Abstract
Accurate prediction and modeling of the quantitative recovery of chlorinated hydrocarbons in an aquifer by anionic-nonionic gemini surfactants requires estimates of their mass-transfer models and capture mechanisms. In this work, a series of synthesized anionic-nonionic gemini surfactants (GEOnS-m) with different molecular structures were used to solubilize different chlorinated hydrocarbons that contaminate the aquifer. GEOnS-m aggregate showed vesicle, rodlike micelle, and spherical micelle as the ethylene oxide content (EO) number increases. Non-polar chlorinated hydrocarbons (PCE, CT) mainly solubilized in the hydrophobic interior of micelles, and polar chlorinated hydrocarbons (TCE, MCB) mainly solubilized in the “palisade layer” of micelles. Solubilization processes were followed employing first-order and second-order kinetics. The solubilization rate increases with the decrease of EO number of GEOnS-m molecules. In essence, lower interfacial tension reduces the mass-transfer resistance of chlorinated hydrocarbons at the two-phase interface. The diameter of vesicles and spherical micelles increases, and rodlike micelles evenly changed to vesicles as chlorinated hydrocarbons transfer into micelles. The solubilization process of GEOnS-m for chlorinated hydrocarbons conforms to a novel “oil diffusion & micelle reformation model” that represents the coupling to two pre-existing models. And the solubilization mass-transfer mathematical model demonstrated the solubilization mass-transfer coefficient is affected by the combination of surfactant and solubilized organic properties. This study advances the application of solubilization for chlorinated hydrocarbons using anionic-nonionic gemini surfactants in surfactant-enhanced aquifer remediation (SEAR) design.
Published Version
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