9,10,11,12,13,14] Zeolites have their structure formed for frameworks of aluminosilicates that are based on an infinite three-dimensional network of tetrahedrons of (AlO4)5- and (SiO4)4-, connected to each other by oxygen atoms, forming channels and interconnections of voids, where cations and water molecules are found[15]. The zeolite of the faujasite (FAU) type (X and Y) is used in the processes of catalytic cracking and adsorption by the petroleum industry[16]
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