Controlled Deposition of Particles in Porous Media for Effective Aquifer Nanoremediation

In this study, a model assisted strategy is developed to control the distribution of colloids in porous media in the framework of nanoremediation, an innovative environmental nanotechnology aimed at reclaiming contaminated aquifers. This approach is exemplified by the delivery of humic acid-stabilized iron oxide nanoparticles (FeOx), a typical reagent for in situ immobilization of heavy metals. By tuned sequential injections of FeOx suspensions and of solutions containing a destabilizing agent (i.e. calcium or magnesium), the two fronts, which advance at different rates, overlap at the target location (i.e., the central portion) of the porous systems. Here, the particles deposit and accumulate irreversibly, creating a reactive zone. An analytical expression predicting the position of the clustering zone in 1D systems is derived from first principles of advective-dispersive transport. Through this equation, the sequence and duration of the injection of the different solutions in the medium is assessed. The model robustness is demonstrated by its successful application to various systems, comprising the use of different sands or immobilizing cations, both in 1D and 2D geometries. The method represents an advancement in the control of nanomaterial fate in the environment, and could enhance nanoremediation making it an effective alternative to more conventional techniques.