Nucleation and growth of feitknechtite from nanocrystalline vernadite precursor

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Marco E. Ciriotti
Messaggi: 23421
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Nucleation and growth of feitknechtite from nanocrystalline vernadite precursor

Messaggio da Marco E. Ciriotti » lun 26 giu, 2017 15:27

Prossima pubblicazione.

Referenza:
▪ Grangeon, S., Warmont, F., Tournassat, C., Lanson, B., Lanson, M., Elkaïm, E., Claret, F. (2017): Nucleation and growth of feitknechtite from nanocrystalline vernadite precursor. European Journal of Mineralogy, 29, (in press).

Abstract:
Vernadite is a nanocrystalline manganese oxide, which controls the fate of many trace elements in soils and sediments through sorption and oxidative-degradation mechanisms. This exceptional reactivity directly results from its crystal structure, which may however evolve upon contact with redox-sensitive species. Understanding these changes is a prerequisite to predict and model the geochemical cycle of trace elements in the environment. Here, the structural and morphological modifications affecting synthetic nanocrystalline vernadite (δ-MnO)2) upon contact with increasing concentrations of Mn2+ were investigated using wet chemistry, synchrotron X-ray diffraction and transmission electron microscopy. Fresh δ-MnO)2 crystals had an Mn oxidation state of 3.94 ± 0.05 and a ∼ 10 Å layer-to-layer distance. Crystal size was ∼ 10 nm in the layer plane, and ∼ 1 nm perpendicular to that. Upon contact with aqueous Mn2+ under anoxic conditions, δ-MnO)2 crystals underwent several morphological and mineral evolutions, starting with the stacking, perpendicular to the layer plane, of δ-MnO)2 crystals to form crystals ∼ 10 nm × 2 nm which were then subjected to oriented aggregation both along and perpendicular to the layer plane to form lath-like crystals with dimensions of ∼ 100 nm × 20 nm. Finally, these laths stacked perpendicular to the layer plane to form synthetic feitknechtite (β-MnOOH) crystals with sizes up to ∼ 100 nm × 500 nm when the Mn2+ loading reached 31.9 mmol g-1. Structural transformation from δ-MnO)2 to synthetic feitknechtite was detected at Mn2+ loading equal to or higher than 3.27 mmol g-1.
These mechanisms are likely to influence the geochemical fate of trace elements in natural settings where Mn2+ is abundant. Firstly, the systematic increase in crystal size with increasing Mn2+ loading may impact the sorption capacity of vernadite and feitknechtite by reducing the density of reactive edge sites. Secondly, the fate of trace elements initially sorbed at the vernadite surface is unclear, as they could either be released in solution or incorporated into the feitknechtite lattice.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 23421
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: Nucleation and growth of feitknechtite from nanocrystalline vernadite precursor

Messaggio da Marco E. Ciriotti » gio 28 set, 2017 10:01

Pubblicazione effettuata.

Referenza:
▪ Grangeon, S., Warmont, F., Tournassat, C., Lanson, B., Lanson, M., Elkaïm, E., Claret, F. (2017): Nucleation and growth of feitknechtite from nanocrystalline vernadite precursor. European Journal of Mineralogy, 29, 767-776.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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