Cation adsorption mechanism on kaolinite clay

Two theories for the mechanism of cation adsorption of base exchange clays were investigated. The Charged Lattice theory proposes that the negative charge causing the base exchange is due to substitution of divalent for trivalent and trivalent for tetravalent ions in the alumino-silicate structure. The Ion-Pair theory proposes that the base exchange is due to hydroxyl ions chemisorbed in the surface of the colloidal particles. It was the purpose of this work to apply these two theories to a kaolinite clay and determine the results to ascertain the mechanism or adsorption of cations on the clay. Samples or dialyzed clay were prepared and measured amounts of base were added to each. pH and base ion activity mesurements were made of each sample after equilibrium had been reached. These measurements were applied to mathematical equations representing each theory and the results interpreted through graphs. Further tests of the two theories were made by applying them to a base exchange resin known to have an inherent negative charge. This resin was prepared and treated in the same manner as the clay. It was concluded that the Ion-Pair theory was a possible mechanism, and that the Charged Lattice theory was not a possible mechanism for the adsorption of cations on the kaolinite clay. Neither theory gave completely satisfactory results with the resin, although the Charged Lattice mechanism appeared to hold at low pH values.