Negative Surface Charges of Unground Kaolinites

Abstract

The negative surface charges of some kaolinites from different origins were determined, paying attention to the distribution of the charges on basal and edge surfaces. The relations between the charge density and the particle morphology or crystallinity were considered.The negative charges on the basal and edge surfaces were assessed from the C. E. C. values at pH 4 and from the difference in the C. E. C. values at pH 10 and pH 4, respectively. The crystallinity was evaluated from the ratio of the two peak intensities (I(021)/(I(060)) of X-ray diffraction. The particle shape was observed electron microscopically.The results obtained are summarized as follows;1) The kaolinites of nine species studied could be classified into two groups by the magnitude of the negative charge density.2) Four kaolinites which showed high negative charge densities were poorly stacked to the direction of c-axis. The particles were rather thin shape owing presumably to high degree of isomorphous substitution. The negative charge densities on the basal surfaces, particularly in fine particles, were larger than those on edge surfaces.3) The remaining five kaolinites having low negative chargede nsities were well stacked and the particles were rather thick. The negative charge densities on the basal surfaces were almost same as those on edge-faces.