Modeling of electro‐osmosis of dilute electrolyte solutions in silica microporous media

Abstract

Physicochemical transport due to electro‐osmosis of dilute electrolyte solutions (<1 × 10−3 mol/L) through microporous media with granular random microstructures has been modeled in this work by our three‐step numerical framework. First, the three‐dimensional microstructures of porous media are reproduced by a random generation growth method. Second, the effects of chemical adsorption and electrical dissociation at the solid‐liquid interfaces are modeled to determine the electrical boundary conditions, which vary with the ionic concentration, pH, and temperature. Finally, the nonlinear governing equations for electrokinetic transport are solved using a highly efficient lattice Poisson‐Boltzmann algorithm. The simulation results indicate that the electro‐osmotic permeability through the granular microporous media increases monotonically with the porosity, ionic concentration, pH, and temperature. When the surface electric potential is higher than about −50 mV, the electro‐osmotic permeability exponentially increases with the electric potential. The electro‐osmotic permeability increases with the bulk ionic concentration even though the surface zeta potential decreases correspondingly, which deviates from the conclusions based on the thin layer model. The electro‐osmotic permeability increases exponentially with pH and linearly with temperature. The present modeling results improve our understanding of hydrodynamic and electrokinetic transport in geophysical systems and help guide the design of porous electrodes in microenergy systems.