UMR CNRS 5805 EPOC
Environnements et Paléoenvironnements
Océaniques et Continentaux

        

Consignes de Sécurité et Numéros d'Urgence
(à l'usage des personnels du laboratoire)

le 25-10-2017 à 14:00

Lieu Salle de Conférences, ISM, 3ème étage Est, Bât. A12, Université de Bordeaux Intervenant(s) Davide VIONE, enseignant-chercheur, Université de Turin (UNITO)

The Fenton reaction is a promising technique for the abatement of pollutants in water and wastewater and it is currently finding applications in the fields of environmental remediation and industrial wastewater treatment. It has been developed into several variants, including the thermal (dark) process and the photo-Fenton one, which makes preferably use of solar radiation. The (photo-)Fenton process is based on Fe(II) and H₂O₂ to produce oxidizing species (most notably, but not exclusively, the hydroxyl radical) [1]. The two reactants can be provided as such or generated photochemically, electrochemically or sonochemically from several precursors, giving rise to the different variants of the Fenton reaction. Moreover, the use of other metals or peroxides in the same process has given rise to the vast Fenton-like family of reactions [2].
A major drawback of the classical Fenton process is that Fe(II) + H₂O₂ yields Fe(III), insoluble at the ~neutral pH at which treated water is used or discharged, giving a slurry as process waste. The use of ligands to keep Fe(III) dissolved is an option [3], but residual dissolved Fe could easily exceed the water quality requirements and, in this case, a precipitation step would still be needed. An alternative is the use of solid and Fenton-active Fe-containing materials, which provide a low amount of dissolved Fe(II) for Fenton operation and can be recycled for further reaction cycles. Solid recovery is easier with magnetic materials such as magnetite (Fe₃O₄) and Fe° (ZVI: zero-valent iron). On such bases, this talk describes the use of magnetite and ZVI in (photo-)Fenton and (photo-)Fenton-like processes.
Nanometric magnetite undergoes easy surface oxidation to Fe(III) and it is often inactive in the dark Fenton process, but it can be activated by UV irradiation. In this case, one can produce °OH radicals with Fe₃O₄ + H₂O₂ + UV [4], and SO₄^2-° radicals with Fe₃O₄ + S₂O₈^2- + UV [5]. The latter process yields SO₄^2-° that is a more selective oxidant than °OH and can often achieve decontamination with limited interference from dissolved organic matter [2]. Non-stoichiometric magnetite, with a Fe(II) excess in the inner lattice is to be preferred over stoichiometric Fe₃O₄ because of its much higher activity. ZVI + H₂O₂ triggers a dark Fenton reaction and it enables the use of passivated ZVI, which is a spent residual (waste) of ZVI-based reductive decontamination treatments (e.g., of chlorinated hydrocarbons). One can achieve further oxidative degradation of already dechlorinated compounds by just adding H₂O₂ to the residues of the dechlorination step.

[1] O. Pestovsky, S. Stoian, E. L. Bominaar, X. P. Shan, E. Munck, L. Que and A. Bakac, Angew. Chem. Int. Ed., 2005, 44, 6871.
[2] S. Gligorovski, R. Strekovski, S. Barbati and D. Vione, Chem. Rev., 2015, 115, 13051.
[3] W. Y. Huang, M. Brigante, F. Wu, C. Mousty, K. Hanna and G. Mailhot, Environ. Sci. Technol., 2013, 47, 1952.
[4] M. Minella, G. Marchetti, E. De Laurentiis, M. Malandrino, V. Maurino, C. Minero, D. Vione and K. Hanna, Appl. Catal., B, 2014, 154, 102.
[5] P. Avetta, A. Pensato, M. Minella, M. Malandrino, V. Maurino, C. Minero, K. Hanna and D. Vione, Environ. Sci. Technol., 2015, 49, 1043.