Investigating the transport and colloidal behavior of FeO nanoparticles in aqueous and porous media under varying solution chemistry parameters.

The possible adverse effects of engineered iron oxide nanoparticles, especially magnetite (FeO NP), on human health and the environment, have raised concerns about their transport and behavior in soil and water systems. Accumulating these NPs in the environment can substantially affect soil and water quality and the well-being of aquatic and terrestrial organisms. Therefore, it is essential to examine the factors that affect FeO NP transportation and behavior in soil and water systems to determine their possible environmental fate. In this work, experiments were conducted in aqueous and porous media using an environmentally relevant range of pH (5, 7, 9), ionic strength (IS) (10, 50, 100 mM), and humic acid (HA) (0.1, 1, 10 mg L) concentrations. FeO NPs exhibited severe colloidal instability at pH 7 (⁓ = pH) and showed an improvement in apparent colloidal stability at pH 5 and 9 in aquatic and terrestrial environments. HA in the background solutions promoted the overall transport of FeO NPs by enhancing the colloidal stability. The increased ionic strength in aqueous media hindered the transport by electron double-layer compression and electrostatic repulsion; however, in porous media, the transport was hindered by ionic compression. Furthermore, the transport behavior of FeO NPs was investigated in different natural waters such as rivers, lakes, taps, and groundwater. The interaction energy pattern in aquatic systems was estimated using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. This study showed the effects of various physical-chemical conditions on FeO NP transport in aqueous and porous (sand) media.