Modeling of nanoparticle fate and transport in saturated porous media

In recent years nanoparticles have been proposed for numerous applications including in-situ groundwater remediation. A critical step for the development of such a technology is the effective deliverability of the nanoparticles suspension to the zone of contamination. Because of their relatively high surface energy, bare nanoparticles may undergo significant aggregation and deposition within the porous media, thereby limiting its transport. To enhance the mobility of engineered nanoparticle, surface coating with various materials have been considered. This paper reviews the state of the art understanding of engineered nanomaterial fate and transport processes and the factors influencing nanoparticle transport in porous media. In particle we examine the effect of nanoparticle concentration on its mobility. The nanoparticle considered in this study is Poly(Acrylic Acid) (PAA) supported magnetite (Fe₂O₃). The transport experiments were conducted in a water-saturated sand-packed column for nanoparticle suspensions. Particle size analysis of the synthesized nanoparticle solutions showed that PAA provides good size stability. Time-moment analysis of the nanoparticle breakthrough curves, on the other hand, revealed that nanoparticles mass recovery from the column decreased consistently with dilution, with greater attenuation, sharper fronts and longer tails compared to that of the tracer. To further interpret the experimental results, a nanoparticle transport model that accounts for deposition/detachment kinetics was developed. The best agreement between the observed breakthrough curves and model simulations was obtained using a kinetic time-dependent deposition term with finite deposition capacity and a kinetic detachment term. The model results suggest that the decrease in mass recovery with decrease in input particle concentration may be due to time-dependent blocking that hinders further deposition. The implications of these results on the use of engineered nanoparticles for groundwater remediation applications are discussed.