Electrokinetics and zero valent iron nanoparticles: experimental and modeling of the transport in different porous media

In this chapter are presented both the experimental results of nZVI transport under electric fields, on mixtures of kaolin and glass beads to represent different porous media, and a generalized physicochemical and numerical model of this transport.

In the experiments, a low-level direct current was used to enhance the transport of poly(acrylic acid) sodium salt (PAA)-coated nZVI in a modified electrophoretic cell. The cell was equipped with internal auxiliary electrodes and a silver chloride reference electrode. The results showed that there were higher concentrations of iron across the test bed when the direct current was applied.

The model consists in the Nernst–Planck coupled system of equations, which accounts for the mass balance equation of ionic species in a fluid medium when diffusion and electromigration are considered in the ions transport process. In the case of the nZVI (with a negative charge), diffusion, and electrophoretic terms were taken into account. In all the cases, the electroosmotic flow was included in the equation. The use of electrical current to transport the nanoparticles prevents or hinders the nZVI particle aggregation, increasing their mobility. However, opposing directions of electrophoretic transport of negatively charged particles and the electroosmotic advection still produces low nZVI transport. To enhance the transport in soils with high electroosmotic conductivities, we suggest neutrally charged and stabilized nanoparticles that could be transported mainly by electroosmotic advection.