Surfactant sorption to soil and geologic samples with varying mineralogical and chemical properties

The sorptive behavior of two surfactants (Triton X‐1000® and Dowfax® 8390) with two surface soil samples, a subsurface soil sample, a weathered black shale containing large amounts of aged organic matter, an aeolian sand, and two clay minerals (montmorillonite and kaolinite) was examined. Dowfax 8390 (dianionic surfactant) sorption was not detected with any of the samples. In contrast, Triton X‐100, an ethoxylated nonionic surfactant, sorbed to all the samples. The mole surfactant sorbed/g sorbent (mol surf g sorbent) was greater for samples containing large amounts of smectite minerals and nonlinearity of the Triton X‐100 isotherm increased in samples low in organic carbon. The X‐ray diffraction analysis concluded that the ethoxylate group of Triton X‐100 intercalates with montmorillonite. The weathered black shale sample also has a high mol surf g sorbent value when reacted with Triton X‐100 but contains less smectite clay. We suggest that Triton X‐100 may be reacting via hydrophobic groups (branched alkyl chain) with the shale sample. Consequently, sorption of alcohol ethoxylate surfactants cannot be predicted solely on the basis of soil attributes such as clay or organic matter content, for it appears that the organic matter‐clay organization may predominate in these types of interactions.