Cosolvent-enhanced Desorption and Transport of Heavy Metals and Organic Contaminants in Soils

Abstract Numerous sites are contaminated with both heavy metals and polycyclic aromatic hydrocarbons (PAHs) and the technologies to treat such mixed contaminants are very limited. Electrokinetic remedi-ation has the potential to remediate mixed contami-nants in soils, including low permeability soils; however, the efficiency of this technology depends on the extracting solution employed. Previous studies on electrokinetic remediation have focused on the removal of heavy metals and organic compounds when they exist individually in clayey soils. In the present study, the feasibility of using cosolvents to enhance the electrokinetic removal of PAHs from clayey soils in the presence of heavy metals is in-vestigated. A series of laboratory electrokinetic experi-ments was conducted using kaolin soil spiked with phenanthrene and nickel at concentrations of 500 mg/kg each to simulate typical field mixed contamination. Experiments were performed using n-butylamine (cosolvent) at concentrations of 10 and 20 % and deionized water, each mixed with 0.01 M NaOH solution and circulated at the anode to maintain alkaline conditions. A periodic voltage gradient of 2 VDC/cm in cycles of 5 days on and 2 days off was applied in all the tests. During the initial stages when the soil pH was low, nickel existed as a cation and electromigrated towards the cathode. However, as the soil pH increased due to hydroxyl ions generated at the cathode and also flushing of high pH n-butylamine solution from the anode, nickel precipitated with no further migration. Phenanthrene was found migrating towards the cathode in proportion to the concentration of n-butylamine. The extent of phenanthrene removal was found to depend on both the electroosmotic flow and the concentration of n-butylamine, but the pres-ence of nickel did not influence the transport and removal of phenanthrene