Combined effects of porosity, tortuosity and pore water composition on electrokinetic transport dynamics in porous media

Electrokinetic (EK) techniques allow remarkable enhancement of mass transfer processes in porous media. Therefore, EK approaches have great potential for a wide range of subsurface applications since they provide effective delivery of amendments, mobilization and removal of contaminants from soils and groundwater, as well as the recovery of valuable resources such as metals and rare earth elements. However, electrokinetic transport is governed by a complex interplay of flow and transport processes, electrostatic forces, and chemical reactions, all of which are influenced by various physical and chemical parameters of subsurface porous media. This study proposes an approach to determine the electrical tortuosity of granular porous media and investigates the effects of porosity, tortuosity, and water composition and ionic strength on electrokinetic transport dynamics in porous media, using a combination of experimental data and process-based numerical simulations. Our results show that the tortuosity values obtained from electrical conductivity measurements provide reliable estimates to be used for predicting electromigration transport velocities, and that incorporating non-ideal solution behavior and activity coefficients is important for accurate predictions of electrokinetic transport. We also highlight intricate interactions among porosity, tortuosity, ionic strength, and their collective impact on tracer mobility over time. In this context, process-based modeling performed with a COMSOL-PHREEQC coupling was essential to interpret the experimental observations and to quantify the effects and relative influences of physico-chemical, hydraulic, and electrostatic factors. Our findings hold significant implications for the design and optimization of electrokinetic approaches in a wide range of subsurface applications.