Kinetics and compensation effect in kaolinite dehydroxylation

Abstract

Activation parameters (E, A, ΔH≠, and ΔS≠) and the effect of various factors involved in kaolinite dehydroxylation reaction have been studied using isothermal TG measurements. Thermal decomposition of kaolinite is found to be diffusion controlled within 0 < α < 0.65-0.70. The rate of the water release in dehydroxylation has obeyed the expression for diffusion in a spherical particle and/or the rate equation of the second order reaction, depending upon the kaolinite nature. The values of activation energy (140-300 kJ/mol) increased with increasing of partial water pressure in the reaction environment and increasing of structural disorder (natural, or induced by grinding). Activation parameters have shown a compensation behavior, following the equations; {E} = 51.1 + 12.961log {A} and {ΔH≠}= 222.0 + 0.680{ΔS≠} Isokinetic temperature β = (679 ± 2)K derived from these relations is in good agreement with the temperature range of the isothermal measurements performed. © 1985.