The effect of pH on rates of reaction and hydrogen generation during serpentinization

Thomas M. McCollom, Frieder Klein, Peter Solheid, Bruce Moskowitz

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4 Scopus citations

Abstract

A series of three laboratory experiments were conducted to investigate how pH affects reaction pathways and rates during serpentinization. Two experiments were conducted under strongly alkaline conditions using olivine as reactant at 200 and 230°C, and the results were compared with previous studies performed using the same reactants and methods at more neutral pH. For both experiments, higher pH resulted in more rapid serpentinization of the olivine and generation of larger amounts of H2 for comparable reaction times. Proportionally greater amounts of Fe were partitioned into brucite and chrysotile and less into magnetite in the experiments conducted at higher pH. In a third experiment, alkaline fluids were injected into an ongoing experiment containing olivine and orthopyroxene to raise the pH from circumneutral to strongly alkaline conditions. Increasing the pH of the olivine-orthopyroxene experiment resulted in an immediate and steep increase in H2 production, and led to far more extensive reaction of the primary minerals compared to a similar experiment conducted under more neutral conditions. The results suggest that the development of strongly alkaline conditions in actively serpentinizing systems promotes increased rates of reaction and H2 production, enhancing the flux of H2 available to support biological activity in these environments. This article is part of a discussion meeting issue ‘Serpentinite in the Earth System’.

Original languageEnglish (US)
Article number20180428
JournalPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Volume378
Issue number2165
DOIs
StatePublished - Feb 21 2020

Bibliographical note

Funding Information:
Data accessibility. Supporting data for the figures are included in the electronic supplementary material. Authors’ contributions. T.M.M. conceived of and conducted the experiments, interpreted data and led the authorship of the manuscript. F.K. contributed to the interpretation of data, provided thermogravimetric analysis and helped write the manuscript. B.M. and P.S. provided Mössbauer and magnetic analyses, and contributed to the interpretation of data and writing of the manuscript. Competing interests. We declare we have no competing interests. Funding. This research was supported by the NASA Astrobiology Institute through Cooperative Agreement no. NNA15BB02A and NASA Solar Systems Workings program grant no. NNX16AL74G. The IRM is supported by the Instruments and Facilities Program of the NSF Division of Earth Science. Acknowledgements. Christopher Donaldson is thanked for his help with many of the experimental measurements. This is IRM contribution 1902. We thank Benjamin Tutolo, Andrew McCaig and an anonymous reviewer for helpful comments that resulted in significant improvements to this communication.

Publisher Copyright:
© 2020 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

Keywords

  • Hydrogen generation
  • Serpentinization
  • Subsurface life

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