ALTERNATIVE MODEL FOR CATIONIC SURFACTANT ADSORPTION BY LAYER SILICATES

Cationic surfactants are used in a wide range of household and industrial activities and have potential utility in in-situ remediation of contaminated soils and aquifers. Although many models have been proposed to describe the adsorption of cationic surfactants by soils and sediments, none can quantitatively account for the adsorption of quaternary ammonium compounds (QAC) by swelling clays or soils. In this study, we developed an alternative model for adsorption of hexadecyltrimethylammonium, a model QAC, by major clay types common to subsoils. The model uses a randomness parameter to account for the variation of cation exchange selectivity coefficients arising from differences in the distribution of inorganic and surfactant cations on the surfaces or in the interlayers of clays. In addition, the model employs an empirical relationship to predict the amount of QAC adsorption by hydrophobic bonding. Experimental data demonstrate that the model quantitatively describes the major characteristics of QAC-clay interactions for both swelling and non-swelling clays and provides a quantitative linkage between QAC adsorption and the nature of the QAC and clay minerals as well as solution conditions.