CaCO3 formation at -15 °C and non-freezing conditions

The formation of CaCO3 under ambient and low temperature environmental conditions has been extensively studied during the last decades. However, available data on the formation kinetics and mechanisms of CaCO3 at temperatures far below 0 °C are sparse. Here, we present CaCO3 formation pathways at -15 °C using a hypersaline sodium chloride solution at distinct molar Mg:Ca ratios of 0, 0.5, and 1. The (trans)formation process is monitored by pH and in-situ Raman spectroscopy. The freeze-dried precipitates are characterized by X-ray diffraction and the morphology is studied by scanning electron microscopy. These preliminary results help to understand the formation mechanisms of CaCO3 at temperatures below zero degree centigrade from homogeneous media and to refine experimental setups for mimicking extreme environmental carbonate formation conditions, e.g., in Antarctica or extraterrestrial environments.