Multispecies reactive transport modelling of electrokinetic remediation of harbour sediments

Abstract

We implemented a numerical model to simulate transport of multiple species and geochemical reactions occurring during electrokinetic remediation of metal-contaminated porous media. The main phenomena described by the model were: (1) species transport by diffusion, electromigration and electroosmosis, (2) pH-dependent buffering of H, (3) adsorption of metals onto particle surfaces, (4) aqueous speciation, (5) formation and dissolution of solid precipitates. The model was applied to simulate the electrokinetic extraction of heavy metals (Pb, Zn and Ni) from marine harbour sediments, characterized by a heterogeneous solid matrix, high buffering capacity and aged pollution. A good agreement was found between simulations of pH, electroosmotic flow and experimental results. The predicted residual metal concentrations in the sediment were also close to experimental profiles for all of the investigated metals. Some removal overestimation was observed in the regions close to the anode, possibly due to the significant metal content bound to residual fraction.

Modeling of electrokinetic remediation combining local chemical equilibrium and chemical reaction kinetics

“…Transport processes and chemical reactions were implemented using a two-steps sequential split-operator scheme [7,8]. In the first step, the transport equation system (accounting for diffusion, electromigration and electroosmosis and the water electrolysis reactions at the electrode, under electroneutrality conditions) is numerically integrated by means of a finite element method.…”

“…Models for reactive transport in porous media based on chemical equilibrium assume that the rates of reversible chemical reactions are faster (in both the forward and the backward directions) than the rates of the transport phenomena involved in the process, namely: diffusion, electromigration and electroosmosis [1]. This approach is frequently denoted as the assumption of local chemical equilibrium (LCE) [2], and it has been demonstrated as a suitable approach in many cases [3][4][5][6][7][8][9][10]. However, simulation results often displayed some disagreement with the experimental data in terms of concentration profiles with excessively sharp gradients compared to those obtained experimentally [7,[11][12][13].…”

M4EKR, Multiphysics for ElectroKinetic Remediation of Polluted Soils

“…Electrokinetic soil remediation is one of the most promising techniques for decontamination of low permeability soils, in which the most classical techniques [2] have been found to be less efficient. However, its practical application on a real scale has been rather limited [3] since the phenomena involved in these processes are very complex [4]. For this reason, it is essential to use numerical models that allow us to know the main trends in the behaviour of soils and natural waters subjected to EKR processes [5].…”

Pilot-scale electro-kinetic remediation of lead polluted field sediments: model designation, numerical simulation, and feasibility evaluation

“…In order to thoroughly comprehend the complicated mechanisms and efficiently design the appropriate schemes for a full-scale treatment, modeling becomes an essential tool to deal with the technique issues. Many mathematical models were proposed for the simulation of metal extraction with EKR [20][21][22][23][24][25][26]. Most of them coupled with the Nernst-Planck or Poisson equation with finite element method to describe both transportations and reactions taking place during the EKR [27].…”

“…Despite the considerable efforts were made on model development, poor agreements existed in comparison of predicted and experimental data. On one hand, the geochemical reactions such as precipitation-dissolution, oxidation-reduction, and adsorption-desorption between the species and matrix constituents were not accurately simulated [26]. They are indeed key factors for precise modeling and the limited case studies and data in literatures were the main reasons for the inaccurate simulations [28].…”