The kinetics of dehydroxylation of kaolinite

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Abstract
The dehydroxylation of kaolinite has been investigated by isothermal thermogravimetry. Kinetic analysis using the Avrami equation shows that a combination of atomic mechanisms operates throughout the temperature range 734 K to 890 K. An empirical activation energy of 222 kJ mol-1 was calculated from the Arrhenius relationship using rate constants based on diffusion and homogeneous models. The activation energy (Ea) was calculated for a series of degrees of dehydroxylation by the time to a given fraction method, showing an increase in Ea during the early stages of the reaction. The isothermal plots indicate that OH is retained in the final stages of the reaction. The observations are explained in terms of a reaction mechanism in which kaolinite grains dehydroxylate from the edges inwards, parallel to (001).