National Engineering Research Center for Facilities Agriculture, Institute of Modern Agricultural Science and Engineering, Tongji University , Shanghai 200092, China.
Environ Sci Technol. 2013 Aug 6;47(15):8256-64. doi: 10.1021/es400288c. Epub 2013 Jul 24.
The prediction of colloid transport in unsaturated porous media in the presence of large energy barrier is hampered by scant information of the proportional retention by straining and attractive interactions at surface energy minima. This study aims to fill this gap by performing saturated and unsaturated column experiments in which colloid pulses were added at various ionic strengths (ISs) from 0.1 to 50 mM. Subsequent flushing with deionized water released colloids held at the secondary minimum. Next, destruction of the column freed colloids held by straining. Colloids not recovered at the end of the experiment were quantified as retained at the primary minimum. Results showed that net colloid retention increased with IS and was independent of saturation degree under identical IS and Darcian velocity. Attachment rates were greater in unsaturated columns, despite an over 3-fold increase in pore water velocity relative to saturated columns, because additional retention at the readily available air-associated interfaces (e.g., the air-water-solid [AWS] interfaces) is highly efficient. Complementary visual data showed heavy retention at the AWS interfaces. Retention by secondary minima ranged between 8% and 46% as IS increased, and was greater for saturated conditions. Straining accounted for an average of 57% of the retained colloids with insignificant differences among the treatments. Finally, retention by primary minima ranged between 14% and 35% with increasing IS, and was greater for unsaturated conditions due to capillary pinning.
在存在大能量障碍的情况下，预测非饱和多孔介质中的胶体运移受到限制，因为在表面能最小处的应变和吸引力相互作用的比例保留信息很少。本研究旨在通过进行饱和和非饱和柱实验来填补这一空白，在实验中，将胶体脉冲以 0.1 至 50mM 的各种离子强度（IS）添加到不同位置。随后用去离子水冲洗，将胶体从次级最小处释放出来。接下来，破坏柱子可以释放被应变固定的胶体。在实验结束时未回收的胶体被定量为保留在初级最小处。结果表明，净胶体保留量随 IS 增加而增加，在相同 IS 和达西速度下与饱和度无关。尽管相对于饱和柱，孔隙水速度增加了 3 倍以上，但非饱和柱中的附着速率更大，因为在易于获得的空气相关界面（例如空气-水-固界面）上的额外保留效率很高。补充的可视化数据显示在 AWS 界面上有大量的保留。随着 IS 的增加，次级最小处的保留范围在 8%至 46%之间，饱和条件下的保留更大。应变平均占保留胶体的 57%，各处理之间差异不显著。最后，随着 IS 的增加，初级最小处的保留范围在 14%至 35%之间，非饱和条件下的保留更大，这是由于毛细固定。
