Colloid Retention in Unsaturated Porous Media due to Capillary Forces

胶体运移是污染物通过包气带向地下水迁移的重要机制。然而，对非饱和土壤中胶体运移的直接观测通常是有限的。因此，对于气相对胶体保留的影响，已经提出了不同的和相互冲突的胶体传输机制，到目前为止几乎没有预测能力。提出了非饱和天然砂中胶体运动和滞留的孔隙尺度可视化研究。这些观察，加上突破性的测量，将使我们能够更好地了解非饱和介质中胶体传输的实际机制。我们的假设是，毛细管力决定了在非饱和多孔介质中空气-水和水-固界面相互接近的薄水膜中胶体保持和释放的独特特征。我们将研究界面相互作用能的性质和大小，通过改变多孔介质的性质，如表面粗糙度和胶体性质，如何导致毛细管力依赖的保留行为发生可观察和可预测的变化，包括水的半月面接触角、在空气-水-固体界面的保留程度和位置；使用亮场显微镜和共焦扫描激光显微镜获得的图像的三维重建将被数字化分析，并用于量化胶体的移动和保留速度。这些实验结果将被用来测试和量化控制胶体在非饱和多孔介质中保留和迁移的机制。最近的经验证实，在环境监管和评估领域，胶体迁移在地下水污染中的作用通常被忽视。这项研究将提高对微米级胶体在非饱和水文系统中如何运动的认识，从而有助于改进模型，以便能够更准确地预测地下水污染可能发生的条件。

Colloid transport is an important mechanism in the movement of contaminants through the vadose zone to groundwater. However, direct observations of colloid transport in unsaturated soils have typically been limited. As a result, differing and conflicting colloid transport mechanisms have been proposed for the effects that the air phase plays on the retention of colloids, with little predictive ability to date. Proposed are pore-scale visualization studies of colloid movement and retention in unsaturated natural sand. These observations, coupled with breakthrough measurements, will allow greater understanding of the actual mechanisms governing colloidal transport in unsaturated media. Our hypothesis is that capillary forces determine the unique features of colloid retention and release in the thin water films where the air-water and water-solid interfaces closely approach each other in unsaturated porous media. We will investigate how the nature and magnitude of interfacial interaction energies through changes in properties of both the porous media such as surface roughness and the colloid properties will result in observable and predictable changes in capillary force-dependent retention behavior including water meniscus contact angle, extent and location of retention at the air-water-solid interface; 3 D reconstructions of images obtained using bright-field microscopy and confocal scanning laser microscopy will be analyzed digitally and used to quantify the movement and retention, rates of colloids. These experimental results will then be used to test and quantify the mechanisms that governing colloid retention and transport in unsaturated porous media.Recent experience confirms that the role of colloidal transport in groundwater contamination is typically ignored in the environmental regulatory and assessment sphere. The research will improve the knowledge on how micrometer-size colloids move in unsaturated hydrological systems and thereby will help improve models in order to make possible more accurate predictions of conditions under which groundwater contamination can take place.