KAOLINITE DISSOLUTION AT 25-DEGREES-C, 60-DEGREES-C, AND 80-DEGREES-C

The constant dissolution rates, kr in moles Si per cm2 per second, of kaolinite at 25°, 60° and 80°C are dependent on solution pH and temperature. Based on the dissolution behaviour of kaolinite as a function of time, solution pH, and temperature we conclude that during constant congruent dissolution Al detachment is rate determining at low pH, and Si detachment is rate limiting at high pH. The calculated activation energies, Ea, of the constant kaolinite dissolution rate are dependent on solution pH. Ea decreases from 16.0 to 1.7 (kcal mole-1) from pH=1 to 7 but increases from 3.4 to 9.8 (kcal mole-1) from pH=8 to 12. -from Authors