Effect of clay minerals present in aquifer soils on the adsorption and desorption of hydrophobic organic compounds

Abstract

Adsorption of hydrophobic organic compounds (HOCs) onto clay minerals and organic matter present in soils results in retarding their mobility. To study the impact of clay minerals on HOC sorption, kinetic and equilibrium studies were performed using naphthalene as a test surrogate contaminant. The results of these studies indicated that expandable clay minerals (clays that expand and expose large internal surface area on wetting), such as montmorillonite and vermiculite, had a significant impact on naphthalene partitioning. A mathematical model was developed from the equilibrium data which related clay mineral concentrations with the naphthalene partition coefficient. Equilibrium desorption studies were also performed by adding a micellar solution of a surfactant mixture (50:50) of Tween 20 and Aerosol AY-65 to mobilize the adsorbed naphthalene. The surfactant mixture was generally unable to mobilize the sorbed contaminant due to sorption irreversibility and adsorption hysteresis.