SURFACTANT ENHANCED MOBILIZATION OF MINERAL OIL WITHIN POROUS MEDIA

摘要

The remediation of non-aqueous phase liquids (NAPL) using conventional aquifer treatment technologies is limited by the low solubility of NAPL. Surfactants can promote the enhanced removal of NAPL through mobilization, a mechanism that relies on the reduction of interfacial tension (IFT) at the flushing solution / NAPL interface. The conditions governing mobilization can be represented by the total trapping number (N_T), a dimensionless quantity relating viscous and buoyancy forces to the capillary forces trapping the NAPL residual. Column studies were conducted with dilute Triton X-100 solutions delivered through Ottawa sand spiked with light white mineral oil. At the higher flow rate, the surfactant solutions yielded N_T values greater than the critical N_T necessary to initiate mobilization, thereby promoting greater NAPL recovery as IFT dropped. While the critical N_T was not surpassed at the lower flow rate, variations in mineral oil recovery during flushing clearly indicate a surfactant effect. The surfactant-induced enhancement and retardation of NAPL removal at the lower flow rate both highlight the limitations of the N_T approach. For systems where free product NAPL is present, the total trapping number approach requires further refinement to define its applicability as an indicator for NAPL mobilization.