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| Titel |
The effect of electrolytes on dolomite dissolution: nanoscale observations using in situ Atomic Force Microscopy |
| VerfasserIn |
Maja Urosevic, Encarnacion Ruiz-Agudo, Christine V. Putnis, Carolina Cardell, Carlos Rodriguez-Navarro, Andrew Putnis |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036856
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| Zusammenfassung |
| Dissolution of carbonate minerals is one of the main chemical reactions occurring at shallow
levels in the crust of the Earth and has a paramount importance for a wide range of geological
and biological processes. Calcite (CaCO3), and to a lesser extent dolomite (CaMg(CO3)2),
are the major carbonate minerals in sedimentary rocks and building stone materials. The
dissolution of calcite has been thoroughly investigated over a range of conditions and solution
compositions. In contrast, dolomite dissolution studies have been traditionally hampered by
its low reaction rates compared to calcite and its poorly constrained relationship
between cation ordering and reactivity (Morse and Arvidson, 2002). Yet important
questions like the so-called ‘dolomite problem’ (e.g. Higgins and Hu, 2005) remain
unresolved and more experimental work is needed in order to understand the role of
other dissolved species, such as soluble salts, on the kinetics and mechanism of
dolomite dissolution and precipitation. We have explored the effect of different
electrolytes on the dissolution rate of dolomite by using in situ Atomic Force Microcopy
(AFM). Experiments were carried out by passing alkali halide, nitrate and sulfate
salt solutions (NaCl, KCl, LiCl, NaI, NaNO3 and Na2SO4) with different ionic
strengths (IS = 10-3, 10-2 and 10-1) over dolomite {1014} cleavage surfaces.
We show that all electrolytes tested enhance dolomite dissolution. Moreover, the
morphology and density of etch pits are controlled by the presence of different ions in
solution. The etch pit spreading rate and dolomite dissolution rate depend on both
(1) the nature of the electrolyte and (2) the ionic strength. This is in agreement
with recent experimental studies on calcite dissolution (Ruiz-Agudo et al., 2010).
This study highlights the role of electrolytes in dolomite dissolution and points to a
common behavior for carbonate minerals. Our results suggest that soluble salts
may play a critical role in the weathering of carbonate rocks, both in the natural
environment, as well as in stone buildings and statuary, where the amount of solutes in
pore waters is significant and can vary depending on evaporation and condensation
phenomena.
References
Higgins, S.R.; Hu, X. Self-limiting growth on dolomite: Experimental observations with
in situ atomic force microscopy. Geochimica et Cosmochimica Acta, 2005, 69 (8),
2085-2094.
Morse, J.W.; Arvidson, R.S. The dissolution kinetics of major sedimentary carbonate
minerals. Earth-Science Reviews, 2002, 58, 51–84.
Ruiz-Agudo, E.; Kowacz, M.; Putnis, C.V.; Putnis, A. The role of background electrolytes
on the kinetics and mechanism of calcite dissolution. Geochimica et Cosmochimica Acta,
2010, 74, 1256-1267. |
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