Adsorbed Cations and Water Film Thickness on the Kaolinitic Clay Surface

The relation between the plasticity of green bodies of natural kaolinitic clays (Kibushi- and Gairome-clay, Georgia-, New Zealand-, and Green Bush-kaolins) and the amounts of adsorbed cations on the surface of clay particles were investigated. Based on the Pfefferkorn method, the plasticity of green bodies was evaluated and the water film thickness was determined. For the adsorbed cations, the cation exchange capacities and the amounts of cations extracted with 1N KCl and 1N CH3COON4 solutions were measured. It was found that the plasticity of green bodies was closely related to the water film thickness depending upon the amount of adsorbed cations on the clay particle surface. Obtained results are as follows: (1) the water film thickness is almost independent of the amount of adsorbed mono-valent cations. It increases with increasing amount of adsorbed di-valent cations and decreases with increasing amount of adsorbed tri-valent cations, especially Al3+ ion, (2) kaolinites from weathering origins, i.e. Kibushi- and Gairome-clays are richer in di-valent and mono-valent cations (Ca2+, Mg2+, K+) than those from hydrothermal origins, Georgia-, New Zealand-, and Green Bush-kaolins.