Preparation and performance evaluation of a novel Tween 80-based microemulsion system for the remediation of petroleum hydrocarbon-contaminated soil using soil washing test.

Soil contamination by petroleum hydrocarbons represents a significant threat to environmental and ecological security. Due to their superior solubilization and emulsification capabilities, microemulsion systems have emerged as a highly promising remediation agent for petroleum hydrocarbon-contaminated soils. In this study, a microemulsion system was formulated with Tween 80 (surfactant), n-butanol (cosurfactant), and olive oil (oil phase). The phase behavior, key physicochemical properties, and soil remediation performance of the system were systematically investigated. The Shah titration method and alcohol scanning test were used to determine the optimal component ratios, while key physicochemical properties were characterized (such as surface tension, viscosity, electrical conductivity, HLB value, particle size and stability). Soil column flushing tests were conducted to compare the total petroleum hydrocarbon (TPH) removal efficiency of the microemulsions with Tween 80 solution and distilled water. The results showed that when the mass ratio of Tween 80 to n-butanol was 1:2, the microemulsion had the best stability and the largest phase region. As the content of n-butanol increased, the system underwent phase transitions from Winsor I (oil-in-water) and then to Winsor Ⅲ (bicontinuous) to Winsor II (water-in-oil). An oil content in the range of 5%-10% was found to be most suitable for microemulsion formation and soil flushing. Soil column tests demonstrated that microemulsions achieved TPH removal efficiencies of over 96%, significantly superior to Tween 80 solution and distilled water. This study provides a feasible and efficient microemulsion technology, offering a reference for the remediation of petroleum hydrocarbon-contaminated soil.