Impacts of aqueous carbonate accumulation rate, magnesium and polyaspartic acid on calcium carbonate formation (6-40 degrees C)

Abstract

The experimental data clearly reveal that the time for CaCO3 nucleation depends strongly on ACAR, T, [Mg2+] (>0.5 mmol l(-1)), and [Pasp] (>0.1 mg l(-1)) but not on the formation of different CaCO3 polymorphs. Elevated ACAR results in earlier CaCO3 formation and causes Mg2+ to have less of an impact on the retardation of nucleation. The ion activity product (IAP) required for CaCO3 nucleation is positively correlated to the subsequent CaCO3 precipitation rates but is independent of whether aragonite or calcite formation is induced. The type of CaCO3 polymorph from the primary nuclei is controlled by the influences of Mg2+ and Pasp, which are coupled to ACAR and T. Elevated ACAR, T, and [Mg2+] promote the formation of aragonite, and high [Mg2+] levels suppress the formation of vaterite. In contrast, [Pasp] > 0.02 mg l(-1) inhibits aragonite and favours vaterite formation. Thus, if both Mg2+ and Pasp are present, the formation of calcite is favoured. The precipitation rates for ongoing calcite and aragonite formation are nearly the same at analogous conditions and particularly for a given IAP. According to our experimental results, the combined impacts of ACAR, T, [Mg2+], and [Pasp] must be considered to identify distinct conditions of CaCO3 polymorph formation and precipitation kinetics. (C) 2013 Elsevier B.V. All rights reserved.

Keywords

Calcite; Aragonite; Vaterite; Magnesium; Polyaspartic acid; Precipitation rate

Published in

Chemical Geology
2013, volume: 340, pages: 105-120
Publisher: ELSEVIER SCIENCE BV

SLU Authors

• Köhler, Stephan

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    
  • Graz University of Technology

UKÄ Subject classification

Geochemistry

Publication identifier

• DOI: https://doi.org/10.1016/j.chemgeo.2012.12.014

Permanent link to this page (URI)

https://res.slu.se/id/publ/54314