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.