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Effects of magnesium, temperature and supersaturation on calcium carbonate precipitation

Calcium carbonate (CaCO3) is an abundant mineral ; it makes up approximately 5 wt% of the Earth's crust, [1] but it can also be found in organisms and biological systems, like mollusks and egg shells, pearls, corals and exoskeletons of arthropods.[2] Calcium carbonate precipitates in the form of several distinct solid phases: amorphous calcium carbonate (ACC), two hydrates (monohydrate and hexahydrate), and three anhydrous polymorphs (calcite, aragonite and vaterite) of which calcite is the most stable form under standard conditions. Aragonite occurs mainly in skeletons of mollusks and corals, in pearls and in hot springs' sediment.[3, 4] Magnesium ions and temperature are two key parameters which control the aragonite formation. In this study, the influence of Mg2+ and temperature on the phase composition, aggregation and morphology of precipitated calcium carbonate crystals is investigated. However, the supersaturation was also considered as a critical parameter of precipitation. It was found that in the low- supersaturation system, at increased Mg2+ concentration and at increased temperature, the aragonite crystals are less aggregated. In addition the amount of crystals sharing {; ; 110}; ; faces and having larger extension of {; ; 001}; ; faces increases. On the contrary, in the high- supersaturation system formation of high magnesium calcite was observed. The obtained results may be relevant in biological, geochemical and technological contexts. [1] W. D. Carlson, Rev. Mineral., 1983, 11, 191–225. [2] G. Falini and S. Fermani, Cryst. Res. Technol., 2013, 48, 864–876. [3] G. Falini, S. Fermani and S. Goffredo, Semin. Cell Dev. Biol., 2015, 46, 17–26. [4] C. Perdikouri, A. Kasioptas, T. Geisler, B. C. Schmidt and A. Putnis, Geochim. Cosmochim. Acta, 2011, 75, 6211–6224.

calcium carbonate ; precipitation ; magnesium ; temperature

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