The role of the solving strategy in electrokinetic transport modelling in saturated porous media

Abstract

The characterisation of the reactive transport of solutes is a complex problem that is applied in many fields of industry and environmental management. However, this problem has been treated with multiple mathematical approaches. This paper reviews several strategies for solving the different physical constraints that must be applied to this type of problem using COMSOL Multiphysics. The number of mass balance equations of the chemical species is evaluated together with the use of Gauss’s Law or electric charge balance to analyse the no-charge accumulation or electroneutrality conditions as electrical constraints. Problems of natural diffusion and electrokinetic transport in saturated porous materials are evaluated for electroconductive and nonconductive solid matrices in both potentiostatic and galvanostatic operation modes. Of all the solving strategies proposed, only one is valid and consistent for all types of problems presented. This approach is based on posing a mass balance equation of less (N-1) than the species in solution (N), solving for the mass of the missing species by electroneutrality and imposing the condition of no electric charge accumulation on the charge balance equation.