Enhanced electrokinetic remediation of mixed contaminants from a high buffering soil by focusing on mobility risk

Electrokinetic (EK) experiments were conducted for investigating the mobility and risk assessment of inorganic (lead, zinc, and nickel) contaminants beside phenanthrene (PHE) in a natural soil with high buffering capacity; moreover, the optimum simultaneous treatment of the contaminants was considered with regard to the removal efficiency, energy consumption and risk assessment. Nonionic surfactants (Tween 80 and Brij 35) combined with disodium ethylene diamine tetraacetate salt (Na-2-EDTA) were examined during 15-day electrokinetics. The operating conditions including pH-control, refreshing electrolyte and changing voltage gradient were tested to improve the soil remediation. A five-step sequential extraction was used to figure out the potential risk of metals in the treated soil. Lead had the highest removal of 79% among the other contaminants. The priority of heavy metals removal under the optimum conditions (Tween 80 + Na-2 EDTA) was lead > zinc > nickel. Electrolyte refreshment was favorable for remediation of selected heavy metals, while pH conditioning increased energy consumption and hindered the migration in the high buffering soil. Data analyses by Bioavailability Index (BI) and Mobility Factor (MF) confirm that the enhanced EK technology could increase the mobility risk of heavy metals, especially near the anode chamber; thus, the availability of the remained contaminants should be considered alongside the removal efficiency and energy consumption for evaluating EK strategies.