Mechanochemical synthesis of granulated LTA zeolite from metakaolin

LTA zeolite can be prepared from dry mixes in a vibratory mill with an impact-shear loading conditions. For the synthesis of LTA zeolite, it is necessary to use the anhydrous ingredients (Al2Si2O7–metakaolin, γ-Al2O3). The process of synthesis is controlled by X-ray diffraction, IR-spectroscopy, and atomic-force microscopy. The presence of structural water in the initial ingredients (Al2Si2(OH)4–kaolin or Al(OH)3) leads to the formation of feldshpatoids (nepheline, sodalite). It was established that the process of mechanical activation requires the synthesis of sodium aluminate of cubic and/or tetragonal crystal systems with a lattice parameters close to those for LTA zeolite. These sodium aluminate acts as a steric template for an “assembly” of the zeolite. The presence of sodium aluminate with some other crystal structure results in the formation of sodalite. There is an optimal time of mechanochemical activation, which is determined by the synthesis of sodium aluminate with cubic or tetragonal crystal structure. A model of the mechanochemical synthesis of LTA zeolite was proposed.