Littlewood, JL, Shaw, S, Peacock, CL orcid.org/0000-0003-3754-9294 et al. (3 more authors) (2017) Mechanism of enhanced strontium uptake into calcite via an amorphous calcium carbonate (ACC) crystallisation pathway. Crystal Growth and Design, 17 (3). pp. 1214-1223. ISSN 1528-7483
Abstract
Calcite formation via an amorphous calcium carbonate (ACC) precursor phase potentially offers a method for enhanced incorporation of incompatible trace metals, including Sr2+. In batch crystallisation experiments where CaCl2 was rapidly mixed with Na2CO3 solutions the Sr2+ : Me2+ ratio was varied from 0.001 to 0.1; and, the pathway of calcite precipitation was directed by either the presence or absence of high Mg2+ concentrations (i.e. using a Mg2+ : total Me2+ ratio of 0.1). In the Mg-free experiments crystallisation proceeded via ACC → vaterite → calcite and average Kd Sr values were between 0.44-0.74. At low Sr2+ concentrations (Sr2+ : Me2+ ratio ≤ 0.01) EXAFS analysis revealed that the Sr2+ was incorporated into calcite in the 6 fold coordinate Ca2+ site. However, at higher Sr2+ concentrations (Sr2+ : Me2+ ratio = 0.1), Sr2+ was incorporated into calcite in a 9-fold site with a local coordination similar to Ca2+ in aragonite, but calcite-like at longer distances (i.e. > 3.5 Å). In the high-Mg experiments the reaction proceeded via an ACC → calcite pathway with higher Kd Sr of 0.90-0.97 due to the presence of Mg2+ stabilising the ACC phase and promoting rapid calcite nucleation in conjunction with higher Sr2+ incorporation. Increased Sr2+ concentrations also coincided with higher Mg2+ uptake in these experiments. Sr2+ was incorporated into calcite in a 9-fold coordinate site in all the high-Mg experiments regardless of initial Sr2+ concentrations, likely as a result of very rapid crystallisation kinetics and the presence of smaller Mg2+ ions compensating for the addition of larger Sr2+ ions in the calcite lattice. These experiments show that the enhanced uptake of Sr2+ ions can be achieved by calcite precipitation via ACC, and may offer a rapid, low temperature, low-cost, method for removal of several incompatible Me2+ ions (e.g. Pb2+, Ba2+, Sr2+) during effluent treatment.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2017 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Crystal Growth and Design, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.cgd.6b01599. Uploaded in accordance with the publisher's self-archiving policy. |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Earth Surface Science Institute (ESSI) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 24 Jan 2017 11:31 |
Last Modified: | 19 Jan 2018 01:38 |
Published Version: | https://doi.org/10.1021/acs.cgd.6b01599 |
Status: | Published |
Publisher: | American Chemical Society |
Identification Number: | 10.1021/acs.cgd.6b01599 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:111108 |