Influence of Soil Texture on Rate-Limited Micellar Solubilization

Observations from 1D soil column experiments are used to explore the factors influencing surfactant-enhanced solubilization of entrapped non-aqueous-phase liquids in sandy porous media. These experiments were designed to quantify the influence of porous medium properties and flow system parameters on the rate of contaminant removal. A 1% flushing solution of polyoxyethylene sorbitan monooleate (Witconol 2722) was employed to recover residual phase decane from a range of Ottawa sands. Deviations from local equilibrium conditions were observed in all experiments. For solution phase Darcy velocities ranging from 0.83 to 8.3 cm/h, maximum column effluent concentration levels were consistently <55% of the batch-measured equilibrium value. Column data were used to develop an empirical modified Sherwood correlation for the prediction of initial, pseudo steady-state, solubilization rates assuming a linear driving force mass transfer expression. This correlation incorporates the Reynolds number, the mean grain size, and the sand uniformity index. The adequacy of this correlation for the prediction of initial steady-state solubilization rates in other sandy media is demonstrated for a natural aquifer material. Results of this study suggest a similar dependence of mass transfer rates on system hydrodynamics and soil properties for both micellar solubilization and dissolution.