Modeling the Transport and Retention of Poly(acrylic Acid) Supported Magnetite Nanoparticles in the Subsurface

In this study we investigate the impact of input concentration on the mobility of poly(acrylic acid) supported magnetite nanoparticles in saturated porous media. Transport experiments were conducted in a water-saturated sand-packed column for nanoparticle suspensions with total Fe concentrations ranging from 100 to 600 mg/L. Particle size analysis of the synthesized nanoparticle solutions showed that PAA provides good size stability for Fe concentrations as low as about 1 mg/L. 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.