| Abstract: |
The surface of kaolinite is modeled as a combination of Al and Si surface sites in order to understand its aqueous dissolution behavior. The pH dependence of the initial nonstoichiometric dissolution of kaolinite at 25°C can be related to the pH dependence of protonation and deprotonation of the surface Si and Al sites. The analysis indicates Al dissolution rates are greater than Si at pH < 4 with Si dissolution rate greater than Al at 4 < pH < 11 and initial stoichiometric dissolution at pH > 11. An analysis of the surface site density of kaolinite from surface potentiometric titration data is presented. This indicates that the surface area of kaolinite and possibly other clay minerals available for forming surface complexes and sites for cation detachment is significantly larger than that measured by standard gas adsorption methods. It is believed that H+ and OH- can penetrate between layers in the sheet silicates which is not possible for the gas, Kr, used in the BET analysis. |
