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 promisi ng method for significantly increasing the efficiency of remediation o f aquifers contaminated with nonaqueous phase liquids (NAPLs). In this study, the influence of three parameters on the micellar solubilizati on of NAPLs by a mixture of ethoxylated dodecyl alcohol surfactants wa s investigated: Presence of model aquifer materials, extent of equilib rium partitioning of surfactant into the nonaqueous phase, and sample mixing regime. The micellar solubilization of two NAPLs, hexane, repre sentative of nonbranched alkanes, and 1,2-dichlorobenzene, representat ive of polar and aromatic compounds, was studied. Batch experiments in dicated that surfactant losses to sorption on organic-coated silica we re relatively small for these experimental systems. Surfactant partiti oning into hexane was not significant, but there was significant surfa ctant partitioning into the 1,2-DCB phase, resulting in a total surfac tant 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, resultin g in an aqueous phase surfactant mixture with different solubilization properties than the original. Mixing conditions had a significant eff ect on the extent of solubilization of 1,2-DCB, attributed to the grea ter tendency of 1,2-DCB versus hexane to form emulsions. Results indic ate that partitioning may be significant for certain nonionic surfacta nt/NAPL systems and should be investigated prior to remedial activitie s. 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 reserv ed.