Performance of ethanol transformable microemulsions and remediation of salinized oil - contaminated soils

The effective and efficient separation of oil pollutants solubilized in microemulsions (MEs) represents a significant challenge in the remediation of oil-contaminated soils (OS). In this study, phase-transformable W/O microemulsions (W/O-MEs) were configured for efficient elution of salinized OS. Meanwhile, the phase transformation mechanism was demonstrated by investigating of the effect of ethanol concentration on microemulsions phase behavior. Firstly, W/O-MEs with an oil removal efficiency (Re) of 90.2 wt% were formulated through an analysis of the phase distribution and elution effect. Furthermore, the impact of ethanol concentration on microemulsion phase behavior was investigated in depth using dynamic light scattering (DLS), interfacial tension (IFT), and UV-visible spectroscopy. The findings substantiated that ethanol can facilitate the transformation of W/O-MEs (Winsor II) to O/W-MEs (Winsor I), thereby enhancing oil Re and separation capability. Moreover, a microemulsion elution route for salinized OS was devised on the basis of the principles of continuity and recycling in industrial cleaning processes. The results demonstrated that the ethanol and water facilitated the desorption of residues, including residual oils, surfactants, salts and alkalis, achieving an oil Re of 97.2 wt%. In particular, the recovered ethanol and water can be recycled for microemulsion preparation. Finally, the efficiency and feasibility of the microemulsion elution process is evaluated using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), fluorescence imaging, and contact angle (CA) analysis. This study provides theoretical guidance for the application of microemulsion elution in the remediation of industrial OS.