Simulation of magnetite nanoparticle mobility in a heterogeneous flow cell

Abstract

Engineered nanomaterials have been proposed for a range of subsurface applications including groundwater remediation, treatment of contaminated soils, and characterization of flow. The ability to accurately predict nanoparticle (NP) mobility in the environment is critical for assessing NP performance and designing subsurface applications. The objective of this study was to evaluate the ability of a numerical simulator that accounts for the influence of varying electrolyte and NP concentrations to predict experimental observations of polymer-coated magnetite nanoparticle (nMag) transport and retention in a heterogeneous, multi-dimensional flow cell (0.64 m length × 0.38 m height × 1.4 cm internal thickness, referred to as “2.5-dimensional” or “2.5D” due to the internal thickness width). A series of column experiments was performed to independently determine model input parameters, including the maximum NP retention capacity and attachment rate. Localized injection of nMag into the heterogeneous flow cell demonstrated preferential flow around a lower permeability lens and the downward migration of higher density nMag suspensions. Numerical simulations successfully captured the observed flow path of the nMag pulse injections, and provided close fits to spatially distributed aqueous and solid-phase nMag measurements obtained within the heterogeneous flow field. Experimental and modeling results demonstrated that relatively small contrasts in fluid density (e.g., 0.01 g mL⁻¹) can result in flow instabilities and downward migration of nMag. This work provides the first direct comparison between model simulations and experimental observations of NP transport and retention in a 2.5D heterogeneous flow domain and demonstrates the importance of accounting for relevant physical and chemical properties in order to accurately describe NP fate and transport.