Pyroxene control of H2 production and carbon storage during water-peridotite-CO2 hydrothermal reactions

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Abstract

Strategies of H2 production and CO2 mineralization were combined through olivine [(Mg,Fe)2SiO4] serpentinization and carbonation in a CO2-rich hydrothermal system. However, natural mantle peridotites commonly contain not only olivine but also orthopyroxene and/or clinopyroxene, which have effects that are not well understood. The present study investigated the reactions in H2O-olivine/orthopyroxene-CO2 systems by performing hydrothermal experiments in 0.5 M NaHCO3 solutions at 300 °C and 10 MPa. The yields of H2 and HCOOH initially were first suppressed in the presence of orthopyroxene; however, after orthopyroxene consumption, the rate of H2 production increased significantly. H2 yield increased to 348.3 mmol/kgmineral in 120 h with the presence of 20 wt% orthopyroxene at the beginning of the reaction. The initial suppression of H2 generation was due to incorporation of more Fe(II) into serpentine [(Mg,Fe)3Si2O5(OH)4] in the high SiO2(aq) concentration system. The presence of orthopyroxene also dramatically accelerated serpentine formation. In contrast, magnesite [(Mg,Fe)CO3] formation was inhibited upon addition of orthopyroxene, which also contributed to the release of Fe(II). Therefore, peridotite containing ≤20 wt% of pyroxenes is more suitable for long-term H2 production than pure olivine. When considering the reaction output of a water-peridotite-CO2 system, controlling the percentage of pyroxenes in the starting mineral may be more important than expected.

Original languageEnglish
Pages (from-to)26835-26847
Number of pages13
JournalInternational Journal of Hydrogen Energy
Volume44
Issue number49
DOIs
Publication statusPublished - 2019 Oct 11

Keywords

  • Carbonation
  • H production
  • Olivine
  • Pyroxene
  • Serpentinization
  • Silica

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Fuel Technology
  • Condensed Matter Physics
  • Energy Engineering and Power Technology

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