A comparative study of the adsorption of non-ionic alkyl aryl polyoxyethylated detergents on sand by different methods has been made in an attempt to determine the fundamental mechanisms of non-ionic detergent adsorption. The techniques used in this study were: (1) the radiotracer method with which the CI4-tagged ethylene oxide chains (hydrophilic) were traced, (2) the spectrophotometric method, with which the phenol groups (hydrophobic) were determined, and (3) the surface tension method, with which the surface-active species were determined. The adsorption and suspension isotherms of RLS-3066-90 and Ijgepal CO-710 have been determined. The adsorption of RLS appears to follow the Langmuir isotherm. The adsorption determined by the surface tension method is greater than that determined by spectrophotometry which, in turn, is greater than that determined by the radiotracer method. These differences are interpreted to indicate selective adsorption of smaller molecular species. Polyoxyethylated non-ionic detergents are mixtures of different molecular species with various ethylene oxide chain lengths. The anomalous maxima and minima of the Igepal adsorption isotherms may be explained, respectively, by selective adsorption of smaller molecular species at lower concentrations with more uniform adsorption at higher concentrations, and the adsorption of a multimolecular layer. The anomalous adsorption and suspension isotherms of Igepal, although different in shape, also may be correlated by these postulates.

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