Chemical stability of hydrogen-montmorillonite suspensions

The chemical unstability of hydrogen clays may be correlated with the dissolution by the protons of the central gibbsitic layer. The parabolic rate law of the spontaneous transformation of a hydrogen clay into an aluminium clay indicates a diffusion process of the hydrogen ions adsorbed on the faces of the crystals against a flow of aluminium ions originating at the edges. The solution of the diffusion equation for these assumed initial and boundary conditions agree with the experimental rate curves. It is thereby possible to calculate the diffusion coefficient for this surface migration process. Very low values of an order of magnitude of 10−20 cm2 sec−1 at room temperature are found. The standard free energy of activation of the process being about 25 kcal/mole. No diffusion takes place in anhydrous montmorillonite, there is however no practical method for stabilizing a hydrogen clay without any appreciable decrease of the maximum initial hydrogen ion content. The diffusion equation used for the hydrogen-aluminium migration on montmorillonite describes satisfactorily the rate of ion exchange in vermiculite.