Partitioning of hydrophobic organic chemicals (HOC) into anionic and cationic surfactant-modified sorbents

Surfactant-modified sorbents have been proposed for the removal of organic compounds from aqueous solution. In the present study, one cationic (HDTMA) and three anionic (DOWFAX-8390, STEOL-CS330, and Aerosol-OT) surfactants were tested for their sorptive behavior onto different sorbents (alumina, zeolite, and Canadian River Alluvium). These surfactant-modified materials were then used to sorb a range of hydrophobic organic chemicals (HOCs) of varying properties (benzene, toluene, ethylbenzene, 1,2-dichlorobenzene, naphthalene, and phenanthrene), and their sorption capacity and affinity (organic-carbon-normalized sorption coefficient, Koc) were quantified. The HDTMA–zeolite system proved to be the most stable surfactant-modified sorbent studied because of the limited surfactant desorption. Both anionic and cationic surfactants resulted in modified sorbents with higher sorption capacity and affinity than the unmodified Canadian River Alluvium containing only natural organic matter. The affinities of the surfactant-modified sorbents (Koc) for most HOCs are lower than octanol/water partition coefficient (Kow) normalized to the organic carbon content (foc) and the density of octanol (Koc octanol); naphthalene and phenanthrene are the exceptions to this rule.