Nanoparticles in environmental applications. First laboratory assessments of nanoparticles mobility in porous media

Nanoparticles, due to small size and capacity to remain in suspension, are very efficient to remediate aquifers contaminated. However, due to their small size, while nanoparticles are traveling through porous media, they can rapidly aggregate, causing their settling and deposition. These phenomena produce issues for in situ remediation, such as the loss in chemical reactivity and the unknowing about the nanoparticles distribution when they are injected in situ. Laboratory experiment has been carried out with groundwater flow in a two-dimensional laboratory-scale tank to assess the nanoparticles mobility and redistribution processes. Zerovalent iron nanoparticles (nZVI), Nanofer 25S, has been used and glass beads have been utilized as porous medium. The set of the laboratory experiment also included the use of a digital camera for the acquisition of the images. An image analysis procedure has been used to assess the saturation distribution of nanoparticles during infiltration and redistribution processes. This image analysis method allows the mapping of nanoparticles distribution through the glass beads, used as porous medium, by the monitoring of nanoparticles saturation frequency variation. The system consists of two distinct phases: nZVI and water, neglecting the solid phase. Saturation is defined as the ratio of the volume occupied by the nanoparticles and the pore volume. By the image analysis, the information returned by the pixel value must assess the presence of nZVI (0) or its absence (255). Saturation is calculated by implementing a regular grid, with dimensions of cells proportional to the number of pixels contained. It takes values range from 0, no pixels with nanoparticles, and 1, pixels with only nanoparticles. This laboratory experiment, linked to image analysis, represents a first phase of the study to analyze the distribution of nanoparticles, if injected into a porous medium.