The formation and transformation mechanism of calcium carbonate in water |
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| Institution: | 1. Department of Earth and Space Sciences, University of Washington, Seattle, WA, United States;2. Department of Earth Sciences, Syracuse University, Syracuse, NY, United States;3. Departamento de Ecología, Pontificia Universidad Católica de Chile, Santiago, Chile;4. Institute of Ecology and Biodiversity, Santiago, Chile;5. Departamento de Microbiología y Genética Molecular, Pontificia Universidad Católica de Chile, Santiago, Chile;1. BRGM – 3 avenue Claude Guillemin, 45100 Orléans, France;2. Université d’Orléans-CNRS/INSU-BRGM, UMR ISTO 7327, 45071 Orléans, France;3. LUNAM, Université du Maine, Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France;1. Institute of Applied Geosciences, Graz University of Technology, Rechbauerstrasse 12, A-8010 Graz, Austria;2. Competence Center Mineralogy & Beneficiation, Omya GmbH, Gersheim Strasse 1-2, 9722 Gummern, Austria;3. Géosciences Environnement Toulouse (GET), CNRS, UMR 5563, Observatoire Midi-Pyrénées, 14 Avenue Edouard Belin, 31400 Toulouse, France;4. Omya International AG, Baslerstrasse 42, CH-4665 Oftringen, Switzerland;5. School of Chemical Engineering, Department of Bioproducts and Biosystems, Aalto University, FI-00076 Aalto, Helsinki, Finland;1. Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA;2. Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99354, USA;3. Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA |
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| Abstract: | Highly supersaturated solutions of Ca2+ and CO2?3 ions rapidly precipitate amorphous calcium carbonate, ACC, the logarithmic thermodynamic solubility product of which is about ?6.0 at 25°C. The ACC initially formed is transformed to a mixture of several crystalline calcium carbonate polymorphs within several minutes. The transformed polymorphs are vaterite and calcite at low temperature (14 to 30°C), and aragonite and calcite at high temperature (60 to 80°C). At intermediate temperatures (40 to 50°C) the formation of all three polymorphs was observed. Metastable polymorphs are gradually transformed to the stable form, calcite. It takes about 200 min at 25°C and 370 min at 30°C for the complete transformation of vaterite to calcite, and 1000–1300 min for that of aragonite to calcite at 60–80°C. At 50°C, vaterite is predominantly transformed at first to aragonite within 60 min, and then the aragonite is transformed to calcite in about 900 min. The results of the change in the ion activity product of the solution and the abundances of the polymorphs strongly suggest that the polymorphic transformation of vaterite and aragonite to calcite takes place through dissolution of the metastable phase and growth of the stable phase, calcite. The rate-determining step of the transformation is the growth of calcite. The relative abundance of vaterite becomes higher at 25°C with increasing concentrations of calcium and carbonate ions in the supersaturated solution. When the ion activity product of the initial supersaturated solution is lower than the solubility product of ACC at 25°C, only vaterite directly precipitates after some induction period. The vaterite crystals formed are free of calcite seeds and the vaterite saturated solutions are stable for several days. |
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