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

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 eva luated based on the removal of PCP from the soil throughout the process. Mi xtures with at least 50% (mass) ethanol extracted statistically equivalent amounts of PCP, removing as much as 730 mg/kg for one soil. Kinetic experim ents demonstrated that soil-solvent contact times of approximately 1 h were adequate to remove a majority of the PCP. A crosscurrent soil washing proc edure 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 f ield 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 soil s. 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. ( C) 1999 Elsevier Science B,V. All rights reserved.