A comparative study of some kaolinites surface properties

The surface properties of five kaolinites of various origins were analyzed using potentiometric titration, electrokinetic measurements and low-pressure gas adsorption associated to derivative isotherm summation (DIS) modeling. The data show that sample structure is important in determining the surface properties. The combined analytical results clearly shows the existence of a permanent negative layer charge for all the samples. The general features that could be observed for the five kaolinites are: the titration curves are shifted to lower pH with increasing ionic strength due to the layer charge; the amount of consumed proton is influenced by the permanent layer charge; although low, the permanent charge determines the electrokinetic behavior. The shape anisotropy and the charge distribution on the basal and edge surfaces are crucial parameters to understand the behavior of kaolinite particles in aqueous media. The Cameroonian sample of the set exhibits a significant permanent charge together with large specific surface area associated to fine particle size and considerable shape anisotropy.