Morphology Controls on Calcite Recrystallization.
Environmental scientists and geoscientists working in different fields regard the reactivity of calcite and corresponding changes in its trace elemental- or isotopic composition from diametrically opposed points of view. As one extreme, calcite based environmental remediation strategies rely on the fast recrystallization of calcite and the concurrent uptake and immobilization of pollutants. Paleo-ecological investigations denote the other extreme, and rely on the invariability of calcite composition over geological periods of time. We use long-term radiotracer experiments to quantify recrystallization rates of seven types of calcite powder with diverse morphology and particle size distribution. On the one hand our results demonstrate the long-term metastability of calcite with equilibrated crystal surfaces even at isotopic dis-equilibrium. On the other hand, we document the extremely high reactivity and interfacial free energy of freshly ground, rough calcite. Our results indicate that bulk calcite recrystallization is an interfacial free energy driven Ostwald-ripening process, in which particle roughness effects dominate over the effect of crystal habitus and particle size. We confirm that the dynamic equilibrium exchange of crystal constituents between kink sites involves an activation barrier of about 25 kJ/mol. At room temperature the equilibrium exchange is limited to a near surface region and proceeds at a rate of (3.6 ± 1.4)·10-13mol/(m2·s).
Institute for Nuclear Waste Disposal, Karlsruhe Institute of Technology , Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Frank
F
Heberling
Institute for Geography and Geoecology, Karlsruhe Institute of Technology , Kaiserstraße 12, 76131 Karlsruhe, Germany.
Leonie
L
Paulig
College of Chemistry and Molecular Engineering, Peking University , 5 Yiheyuan Road, 100871 Beijing, China.|Institute for Nuclear Waste Disposal, Karlsruhe Institute of Technology , Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Zhe
Z
Nie
Institute for Nuclear Waste Disposal, Karlsruhe Institute of Technology , Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Dieter
D
Schild
Institute for Nuclear Waste Disposal, Karlsruhe Institute of Technology , Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Nicolas
N
Finck
D002119:Calcium Carbonate / Q000737:chemistry*; D010316:Particle Size
D002119:Calcium Carbonate