Published in Advances in Water Resources, this research presents a new Lagrangian formulation for simulating multispecies ionic solute transport in porous media, incorporating electrostatic coupling effects into Random Walk Particle Tracking models.

The accurate simulation of charged chemical species in groundwater requires accounting for electrostatic interactions, as ions in solution do not move independently. Their transport is influenced by electric charges, diffusion coefficients and concentration gradients of all species present in the system.

While electrostatic coupling has traditionally been addressed through Eulerian transport formulations, this study introduces a particle-based alternative capable of representing these interactions in both homogeneous and heterogeneous porous media.

The proposed approach is based on a Fokker–Planck form of the Nernst–Planck transport equation, allowing the authors to define nonlinear particle displacement coefficients that account for electrostatic coupling between species.

📈 Key insights from the paper:

🔹 The study introduces a new Random Walk Particle Tracking formulation for multispecies ionic solute transport in porous media.
🔹 The model incorporates electrostatic coupling directly into particle displacements, allowing charged species to interact during transport.
🔹 The formulation is based on the Nernst–Planck equation and its equivalent Fokker–Planck representation.
🔹 The approach was validated against experimental data and previously tested Eulerian solutions, showing consistent and accurate results.
🔹 Benchmark simulations reproduced breakthrough concentrations and transverse pH fronts in homogeneous flow-through systems.
🔹 The model was also successfully applied to a synthetic heterogeneous aquifer, demonstrating its suitability for complex groundwater flow fields.
🔹 The results open new perspectives for particle-based modelling of ionic solute transport and future coupling with geochemical reaction models.

This work contributes to advancing knowledge on reactive transport, groundwater modelling, charged species migration and numerical methods for simulating solute transport in heterogeneous porous media.