SORPTION OF LINEAR ALCOHOL ETHOXYLATE SURFACTANT HOMOLOGS TO SOILS

Sorption onto five saturated soils of the homologs within the commerci al surfactant mixture Brij 35 (registered trademark of ICI Americas) w as investigated. Brij 35 is a mixture of linear ethoxylated alcohols, having an average of 23 ethoxy (EO) groups per molecule and alcohol ch ain of primarily 12 carbons in length (C12H25(OCH2CH2)(23)OH). In expe riments, saturated soils were exposed to various concentrations of the surfactant mixture for specified times, the slurries were centrifuged to separate the phases, the aqueous phases were extracted with 1,2-di chloroethane, and the residual homologs were derivatized with 3,5-dini trobenzoyl chloride and analyzed by normal phase HPLC. Homologs contai ning 4-43 EO groups were chromatographically separated at near baselin e. At aqueous Brij 35 concentrations below the critical micelle concen tration (cmc), the proportion of each homolog sorbed to each of the so ils increased with increasing EO chain length through the homologous s eries. As a result, in experiments where a significant proportion of t he surfactant adsorbed, significant shifts in the aqueous phase compos itions occurred to mixtures with lower mean EO numbers. A sharp break in the adsorption isotherms occurs at the cmc. (C) 1997 Elsevier Scien ce B.V.