GEOTHERMAL TECHNOLOGIES LEGACY COLLECTION - Bibliographic Citation


Bibliographic Citation


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Title: Mechanisms of iron oxide transformations in hydrothermal systems.
Creator/Author: Otake, Tsubasa [Pennsylvania State University] ; Wesolowski, David J [ORNL] ; Anovitz, Lawrence {Larry} M [ORNL] ; Allard Jr, Lawrence Frederick [ORNL] ; Ohmoto, Hiroshi [Pennsylvania State University]
Publication Date:2010 Jan 01
OSTI Identifier:OSTI 1021991
Report Number(s):None
DOE Contract Number:DE-AC05-00OR22725
Document Type:Journal Article
Specific Type:
Coverage:
Resource Relation:Journal Name: Geochimica et Cosmochimica Acta; Journal Volume: 74; Journal Issue: 21
Other Number(s):
Research Org:Oak Ridge National Laboratory (ORNL)
Sponsoring Org:SC USDOE - Office of Science (SC)
Subject:15 GEOTHERMAL ENERGY; CHEMICAL COMPOSITION; CHEMISTRY; CRYSTALS; DISSOLUTION; EQUILIBRIUM; FLUIDS; HEMATITE; HYDROTHERMAL SYSTEMS; IRON OXIDES; KINETICS; MAGNETITE; MINERALS; REDOX POTENTIAL; SOLUTIONS; TRANSFORMATIONS
Keywords:
Description/Abstract:Coexistence of magnetite and hematite in hydrothermal systems has often been used to constrain the redox potential of fluids, assuming that the redox equilibrium is attained among all minerals and aqueous species. However, as temperature decreases, disequilibrium mineral assemblages may occur due to the slow kinetics of reaction involving the minerals and fluids. In this study, we conducted a series of experiments in which hematite or magnetite was reacted with an acidic solution under H2-rich hydrothermal conditions (T = 100 250 C,) to investigate the kinetics of redox and non-redox transformations between hematite and magnetite, and the mechanisms of iron oxide transformation under hydrothermal conditions. The formation of euhedral crystals of hematite in 150 and 200 C experiments, in which magnetite was used as the starting material, indicates that non-redox transformation of magnetite to hematite occurred within 24 h. The chemical composition of the experimental solutions was controlled by the non-redox transformation between magnetite and hematite throughout the experiments. While solution compositions were controlled by the non-redox transformation in the first 3 days in a 250 C experiment, reductive dissolution of magnetite became important after 5 days and affected the solution chemistry. At 100 C, the presence of maghemite was indicated in the first 7 days. Based on these results, equilibrium constants of non-redox transformation between magnetite and hematite and those of non-redox transformation between magnetite and maghemite were calculated. Our results suggest that the redox transformation of hematite to magnetite occurs in the following steps: (1) reductive dissolution of hematite to and (2) non-redox transformation of hematite and to magnetite.
Publisher:
Country of Publication:US
Language:English
Size/Format:Medium: X; Size: 6141
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System Entry Date:2013 Jun 06
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