Solubilization of Naphthalene by Pure and Mixed Surfactants

Surfactant-enhanced remediation technology has shown promising potential for removing residual organics from contaminated soils and groundwater. Using a homologous series of cationic surfactants, alkylpyridinium bromide, it was found that the molar solubilization ratio (MSR) for naphthalene decreases with decreasing carbon number in the hydrophobic tail. In contrast, with nonylphenyl ethoxylates (nonionic surfactants), the MSR for naphthalene does not show appreciable changes with varying number of ethylene oxide groups in the hydrophilic head. MSR values for naphthalene in the presence of ionic surfactants with similar tail length depend on the charge of the headgroup. In addition, the behavior of naphthalene solubilization using cationic-nonionic and anionic-nonionic surfactant mixtures deviates considerably from that of ideal mixing. More interestingly, however, results from batch and column experiments reveal that the interactions between surfactant molecules and sand surfaces, particularly surfactant adsorption, play a critical role in determining the organics removal efficiency from sand matrixes.