Numerical simulation of retention and release of colloids in porous media at the pore scale

Transport of a solid colloidal particle was simulated at the pore scale in presence of surface roughness and particle/pore physicochemical interaction by adopting a “one fluid” approach. A code developed in our laboratory was used to solve equations of motion, while implementing additional modules in order to take into account lubrication and physicochemical forces. Particles were recognized through a phase indicator function and the particle/fluid interface position at each instant was obtained by solving a transport equation. Roughnesses of different shapes were considered and the magnitude of the particle/pore physicochemical interaction was monitored through the change of the ionic strength of the suspending fluid. We first show that if pore surface is smooth no retention of the transported particle occurs whether the particle/pore surface is attractive or repulsive. However for shape roughnesses of “peak” or “valley”, particles may be retained inside pores or not depending on the considered ionic strength. In absence of particle retention, the residence time (the time needed for a particle to travel a characteristic pore distance) is finite and was found to be an increasing function of ionic strength for every considered roughness at fixed hydrodynamic conditions.