Surfactant-enhanced Electrokinetic Remediation of Mixed Contamination in Low Permeability Soil

Abstract

Thousands of sites are contaminated with both heavy metals and organic compounds and these sites pose a major threat to the environment. Very few technologies, such as soil washing/flushing and stabilization/solidification, are available to remediate these sites; however, all these technologies are ineffective under low permeability and heterogeneous soil conditions. Previous studies have shown that electrokinetic remediation has potential to remove heavy metals and organic compounds when they exist individually in clayey soils. In the present study, the feasibility of using surfactants in electrokinetic remediation was evaluated to remove the PAHs in the presence of heavy metals from clayey soils. Kaolin was selected as a model clayey soil and it was spiked with phenanthrene and nickel at a concentration of 500 mg/kg-dry each to simulate typical mixed contamination. Bench-scale electrokinetic tests were performed using deionized water and two different surfactants, Igepal CA-720 and Tween 80, at 3% and 5% (in weight) each at the anode. These solutions at the anode were circulated and were buffered with 0.01 M NaOH to maintain neutral pH conditions. A periodic voltage gradient of 2 V/cm (with 5 days on and 2 days off cycles) was applied for all the tests. There was a significant migration of phenanthrene towards cathode in all the tests. Among all the extracting solutions used, complete removal of phenanthrene was observed using 5% Igepal CA-720. In case of Tween 80, the low electroosmotic flow limited the delivery of Tween 80 into the soil and therefore, limiting the phenanthrene solubilization and transport. It was observed that solubilization, electroosmotic flow, and concentration of the extracting solution are the critical factors that contribute to the removal of phenanthrene. Nickel electromigrated as cation towards the cathode and precipitated in the soil near the cathode due to high pH in all tests. Overall, nickel migration pattern was not affected by the presence of phenanthrene and the extracting solutions used in this study.