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

The sorptive behavior of two surfactants (Triton X-100(R) and Dowfax(R) 839 0) with two surface soil samples, a subsurface soil sample, a weathered bla ck 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 sampl es. In contrast, Triton X-100, an ethoxylated nonionic surfactant, sorbed t o 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 orga nic carbon. The X-ray diffraction analysis concluded that the ethoxylate gr oup of Triton X-100 intercalates with montmorillonite. The weathered black shale sample also has a high mol surf/g: sorbent value when reacted with Tr iton X-100 but contains less smectite clay. We suggest that Triton X-100 ma y be reacting via hydrosphobic 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 m atter content, for it appears that the organic matter-clay organization may predominate in these types of interactions.