3.3.1 Cations
During the application of EK process, electromigration and electroosmosis were two main mechanisms (Klouche et al., 2020). Electromigration results in the migration and movement of ionic compounds, while the electroosmosis mechanism is drive the flow of water along with solutes from anode to the cathode. Fahadani et al (2018) noticed that at low contamination, the dominant phenomenon in migrating the contaminations is electromigration process, and in case of high contamination, the electroosmosis process is dominant.
Fig.4 and Fig. S4 shows the concentration distributions of cations include Na+ (exogenous added ion), K+, Mg2+ and Ca2+in different soil layers after V-EK treatment. For control column (applied voltage = 0 V), the Na+ concentration decreases from the bottom up but accumulates in the surface layer. It is because the ion exchange reaction that displacement of Ca2+ and Mg2+ from a soil adsorption complex by Na+ resulting in the loss of Na (Sun et al., 2012; Kim et al., 2010), and this can be seen from the increase tendency of Ca2+ and Mg2+.
Even so, the maximum increasement percentage of Na+, K+, Ca2+ and Mg2+were 1528%, 318%, 2182% and 2451% respectively compared with the initial value of soil.