The NaOH/metakaolin ratio and crystallization time were studied for the synthesis of zeolite NaA from a sample of kaolin from a Capim mine. The tests were carried out by using statistical design with axial points and replication of the central point. The samples obtained were characterized by X-ray diffraction (DRX), scanning electron microscopy and chemical analysis using a microprobe EPMA. The results showed that there is a relationship between the amount of NaOH added and crystallization time. The tests carried out using the lowest NaOH/metakaolin ratio (0.5) and the shortest time (4 h) produced a non-crystalline material. On the other hand, increasing the NaOH/metakaolin ratio and the crystallization time led to the formation of a NaA phase with a high structural level, but with the presence of a sodalite phase as an impurity.
The synthesis of zeolite A employing kaolin waste from paper coating was studied. The kaolin waste was pre-treated at 550 to 800 °C. For comparison purposes, a sample of zeolite A was also prepared using the IZA procedure. The materials were characterized by 27Al MAS NMR, X-ray diffraction and scanning electron microscopy using a microprobe. Pretreatment was necessary, and the best temperatures were between 600 and 700 °C. The zeolite A formation was observed in all the prepared materials, reaching 52% crystallinity. On the other hand, the sodalite phase and amorphous materials were also formed.
The industrial costs of zeolite synthesis can be diminished by the substitution of traditional raw materials by natural sources. In this work, we obtained LTA zeolite from four natural materials, three different diatomites and expanded perlite, and characterize them by X-ray diffraction, X-ray fluorescence and scanning electron microscopy. It was possible to observe the formation of the zeolitic materials through the identification of the Bragg reflections and the cubic morphology characteristic of the aluminosilicate. The Si/Al ratio of the samples resulted next to the unit as expected for this topology. We found small differences between the zeolitic products, remarking the possibility of adapting this process using natural materials to industry. These results were used for the Green Star evaluation, calculating the synthesis degree of greenness, resulting greener due to the complete substitution of the traditional silica source.
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