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Mechanistic Insights of Mild Hematite Reduction in Hydrogen Storage Sites

Hydrogen is a prospective energy carrier whose storage in extensive volumes is still an unsolved problem. One approach is underground hydrogen storage, in which geological formations such as salt caverns or depleted natural gas and oil reservoirs are used to hold large amounts of gas under pressure. However, in those formations minerals can react with the hydrogen stored and therefore deplete or contaminate the gas recovered. In our previous project we have shown that various minerals (e.g. pyrite, smectite, hematite) reacted with hydrogen under storage conditions (~120°C, <100 bar). Especially the Fe3+/Fe2+ switch in a reaction in which hematite is reduced to magnetite forming water (3 Fe2O3 + H2 → 2 Fe3O4 + H2O) was found to be active. Mechanistic data of that reduction is abundantly available at high temperatures (>500°C). However, studies at storage conditions (45-120°C) are rare up to this point. Especially the influence of pressure is unclear. The work presented aims to understand the processes by which hematite is reduced under those conditions. For that purpose, we built a system in which we measure the decreasing hydrogen concentration periodically. Is consists of a heated pressure vessel on whose outlet a 10-port-valve flushes a gas-sample to a mass spectrometer. The resulting H2-peaks in the MS-spectra are quantified using Ne as internal standard. This way we are able to obtain time-resolved data on the consumption of H2 as well as formation of H2O by hematite. Additionally, we quantify the hematite to magnetite ratio using XRD after the experiment.


Sonja Keller, Christian Ostertag-Henning
Federal Institute for Geosciences and Natural Resources, Germany
GeoKarlsruhe 2021