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PRINCIPAL PUBLICATION AND AUTHORS
Selenium Nanowire Formation by Reacting Selenate with Magnetite, A. Poulain (a), A. Fernandez-Martinez (a), J.-M. Greneche (b), D. Prieur (c,e), A.C. Scheinost (c,e), N. Menguy (d), S. Bureau (a), V. Magnin (a), N. Findling (a), J. Drnec (e), I. Martens (e), M. Mirolo (e), L. Charlet (a), Environ. Sci. Technol. 56, 14817-14827 (2022); https:/doi.org/10.1021/acs.est.1c08377 (a) ISTerre, Univ Grenoble Alpes & CNRS, Grenoble (France) (b) Institut des Molécules et Matériaux du Mans, Le Mans Université & CNRS, Le Mans (France) (c) HZDR Institute of Resource Ecology, Dresden (Germany) (d) Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Sorbonne Université & CNRS, Paris (France) (e) ESRF
REFERENCES
[1] A. Fernandez-Martinez & L. Charlet, Environ. Sci. Biotechnol. 8, 81-110 (2009). [2] A.C. Scheinost & L. Charlet, Environ. Sci. Technol. 42, 1984- 1989 (2008). [3] S. Goberna-Ferrón et al., Environ. Sci. Technol. 55, 3021- 3031 (2021). [4] A.C. Scheinost et al., J. Contam. Hydrol. 102, 228-245 (2008).
at pH 5, but also at the near-neutral pH conditions that would be present in the geological medium surrounding the underground repository. The positive charge developed at pH 5 at the magnetite-water interface means that selenate adsorption is relatively high. At this pH, Fe(II) is also released from the magnetite, readsorbing in a concomitant way with the selenate oxyanions, and thus playing a role of catalyser of the redox reaction.
The XAS results show that selenate is reduced to elemental selenium in the form of Se(0) nanowires (Figure 114). A Se(IV) intermediate is observed in the reduction (Figure 115), pointing to a multi-step pathway of selenium reduction, probably involving many adsorption and reduction steps. The low solubility of Se(0) makes this reductive precipitation mechanism a potential way to reduce the risks of selenium leakage to the environment.
However, the formation of these very anisotropic Se(0) precipitates contrasts with the very isotropic distribution of magnetite nanoparticles, suggesting the transport of reduced species from the site where the reduction takes place to the tips of the Se nanowires their growth sites. This implies that the reduced species of selenium, which are usually considered as non-mobile, show some mobility under these conditions. The existence of this unknown mechanism for transport of reduced selenium species has important implications for the safety assessment of technological applications such as underground sites for nuclear waste storage.
Fig. 115: Selenium K-edge X-ray absorption near-edge structure (a) and extended X-ray absorption fine structure (b) spectra. Analyses of the data reveal a quick adsorption and reduction to elemental selenium via the formation of a selenite intermediate.
