Effects of granular size and flow rate on transport of silver nanoparticles in saturated porous media

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. © All Right Reserved.