Comprehensive treatment of oil-contaminated soils using CO2-Responsive O/W microemulsions

In exploration of petroleum resources, a considerable amount of soils are inevitably contaminated, leading to many long-term environmental impacts. However, the treatment of oil-contaminated soils to reduce the residual oil for safe disposal at low energy intensity is a challenging task. In this study, a CO2-responsive microemulsion was formulated to treat oil-contaminated soils effectively at ambient temperatures of low energy consumption. Such effective treatment reduced the oil level of the contaminated soils from ∼15 wt% to below the discharge limit of 1 wt%. Purging of CO2 through the spent microemulsions for 30 s caused a rapid dissociation of the superamphiphile in the microemulsions, leading to a complete phase separation with the cleaned soils settled to the bottom for safe disposal, followed by an aqueous phase in the middle for recycling and a value-added oil product on top. The rapid and deep cleaning of oil-contaminated soils was attributed to an ultra-low interfacial tension and high level solubilization of oily contaminants in the O/W microemulsions. Such approach leads to a zero-waste discharge operation of remediating oil-contaminated soils while recovering value-added oil. Compared with other treatment methods operated at high temperature and/or pressure conditions, treatment of oil-contaminated soils using CO2-responsive microemulsions is easier to reach the discharge limit of residual oil while operating at ambient temperatures without any expensive equipment or extreme working conditions, making this microemulsion method a promising candidate for commercial applications of treating oil-contaminated soils in the oil field.