Adsorption of Non-ionic Surfactants onto Sand and Its Importance in Naphthalene Removal

Abstract

The kinetic and equilibrium adsorption studies of four NP (nonylphenyl ethoxylates) series non-ionic surfactants with different EO (ethylene oxide) groups on sand are presented here. The adsorption behavior of a NP series of surfactants is compared in batch and continuous column studies. The adsorption isotherms are found to be similar in nature in all cases, and the maximum amount adsorbed per gram of sand decreases with an increasing number of EO groups. The comparison of maximum amounts adsorbed in the batch and column shows that the amount adsorbed is the same for both cases. When two surfactants were mixed with a calculated average EO number, the mixed solution showed the same equilibrium amount adsorbed to that of the actual EO number, although transportation through the column showed different behavior. The organic removal efficiency of the surfactants from a sand column depends on the adsorption density on the sand surface and the lowering of the surface tension at the air-water interface. The order of naphthalene removal efficiency of different NP surfactants from a sand column are NP-40 < NP-15 < NP-9. The main objective of this study is to improve the knowledge of surfactant adsorption and its importance in organic removal from the sand surface for the application of soil and groundwater remediation.