Thermochemistry of kaolinite dehydroxylation to “metakaolin”

Metakaolin is an important pozzolanic material in the construction industry. It is produced from the dehydroxylation of kaolinite at high temperatures (550 - 750 °C) [1]. “Metakaolin” is not uniquely defined and the degree of dehydroxylation (and mass/water loss) is a function of temperature and time. In order to optimise the production process of metakaolin and calcined clays, it is important to quantify the reaction enthalpy changes during dehydroxylation. In this work, a drop calorimeter is used to understand the energetics of kaolinite calcination at 550°C, which is at the lower end of the temperature range that causes the release of the hydroxyl groups from kaolinite [1]. The work is complemented by tracking water loss via dehydroxylation using thermogravimetric analysis (TGA).