Experimental Evidence for Non-Redox Transformation Between Magnetite and Hermatite Under H2-Rich Hydrothermal Conditions
- Pennsylvania State University
- ORNL
Transformations of magnetite (Fe{sup II}Fe{sub 2}{sup III}O{sub 4}) to hematite (Fe{sub 2}{sup III}O{sub 3}) (and vice versa) have been thought by many scientists and engineers to require molecular O{sub 2} and/or H{sub 2}. Thus, the presence of magnetite and/or hematite in rocks has been linked to a specific oxidation environment. However, the availability of reductants or oxidants in many geologic and industrial environments appears to have been too low to account for the transformations of iron oxides through redox reactions. Here, we report the results of hydrothermal experiments in mildly acidic and H{sub 2}-rich aqueous solutions at 150 C, which demonstrate that transformations of magnetite to hematite, and hematite to magnetite, occur rapidly without involving molecular O{sub 2} or H{sub 2}: Fe{sub 3}O{sub 4}(Mt) + 2H{sub (aq)}{sup +} {leftrightarrow} Fe{sub 2}O{sub 3}(Hm) + Fe{sub (aq)}{sup 2+} + H{sub 2}O The transformation products are chemically and structurally homogeneous, and typically occur as euhedral single crystals much larger than the precursor minerals. This suggests that, in addition to the expected release of aqueous ferrous species to solution, the transformations involve release of aqueous ferric species from the precursor oxides to the solution, which reprecipitate without being reduced by H{sub 2}. These redox-independent transformations may have been responsible for the formation of some iron oxides in natural systems, such as high-grade hematite ores that developed from Banded Iron Formations (BIFs), hematite-rich deposits formed on Mars, corrosion products in power plants and other industrial systems.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 930894
- Journal Information:
- Earth and Planetary Science Letters, Vol. 257, Issue 2; ISSN 0012-821X
- Country of Publication:
- United States
- Language:
- English
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