Thermochemistry of strontium incorporation in aragonite from atomistic simulations

Abstract

We have investigated the thermodynamics of mixing between aragonite (orthorhombic CaCO 3 ) and strontianite (SrCO 3 ). In agreement with experiment, our simulations predict that there is a miscibility gap between the two solids at ambient conditions. All Sr x Ca 1Àx CO 3 solids with compositions 0.12 < x < 0.87 are metastable with respect to separation into a Ca-rich and a Sr-rich phase. The concentration of Sr in coral aragonites (x $ 0.01) lies in the miscibility region of the phase diagram, and therefore formation of separated Sr-rich phases in coral aragonites is not thermodynamically favorable. The miscibility gap disappears at around 380 K. The enthalpy of mixing, which is positive and nearly symmetric with respect to x = 0.5, is the dominant contribution to the excess free energy, while the vibrational and configurational entropic contributions are small and of opposite sign. We provide a detailed comparison of our simulation results with available experimental data.

Biogenic and diagenetic indicators in archaeological and modern otoliths: Potential and limits of high definition synchrotron micro-XRF elemental mapping

“…The highest Sr concentrations measured in HP-12 and GP-292 exceed the 58 μmol·g −1 equilibrium solubility of Sr in bulk aragonite reported from crystallisation experiments (Plummer and Busenberg, 1987). Theoretical studies, however, indicate significantly higher values (up to 1100 μmol·g − 1 ) (Ruiz-Hernandez et al, 2010), well above the highest Sr concentrations measured in this work. To the authors' knowledge no elemental data have been previously published for G. peruvianus.…”

Preliminary investigations on picoplankton-related precipitation of alkaline-earth metal carbonates in meso-oligotrophic lake Geneva (Switzerland)

“…5), equal to that found by Lauchnor et al (2013) in microbially induced Ca and Sr co-precipitates. This value lies in the miscibility region of the phase diagram of Sr x Ca 1-x CO 3 solids (Ruiz-Hernandez et al, 2010). As already mentioned, in lake Constance this ratio -computed for well crystallised calcite -is only 0.0084 (Stabel et al, 1991).…”

Cation distribution and mixing thermodynamics in Fe/Ni thiospinels

“…Grau-Crespo et al (2003 and Ruiz-Hernandez et al (2010)). This program uses the crystal symmetry to reduce the configurational space that must be evaluated with the DFT calculations, selecting only the symmetrically inequivalent configurations.…”