Surface properties and flow behavior of kaolinite. Part I: Electrophoretic mobility and stability of kaolinite sols

Abstract

The electrophoretic mobility of kaolinite sols has been studied as a function of electrolyte concentration in NaHCO 3-Na 2CO 3 buffer at pH 10.4. The positive charges which occur on the edges of the kaolinite particles in acid solution are no longer present at this pH and the particles are negatively charged owing to defects in the crystal lattice. Most of the exchangeable cations are evidently quite firmly attached to the particles in a Stern layer. The calculated ζ-potentials are considered to give a measure of the potential ( Ψ δ ) at the outer edge of the Stern layer (i.e., the diffuse double layer potential), and this is used to calculate the potential energy of repulsion between the particles as a function of distance. Rapid coagulation of the sol by a uni-univalent electrolyte at this pH occurs at an ionic strength of about 0.016 g. ion/l.; this is consistent with a value for the van der Waals' constant, A, of 2 × 10 −12 erg, in agreement with the values previously suggested by Street and Buchanan, Ottewill and Watanabe, and Overbeek.