INFLUENCE OF POTASSIUM CONCENTRATION ON THE SWELLING AND COMPACTION OF MIXED (NA,K) ION-EXCHANGED MONTMORILLONITE

Oedometer swelling and compaction tests up to a maximum pressure of 32 bars were made on the Wyoming montmorillonite SWy-1 with a range of mixed (Na,K) exchange ion compositions. The permeabilities and water diffusivities of the compacted clays were calculated using soil physics theory. Significant inhibition of swelling from that of the Na-montmorillonite is developed for K fractions in the range 0.30 < K+ < 0.56. However, the water diffusivity increases by a factor of approximately six as the K exchange fraction increases from 0 to 0.7. Permeabilities to water flow show a power-law dependence on the void ratio e. XRD measurements at controlled humidity yield equilibrium interlayer spacings which in general increase with both increasing relative humidity and increasing Na exchange fraction. The extent of swelling is strongly inhibited in clays having Na exchange fractions of 0.44 or less, in good agreement with the oedometer studies.