Hodkin, DJ orcid.org/0000-0003-1265-6472, Stewart, DI orcid.org/0000-0001-5144-1234, Graham, JT et al. (2 more authors) (2018) Enhanced Crystallographic incorporation of Strontium(II) ions to Calcite via Preferential Adsorption at Obtuse growth steps. Crystal Growth & Design, 18 (5). pp. 2836-2843. ISSN 1528-7483
Abstract
Sr-containing calcium carbonates were precipitated from solutions containing Ca(OH)₂, SrCl₂ and Na₂CO₃ in a reactor where constant solution composition was maintained. The total concentration of divalent ions was same in all experiments, but the Sr/Ca ratio was varied between 0.002 and 0.86, and the pH value was between 12.02 and 12.25. All solutions were oversaturated with respect to calcite (SIcalcite = 1.2-1.5). Calcite was the only product formed at low Sr/Ca ratios, but at Sr/Ca ≥ 0.45 strontianite was detected in some systems. Sr-rich precipitate was observed in both a surface layer on (6.9-6 µm) rhombic calcite seed crystals and as smaller (> 3.64-1.96 µm) calcite crystals that were elongated along their C-axis. The degree of crystal elongation increased with the Sr/Ca ratio in those crystals. Precipitates recovered from low Sr/Ca ratio experiments exhibited an XRD spectrum identical to that of rhombic calcite, however the peaks attributed to Sr-containing calcite shifted progressively to lower 2θ values with increasing solution Sr/Ca ratio, indicating increased lattice volume. Sr K-edge EXAFS analysis of the precipitates showed that the shift in morphology and lattice volume is accompanied by a change in the local coordination of Sr²⁺ in calcite. The Sr-O bond lengths were similar to the Ca-O bond lengths in calcite, but Sr-O coordination increased from 6 fold in crystals containing 0.21 Wt. % Sr, to 8 fold in crystals containing 9.47 Wt. % Sr, and the Sr-Ca coordination decreased from 6 and 6 (for the first and second Sr-Ca shells respectively) to 4 and 1. It is suggested that Sr²⁺ undergoes preferential incorporation at obtuse (+) growth sites on the calcite surface due to its large ionic radius (1.13 Å), and this increases the growth rate parallel to the C-axis, resulting in the observed elongation in this direction.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | (c) 2018, American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Crystal Growth & 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.7b01614 |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Civil Engineering (Leeds) 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: | 17 Apr 2018 11:40 |
Last Modified: | 11 Apr 2019 00:43 |
Status: | Published |
Publisher: | American Chemical Society |
Identification Number: | 10.1021/acs.cgd.7b01614 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:129662 |