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 the deposition kinetics of in situ mobilized colloidal particles in a non-calcareous soil in mixed electrolytes containing sodium and calcium as counter ions. Particle deposition rate constants were measured by combining deposition experiments in packed columns and aggregation measurements by dynamic light scattering. The relative deposition and aggregation rate constants follow 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 classical Schulze-Hardy rule. In mixed sodium–calcium electrolytes, a gradual transition of the CCC and CDC between the values obtained for the corresponding pure (single) electrolyte systems is observed. The present approach provides a facile route for assessing deposition rates of mobile colloidal particles in natural porous media.