Transport of carboxymethyl cellulose stabilized iron nanoparticles in porous media: column experiments and modeling.

Carboxymethyl cellulose (CMC) can facilitate in situ delivery of zero-valent iron (ZVI) nanoparticles in contaminated aquifer. This work investigated transport of CMC-stabilized ZVI nanoparticles (CMC-Fe) using column breakthrough experiments and model simulations. The nanoparticles (18.1+/-2.5 nm) were transportable through four saturated model porous media: coarse and fine glass beads, clean sand, and sandy soil. The transport data were interpreted using both classical filtration theory and a modified convection-dispersion equation with a first-order removal rate law. At full breakthrough, a constant concentration plateau (Ce/C0) was reached, ranging from 0.99 for the glass beads to 0.69 for the soil. While Brownian diffusion was the predominant mechanism for particle removal in all cases, gravitational sedimentation also played an important role, accounting for 30% of the overall single-collector contact efficiency for the coarse glass beads and 6.7% for the soil. The attachment efficiency for CMC-Fe was found to be 1-2 orders of magnitude lower than reported for ZVI nanoparticles stabilized with other commercial polymers. The particle removal and travel distance are strongly dependent on interstitial flow velocity, but only modestly affected by up to 40 mM of calcium. Simulation results indicate that once delivered, 99% of the nanoparticles will be removed by the soil matrix within 16 cm at a groundwater flow velocity of 0.1 m/day, but may travel over 146 m at flow velocity of 61 m/day.