Polymorph and morphology of CaCO3 in relation to precipitation conditions in a bubbling system

Simulating the typical carbonation step in a mineral CO2 sequestration, precipitated calcium carbonate (PCC) was prepared by bubbling CO2 gas into a rich Ca solution. These carbonation reactions were conducted at three pH ranges, namely 10.0-9.0, 9.0-8.0, and 8.0-7.0, in which temperature and CO2 flow rate are additional experimental variables. The PCC obtained in experiments was examined by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). It was found that supersaturation determined by pH value and flow rate of CO2 has significant influence on polymorph of PCC. Vaterite was preferably formed at high supersaturation, while dissolution of metastable vaterite and crystallization of calcite occurred at low supersaturation. High temperature is a critical factor for the formation of aragonite. At 70 °C, vaterite, calcite and aragonite were observed to coexist in PCC because transformation from vaterite to aragonite via calcite occurred at this temperature. Scanning electron microscopy (SEM) technology was performed on prepared PCC, and various morphologies consistent with polymorphs were observed.