Injection of non-Newtonian dispersions of iron particles in porous media: modeling of clogging processes

In the context of groundwater remediation, an increasing interest was found towards nanoscale and microscale zero-valent iron particles (NZVI and MZVI, respectively). However, MZVI and NZVI are not stable when dispersed in water, due to fast aggregation and sedimentation. Consequently, the use of shear thinning solutions of green biopolymers have been recently studied as viscous carrier fluids for the delivery of MZVI and NZVI. In this work, co-funded by European Union project AQUAREHAB (FP7 - Grant Agreement Nr. 226565), a modeling approach is described to simulate the transport in porous media of nanoscale iron slurries, implemented in the E-MNM1D software, previously developed by the authors (www.polito.it/groundwater/software). The key aspects included in the E--MNM1D are clogging phenomena (i.e. reduction of porosity and permeability due to particles deposition), and the rheological properties of the carrier fluid (in this project, guar gum solution) for a correct estimate of pressure drops. Colloid transport is modeled with a dual-site (physico-chemical interactions plus straining) advection-dispersion-deposition equation. A general formulation for attachment/detachment dynamics is adopted. The influence of colloid transport on porosity, permeability, and fluid viscosity is explicitly embedded into the model through correlations from the literature, or derived on purpose. The shear-thinning behavior of the iron slurries is described with a modified Darcy law generalized to non Newtonian fluids. ions of MZVI and NZVI –based remediation, for the estimate of the radius of influence of the slurry injection.