The surface chemistry of kaolinite. III. Microelectrophoresis

Aqueous suspensions of kaolinite from Mt. Egerton, Victoria, have been leached at pH 6.0. In agreement with a theoretical prediction derived from a combination of solubility data and equilibrium constants, more silicon species than aluminium species were found in the leaching liquor. The electrophoretic mobility increases (ie. moves to less negative values) as the leaching at pH 6 proceeds. This has been correlated with the surface hydroxyl groups being more effectively under the control of the less electropositive metal, aluminium. In a binary oxide mineral like kaolinite, the electrical double layer at the particle surface is influenced by the pH dependence of the ionic species in the solution as well as by the pH dependence of the nature of the surface. The results of an electrophoretic study of unleached kaolinite in various aqueous electrolyte solutions is also presented.