Stability and Transportation of Iron Oxide Nanoparticles in Subsurface Water and Soil

Iron oxide nanoparticles are utilised in a broad range of applications (magnetic data storage, biosensing, drug delivery, treatment and remediation of contaminated soil and groundwater); causing noticeable quantities of iron oxide nanoparticles to be released into the environment. In this study, aggregation and stability of iron oxide nanoparticles in water were investigated within the range of pH 3 – pH 9 at a constant concentration of iron oxide nanoparticles and humic acid. The pH of the solution was selected to be continuously monitored at pH 7 to investigate the transportation and deposition behaviour of iron oxide nanoparticles in porous media at different velocities. It was found that iron oxide nanoparticles were aggregated and settle down as settled particles at low pH (pH 3 – pH 5). Iron oxide nanoparticles were stable, mobile and transported at a high pH, which is the pH range of natural water (pH 6.5 – pH 8.5). Iron oxide nanoparticles were strongly attached to the silica sand at natural water velocity in porous media, which is 2.93 ml min-1. Overall, the presence of humic acid in aquifers and porous media, the pH range of natural water (pH 6.5 – pH 8.5) and the slow speed (2.93 ml min-1) of water are expected to be a key factor that enhances the stability and mobility of iron oxide nanoparticles in natural water and porous media.