Síntese mecanoquímica de zeólita LTA a partir do caulim

Abstract

Due to limitations in traditional zeolite synthesis processes, the search for new and improved methods remains a topic of academic and industrial relevance. Solvent-free synthesis techniques have the advantage of being a more sustainable process, in addition to the high yield in product formation, compared to solvent synthesis. In this way, mechanochemistry has been a growing approach and allows reducing the process to a single step. The ball mill is a suitable equipment for performing mechanochemistry. Ball milling is a simple, reproducible and environmentally friendly method for converting materials to nanometer sizes and has been recognized as an efficient method for optimizing the properties of powder materials. The study and synthesis of zeolitic materials by grinding was carried out. The first study dealt with the grinding of three different types of kaolin, varying speed and grinding time, aiming at application as a source of silicon and aluminum in the synthesis of LTA zeolite. The second study addressed the synthesis of LTA zeolite with calcined kaolin and with ground kaolin varying the speed, milling time and synthesis time. The third and fourth study addressed the synthesis of LTA zeolite from kaolin without pretreatment ground together with the dry reagents and the synthesis of LTA zeolite from kaolin without pretreatment ground together with the dry reagents and an aliquot of water, respectively, by varying the speed, grinding time, and synthesis time. The obtained materials were characterized by XRD, XRF and SEM. In the milling process, the rotation speed of 600 rpm during 60 minutes was selected as the most efficient for the amorphization of kaolin, among the conditions studied. Rotation speed of 400 rpm during 30 minutes was selected as the mildest parameter in which variations in the kaolins were perceived. The syntheses were carried out employing the kaolins ground for 30 and 60 minutes with rotation speeds of 400 and 600 rpm. The syntheses performed by mixing reagents directly in the ball mill used the same time and speed conditions as used in the kaolin grinding experiments. The calcination condition employed was not sufficient for complete amorphization of all kaolins studied. Increased grinding speed and time have a greater influence on the formation of the zeolite LTA. The synthesis performed by mixing the dry reagents directly in the mill has a positive influence on the formation of zeolite LTA, which is obtained at lower milling speed and time conditions.