Treatment of Contaminated Soils with Organoclays to Reduce Leachable Pentachlorophenol

Abstract

The toxicity characteristic leaching procedure (TCLP, method 1311) (USEPA, 1990) was used to evaluate the effectiveness of nine organoclays in reducing the leachability of pentachlorophenol (PCP) from three highly contaminated (3000–5000 mg kg⁻¹) soils from wood treatment facilities. The soils differed in their PCP, oil and grease, and organic C contents. The organoclays were smectite exchanged with quaternary ammonium cations of the form [(CH₃)₃NR]⁺ or [(CH₃)₂NR₂]⁺ where R is an aliphatic or aromatic hydrocarbon. A cement‐based solidification agent (Sorbond) was also added to the soil to evaluate its effects on the leachability of PCP. Organoclays with large (>C₁₀) aliphatic R groups (organophilic organoclays) were compared with those with small aromatic or aliphatic groups (adsorptive organoclays). The adsorptive organoclays were much less effective than the organophilic clays in reducing PCP levels in the TCLP leachate. The organophilic clays dramatically reduced the leachability of PCP from all of the soils. The most effective clay tested was the dimethyldicocoammonium smectite; a 20% addition of this organoclay to the soil resulted in leachable PCP levels below the detection limit (0.2 mg L⁻¹). The addition of Sorbond to the soil increased both the pH (from 4.95 to 12.00) and the PCP concentrations (from 6.8 to 100.8 mg L⁻¹) in the leachate. However, when Sorbond was added with an organophilic clay, the PCP concentration was decreased below detection limits despite the increase in pH. These results demonstrate the potential effectiveness of organoclays for reducing the leaching of PCP from highly contaminated soils.