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SOLVENT EXTRACTION AND SOIL WASHING TREATMENT OF CONTAMINATED SOILS FROM WOOD PRESERVING SITES: BENCH SCALE STUDIES
Citation:
SahleDemessie*, E, D W. Grosse*, AND E R. Bates*. SOLVENT EXTRACTION AND SOIL WASHING TREATMENT OF CONTAMINATED SOILS FROM WOOD PRESERVING SITES: BENCH SCALE STUDIES. Remediation Journal. John Wiley & Sons Incorporated, New York, NY, 10(3):85-109, (2000).
Description:
Bench-scale solvent extraction and soil washing studies were performed on soil samples obtained from three abandoned wood preserving sites that included in the NPL. The soil samples from these sites were contaminated with high levels of polyaromatic hydrocarbons (PAHs), pentachlorophenol (PCP), dioxins and heavy metals. The effectiveness of the solvent extraction process was assessed using liquified propane or dimethyl ether as solvents over a range of operating conditions. These studies have demonstrated that a two-stage solvent extraction process using dimethyl ether as a solvent at a ratio of 1.6 liter per kg of soil could decrease dioxin levels in the soil by 93.0 to 98.9%, and PCP levels by 95.1%. Reduction percentage for benzo(a) pyrene (BaP) potency estimate and total detected PAHs were 82.4 and 98.6% respectively. Metals concentrations were not reduced by the solvent extraction treatment. These removal levels could be significantly improved using a multistage extraction system. Commercial scale solvent extraction using liquified gases costs about $220 per ton of contaminated soil However, field application of this technology at the United Creosote Site, Conroe, TX failed to perform to the level observed at bench scale due to the excessive foaming and air emission problem. Soil washing using surfactant solution and wet screening treatability studies were also performed on the soil samples in order to assess remediation strategies for sites. Although, aqueous phase solubility of contaminants seemed to be the most important factor affecting removal of contaminants from soil, surfactant solutions (3% by wt.) having non-ionic surfactants with hydrophile-lipophile balance (HLB) of about 14 (Makon-12 and Igepal CA 720) reduced the PAH levels by an average of 71%, compared to no measurable change when pure deionized water was used. Large fraction of clay and silt (<0.06mm), high levels of organic contaminants and humic acid can make soil washing less applicable.