A model for the removal of Cr(VI) in water by nanoscale zero-valent iron: quantifying the reaction process and calculating the electron efficiency

Synergistic Removal of Cr(VI) with Stable Nanozerovalent Iron Particles and Ultrasound Assistance in the Presence of Organic Additives

“…The mechanism of Cr(VI) removal by nZVI (in the absence of CAs and US, pathway (III)) may comprise three distinct processes according to recent works: ,, (1) Cr(VI) adsorption onto the external nZVI surface, (2) Cr(VI) reduction to Cr(III), facilitated by the transfer of electrons from nZVI and/or Fe(II) species, and (3) mass transport processes resulting in the precipitation or coprecipitation of Cr(III) and Fe(III) hydroxides. Although the detailed mechanism is still controversial, it is generally accepted that Cr(VI) is reduced to Cr(III); and correspondingly, Fe 0 is oxidized to Fe 2+ (eq ) and/or Fe 3+ (eq ), although the Fe 2+ generated in eq would be rapidly oxidized to Fe(III) by Cr(VI) (eq and pathway (IV)). ,,, Indeed, at 180 min of reaction, almost identical Cr(VI) removals (0.26 and 0.18 mM for Cit and EDTA, respectively, Figure ) and Fe T in solution (0.29 and 0.16 mM for Cit and EDTA, respectively, Figure ) were obtained for the experiments with NSTAR and CAs under US, reflecting an 1:1 Cr(VI)/Fe 0 molar ratio.…”