Effects of electrolyte characteristics on soil conductivity and current in electrokinetic remediation of lead-contaminated soil

• Characteristics of electrolytes significantly affect soil current.
• Proton-transfer reaction between H+ and Ac− ions induced potential gradient peak.
• Potential gradient peak induced lead-focusing effect in soil.
• Fe2+ ions do not enhance the desorption of lead from soil.
• Na/HAc is not an optimal catholyte in EKR of Pb-contaminated soil.

Characteristics of electrolytes as boundary conditions of soil affect the soil ionic composition and conductivity during electrokinetic remediation (EKR), which directly affect the effectiveness, energy efficiency and duration of EKR. This experiment studied how the characteristics of catholytes and anolytes affect the soil conductivity. The results showed that H+ ions of higher ionic conductivity induced the increase in soil conductivity; by contrast, Fe2+ ions of lower ionic conductivity induced the decrease in soil conductivity. This experiment also found that when H+ ions from anolyte met Ac− ions from catholyte in soil, they associated into neutral HAc molecules resulting in the decrease in the soil conductivity, which reached the lowest at pH ≈ 3.7. This proton-transfer reaction induced a potential gradient peak which caused a lead-focusing in the soil. The pH value for lead desorption from soil is no more than 4.0, and therefore HAc is not an optimal candidate for catholytes in the electrokinetic remediation of lead-contaminated soil. Results also showed that Fe2+ ions did not enhance desorption of lead from soil. This study provided a methodology to explain the change pattern of soil conductivity and current, and guide the selection of electrolytes.