Abstract
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.
Highlights
Nanoremediation is an innovative technology employed for the remediation of contaminated aquifers[1,2]
An innovative single point injection strategy was proposed and applied to control the fate of humic acid coated goethite nanoparticles, an effective reagent for the remediation of aquifer systems contaminated by heavy metals
The proposed strategy allowed the creation of reactive zones in the center of 1D and 2D experimental setups with a single injection point or well
Summary
Nanoremediation is an innovative technology employed for the remediation of contaminated aquifers[1,2] It involves subsurface injection of a reactive suspension of engineered nanoparticles for in situ degradation, transformation, or immobilization of pollutants[3,4,5]. Transport tests previously conducted with these suspensions showed that particles are highly mobile under conditions typically found in subsurface environments[12]. In field applications, this could result in an undesirable distribution of the particles, which would continue their migration in the aquifer, bypassing the polluted areas and potentially representing a secondary source of contamination for humans and the environment. Nanoparticles need to be precisely delivered to the target zone and to be stable over time, to extend the lifetime of the remediation and to prevent their uncontrolled migration
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