Institute for a Secure and Sustainable Environment, Department of Biosystems Engineering and Soil Science, The University of Tennessee, Knoxville, TN 37996-4134, USA.
Water Res. 2010 Feb;44(4):1270-8. doi: 10.1016/j.watres.2009.12.012. Epub 2009 Dec 23.
Transport of colloids with transient wetting fronts represents an important mechanism of contaminant migration in the vadose zone. The work presented here used steady-state saturated and transient unsaturated flow columns to evaluate the transport of a fluorescent latex microsphere (980 nm in diameter) with capillary wetting fronts of different solution surface tensions and ionic strengths. The saturated transport experiments demonstrated that decreasing solution surface tension and ionic strength decreased colloid deposition at the solid-liquid interface and increased colloid recovery in the column effluent. The effect of solution surface tension on colloid transport and deposition was greater at lower ionic strength, suggesting an interaction between these two factors. Under transient unsaturated flow conditions, the number of colloids retained in sand decreased exponentially with travel distance through the porous media. However, lowering the solution surface tension and ionic strength resulted in a more even distribution of colloids along the column. The measured zeta potentials of colloids in different solutions suggest that both lowering surface tension and ionic strength would enhance the electrostatic repulsion between colloid and sand. The experimental results revealed that the effects are nonlinear, implying the possible existence of critical threshold values, beyond which the effects were not significant. In addition, colloid migration slowed down as solution surface tension decreased due to reduction of capillary forces that drove liquid movement.
带瞬态润湿锋的胶体运移代表了包气带中污染物迁移的一个重要机制。本文使用稳态饱和和瞬态非饱和流柱来评估具有不同溶液表面张力和离子强度的毛细润湿锋的荧光乳胶微球（直径 980nm）的运移。饱和运移实验表明，降低溶液表面张力和离子强度会减少固-液界面处胶体的沉积，并增加柱出水中胶体的回收。在较低离子强度下，溶液表面张力对胶体运移和沉积的影响更大，表明这两个因素之间存在相互作用。在非饱和瞬态流条件下，胶体在多孔介质中随距离迁移的数量呈指数级减少。然而，降低溶液表面张力和离子强度会导致胶体在柱内更均匀地分布。不同溶液中胶体的测量 ζ 电位表明，降低表面张力和离子强度都会增强胶体和沙子之间的静电排斥。实验结果表明，这些影响是非线性的，这意味着可能存在临界阈值，超过该阈值影响就不显著了。此外，由于驱动液体运动的毛细力减小，胶体迁移随着溶液表面张力的降低而减缓。
