EFFECT OF CLAY-MINERALS PRESENT IN AQUIFER SOILS ON THE ADSORPTION AND DESORPTION OF HYDROPHOBIC ORGANIC-COMPOUNDS

Adsorption of hydrophobic organic compounds (HOCs) onto clay minerals and organic matter present in soils results in retarding their mobilit y. To study the impact of clay minerals on HOC sorption, kinetic and e quilibrium studies were performed using naphthalene as a test surrogat e contaminant. The results of these studies indicated that expandable clay minerals (clays that expand and expose large internal surface are a on wetting), such as montmorillonite and vermiculite, had a signific ant impact on naphthalene partitioning. A mathematical model was devel oped from the equilibrium data which related clay mineral concentratio ns with the naphthalene partition coefficient. Equilibrium desorption studies were also performed by adding a micellar solution of a surfact ant mixture (50:50) of Tween 20 and Aerosol AY-65 to mobilize the adso rbed naphthalene. The surfactant mixture was generally unable to mobil ize the sorbed contaminant due to sorption irreversibility and adsorpt ion hysteresis.