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Oxidation and Reduction of Structural Iron in Chlorite at 480°C

Published online by Cambridge University Press:  02 April 2024

Ole K. Borggaard ,
Holger B. Lindgreen  and
Steen Mørup
Ole K. Borggaard
Affiliation:
Chemistry Department, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871, Copenhagen V, Denmark
Holger B. Lindgreen
Affiliation:
Geochemistry Department, Danish Geological Survey, Thoravej 31, DK-2400 Copenhagen NV, Denmark
Steen Mørup
Affiliation:
Laboratory of Applied Physics II, Technical University of Denmark, DK-2800 Lyngby, Denmark
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Abstract

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An iron-rich chlorite, ripidolite, was oxidized by air-heating at 480°C, i.e., below the dehydroxylation temperature and subsequently reduced in hydrogen at the same temperature. On the basis of chemical, differential thermal, infrared, Mössbauer, and X-ray powder diffraction analyses, Fe(II) seems to be present only in the 2:1 layer of the original chlorite in a type of site similar to that of Fe(II) in biotite, with OH in cis-positions. These data also suggest that octahedral Al and Fe(III) are located in the hydroxide sheet of the original chlorite. The structural changes of the mineral due to the oxidation and the subsequent reduction appear limited to minor structural rearrangements and, perhaps, to the introduction of OH in both cis- and trans-positions. The results of the investigation are in agreement with a reaction of the form: [Fe(II)OH]+ ⇋ [Fe(III)O]+ + H(H+ + e−).

Резюме

Резюме

Резюме—Хлорит богатый в железо, рипидолит, был окислен путем нагрева в воздухе при 480°С, то есть ниже температуры дегидроксиляции. Окисленный хлорит был последовательно восстанов-лен в водороде при такой же температуре. По данным химического, термодифференциального, инфракрасного, Мессбауеровского, и рентгеновского анализов кажется, что Fe(II) существует только в 2:1 слоях исходного хлорита в местах, похожих на те, которые Fe(II) занимает в биотите, с группами OH в положениях cis. Эти данные указывают также на то, что октаэдрические А1 и Fe(III) расположены в гидроокисных пластах исходного хлорита. Структурные изменения минерала, возникающие в результате окисления и последовательного восстановления кажутся быть ограниченными до небольших структурных перестроек, и, возможно до введения групп OH в обоих cis и trans положениях. Результаты исследований согласны со следующей формой реак-ции: [Fe(II)OH]+ ⇌ [Fe(III)O]+ + H(H+ + e−). [E.C.]

Resümee

Resümee

Ein eisenreicher Chlorit, Ripidolith, wurde durch Erhitzen auf 480°C an der Luft, (d.h. unter die Dehydratationstemperatur) oxidiert und anschließend im Wasserstoff bei der gleichen Temperatur reduziert. Aufgrund chemischer Analysen, Differentialthermo-, Infrarot-, Mössbauer- und Röntgendiffraktometer-Untersuchungen scheint das Fe2+ nur in der 2:1 Schicht des ursprünglichen Chlorites vorhanden zu sein, wobei die Art des Platzes, den das Fe2+ besetzt, dem des Fe2+ in Biotit ähnelt und das (OH) in cis-Stellung ist. Diese Ergebnisse deuten weiters darauf hin, daß oktaedrisches AI und Fe3+ in den Hydroxidschichten des ursprünglichen Chlorits sind. Die strukturellen Veränderungen des Minerals aufgrund der Oxidation und der darauffolgenden Reduktion scheinen auf geringe strukturelle Neuordnungen und, vielleicht, auf die Einführung von (OH) sowohl in cis-als auch in trans-Stellung beschränkt zu sein. Die Ergebnisse dieser Untersuchung stimmen mit folgender Reaktion überein: [Fe2+OH]+ ⇌ [Fe3+O]+ + H(H+ + e−). [U.W.]

Résumé

Résumé

Une chlorite riche en fer, la ripidolite, a été oxidée par échauffement à l'air à 480°C, c'est à dire sous la température de déshydroxylation, et la chlorite oxidée a subséquemment été réduite dans l'hydrogène à la même température. Basé sur des analyses chimiques, thermales différentielles, infrarouges, de Mössbauer, et de diffraction poudrée aux rayons-X, Fe(II) ne semble être présent que dans la couche 2:1 de la chlorite originale, dans un genre de site semblable à celui de Fe(II) dans la biotite, avec OH dans les positions-cis. Ces données suggèrent aussi qu'Al octaèdral et Fe(III) sont situés dans la feuille hydroxide de la chlorite originale. Les changements structuraux du minéral causés par T oxidation et la réduction subséquente semblent limités à des réarrangements mineurs, et peut-être à l'introduction d'OH dans les positions -cis et -trans. Les résultats de l'investigation s'accordent avec une réaction de la forme: [Fe(II)OH]+ ⇌ [Fe(III)O]++H(H+ + e−]. [D.J.]

Keywords

ChloriteInfrared spectroscopyIronMössbauer spectroscopyOxidationReduction
Type
Research Article
Information
Clays and Clay Minerals , Volume 30 , Issue 5 , October 1982 , pp. 353 - 363
Copyright
Copyright © 1982, The Clay Minerals Society

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