Simultaneous aggregation and oxidation of nZVI in Rushton equipped agitated vessel. Experimental and modelling

The aim of this work was to investigate the aggregation of metallic iron nanoparticles in a Rushton equipped agitated vessel open at the atmosphere. The particles were synthetized using oxygen-free reagent solutions and subsequently were suspended in water in an open lab-scale agitated vessel. The particle size distribution, zeta-potential, pH and Fe(0) content were monitored over the time, up to the complete oxidation of the particles. During the oxidation process, the particle size distribution varied from a unimodal to a bi-modal and tri-modal distribution, clearly showing the generation of aggregates, characterized by irreversible bonds among the particles. The aggregation phenomenon was described by a simplified model, whereas the oxidation process was modelled according to the classical shrinking core model. The regressed dissolved oxygen diffusion coefficient, D p = 6.79 × 10 −13 m 2 s −1 was in line with the theoretical expectations, as well as the intrinsic kinetic constant rate, k c = 2.83 × 10 −7 m s −1 . As expected, the oxidation process was found to be a diffusion-controlled reaction, according to the low value of the second Damkohler number (equal to 7.5 × 10 −3 ).