COLLOID GENERATION BY EROSION OF COMPACTED BENTONITE UNDER DIFFERENT GEOCHEMICAL CONDITIONS

Bentonite colloid generation was investigated for mono- and divalent electrolytes (Na + , Ca 2+ ) with various ionic strengths, pH and filter pore sizes (2 μm, 10 μm, 100 μm). Colloid concentration and average colloid diameter was measured with Laser-induced Breakdown Detection (LIBD). A pH and ionic strength dependent colloid generation was observed. For ionic strengths lower than the critical coagulation concentration (CCC) a colloid generation can be confirmed. The strong pH dependency of colloid stability in the sodium system previously investigated in coagulation experiments was confirmed in the colloid generation experiments presented in this study. A filter pore size dependent colloid generation mechanism could not be observed in the course of this study. In all experiments the colloid concentration reaches with time a plateau value. Exchange of the contact water leads to a rapid new-formation of colloids reaching again a plateau value. The reason for this observation (a) dynamic generation/aggregation equilibrium or (b) depletion of the colloid source is discussed in the manuscript.