Removal of nickel and phenanthrene from kaolin soil using different extractants

Numerous sites exist where low permeability clayey soils have been contaminated with both polycyclic aromatic hydrocarbons (PAHs) and heavy metals. To remediate these sites, innovative treatment methods are urgently required. Electrokinetically enhanced in situ flushing offers great potential to remediate low permeability soils, but this method is highly dependent on the type of extracting solution used. This study investigated the feasibility of using different extracting solutions at various concentrations to remove PAHs as well as heavy metals from low permeability clayey soils. The most efficient extracting solutions could be used as purging/extracting solutions in electrokinetic remediation and other technologies such as soil washing. For the present study, kaolin was selected as a model clayey soil, and it was spiked with phenanthrene as well as nickel at concentrations of 500 mg/kg each to simulate typical field contamination. Several batch tests were conducted using a known amount of the spiked kaolin mixed with different extracting solutions at various concentrations to enhance the removal efficiency and to optimize the concentration of each extractant. The extraction solutions selected were surfactants, cosolvents, chealting agents, organic acids, and cyclodextrins. Based on the test results, surfactants and cosolvents were effective for the removal of phenanthrene, but they were inefficient for the removal of nickel. On the other hand, chelating agents and organic acids were effective for the removal of nickel, but were ineffective for the removal of phenanthrene. Cyclodextrins were found to be ineffective for the removal of both nickel and phenanthrene. To remove both phenanthrene and nickel, sequential use of the extractants was investigated, and it was found that 5% Tween 80 followed by 1 M citric acid or 1 M citric acid followed by 5% Igepal CA-720 were effective for the removal of both nickel and phenanthrene from the kaolin soil. Overall, it can be concluded that sequential use of selected extracting solutions can be effective for the removal of both heavy metals and PAHs from clayey soils such as kaolin.