A novel solubilization of phenanthrene using Winsor I microemulsion-based sodium castor oil sulfate

Problems associated with polycyclic aromatic hydrocarbons (PAHs) contaminated site in environmental media have received increasing attention. Ex situ soil washing is commonly used for treating contaminated soils by separating the most contaminated fraction of the soil for disposal. Surfactant-enhanced soil washing is being considered with increasing frequency to actually achieve soil-contaminant separation. In this research, a novel solubilization of phenanthrene and extraction of phenanthrene from spiked soil by sodium castor oil sulfate (SCOS) microemulsion was presented and compared with the conventional surfactants, Triton X-100 (TX100), Tween 80 (TW80), Brij35, sodium dodecylbenzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS). Unlike conventional surfactants, SCOS forms stable microemulsion in water and thus behaves much like a separate bulk phase in concentrating organic solutes. The extent of solubility enhancement is linearly proportional to the concentration of SCOS microemulsion, in contrast with the effect of a conventional surfactant in which a sharp inflection occurs in the vicinity of the measured critical micelle concentration. SCOS microemulsion exhibits the largest mass solubilization ratio among the selected surface active agents (SAAs) in both soil-free system and soil-water system. The partitioning coefficients of phenanthrene between the emulsified phase and the aqueous phase, Kem, is slightly larger than those between the micellar pseudo phase and the aqueous phase, Kmc. The extraction experiments demonstrate high and fast desorption of phenanthrene from spiked soil by SCOS microemulsion perhaps due to its high solubilization capacity compared with the conventional surfactant solutions. The results show that SCOS could be an attractive alternative to synthetic surfactants in ex situ washing for PAH-contaminated soils.