Aggregation and deposition kinetics of mobile colloidal particles in natural porous media

A novel method for assessing the deposition kinetics of colloidal particles in natural porous media is presented. The method is applied for studying t he deposition kinetics of in situ mobilized colloidal particles in a non-ca lcareous soil in mixed electrolytes containing sodium and calcium as counte r ions. Particle deposition rate constants were measured by combining depos ition experiments in packed columns and aggregation measurements by dynamic light scattering. The relative deposition and aggregation rate constants f ollow very similar trends, featuring fast (favorable) and slow (unfavorable ) regimes at high and low salt concentrations, respectively. These regimes are separated by the critical coagulation or deposition concentrations (CCC or CDC, respectively), which sensitively depend on the type of counterion. In systems containing a single electrolyte, the CCC and CDC follow the cla ssical Schulze-Hardy rule. In mixed sodium-calcium electrolytes, a gradual transition of the CCC and CDC between the values obtained for the correspon ding pure (single) electrolyte systems is observed. The present approach pr ovides a facile route for assessing deposition rates of mobile colloidal pa rticles in natural porous media. (C) 2001 Elsevier Science B.V. All rights reserved.