Generation and sedimentation of colloidal bentonite particles in water

Generation and sedimentation of colloidal bentonite particles in water were examined by using a single particle counting technique. A colloid-population from Ca-type or Na-type bentonite pellets initiated rapidly within I h in a batch. The colloid population may be attributed to the detachment of colloidal particles, accompanied by a change in the structure of hydrated clay pellets and self-diffusion of the colloidal particles. After the initial particle formation period, the colloid size distributions varied over several hundred hours, in which colloidal particles were populated by spontaneous diffusion from the colloid bed and aggregation of small particles in the suspension. Colloid generation from the bentonite pellets was strongly reduced in a highly saline solution. This is related to the stability of colloidal particles dispersed in water. Sedimentation was highly dependent on the particle size. The colloid size distributions reached similar pseudo-equilibrium states, starting from a clay pellet or from a concentrated clay suspension. The pseudo-equilibrium size distributions depended on the salinity of the solution and were similar for Ca-type FEBEX bentonite and Na-type Kunigel bentonite in 10(-3) M or 10(-2) M NaCl solutions. (C) 2008 Published by Elsevier B.V.