Changes in basal spacing of montmorillonite in electrolyte solutions

Abstract

The changes in basal spacings of various mono- and divalent homo-ionic montmorillonites have been determined as a function of the molality (from 0.7 to near saturation) of the electrolyte solution in which the clay is immersed. The expansion from two to three layers of water between the clay lamellae has been analyzed in terms of hydration and image forces. The manner in which the spacings alter with decreasing electrolyte concentration, conforms to a co-operative opening of the lamellae by the water molecules. The intercalation of the water layer renders it more difficult for the neighboring lamellae in the crystal to separate. The free energy of the expansion process increases with the hydration energy of the exchangeable cation and with the inability of the cation to pack into the monolayer of water in contact with each face of the montmorillonite lamellae. Some information on the gel structure of clays has been obtained by comparing the amount of water absorbed by the clay from the gas phase with that adsorbed from solution.