THE HYDROTHERMAL TRANSFORMATION RATE OF KAOLINITE TO MUSCOVITE ILLITE

Batch reactor experiments were performed to measure the rate of the reaction 1.5 kaolinite + K+ = muscovite + H+ + 1.5 water at temperatures ranging from 250 to 307°C. In these experiments, the rate of kaolinite conversion to muscovite/illite was monitored as the rate of production of H+. Runs were performed in small volume (50 mL) titanium hydrothermal reactors charged with well-crystallized Georgia kaolinite, Indian Ruby muscovite, and 25 mL of KCl solution (0.5-2.0 m). Both solids and solutions were monitored at specific intervals throughout each experiment. The determined rate law is dmH dt=- dmK dt= Am M(k+MK+- k_mh+ where mk+ and mH are the concentrations of potassium ion and hydrogen ion, k+ and k- are the forward and reverse rate constants in kg m-2 sec-1, Am is the total surface area of the muscovite in m2, and M is the mass of the solution in kg. The initial rate method was used to find k+, and k- was found by fitting data to an integrated rate equation. Temperature functions for the rate constants are In k+ = 12.90 - ( 1.87 × 104/T), R2 = 0.98, and In k- = 6.03 - ( 1.21 × 104/T), R2 = 0.95. The activation energies (Ea) for the forward and reverse reaction are 155 ± 15 kJ mol-1 and 101 ± 10 kJ mol-1, respectively. © 1990.