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.