RESUMEN
A novel surfactant-free microemulsion (SFME) system was proposed in this study, and applied in the crude oil removal and recovery from oily sludge (OS). Based on an investigation of the SFME phase behavior and solution properties, a complete ternary phase diagram was constructed. The SFME with three-liquid phase equilibrium (Winsor III type) was selected for the treatment of OS to achieve simultaneous efficient removal (up to 95.1 %) and recovery (up to 83.2 %) of crude oil. The SFME could be reused continuously for OS treatment without purification. The removal efficiency could still keep >75.9 % after 5 times of reuse, showing high reusability. The detached crude oil could be automatically recovered based on the phase equilibrium principle without additional separation. In the washing experiments, single-factor and multi-factor orthogonal tests were applied to investigate the effects of different experimental conditions on oil removal efficiency and determine the optimal experimental scheme. The treated OS was sufficiently decontaminated according to the morphology, composition, and properties analysis by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and contact angle. The composition of the recovered crude oil was identical to that of commercial crude oil according to gas chromatography-mass spectrometry analysis, showing a high recovery value. The kinetic analysis revealed that crude oil desorption experienced three main stages: membrane diffusion, intra-particle diffusion and surface desorption, and identified the chemisorption was the main interaction between the oil-soil. Finally, the mechanism of SFME action was assessed for dissolution and activation based on ultra-low IFT.