Electrophoretic and potentiometric signatures of multistage CaCO3 nucleation

Marzena Prus; Karolina Szymanek; Jennifer Mills; Laura Nielsen Lammers; Wojciech Piasecki; Karolina Kedra-Królik; Piotr Zarzycki

doi:10.1016/j.jcis.2019.03.002

Electrophoretic and potentiometric signatures of multistage CaCO₃ nucleation

J Colloid Interface Sci. 2019 May 15:544:249-256. doi: 10.1016/j.jcis.2019.03.002. Epub 2019 Mar 2.

Authors

Marzena Prus¹, Karolina Szymanek², Jennifer Mills³, Laura Nielsen Lammers³, Wojciech Piasecki², Karolina Kedra-Królik¹, Piotr Zarzycki⁴

Affiliations

¹ Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland.
² Department of Chemistry and Biochemistry, Józef Piłsudski University of Physical Education, Warsaw, Poland.
³ Department of Environmental Science, Policy and Management, University of California, Berkeley, CA, United States.
⁴ Energy Geosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, United States; Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland. Electronic address: ppzarzycki@lbl.gov.

PMID: 30851686
DOI: 10.1016/j.jcis.2019.03.002

Abstract

Hypothesis: Calcium carbonate nucleation is often a complex and multistep process that is difficult to follow in situ. The time-resolved electrochemical and electrophoretic methods can provide a new insight into the nucleation pathway.

Experiments: Here, we used a combination of speciation calculations with time-resolved electrophoretic and potentiometric methods to monitor calcium carbonate precipitation from a slightly supersaturated solution.

Findings: After an initial mixing period of three minutes in which metastable CaCO₃ phases may have nucleated and subsequently dissolved due to locally-high supersaturations, bulk solution pH and Ca²⁺ concentrations stabilize before decreasing in tandem with the precipitation of a CaCO₃ phase. After an hour, the precipitate is dominated by calcite that grows at the expense of dissolving vaterite. The time-dependent electrokinetic potential shows analogous signatures of multistage nucleation process: initial rapid changes in ζ-potential are followed by much slower equilibration starting about one hour after reagents are mixed. The changes in ζ-potential, solution pH, saturation indexes, and particle morphology are consistent with vaterite to calcite transformation via dissolution of the former and recrystallization of the latter. These findings highlight the potential use of ζ-potential measurements for monitoring polymorphic transformations of carbonate phases in-situ.

Keywords: Amorphous calcium carbonate; Calcite; Calcium carbonate; Carbonate speciation; Electrical double layer; Multistage nucleation pathway; Vaterite; ζ-potential.