Surfactant flushing of soils contaminated with non-aqueous phase liquids (NAPLs) has shown significant potential as an effective remediation tool. However, an important aspect that has been neglected is the formation of emulsions and their eventual transport in the subsurface. In this study, the effect of the cationic surfactant cetyltrimethylammonium bromide (CTAB) in modifying the surface properties of sand and emulsion droplets and its consequence on the transport of emulsions in porous media has been investigated with the aim of determining the emulsion-mediated transport of NAPLs in the subsurface. Flow experiments in sand-packed columns were conducted to determine the deposition of hexadecane-in-water emulsions on quartz sand at various CTAB concentrations. Adsorption of CTAB influences the electrokinetic potential of sand and emulsion droplets along with the surface hydrophilicity of the sand surface, thereby influencing the deposition of emulsion droplets. Deposition is found to be a maximum at a CTAB concentration of 5 × 10 -6 M, at which the sand surface is of opposite charge to that of the emulsion droplets. Below this concentration, the deposition efficiency is reduced due to the electrostatic repulsion between the negatively charged droplets and the sand. Above this concentration, the deposition is again reduced due to the surfaces of sand and droplets being positively charged. The experimental deposition efficiencies agree qualitatively with the energy barriers calculated using the DLVO theory. The results suggest that the transport of emulsions in porous media can be regulated by the adsorption of surfactants.
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