Abstract：
The mobilization and redistribution of organic contaminants in groundwater is the basis and key to explore its dynamic evolution and appropriate remediation. The naturally occurring diametrical temperature gradient during freezing and thawing cycle leads to distinct behaviors of organic contaminants in groundwater. In this study, the pore-scale distribution of diesel oil in the porous media was quantitatively divided into capillary fluid state (CFS) and free fluid state (FFS) based on multiphase flow dynamics, employing low-field nuclear magnetic resonance (LF-NMR) technology. The pore-scale distribution of diesel oil depends not only on the freezing and thawing cycle but also on the temperature gradient according to LF-NMR results. The content of diesel oil in the CFS generally increases with a positive temperature gradient (e.g. freezing) compared to a negative temperature gradient (e.g. thawing), while the content of diesel oil in the FFS generally decreases. This dependence of the temperature gradient on pore-scale distribution of the diesel oil is positively correlated with the particle size of the porous medium. Furthermore, the pore-scale distribution of the diesel oil during the freezing and thawing cycle is influenced by the kinematic viscosity of the diesel oil. There is an exponential relationship between the diesel oil content and the kinematic viscosity, independent of the freezing or thawing process. During the freezing process, the diesel oil migrates from FFS to CFS, while this migration is reversed during the thawing process. The reverse migration of the diesel oil between the freezing and thawing processes leads to a spatial redistribution of the diesel oil, which is controlled by both the fluid energy and the capillary force. The present work provide meaningful guidance for the remediation of groundwater contamination in cold regions.
摘要：
地下水中有机污染物的迁移和再分配是探索其动态演化和适当修复的基础和关键。冻融循环过程中自然发生的直径温度梯度导致地下水中有机污染物的不同行为。在这项研究中,基于多相流动力学将多孔介质中柴油的孔隙尺度分布定量划分为毛细管流体态(CFS)和自由流体态(FFS),采用低场核磁共振（LF-NMR）技术。根据LF-NMR结果，柴油的孔尺度分布不仅取决于冻融循环，还取决于温度梯度。与负温度梯度（例如解冻）相比，CFS中的柴油含量通常随着正温度梯度（例如冻结）而增加，而FFS中柴油的含量通常会降低。温度梯度对柴油孔隙尺度分布的这种依赖性与多孔介质的粒径正相关。此外，冻融循环过程中柴油的孔隙尺度分布受柴油运动粘度的影响。柴油含量与运动粘度之间存在指数关系，独立于冷冻或解冻过程。在冻结过程中,柴油从FFS迁移到CFS，而这种迁移在解冻过程中是相反的。柴油在冷冻和解冻过程之间的反向迁移导致柴油的空间再分配，这是由流体能量和毛细管力控制。本工作为寒区地下水污染治理提供了有意义的指导。
