Enhanced diesel removal from contaminated soil: A coupled approach of negative-pressure extraction and subzero-temperature-induced migration

To reduce the energy demand of conventional high-temperature thermal desorption and related technologies for remediating organic-contaminated soils, and to elucidate the evolution of liquid-phase contaminants in soils subjected to coupled temperature–pressure fields, this study develops a remediation process that couples negative-pressure extraction with subzero-temperature-induced migration of diesel in porous media. The method exploits the depression of liquid boiling points under reduced pressure and the acceleration of fluid transport driven by temperature gradients in porous media. Saturated diesel-contaminated soils with different initial dry densities (ρ_d) were treated under low-temperature negative-pressure conditions, and diesel removal tests were conducted. The results show that, for all ρ_d considered, the removal efficiency exhibits a characteristic three-stage temporal evolution. Under subzero temperature and negative pressure, the residual diesel mass fraction in the samples stabilizes at approximately 10–12%, approaching the residual liquid content of the soil and indicating that late-stage removal is controlled by high-boiling fractions and strong sorption. Post-test energy-dispersive X-ray spectroscopy further confirms that the carbon content in the soil decreases from about 35% to 13%, demonstrating a substantial reduction in organic contamination. Overall, the proposed approach achieves stepwise, high-efficiency removal of high-boiling organic pollutants at moderate to low energy input, and provides quantitative criteria for the scale-up design and energy optimization of subzero negative-pressure remediation processes.