Ionic Strength Dependent Transport of Microparticles in Saturated Porous Media: Modeling Mobilization and Immobilization Phenomena under Transient Chemical Conditions

This study investigates ionic strength dependent deposition and release of microparticles in saturated porous media. Controlled micrometer-sized particle deposition experiments were conducted, followed by stepwise modifications in porewater chemistry to induce retained particle mobilization. A transient dual site transport model was tested against deposition and release, systematically addressing the effect of variations in solution ionic strength by coupling the equations for colloid transport with that for solute transport. The attachment and detachment coefficients of the model equations were explicitly tied to the salt concentration through proposed empirical functions, derived from experimental and theoretical considerations. Two regimes of attachment (and detachment) were hypothesized, showing favorable behavior beyond modeled values of a critical deposition concentration (and critical release concentration). Blocking phenomena were accounted for as well. This work shows how the intimate inclusion of salt concentration in a unique model equation system is able to describe both deposition and release behaviors of the particles under transient chemical conditions.