SYNTHESIS OF GRANULAR LOW-MODULUS ZEOLITES FROM METAKAOLIN USING MECHANOCHEMICAL ACTIVATION AND ULTRASONIC TREATMENT

Abstract

The process of synthesis of granular low-modulus zeolites from a mixture of metakaolin and solid sodium hydroxide depending on the method of pre-treatment (mechanochemical activation or ultrasonic treatment) has been investigated. The vibration roller-ring mill VM-4 (vibration frequency 930 min–1) was used for mechanochemical activation (MCA) of the powder mixtures. Ultrasonic treatment of the aqueous suspensions was carried out in the ultrasonic disperser UD-20 (oscillation frequency 22 kHz). X-ray diffraction analysis, IR spectroscopy and scanning electron microscopy have been used for the study. It was established that Na2Al2O4 and SiO2 are formed in the system after MCA as a result of leaching, and after UST, Na2Al2O4 is formed only. It was shown that thermal treatment at 650 °C of the mixture after mechanochemical activation and ultrasonic treatment leads to the synthesis of sodium aluminosilicates of cubic syngony, but with different parameters of the crystal lattice. Thermal treatment of the mixture without treatment gives the formation of sodium aluminosilicates and silicon oxide. It was found that after hydrothermal crystallization in NaOH solution with a concentration of 2 mol l–1, the LTA zeolite is synthesized. Crystallization in an alkali solution with a concentration of 6 mol l–1 gives the formation of SOD. It was ascertained that the use of ultrasonic treatment of the initial mixture results in the synthesis of a maximum amount of LTA zeolite (80 %) and SOD (98 %).