MECHANOCHEMICAL ACTIVATION AS METHOD OF INTENSIFYING SYNTHESIS PROCESSES OF LOW-MODULUS ZEOLITES

The systematization and generalization of the available literature data in the field of application of mechanochemical activation of the initial mixtures used for the synthesis of zeolites have been carried out in this paper. It was shown that the zeolites synthesis refers to the so-called "non-covalent synthesis", and therefore, it depends on the process conditions. On an example of obtaining NaA zeolite, it was analyzed the factors determining the synthesis result, namely, the raw material type, the activation time, the initial components ratio, the temperature at the thermal treatment stage, the effect of the solution pH on the hydrothermal crystallization stage. In the work it was clearly demonstrated that the use of hydrated compounds as raw material results in the formation of feldspathoids with close-packed structure (sodalite, nepheline). The composition of the interaction products of kaolinite with alkaline ingredients depends on its basicity. A decrease in the alkalinity of the raw material promotes an increase in the silicate module of the synthesized samples. For the zeolite synthesis, it is necessary to introduce a substance which should serve as a structure-directing agent. In the process of low-modulus zeolites synthesis, sodalite cells and sodium aluminates of cubic and tetragonal systems perform this function. Conducting a mechanochemically induced process requires alignment with the subsequent stage of the thermal treatment. At this stage, the increase in the strength of the pellets as a result of the formation of ceramic bonds between the particles occurs, as well as bilding the zeolites framework takes place. Thus, it was shown that mechanochemical activation makes it possible to simplify considerably the traditional methods for the synthesis of zeolites from gels, which largely depend on the conditions of the processes. It was demonstrated that the process time is shortened by reducing the number of stages and accelerating the nucleation, and also the components consumption decreases. This provides a reduction in sensitivity to the conditions of synthesis. In addition, the mechanochemical activation allows to create the granulated zeolite and the cation-exchanged zeolite forms by direct synthesis.