On the nucleation of ikaite (CaCO3x6H2O) – A comparative study in the presence and absence of mineral surfaces

Strohm, Samuel B.; Inckemann, Sebastian E.; Gao, Kun; Schweikert, Michael; Lemloh, Marie-Louise; Schmahl, Wolfgang W. und Jordan, Guntram (2022): On the nucleation of ikaite (CaCO3x6H2O) – A comparative study in the presence and absence of mineral surfaces. In: Chemical Geology, Vol. 611, 121089

Abstract

The formation of ikaite (CaCO3x6H2O) was studied in the presence and absence of quartz and mica surfaces using desupersaturation curves from cryo-mixed-batch-reactor experiments. Upon nucleation and growth within the reactor, the solution approached solubility of the precipitating carbonate phase. For ikaite, a solubility constant of log Ksp ikaite = -7.3 ± 0.1 was found (T = 0 °C). At supersaturations Ωikaite < 15, the nucleation of ikaite was significantly promoted by the presence of quartz or mica. This promotion prevented a competing nucleation of anhydrous calcium carbonates. In the presence of quartz or mica, therefore, ikaite forms over a much broader supersaturation range than in the absence. Similarly strong promotors of ikaite nucleation rather than anhydrous carbonate nucleation were previously attributed to calcite-inhibiting substances only. At supersaturations Ωikaite ≥ 8, application of classical nucleation theory on induction periods of ikaite formation yielded an effective interfacial energy of 15 ± 3 mJ/m2. Compared to data of anhydrous CaCO3 phases, this interfacial energy is low and expresses the highly hydrated character of ikaite. At supersaturations Ωikaite ≥ 18, a transient amorphous phase appeared besides ikaite. Our results show that a comprehensive understanding of ikaite formation in natural settings requires consideration not only of supersaturation and presence of calcite-inhibitors but also of the presence or absence of mineral surfaces capable of promoting heterogeneous nucleation of ikaite.

• Item Type: Journal article
• Form of publication: Publisher's Version
• Keywords: Ikaite, Heterogeneous nucleation, Non-classical nucleation, ACC, Surfaces, Hydrous carbonate minerals
• Faculties: Geosciences > Department of Earth and Environmental Sciences > Crystallography and Materials Science
• Subjects: 500 Science > 500 Science; 500 Science > 550 Earth sciences and geology
• ISSN: 0009-2541