Transport behaviour of different metal-based nanoparticles through natural sediment in the presence of humic acid and under the groundwater condition

Abstract

The production of nanoparticles (NPs) has increased significantly, given that they have numerous commercial and medical applications. There might have some risk associated with the release of these NPs in the environment. To assess the possible risk of releases of NPs in the groundwater, it is important to evaluate the fate and transport behaviour of NPs through porous media. The objective of this study is, therefore, to evaluate the transport behaviour of widely used NPs [i.e., silver (Ag), iron oxide (FexOy), titanium dioxide (TiO2) and zinc oxide (ZnO)] through porous media in the presence and/or absence of organic matter [i.e., humic acid (HA)] under controlled de-ionized and natural groundwater condition. To achieve the objective, first, the detailed characterizations of NPs are carried out in the presence and absence of HA. Column transport experiments were performed using a 1-D sand-packed column. Different NPs were injected from one end of the column with a flow rate of 0.0054 cm/sec. The result suggests that nAg, nTiO2, and nZnO particles are colloidal stable in the suspension, while nFexOy particles tend to aggregate and settle down very rapidly. However, in the presence of HA, the colloidal stability of nFexOy in the suspension increases significantly. Evaluation of transport behaviour of different metal NPs suggests that a high amount of nFexOy (C/C0=0.01) and nZnO (C/C0=0.09) particles are retained in the porous media. However, in the presence of HA, the transport efficiency of nFexOy (C/C0=0.64) increases significantly. The extensively high amount of nAg and nTiO2 particles are transported in the absence/presence of HA. The surface charge of particles and thus the interaction energy between the NPs and the sand is the main factor controlling the deposition of NPs. Overall, it could be stated that there is a risk of migration of nAg and nTiO2 particles irrespective of the presence of organic matter or of nFexOy particles in the presence of organic matter through the aquifer porous media. However, in the natural groundwater system, when the different ion is present, the extent of transport of NPs is expected to be less, and the risk associated with releasing of NPs in the groundwater would be comparatively low than that is predicted under the controlled de-ionized water condition. However, the nTiO2 particles always have a high risk of release into the groundwater.