An enhanced filtration model for the transport of nanoscale iron in aquifer systems.

In the field of remediation of contaminated aquifers the use of nanoscale zerovalent iron (NZVI) is one of the most interesting and promising technology. Nanoscale iron particles are characterized by tiny diameters (1-100 nm) and by specific surface areas that are up to a hundred times higher than millimetric iron, thus also their reactivity is much higher. These particles can be suspended in a slurry and directly injected into the source of contamination, overtaking most of the limitations of the more common permeable reactive barriers (PRBs). The iron nanoparticles behaviour in an aquifer system (i.e. saturated porous media) is significantly different from stable colloids one. Particles strongly tend to aggregate and depose on the solid matrix. In particular, aggregation of suspended particles and deposition on solid grains seem to be mainly due to magnetic interactions, which are not considered in the classic colloidal filtration theory. In this work an extension of the classical steady state clean bed filtration theory is proposed, based on a transient dual-phase advection-dispersion transport model. In order to account for the change of deposition rates over time and for straining, time dependent coefficients are included into the governing equation. The above mentioned model is implemented analytically and numerically and the resulting curves are fitted to experimental column tests data.