DEHYDROXYLATION KINETICS OF KAOLINITE AND MONTMORILLONITE FROM QUEENSLAND TERTIARY OIL-SHALE DEPOSITS

Water released during clay dehydroxylation was measured using a small reactor coupled to a mass spectrometer. Dehydroxylation of Rundle montmorillonite and Nagoorin kaolinite occurs over the temperature ranges 250-700 °C and 280-600 °C, respectively. The low temperature of montmorillonite decomposition suggests iron substitution for aluminium in the crystal lattice (a nontronite structure). The montmorillonite dehydroxylation kinetics best fit a diffusion-controlled reaction in a sphere (a D(3) mechanism) to about 80% reaction. Kaolinite dehydroxylation is best represented by second-order kinetics (to at least 90% of reaction). Activation energies for the dehydroxylation reactions were determined as 145 ± 15 and 99 ± 8 kJ mol-1 for kaolinite and montmorillonite, respectively. © 1990.