Precipitation of Mg-carbonates at elevated temperature and partial pressure of CO2

At all investigated temperatures, we observed direct precipitation of magnesite while at 120 °C and 150 °C also simultaneous precipitation of magnesite and hydromagnesite followed by the transformation of the latter into the former. Under highly supersaturated conditions with respect to magnesite, SM as large as 20, magnesite nucleated rapidly when the system was also supersaturated with respect to hydromagnesite, SH as large as 1.5; whereas no nuclei formed within 20 h, otherwise. The analysis of the data collected at 120 °C and at 150 °C highlighted that the change in the type of mechanism was associated with the initial supersaturation ratios and the initial concentration of magnesium in solution. At 120 °C, the transformation process lasted for 2 h, slowing down the formation of magnesite, despite of the large SM; whereas at 150 °C, the transformation process was only 5 min long, without affecting magnesite precipitation.