Characteristics of precipitated calcium carbonate by hydrothermal and carbonation processes with mega-crystalline calcite using rotary microwave kiln

In the conventional kiln, mega-crystalline calcite (m-CC) breaks apart easily during calcinations, and cannot be easily converted to CaO due to that it requiring a lot of heat. In this study, m-CC was calcined to CaO of around 1 mm using the rotary microwave kiln. Furthermore, CaCO3 was produced by the carbonation process and hydrothermal process, and the form of CaCO3 was characterized.Calcination of m-CC using the rotary microwave kiln resulted in CaO (97 wt%) of relatively fine size.CaCO3 of colloidal-shaped and 6 μm in size could be prepared by applying the carbonation process to Ca(OH)2 using a bubble reactor at 25 °C. As the carbonation temperature increased from 25 to 80 °C, the shape of prepared CaCO3 changed from a colloidal-type to spindle-type of 1 μm due to self-assembly. Also, hexagonal-shaped aragonite could be prepared by the hydrothermal process with the supersaturated Ca(HCO3)2 solutions.