Structural and physicochemical characterization of basic calcium carbonate (BCC), Ca₃(CO₃)₂(OH)₂•H₂O

Autor(en)

Manuel Ripken, Florian Gallien, Thomas Schlotterbach, Christian L. Lengauer

Abstrakt

Calcium carbonate hydroxide hydrate or basic calcium carbonate (BCC) is a metastable, relevant phase occurring in various industrial carbonation processes and biologically induced calcium-carbonate precipitation. The best conditions for the longterm storage of BCC are in a dry, non-heated environment. This is confirmed by powder X-ray analysis. Under humid conditions sample material transforms into vaterite-type calcium carbonate, while under a dry heating process it dehydrates and dehydroxylates to calcite-type calcium carbonate. Under ambient humidity and temperature conditions the dehydrated modification does not convert back to BCC or calcite-type calcium carbonate, but also transforms to the vaterite-type calcium carbonate. High-quality scanning electron microscopy images of a rapidly converted vaterite-type calcium carbonate reveal imperfect pseudomorphs of vaterite after the platy BCC. Literature data reported the chemical formula of BCC as a sesquihydrate. The observed and calculated weight losses are close to the calculated value for a monohydrate, which leads to the corrected chemical formula of BCC as Ca3(CO3)2(OH)2·H2O or 2CaCO3·Ca(OH)2·H2O. Structure solution and Rietveld refinement (Rwp = 11.2%) based on powder X-ray patterns reveal the hitherto unknown atomic arrangement. It crystallizes to a monoclinic lattice with space group Pc (no. 7); the cell parameters of the pseudoorthorhombic cell are a = 8.6552(2), b = 6.5529(2), c = 7.0801(2)Å, ß = 90.059(4)°, V = 401.56(2)Å3, Z = 2 and calc = 2.417 g·cm3. The structure model of BCC consists of three edge-sharing Ca-polyhedra interconnected by two CO3 groups. Based on bond-valence calculation two oxygen positions can be attributed to hydroxyl groups, one oxygen position represents a water molecule. The main structural motif is a chain of edge-sharing Ca-O2(OH)4 octahedra running parallel to the c-axis. The structure exhibits similarities to those of vaterite, portlandite and hydromagnesite.

Organisation(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

Omya GmbH

Journal

European Journal of Mineralogy: an international journal of mineralogy, geochemistry and related sciences

Band

30

Seiten

85-96

Anzahl der Seiten

12

ISSN

0935-1221

DOI

https://doi.org/10.1127/ejm/2018/0030-2702

Publikationsdatum

02-2018

Peer-reviewed

Ja

ÖFOS 2012

105116 Mineralogie, 104017 Physikalische Chemie, 105113 Kristallographie

Schlagwörter

ASJC Scopus Sachgebiete

Geochemistry and Petrology

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/fd17f9d4-7b8a-4430-8b6e-f901c89e505a