As expected from the study of other groundwater systems, it was confirmed that colloid stability is strongly dependent on the pH and Ionic strength ( I ) of the groundwater type (see evolution of hydrodynamic diameters of colloids below).

Therefore, bentonite colloids show high stability under the experimental groundwater conditions in the experimental site (I = 10-3 M and pH = 9.5). In order to verify this, the colloid size distribution was also investigated for longer time periods with colloids obtained from previously washed bentonite and conditioned in the experimental site groundwater. The concentration of the suspension was approximately at 2000 mg/L. The colloid size distribution was found to be rather constant over a period of approximately five months.

Evolution of the hydrodynamic mean diameter of bentonite colloids in a suspension of
different ionic strengths, pH 8.7 +- 0.5


Evolution of the hydrodynamic mean diameter of natural bentonite colloids and different pH