Chemical controls on ikaite formation

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
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Chemical controls on ikaite formation

Messaggio da Marco E. Ciriotti » mer 30 mag, 2018 13:44

Prossima pubblicazione.

Referenza:
▪ Tollefsen, E., Stockmann, G., Skelton, A., Mörth, C.-M., Dupraz, C., Sturkell, E. (2018): Chemical controls on ikaite formation. MIneralogical Magazine, 82, (in press).
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 24842
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: Chemical controls on ikaite formation

Messaggio da Marco E. Ciriotti » ven 09 nov, 2018 20:38

Pubblicazione effettuata.

Referenza:
▪ Tollefsen, E., Stockmann, G., Skelton, A., Mörth, C.-M., Dupraz, C., Sturkell, E. (2018): Chemical controls on ikaite formation. MIneralogical Magazine, 82, 1119-1129.

Abstract:
The hydrated carbonate mineral ikaite (CaCO3·6H2O) is thermodynamically unstable at all known conditions on Earth. Regardless, ikaite has been found in marine sediments, as tufa columns and in sea ice. The reason for these occurrences remains unknown. However, cold temperatures (<6°C), high pH and the presence of Mg2+ and SO42– in these settings have been suggested as factors that promote ikaite formation. Here we show that Mg concentration and pH are primary controls of ikaite precipitation at 5°C. In our experiments a sodium carbonate solution was mixed with seawater at a temperature of 5°C and at a constant rate. To test the effect of Mg2+ and SO42– we used synthetic seawater which allowed us to remove these elements from the seawater. The pH was controlled by different ratios of Na2CO3 and NaHCO3 in the carbonate solution. We found that ikaite precipitated when both seawater and synthetic seawater from which SO4 had been removed were used in the experiments. However, ikaite did not precipitate in experiments conducted with synthetic seawater from which Mg had been removed. In these experiments, calcite precipitated instead of ikaite. By varying the Mg concentration of the synthetic seawater and the pH of the sodium carbonate solution, we constructed a kinetic stability diagram for ikaite and calcite as a function of Mg concentration and pH. One possible explanation of our finding is that Mg2+ inhibits calcite nucleation and thereby allows metastable ikaite to form instead.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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