Evaluation of soil property–dependent interactions of surfactant and diesel in a soil–water system

Abstract

Experimental studies were conducted to remove hydrophobic organic compounds (HOCs) from diesel fuel-contaminated soil. Interactions between non-ionic surfactants and diesel fuel were investigated to understand the partitioning effect in heterogeneous soil–water-surfactant systems. The effective critical micellar concentration (CMC_eff) was identified from surfactant adsorption, which led to the maximum partitioning of HOCs in the system. This partitioning was attributed to the surfactant (i) lowering the interfacial tension between HOC and soil, (ii) solubilizing HOCs, and (iii) mobilizing HOCs from a solid phase to a pseudo-aqueous phase. The strong adsorption capacity of clay in the soil led to an increase of CMC_eff from 20 to 2,500 mg/L of Tween 80. The data for surfactant adsorption and desorption on the soil followed Freundlich’s isotherm and showed irreversible adsorption for surfactant, especially in the presence of clay. The diesel migration from soils to the aqueous phase of surfactant was observed beyond its derived CMC value. The maximum removal efficiency of HOCs could be reached at CMC_eff of surfactant due to the higher solubility and competitive adsorption in the presence of clay. Understanding of the soil-surfactant-diesel behavior helped in the effective field implementation of surfactant-enhanced soil flushing for the remediation of oil-contaminated soil.