Abstract:

Being one of the most widely used engineered nanomaterials well known for its ecological toxicity, silver nanoparticles have big potential to arise severe environmental problems on entry groundwater environment. Unfortunately, thus far how environmental factors may control the mobility of silver nanparticles remain unclear. In this study, column experiments were employed to investigate the interplay of flow rate (1 and 2 ml·min^-1) and granular size characteristics (glass beads of 0.605, 0.115 mm, and the mixture of the two) on the transport of nano silver in saturated porous media. The results suggested that transport of silver nanoparticles in the matrix of large grains (0.605 mm) was controlled mainly by deposition while that in the other two matrix (0.115 mm and the mixture) was controlled by both the deposition and straining processes. For the matrix of the mixed grains, straining was mainly controlled by the fraction of the grains with lower size. Increasing flow rate reduced deposition of the nanoparticles in the matrix with large grains, while for the other two matrices (with small grains or mixed grains), increasing flow rate reduced not only the deposition rate but also the straining rate, resulting in a more significant reduction in particle attenuation by the porous medium. Moreover, the intensified size exclusion effect accompanied by the rising flow rate can also increase the transport velocity of the silver nanoparticles in the matrix of small and mixed grains. These findings were critical to understanding the movement and distribution of nanomaterials in dynamic and complex groundwater environment.

Key words: silver nanoparticle, transport, saturated porous media, flow rate, granular size

摘要：

纳米银（AgNP）作为应用最广、生态毒性最强的工程纳米材料之一，一旦进入地下水环境，将引发环境问题。目前，环境因素对纳米银在地下水环境中运移的影响机理尚不清楚。通过室内柱实验，研究了流速（1、2 ml·min^-1）和介质粒径特征（0.605、0.115 mm以及混合粒径的玻璃珠）对纳米银在饱和多孔介质中迁移的影响。研究结果表明纳米银在粒径较大（0.605 mm）的介质中的迁移主要受吸附沉降控制；在小粒径介质中（0.115 mm以及混合粒径玻璃珠），迁移过程同时受吸附沉降和阻塞沉降两种机理的控制，且阻塞效应主要受小粒径部分介质控制。水流速度提高能降低大粒径介质中纳米银颗粒的沉降效率，从而提高其迁移能力。而对于小粒径介质和混合粒径介质，流速提高除了降低纳米银的沉降效率，还能降低阻塞效应和促进尺寸排除效应，不但能更显著地降低纳米银在介质中的衰减，还能提高纳米银在介质中的穿透速度。研究成果对于理解复杂的场地条件下纳米材料的迁移分布动态具有理论价值。

关键词: 纳米银, 迁移, 饱和多孔介质, 流速, 粒径分布