Mineralogical Changes and H2 Generation Yield During Hydrothermal Alteration of a Magnetite-Siderite Assemblage

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00216208%3A11320%2F25%3A10510395" target="_blank" >RIV/00216208:11320/25:10510395 - isvavai.cz</a>

Result on the web

<a href="https://verso.is.cuni.cz/pub/verso.fpl?fname=obd_publikace_handle&handle=el.nSA8kfG" target="_blank" >https://verso.is.cuni.cz/pub/verso.fpl?fname=obd_publikace_handle&handle=el.nSA8kfG</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1029/2024JB030724" target="_blank" >10.1029/2024JB030724</a>

Result language

angličtina

Original language name

Mineralogical Changes and H2 Generation Yield During Hydrothermal Alteration of a Magnetite-Siderite Assemblage

Original language description

To date, the generation of natural hydrogen (H&lt;inf&gt;2&lt;/inf&gt;) from the alteration of Fe&lt;sup&gt;II&lt;/sup&gt;-bearing minerals has mainly been studied through serpentinization in (ultra)mafic rocks. This study explores Banded Iron Formations (BIF), which are rich in Fe&lt;sup&gt;II&lt;/sup&gt; minerals, as a potential source for H&lt;inf&gt;2&lt;/inf&gt;. We conducted a hydrothermal experiment at 200°C with a combined magnetite-siderite assemblage, two major components of BIF. The experiment, designed with a high water-to-rock ratio and a gas phase (W-R = 300) enabled to assess mineral transformations during the alteration. Thermodynamic simulations were finally conducted, to explore H&lt;inf&gt;2&lt;/inf&gt;-generating yields in more realistic geological scenarios (no gas phase, lower W-R). Our experimental findings show that H&lt;inf&gt;2&lt;/inf&gt; is produced through complete siderite dissolution and magnetite precipitation. Concomitantly, non-stoichiometric primary magnetite (Fe&lt;sup&gt;II&lt;/sup&gt;/Fe&lt;sup&gt;III&lt;/sup&gt; &lt; 0.5) did not enhance H&lt;inf&gt;2&lt;/inf&gt; yield; instead, it acted as a sink for dissolved Fe&lt;sup&gt;2+&lt;/sup&gt;, sequestrating about 10% of the iron from siderite without oxidation to recover a more ideal stoichiometry. This suggests that abundant, non-stoichiometric magnetite in natural settings may reduce H&lt;inf&gt;2&lt;/inf&gt; generation yields. Mass balance calculations indicate that 83% of the expected H&lt;inf&gt;2&lt;/inf&gt; generated was unaccounted for, consistent with suspected CO&lt;inf&gt;2&lt;/inf&gt; reduction and formation of dissolved organic compounds in the fluids. Thermodynamic simulations at varying W-R ratios (from 300 to 1) reveal that H&lt;inf&gt;2&lt;/inf&gt; yield ranges widely (39 mmol-73 μmol H&lt;inf&gt;2&lt;/inf&gt; per kg of siderite), since lower W-R prevent from siderite dissolution and enhance H&lt;inf&gt;2&lt;/inf&gt; consumption via carbon reduction. These findings imply that low W-R ratios in BIF -and other siderite-bearing lithologies, may limit H&lt;inf&gt;2&lt;/inf&gt; resources.

Czech name

—

Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

—

OECD FORD branch

10302 - Condensed matter physics (including formerly solid state physics, supercond.)

Project

—

Continuities

S - Specificky vyzkum na vysokych skolach<br>I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2025

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Name of the periodical

Journal of Geophysical Research: Solid Earth

ISSN

2169-9313

e-ISSN

2169-9356

Volume of the periodical

130

Issue of the periodical within the volume

8

Country of publishing house

US - UNITED STATES

Number of pages

17

Pages from-to

1-17

UT code for WoS article

001547177000001

EID of the result in the Scopus database

2-s2.0-105012627113