Barium isotope fractionation during the experimental transformation of aragonite to witherite and of gypsum to barite, and the effect of ion (de)solvation

Böttcher, Michael E.; Neubert, Nadja; von Allmen, Katja; Samankassou, Elias; Nägler, Thomas (2018). Barium isotope fractionation during the experimental transformation of aragonite to witherite and of gypsum to barite, and the effect of ion (de)solvation. Isotopes in environmental and health studies, 54(3), pp. 324-335. Taylor & Francis 10.1080/10256016.2018.1430692

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In this study, we present the experimental results for stable barium (Ba) isotope fractionation (137Ba/134Ba) during the transformation of aragonite (CaCO3) and gypsum (CaSO4·2H2O) in Ba-bearing aqueous solution to witherite (BaCO3) and barite (BaSO4), respectively. The process was studied at three temperatures between 4 and 60 °C. In all cases, the transformation leads to a relative enrichment of the lighter 134Ba isotope in the solid compared to the aqueous solution, with 137/134Ba enrichment factors between –0.11 and −0.17 ‰ for BaCO3, and –0.21 and –0.26 ‰ for BaSO4. The corresponding mass-dependent 138/134Ba enrichment factors are −0.15 to –0.23 ‰ for BaCO3, and –0.28 to –0.35 ‰ for BaSO4. The magnitude of isotope fractionation is within the range of recent reports for witherite and barite formation, as well as trace Ba incorporation into orthorhombic aragonite, and no substantial impact of temperature can be found between 4 and 80 °C. In previous studies, ion (de)solvation has been suggested to impact both the crystallization process of Ba-bearing solids and associated Ba isotope fractionation. Precipitation experiments of BaSO4 and BaCO3 using an methanol-containing aqueous solution indicate only a minor effect of ion and crystal surface (de)solvation on the overall Ba isotope fractionation process.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences

UniBE Contributor:

Nägler, Thomas

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

1025-6016

Publisher:

Taylor & Francis

Language:

English

Submitter:

Thomas Nägler-Jenni

Date Deposited:

30 Jan 2019 10:19

Last Modified:

30 Jan 2019 10:19

Publisher DOI:

10.1080/10256016.2018.1430692

PubMed ID:

29400989

URI:

https://boris.unibe.ch/id/eprint/122258

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