Experimental kinetic rate laws for aqueous pyrite reduction at underground hydrogen storage conditions (60–150 °C, up to 150 bar H2)
Abstract
The reaction kinetics of reductive pyrite (FeS 2 ) dissolution by H 2 is important to predict the long-term aqueous and gaseous sulfide release in underground hydrogen storage and other engineered subsurface sites. We investigated the rates of pyrite reduction based on sulfide formation as a function of temperature (60-150 • C), H 2 partial pressure (0-150 bar), and pH in situ (~ 4-10) in deoxygenated 0.03 M NaCl solutions. The experiments used natural pyrite powder (ø = 50-100 µm) and were run in hydrothermal batch reactors made of either titanium or Dursan®-coated 316L stainless steel. After experimental durations of ~ 700-900 h, dissolved S -II (aq) concentrations measured by methylene blue spectrophotometry ranged from 10 -5 to 10 -3 M. Long-term pyrite dissolution and concomitant elevated S -II (aq) concentrations were controlled by the formation of secondary pyrrhotite (Fe 1-x S) and magnetite (Fe 3 O 4 ), which prevented the ion activity product of FeS 2 from achieving rapid saturation. Conversely, in the absence of pyrrhotite and magnetite precipitation, the solutions rapidly equilibrated with respect to pyrite, resulting in low S -II (aq) concentrations. Rates of reductive pyrite dissolution were determined at 12 h from total S - II (aq+gas) concentration vs. time data and were found to increase with temperature and H 2 -partial pressure. The rate dependency on pH at 90 • C, 7 bar P H2 was regressed either with an asymmetric 'V'-shaped (two rate-pH domains) or a 'U'-shaped (three rate-pH domains) relation. For this reason, two separate kinetic rate laws were derived, based on the 'U'-regression (E a = 35.2 kJ mol -1 ): r = 10 -5.42 e -35208/RT (P H2 ) 0.37
or the 'V'-regression (E a = 29.4 kJ mol -1 ): r = 10 -5.13 e -29370/RT (a H + ) 0.13 (P H2 ) 0.37
The performance of both rate laws was validated by reproducing the experimental S -II (aq) concentrations in kinetic models. This comparison determined their applicability to be valid from 60 to 120 • C, 0-150 bar P H2 , and pH ~ 6.7-8.6 ('U' rate law) or pH ~ 4.1-8.6 ('V' rate law). The rate laws are compatible with geochemical reactive transport codes and will enhance the understanding of geochemical fluid-rock-gas interactions in H 2bearing subsurface environments.
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BibTeX
@article{hintzen2026experimental,
title = {{Experimental kinetic rate laws for aqueous pyrite reduction at underground hydrogen storage conditions (60–150 °C, up to 150 bar H2)}},
author = {Robin Hintzen and Roland Hellmann and Vladimir Roddatis and Julia van Winden and Laurent Truche},
journal = {Geochimica et Cosmochimica Acta},
year = {2026},
month = sep,
doi = {10.1016/j.gca.2025.12.034},
url = {https://hal.science/hal-05769852v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Experimental kinetic rate laws for aqueous pyrite reduction at underground hydrogen storage conditions (60–150 °C, up to 150 bar H2)
AU - Robin Hintzen
AU - Roland Hellmann
AU - Vladimir Roddatis
AU - Julia van Winden
AU - Laurent Truche
PY - 2026
DA - 2026/09/29
JO - Geochimica et Cosmochimica Acta
DO - 10.1016/j.gca.2025.12.034
UR - https://hal.science/hal-05769852v1
AB - The reaction kinetics of reductive pyrite (FeS 2 ) dissolution by H 2 is important to predict the long-term aqueous and gaseous sulfide release in underground hydrogen storage and other engineered subsurface sites. We investigated the rates of pyrite reduction based on sulfide formation as a function of temperature (60-150 • C), H 2 partial pressure (0-150 bar), and pH in situ (~ 4-10) in deoxygenated 0.03 M NaCl solutions. The experiments used natural pyrite powder (ø = 50-100 µm) and were run in hydrothermal batch reactors made of either titanium or Dursan®-coated 316L stainless steel. After experimental durations of ~ 700-900 h, dissolved S -II (aq) concentrations measured by methylene blue spectrophotometry ranged from 10 -5 to 10 -3 M. Long-term pyrite dissolution and concomitant elevated S -II (aq) concentrations were controlled by the formation of secondary pyrrhotite (Fe 1-x S) and magnetite (Fe 3 O 4 ), which prevented the ion activity product of FeS 2 from achieving rapid saturation. Conversely, in the absence of pyrrhotite and magnetite precipitation, the solutions rapidly equilibrated with respect to pyrite, resulting in low S -II (aq) concentrations. Rates of reductive pyrite dissolution were determined at 12 h from total S - II (aq+gas) concentration vs. time data and were found to increase with temperature and H 2 -partial pressure. The rate dependency on pH at 90 • C, 7 bar P H2 was regressed either with an asymmetric 'V'-shaped (two rate-pH domains) or a 'U'-shaped (three rate-pH domains) relation. For this reason, two separate kinetic rate laws were derived, based on the 'U'-regression (E a = 35.2 kJ mol -1 ): r = 10 -5.42 e -35208/RT (P H2 ) 0.37 or the 'V'-regression (E a = 29.4 kJ mol -1 ): r = 10 -5.13 e -29370/RT (a H + ) 0.13 (P H2 ) 0.37 The performance of both rate laws was validated by reproducing the experimental S -II (aq) concentrations in kinetic models. This comparison determined their applicability to be valid from 60 to 120 • C, 0-150 bar P H2 , and pH ~ 6.7-8.6 ('U' rate law) or pH ~ 4.1-8.6 ('V' rate law). The rate laws are compatible with geochemical reactive transport codes and will enhance the understanding of geochemical fluid-rock-gas interactions in H 2bearing subsurface environments.
SN - 0016-7037
SN - 1872-9533
ER -