In-situ petroleum hydrocarbons contaminated soils remediation by polymer enhanced surfactant flushing: Mechanistic investigation

Chemicals injection for in-situ remediation of contaminated soils has attracted great attention. Efficiency of this technology relies on various parameters. Among them, chemical formulation of flushing agents has a key role. In this study, synergistic effect of Sodium Dodecyl Sulfate (SDS) ionic surfactant and Xanthan Gum (XG) biopolymer on the emulsification and solubilization of two types of petroleum hydrocarbon pollutants was investigated. Interfacial tension (IFT) measurements, bottle tests, droplet size distributions determination, and visual fluid flow experiments at pore-scale were conducted to assess pollutants removal strength of the proposed polymer enhanced surfactant flushing strategy. Results showed that although SDS surfactant reduced the equilibrium IFT of system to appropriate low value (i.e. less than 3 mN/m), it was not able to form stable oil-in-water emulsions. Nevertheless, addition of XG biopolymer, with no remarkable effect on IFT, improved emulsions formation and stability. Fluid flow experiments showed that oil snap-off and emulsion division are essential mechanisms of in-situ emulsion formation. A significant amount of hydrocarbon pollutants remained in porous medium after injection of 10 pore volumes of SDS. While, smaller size emulsions, as well as better contaminants removal were achieved for SDS solution with 4000 ppm XG at much lower injected pore volumes.