Multi-dimensional modeling of H+ and OH- mass transfer during soil electro-kinetic remediation

PurposeSoil electro-kinetic remediation (EKR) has received significant attention owing to its environmental sustainability. Water electrolysis at electrode surface changes the pH profile of soil water. The pH profile has a strong impact on EKR performances. The aims of this study were to quantify the mass transfer of H+ and OH- and investigate the coupled relationship among H+ and OH- mass transfer, electric field and porous fluid flow.Materials and methodsHerein, multi-dimensional (1D and 2D) models capable of coupling fluid flow and mass transfer were established to study the coupled relationship among H+ and OH- mass transfer, electric field and porous fluid flow. The multi-dimensional (1D and 2D) models were validated by lab scale experiments.Results and discussionThe characteristics of pH front and pH profile was proven to be dominated by electric field, mass transfer and porous fluid flow. The movement of pH front and pH profiles dominates the EKR performance. The conductivity rise and the electric field distribution variations were quantified and proven to be caused by the H+ and OH- mass transfer. After a certain EKR time, in the areas near the electrodes where the H+ and OH- are generated, the mass transfer flux of H+ and OH- is gradually close to its releasing rate, the ionic species H+ and OH- stop accumulating and the concentration of both tends to steady state, so does the conductivity.ConclusionsWe demonstrated that the coupled relationship among mass transfer of H+ and OH-, electric field, and porous fluid flow dominates the movement of pH profiles and the conductivity rise.