Micellar solubilization of nonaqueous phase liquid contaminants by nonionic surfactant mixtures: Effects of sorption, partitioning and mixing

Surfactant micellar solubilization is under investigation as a promising method for significantly increasing the efficiency of remediation of aquifers contaminated with nonaqueous phase liquids (NAPLs). In this study, the influence of three parameters on the micellar solubilization of NAPLs by a mixture of ethoxylated dodecyl alcohol surfactants was investigated: Presence of model aquifer materials, extent of equilibrium partitioning of surfactant into the nonaqueous phase, and sample mixing regime. The micellar solubilization of two NAPLs, hexane, representative of nonbranched alkanes, and 1,2-dichlorobenzene, representative of polar and aromatic compounds, was studied. Batch experiments indicated that surfactant losses to sorption on organic-coated silica were relatively small for these experimental systems. Surfactant partitioning into hexane was not significant, but there was significant surfactant partitioning into the 1,2-DCB phase, resulting in a total surfactant dose required to achieve 1,2-DCB micellar solubilization greater than that predicted from the surfactant critical micelle concentration. Partitioning of surfactant into 1,2-DCB was selective, with the more hydrophobic surfactant molecules Favoring the 1,2-DCB phase, resulting in an aqueous phase surfactant mixture with different solubilization properties than the original. Mixing conditions had a significant effect on the extent of solubilization of 1,2-DCB, attributed to the greater tendency of 1,2-DCB versus hexane to form emulsions. Results indicate that partitioning may be significant for certain nonionic surfactant/NAPL systems and should be investigated prior to remedial activities. Total surfactant concentration, aqueous to nonaqueous phase volume ratio, and surfactant formulation should be chosen to minimize losses to nonaqueous phases. (C) 1998 Elsevier Science Ltd. All rights reserved.