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| Titel |
Effect of temperature on the reaction pathway of calcium carbonate formation
via precursor phases |
| VerfasserIn |
Bettina Purgstaller, Vasileios Mavromatis, Florian Konrad, Martin Dietzel |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127702
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| Publikation (Nr.) |
 EGU/EGU2016-7606.pdf |
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| Zusammenfassung |
| It has been earlier postulated that some biogenic and sedimentary calcium carbonate
(CaCO3) minerals (e.g. calcite and aragonite) are secondary in origin and have originally
formed via a metastable calcium carbonate precursor phase (e.g. amorphous CaCO3, [1-2]).
Such formation pathways are likely affected by various physicochemical parameters
including aqueous Mg and temperature.
In an effort to improve our understanding on the formation mechanism of CaCO3
minerals, precipitation experiments were carried out by the addition of a 0.6 M
(Ca,Mg)Cl2 solution at distinct Mg/Ca ratios (1/4 and 1/8) into a 1 M NaHCO3
solution under constant pH conditions(8.3 ±0.1). The formation of CaCO3 was
systematically examined as a function of temperature (6, 12, 18 and 25 ±0.3˚ C).
During the experimental runs mineral precipitation was monitored by in situ Raman
spectroscopy as well as by continuous sampling and analyzing of precipitates and reactive
solutions.
The results revealed two pathways of CaCO3 formation depending on the initial Mg/Ca
ratio and temperature: (i) In experiments with a Mg/Ca ratio of 1/4 at ≤ 12˚ C as well as in
experiments with a Mg/Ca ratio of 1/8 at ≤ 18˚ C, ikaite (CaCO3 6H2O) acts as a
precursor phase for aragonite formation. (ii) In contrast higher temperatures induced
the formation of Mg-rich amorphous CaCO3 (Mg-ACC) which was subsequently
transformed to Mg-rich calcite. In situ Raman spectra showed that the transformation of
Mg-ACC to Mg-calcite occurs at a higher rate (∼ 8 min) compared to that of ikaite
to aragonite (> 2 h). Thus, the formation of aragonite rather than of Mg-calcite
occurs due to the slower release of Ca2+and CO32− ions into the Mg-rich reactive
solution during retarded ikaite dissolution. This behavior is generally consistent with
the observation that calcite precipitation is inhibited at elevated aqueous Mg/Ca
ratios.
[1] Addadi L., Raz S. and Weiner S. (2003) Advanced Materials 15, 959-970.
[2] Rodriguez-Blanco J. D., Shaw S., Bots P., Roncal-Herrero T. and Benning L. G (2014)
Geochimica et Cosmochimica Acta 127, 204-220 |
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