Electrochemical desalination of bricks – Experimental and modeling

Effect of experimental boundary conditions and treatment-time on the electro-desalination of soils

This study investigates the effect of boundary conditions and treatment-time on the electro-desalination of artificially-contaminated soil. The effect of ion exchange membranes (IEM), calcium chloride (CaCl2), and ethylenediaminetetraacetic acid (EDTA) on the removal of salt (i.e., Na+, Cl-, and Ca2+) and metal (i.e., Co2+ and Fe2+) ions from the soil by electrokinetic (EK) was studied. The outcomes demonstrate that an increase in treatment-time decreases the electroosmosis and ion removal rate, which might be attributed to the formation of acid-base fronts in soil, except in the IEM case. Because a high pH jump and electroosmotic flow (EOF) of water were not observed within the soil specimen due to the IEM, the removal of ions was only by diffusion and electromigration. The collision of acid-base fronts produced a large voltage gradient in a narrow soil region with a reduced electric field (EF) in its remaining parts, causing a decrease in EOF and ion transport by electromigration. The results showed that higher electroosmosis was observed by using CaCl2 and EDTA; thus, the removal rate of Co2+, Na+, and Ca2+ was greater than Cl- due to higher EOF. However, for relatively low EOF, the removal of Cl- exceeded that of Co2+, Na+, and Ca2+, possibly due to a lack of EOF. In addition, the adsorption of Fe2+ in soil increased with treatment-time due to the corrosion of the anode during all EK experiments except in the case of IEM, where an anion exchange membrane (AEM) was introduced at the anode-soil interface.

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

A mathematical model for reactive-transport processes in porous media is presented. The modeled system includes diffusion, electromigration and electroosmosis as the most relevant transport mechanisms and water electrolysis at the electrodes, aqueous species complexation, precipitation and dissolution as the chemical reactions taken place during the treatment time. The model is based on the local chemical equilibrium for most of the reversible chemical reactions occurring in the process. As a novel enhancement of previous models, the local chemical equilibrium reactive-transport model is combined with the solution of the transient equations for the kinetics of those chemical reactions that have representative rates in the same order than the transport mechanisms. The model is validated by comparison of simulation and experimental results for an acid-enhanced electrokinetic treatment of a real Pb-contaminated calcareous soil. The kinetics of the main pH buffering process, the calcite dissolution, was defined by a simplified empirical kinetic law. Results show that the evaluation of kinetic rate entails a significant improvement of the model prediction capability.

Modeling of electrokinetic remediation of Cd- and Pb-contaminated kaolinite

A physiscochemical model is presented for the reactive-transport of chemical scpecies through a contaminated soil during an acid-enhanced electrokinetic remediation treatment. Numerical simulations in the specific case of the removal of cadmium and lead from spiked kaolinite, compared with experimental results from the literature. The reactive-transport based on the local chemical equilibrium assumption, including a surface complexation to model the adsorption of cations (metals and protons). Comparison of simulation results show different beavior of the target metals, as cadmium is mainly retaind by surface interaction while lead is retained by precipitation of a solid phase.