The sorption of 2-methylnaphthalene by Rossburg Soil in the absence and presence of a nonionic surfactant

The sorption of 2-methylnaphthalene by Rossburg Soil was measured in the absence and presence of a nonionic surfactant (Triton® X-100). Sorption of the surfactant by the sorbent was significant and can be adequately described by the Langmuir isotherm equation. At surfactant equilibrium concentrations below the critical micelle concentration (CMC), sorption of the analyte was enhanced by as much as a factor of 2. At high surfactant dosages, the formation of micelles enhanced the aqueous-phase concentration of the sorbate thereby decreasing its sorption by the soil. A reduction in the analyte partition coefficient by as much as a factor of 3 was observed at a surfactant dosage of 3000 mg/L. A simple three-phase model was used to estimate the effects of surfactants on the sorption of nonpolar organic compounds. This model also took into account the effect of the surfactant on sorbent properties. The model results suggest that very hydrophobic substances (Kow > 105.0) were most sensitive to the effects of the surfactant with regard to enhanced sorption below the equilibrium CMC and increases in solution-phase concentration above the CMC. Moreover, it appears that lower relative surfactant dosages above the CMC are required to effectively mobilize these types of pollutants.