Precipitated CaCO₃ with Unique Crystalline Morphology Prepared from Limestone

A carbonation method has been applied to induce the precipitation reaction of calcium carbonate powders with unique morphology. The reaction was strongly influenced by temperature, pH, CO₂ gas flow rate and flow duration. Characterization of the as-prepared CaCO₃ by XRD and SEM demonstrated that the vaterite phase was mostly formed at low temperature and CO₂ gas flow rate. Phase transformation from vaterite to calcite phases at room temperature was initiated by the formation of calcite structure in ¼ spherical shapes and was followed by transformation to the rhombic structure. The highest growth of calcite structure, resulting in purity up to 98.6%, occurred at the CO₂ gas flow rate of 5 SCFH in 36 s. Aragonite particles were produced at CO₂ gas flow rate of 0.5 and 5 SCFH to yield 99.2% and 72.3% phase purities, respectively, with needle-like morphology at a higher temperature of 85oC. Furthermore, the reaction with lower CO₂ gas flow rate (2 SCFH) led to the formation of aragonite with a flower-like morphology.