LAUSR

Abstract Interactions in solid mixtures of 6Al 2 Si 2 O 7 : 12NaOH and 6Al 2 Si 2 O 7 : 12NaOH: 2Al 2 O 3 under thermal treatment were studied. Ultrasonic pre-treatment of suspensions with a frequency of 22 kHz was applied. X-ray phase analysis, scanning electron microscopy, and synchronous thermal analysis were used in this research. It was shown that after evaporation of the suspensions, the hydrated LTA zeolite and sodium hydroaluminate are synthesized. During thermal treatment up to 500 °C, the adsorption water is removed first and then the dehydration of the zeolite and hydroaluminate occurs. Calcination at temperatures above 500° C leads to the synthesis of Na 6 Al 4 Si 4 O 17 and Na 8 Al 4 Si 4 O 18 by the interaction of metakaolin and zeolite with sodium hydroxide. At temperatures above 700 °C, the formation of mullite and nepheline occurs in the temperature range of 500–800 °C. The kinetic parameters have been calculated using Friedman analysis (differential method), Kissinger–Akahira–Sunose and Ozawa-Flynn-Wall analyzes (integral methods). It was shown that all analyzes give similar dependences of the apparent activation energy vs the conversion extent and the values of E are in the range of 70–350 kJ mol −1 . It was established that ultrasonic pre-treatment allows to reduce the values of the apparent activation energy. It was discovered that the Al 2 O 3 excess over the stoichiometry of the LTA zeolite synthesis is an inhibitor of the mullite and nepheline formation reactions.