Investigation of the first and second dehydroxylation of kaolinite

Raw material kaolin Sedlec Imperial and four types of rehydroxylated samples were used to study the processes of the first and second dehydroxylation of kaolinite by thermal analysis and IR spectroscopy. Activation energy (E (a)) of these processes was calculated from DSC curves using five isoconversional methods. IR spectroscopy was used to compare structures of the original and rehydroxylated samples. It was proven that the structure of rehydroxylated metakaolinite can closely resemble that of the raw kaolinite under intensive hydrothermal treatment but does not reach the original structure. The E (a) values of the second dehydroxylation reach 87-92 % of E (a) values of the first dehydroxylation.