Thin Water Films Enable Low-Temperature Magnesite Growth Under Conditions Relevant to Geologic Carbon Sequestration

Injecting supercritical CO2 (scCO2) into basalt formations for long-term storage is a promising strategy for mitigating CO2 emissions. Mineral carbonation can result in permanent entrapment of CO2; however, carbonation kinetics in thin H2O films in humidified scCO2 is not well understood. We investi...

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Bibliographic Details
Published in:Environmental science & technology 2021-09, Vol.55 (18), p.12539-12548
Main Authors: Kerisit, Sebastien N, Mergelsberg, Sebastian T, Thompson, Christopher J, White, Signe K, Loring, John S
Format: Article
Language:English
Subjects:
Aqueous solutions
Basalt
Carbon dioxide
Carbon dioxide emissions
Carbon sequestration
Carbonation
Emissions
Energy and Climate
Entrapment
Film thickness
Forsterite
Growth rate
Infrared spectroscopy
Kinetics
Low temperature
Magnesite
Magnesium
Magnesium carbonate
Reaction kinetics
Silicon dioxide
Supersaturation
Thin films
Water film
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Summary:Injecting supercritical CO2 (scCO2) into basalt formations for long-term storage is a promising strategy for mitigating CO2 emissions. Mineral carbonation can result in permanent entrapment of CO2; however, carbonation kinetics in thin H2O films in humidified scCO2 is not well understood. We investigated forsterite (Mg2SiO4) carbonation to magnesite (MgCO3) via amorphous magnesium carbonate (AMC; MgCO3·xH2O, 0.5 < x < 1), with the goal to establish the fundamental controls on magnesite growth rates at low H2O activity and temperature. Experiments were conducted at 25, 40, and 50 °C in 90 bar CO2 with a H2O film thickness on forsterite that averaged 1.78 ± 0.05 monolayers. In situ infrared spectroscopy was used to monitor forsterite dissolution and the growth of AMC, magnesite, and amorphous SiO2 as a function of time. Geochemical kinetic modeling showed that magnesite was supersaturated by 2 to 3 orders of magnitude and grew according to a zero-order rate law. The results indicate that the main drivers for magnesite growth are sustained high supersaturation coupled with low H2O activity, a combination of thermodynamic conditions not attainable in bulk aqueous solution. This improved understanding of reaction kinetics can inform subsurface reactive transport models for better predictions of CO2 fate and transport.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.1c03370