Reaction mechanism of metakaolin materials prepared by calcining coal gangue

Metakaolin-based auxiliary cementitious materials fabricated by coal gangue were achieved. The temperature and time required for the preparation of metakaolin materials from the calcination of coal gangue were optimized based on the analysis of the reaction characteristics and kinetics during the calcination of coal gangue. The phase, microstructures, and activity analysis of the products were performed, and the effect of calcination conditions on the activity of the product was ascertained. The results of thermal analysis-infrared spectra combined experiments indicated that the dehydroxylation of kaolinite was a one-step reaction during the calcination of coal gangue within a temperature range of 379.8 °C–737.3 °C. According to the General Integration, Flynn-Wall-Ozawa and Kissinger methods, the activation energy E of dehydroxylation of kaolinite is 181.62 kJ·mol ^−1 and pre-index factor A is 10 ^9.27 s ^−1 for calculating the calcination time of metakaolin. The experimental results show that high-activity metakaolin products, that with a dissolution rate of 64.79–71.57 wt% of activated alumina and with an effective dissolution rate of 68.82–94.35 wt% of activated silica, are prepared under the condition of calcination for 15 min and the temperature of 700 °C–825 °C. The kinetic model simulation results for the calcination time at different temperatures correspond to the experimental results.