Remediation of soils contaminated with wood preserving wastes : Crosscurrent and countercurrent solvent washing

Abstract Solvent washing was evaluated as a method to remove pentachlorophenol (PCP) from aged field soils contaminated with wood treating wastes. Several soil:solvent contact ratios were considered. Solvent washing processes were evaluated based on the removal of PCP from the soil throughout the process. Mixtures with at least 50% (mass) ethanol extracted statistically equivalent amounts of PCP, removing as much as 730 mg/kg for one soil. Kinetic experiments demonstrated that soil–solvent contact times of approximately 1 h were adequate to remove a majority of the PCP. A crosscurrent soil washing procedure was developed to determine the solvent volume required to remove PCP from field soils. Consecutive wash stages with the 50% ethanol solvent were followed by water rinse stages. The crosscurrent washes were performed in three- and two-stage processes where soils were washed with the 50% ethanol solvent in three- and two-successive stages followed by water rinse stages. Ethanol recoveries were greater than 90% for both the three- and the two-stage wash trains. In addition to PCP, hydrocarbons were removed from the field soils by the 50% ethanol solvent. Effective removal of PCP by the 50% ethanol solvent was not impeded by the presence of hydrocarbons in the soils. Three-stage countercurrent soil washing with 50% ethanol was successful in reducing PCP contamination on the soil from 785 to less than 40 mg/kg.