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| - Sorption of Perchloroethylene bySurfactant-Modified Zeolite asControlled by Surfactant Loading
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| - The sorption of nonpolar hydrophobic organic compoundsby soil organic matter has long been attributed to apartitioning mechanism, with the sorption coefficientproportional to the fractional organic carbon content ofthe soil. However, deviations from this linear proportionalityhave been observed and reported in the literature bymany authors. In our study a natural zeolite was modifiedwith a cationic surfactant to achieve different fractionalorganic carbon contents and different surfactant moleculeconfigurations on the surface. The sorption of perchloroethylene (PCE) by the surfactant-modified zeolite (SMZ)was found to be dependent on the bound surfactantmolecule configuration as well as on the fractional organiccarbon content. Below monolayer coverage by thesurfactant, the PCE sorption coefficient on SMZ wasproportional to the fractional organic carbon content. Abovemonolayer coverage, increasing fractional organiccarbon content resulted in minimal further increase in thePCE sorption coefficient. The change in PCE sorptionbehavior was attributed to the structural differences betweensorbed surfactant monolayers and bilayers. The surfactantsurface configuration has a significant impact on theeffective volume and density of the bound organic phasethat is responsible for partitioning nonpolar organiccompounds. The ratio of the organic carbon-baseddistribution coefficient (Koc) for the monolayer versus thatfor the bilayer systems was 1.7, similar to the estimatedbilayer to monolayer hydrocarbon density of 1.3. Our resultsreinforce the notion that the structure of natural organicmatter as well as its quantity controls the sorption of nonpolarorganics to soils and sediments.
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