Influence of the electrical diffuse layer and microgeometry on the effective ionic diffusion coefficient in porous media

This study models the effect of the electrical diffuse layer at the pore matrix interface on ionic diffusion processes in a porous medium in presence of a concentration gradient. We find that the equation D = Df/Fo usually used to compute in steady state conditions the effective diffusion coefficient, D, of a porous medium as a function of the salt diffusion coefficient, Df, the electrical formation factor, F, and the porosity, o, should be replaced by: D = ( Df/Fo)ξ, in the presence of an electrical diffuse layer at the pore-matrix interface. The correction factor, ξ arises from the cross-coupling of ionic fluxes due to electroneutrality requirement.