Magnétite

Résumé

La magnétite est une espèce minérale composée d'oxyde de fer(II,III), de formule (parfois écrit ), avec des traces de magnésium Mg, de zinc Zn, de manganèse Mn, de nickel Ni, de chrome Cr, de titane Ti, de vanadium V et d'aluminium Al. La magnétite est un matériau ferrimagnétique. Les variétés riches en titane sont qualifiées de magnétites titanifères, ou plus souvent de titanomagnétites. Des cristaux de magnétite peuvent être biominéralisés, c'est-à-dire biosynthétisés par certaines espèces vivantes, qui semblent pouvoir les utiliser pour s'orienter dans l'espace. Historique de la description et appellations Aimant#Histoire Étymologie La magnétite est connue depuis au moins l'âge du fer ; la première mention écrite date de Pline l'Ancien en 77 ; elle est décrite par Wilhelm Karl Ritter von Haidinger en 1845 ; son nom dérive de l'allemand Magnetit, mot lui-même dérivé du latin magnes, magnetis signifiant aimant et dérivant ultimement du nom de la province d

Source officielle

https://fr.wikipedia.org/wiki/Magn%C3%A9tite

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Iron phosphate mediated magnetite synthesis: a bioinspired approach

Giulia Mirabello

The biomineralization of intracellular magnetite in magnetotactic bacteria (MTB) is an area of active investigation. Previous work has provided evidence that magnetite biomineralization begins with the formation of an amorphous phosphate-rich ferric hydroxide precursor phase followed by the eventual formation of magnetite within specialized vesicles (magnetosomes) through redox chemical reactions. Although important progress has been made in elucidating the different steps and possible precursor phases involved in the biomineralization process, many questions still remain. Here, we present a novel in vitro method to form magnetite directly from a mixed valence iron phosphate precursor, without the involvement of other known iron hydroxide precursors such as ferrihydrite. Our results corroborate the idea that phosphate containing phases likely play an iron storage role during magnetite biomineralization. Further, our results help elucidate the influence of phosphate ions on iron chemistry in groundwater and wastewater treatment.

ROYAL SOC CHEMISTRY2021

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Cluster Catalysis with Lattice Oxygen: Tracing Oxygen Transport from a Magnetite (001) Support onto Small Pt Clusters

Wolfgang Harbich, Giulia Elisabetta Pacchioni, Ke Zhang

Oxidation catalysis on reducible oxide-supported small metal clusters often involves lattice oxygen. The present work aims at differentiating whether the reaction takes place at the cluster/support interface or on the cluster. To that purpose, we trace the path of lattice oxygen from Fe3O4(001) onto small Pt clusters during the CO oxidation. While oxygen vacancies form on many other supports, magnetite maintains its surface stoichiometry upon reduction thanks to high cation mobility. To investigate whether size-dependent oxygen affinities play a role, we study two specific cluster sizes, Pt-5 and Pt-19. By separating different reaction steps in our experiment, migrating lattice oxygen can be accumulated on the clusters. Temperature-programmed desorption (TPD) and sophisticated pulsed valve experiments indicate that CO oxidation occurs with this highly reactive oxygen on the Pt clusters. Scanning tunneling microscopy (STM) shows a decrease in the apparent height of the clusters, which density functional theory (DFT) explains as a restructuring following lattice oxygen reverse spillover.

AMER CHEMICAL SOC2021

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Uranium isotopic signatures can be harnessed to monitor the reductive remediation of subsurface contamination or to reconstruct paleo-redox environments. However, the mechanistic underpinnings of the isotope fractionation associated with U reduction remain poorly understood. Here, we present a coprecipitation study, in which hexavalent U (U(VI)) was reduced during the synthesis of magnetite and pentavalent U (U(V)) was the dominant species. The measured δ238U values for unreduced U(VI) (∼−1.0‰), incorporated U (96 2% U(V), ∼−0.1‰), and extracted surface U (mostly U(IV), ∼0.3‰) suggested the preferential accumulation of the heavy isotope in reduced species. Upon exposure of the U-magnetite coprecipitate to air, U(V) was partially reoxidized to U(VI) with no significant change in the δ238U value. In contrast, anoxic amendment of a heavy isotope-doped U(VI) solution resulted in an increase in the δ238U of the incorporated U species over time, suggesting an exchange between incorporated and surface/aqueous U. Overall, the results support the presence of persistent U(V) with a light isotope signature and suggest that the mineral dynamics of iron oxides may allow overprinting of the isotopic signature of incorporated U species. This work furthers the understanding of the isotope fractionation of U associated with iron oxides in both modern and paleo-environments.

2022

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