Emerging investigator series: ion diffusivities in nanoconfined interfacial water films contribute to mineral carbonation thresholds

The dynamics and reactivity of nanoconfined fluids play critical roles across a wide range of environmental and technological systems, though reaction mechanisms and kinetics are not well understood. The carbonation kinetics of forsterite (Mg 2 SiO 4 ) exposed to 90 atm supercritical carbon dioxide...

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Bibliographic Details
Published in:Environmental science. Nano 2020-04, Vol.7 (4), p.168-181
Main Authors: Miller, Quin R. S, Kaszuba, John P, Kerisit, Sebastien N, Schaef, H. Todd, Bowden, Mark E, McGrail, B. Peter, Rosso, Kevin M
Format: Article
Language:English
Subjects:
Carbon dioxide
Carbonates
Carbonation
Diffusion
Dynamics
Film thickness
Fluid dynamics
Fluids
Forsterite
Free energy
Kinetics
Magnesite
Magnesium
Magnesium carbonate
Mass spectrometry
Mass spectroscopy
Molecular dynamics
Monolayers
Monomolecular films
Reaction kinetics
Reaction mechanisms
Relative humidity
Thick films
Thresholds
Water film
Waterfalls
X-ray diffraction
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Summary:The dynamics and reactivity of nanoconfined fluids play critical roles across a wide range of environmental and technological systems, though reaction mechanisms and kinetics are not well understood. The carbonation kinetics of forsterite (Mg 2 SiO 4 ) exposed to 90 atm supercritical carbon dioxide at 35-65 °C and 85-100% relative humidity (RH) was monitored with in situ X-ray diffraction, and partner molecular dynamics simulations were used to describe the free energy landscape of Mg 2+ adsorption and diffusion on forsterite surfaces covered in water films 3-10 monolayers thick. The collective findings reveal how decreasing the water film thickness by ∼1.4 monolayers, from ∼0.92 to ∼0.64 nm, inhibited reaction rates by up to 97%, promoted anhydrous Mg-carbonate (magnesite, MgCO 3 ) precipitation, and more than doubled the apparent activation energy of carbonation. The transport simulations suggest that four monolayers are required to enable sufficiently facile Mg 2+ diffusion, helping explain previously observed water film thickness-dependent reactivity thresholds. Mineral carbonation reactivity trends and thresholds in nanoconfined water films delineated with in situ X-ray diffraction and molecular simulations.
ISSN:2051-8153
2051-8161
DOI:10.1039/c9en01382b