Diesel contamination poses a serious threat to ecosystem and human health. This study proposes a novel method for simultaneous diesel removal and recovery from heavily diesel-contaminated soil by washing based on three-liquid-phase equilibria of diesel+2-butoxyethanol+water. This work covers both theoretical-cum-experimental explorations. For this brand-new ternary three-liquid-phase system (TPS), Ternary-Gibbs and Fish-Shaped phase diagrams were constructed through the phase behavior investigation to provide theoretical support for diesel removal/recovery. As the experiment demonstrated, the removal efficiency was up to 87.5 % for the contaminated soil with diesel content of 226,723 mg/kg, and the recovery rate reached 73.8 %. In addition, the TPS could also be used continuously during the washing process while avoiding solution purification, and the detached diesel would automatically float into the top phase without complicated separation. The mechanism of diesel removal was determined as the surface "stripping" effect based on ultralow interfacial tension, and the enhanced process involved "stripping+dissolution". The treated soil contained almost negligible organic solvent residue and was therefore appropriate for plant cultivation. The recovered diesel exhibited less variation from commercial diesel in composition and properties, possessing a higher potential for reuse. Moreover, this study also provided key insights into the residual mechanisms of recalcitrant hydrocarbons in the soil.
Keywords: Diesel recovery; Diesel-contaminated soil; Liquid-liquid-liquid equilibria system; Soil remediation; Ternary phase diagram.
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