Surfactant-induced interactions and hydraulic conductivity changes in soil

The use of surfactants for the removal of hydrophobic organics from soil by in situ flushing techniques shows great potential. Sodium dodecylsulfate (SDS), an anionic surfactant, is often chosen for soil flushing processes. The relationship between the aqueous equilibrium concentration and the loss of SDS from solution with and without the presence of an electrolyte (NaCl) was established using batch and column experiments. The results indicate that the maximum amount of SDS adsorption and precipitation was observed when the concentration of SDS was in the region of the critical micelle concentration (CMC), and this amount was even higher in the presence of the electrolyte. The interactions such as adsorption, cation exchange between soil and Na + leading to the release of Ca 2+ and subsequent precipitation of Ca(DS) 2 are discussed. Column experiments were also conducted to investigate the change in hydraulic conductivity due to the interactions between soil and surfactant. Injection of surfactants to a soil matrix decreases the hydraulic conductivity, and this change is related to the clay content of the soil, the type and concentration of the surfactant, and the presence of electrolyte. The mechanisms which could be responsible for the change in hydraulic conductivity are clay expansion, sodium dispersion, fine particle mobilization and precipitation of calcium and magnesium dodecylsulfate. For the soil used in this experiment, the precipitation of divalent salts of surfactants appears to be the primary reason for the reduction of hydraulic conductivity.