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Research Article

Direct electrolytic dissolution of silicate minerals for air CO2 mitigation and carbon-negative H2 production

Greg H. Rau, Susan A. Carroll, William L. Bourcier, Michael J. Singleton, Megan M. Smith, and Roger D. Aines
  1. aInstitute of Marine Sciences, University of California, Santa Cruz, CA 95064; and
  2. bPhysical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, CA 94550

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PNAS first published May 31, 2013; https://doi.org/10.1073/pnas.1222358110
Greg H. Rau
aInstitute of Marine Sciences, University of California, Santa Cruz, CA 95064; and
bPhysical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, CA 94550
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  • For correspondence: rau4@llnl.gov
Susan A. Carroll
bPhysical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, CA 94550
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William L. Bourcier
bPhysical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, CA 94550
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Michael J. Singleton
bPhysical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, CA 94550
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Megan M. Smith
bPhysical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, CA 94550
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Roger D. Aines
bPhysical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, CA 94550
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  1. Edited by Thure E. Cerling, University of Utah, Salt Lake City, UT, and approved May 1, 2013 (received for review January 4, 2013)

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Abstract

We experimentally demonstrate the direct coupling of silicate mineral dissolution with saline water electrolysis and H2 production to effect significant air CO2 absorption, chemical conversion, and storage in solution. In particular, we observed as much as a 105-fold increase in OH− concentration (pH increase of up to 5.3 units) relative to experimental controls following the electrolysis of 0.25 M Na2SO4 solutions when the anode was encased in powdered silicate mineral, either wollastonite or an ultramafic mineral. After electrolysis, full equilibration of the alkalized solution with air led to a significant pH reduction and as much as a 45-fold increase in dissolved inorganic carbon concentration. This demonstrated significant spontaneous air CO2 capture, chemical conversion, and storage as a bicarbonate, predominantly as NaHCO3. The excess OH− initially formed in these experiments apparently resulted via neutralization of the anolyte acid, H2SO4, by reaction with the base mineral silicate at the anode, producing mineral sulfate and silica. This allowed the NaOH, normally generated at the cathode, to go unneutralized and to accumulate in the bulk electrolyte, ultimately reacting with atmospheric CO2 to form dissolved bicarbonate. Using nongrid or nonpeak renewable electricity, optimized systems at large scale might allow relatively high-capacity, energy-efficient (<300 kJ/mol of CO2 captured), and inexpensive (<$100 per tonne of CO2 mitigated) removal of excess air CO2 with production of carbon-negative H2. Furthermore, when added to the ocean, the produced hydroxide and/or (bi)carbonate could be useful in reducing sea-to-air CO2 emissions and in neutralizing or offsetting the effects of ongoing ocean acidification.

  • air capture
  • carbon dioxide
  • electrochemistry
  • hydrogen
  • mineral weathering

Footnotes

  • ↵1To whom correspondence should be addressed. E-mail: rau4{at}llnl.gov.
  • Author contributions: G.H.R. designed research; G.H.R. performed research; G.H.R., S.A.C., and M.J.S. contributed new reagents/analytic tools; G.H.R., S.A.C., W.L.B., M.J.S., and M.M.S. analyzed data; and G.H.R., S.A.C., W.L.B., and R.D.A. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

Freely available online through the PNAS open access option.

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Silicate electrolysis for CO2 mitigation
Greg H. Rau, Susan A. Carroll, William L. Bourcier, Michael J. Singleton, Megan M. Smith, Roger D. Aines
Proceedings of the National Academy of Sciences May 2013, 201222358; DOI: 10.1073/pnas.1222358110

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Silicate electrolysis for CO2 mitigation
Greg H. Rau, Susan A. Carroll, William L. Bourcier, Michael J. Singleton, Megan M. Smith, Roger D. Aines
Proceedings of the National Academy of Sciences May 2013, 201222358; DOI: 10.1073/pnas.1222358110
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