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| Titel |
Cryosalt Formation in Delaminated Clays |
| VerfasserIn |
Merve Yeşilbaş, Jean-François Boily |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250149230
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| Publikation (Nr.) |
 EGU/EGU2017-13563.pdf |
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| Zusammenfassung |
| Hydrohalite (NaCl⋅2H2O) forms by evaporation, sublimation and freezing of aqueous
solutions of NaCl. Although this process is traditionally deemed to occur in aqueous
solutions little attention has been paid on whether this is possible with minerals. Smectite
minerals are particularly interesting in this regard for their ability to accommodate water
between aluminosilicate sheets, allowing them to swell and even delaminate. In particular,
montmorillonite possesses high affinities for water and can play important roles in water
retention and ice formation in nature, as well as in strategies for nuclear waste storage and
even for technological applications. [1,2]
For this study, we aimed to develop insight into the molecular-level nature of hydrohalite
formation at surfaces of montmorillonite particles as well as in their interlayers. Thin films of
Na+ and Ca2+ exchanged montmorillonites deposited on a diamond-based Attenuated Total
Reflectance (ATR) cell were interacted with (0.01, 0.1, 1 and 5M) NaCl solutions, and then
frozen to -10˚ C. The resulting frozen montmorillonites pastes were then probed by ATR
Fourier Transform Infrared (FTIR) spectroscopy, which is a highly sensitive technique for
probing hydrogen bonding in minerals and water. Our results on Na-montmorillonite showed
that hydrohalite, with its characteristic O-H stretching (νOH ∼ 3245-3265, 3408,
3462, 3555 cm−1) and bending (δOH ∼ 1614 and 1641 cm−1) bands, formed
from solutions of at least 0.1 M NaCl, yet well below the typical homogeneous
crystallization of this phase from pure aqueous solutions.[3] Further analysis of
the O-H stretching and silicate (νSi−O ∼1000 cm−1) regions of frozen paste of
montmorillonites revealed that hydrohalite formed within interlayers and at surfaces of
Na-montmorillonite. Ca-montmorillonite did not, on the other hand, promote hydrohalite
formation but did undergo Ca2+/Na+ ion exchange due to exposure of the NaCl
solutions.
Given the inability of Ca-montmorillonite at hosting hydrohalite, the results of this study
can be used to suggest that delaminated Na-montmorillonite sheets encapsulate the
salt solutions and by preventing sublimation of water, promotes crystallization of
hydrohalite. As delamination is not possible in Ca-montmorillonite, water more
readily sublimated from the system, leaving behind a dry Ca-montmorillonite/NaCl
assemblage. As such, this work identified processes through which clay minerals
can affect the formation of cryosalts that are not only of importance to terrestrial
environments of the cryosphere but also to atmospheric processes involving dust
aerosols.
[1] Yeşilbaş, M. and Boily, J.-F. (2016), Scientific Reports. 6, 32136.
[2] Yeşilbaş, M. and Boily, J.-F. (2016), J. Phys. Chem. Lett. 7, 2849-2855.
[3] Wagner, R., Möhler O., Schnaiter, M. (2012), 33, 8557-8571. |
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