Two-step Precipitation Synthesis of CaCO<sub>3</sub> from Steelmaking Slag in Glycerol Solution

Synthesis of CaCO3 from steelmaking slag is possible to CO2 fixation. This study investigated a two-step precipitation method to synthesize CaCO3 powders of varying whiteness and particle sizes from steelmaking slag in an aqueous glycerol solution. The calcium (free-CaO) in the steelmaking slag was readily extracted upon contact with a glycerol solution. Subsequently, introducing CO2 into the solution reduced the pH due to its high alkalinity, leading to the precipitation of CaCO3. Additionally, precipitation of CaCO3 was observed upon aging the filtrate solution post-CaCO₃ separation. By adjusting the solution's pH to 6.7 and introducing CO2, the whiteness of the precipitated CaCO3 was 76.6%, while that of the post-precipitated CaCO3 was 86.5%. The average particle size of the post-precipitated CaCO3 was around 4.5 μm, which was 2.5 times larger than that of the initial-precipitate. Increasing the pH of the solution resulted in a decrease in the whiteness of the post-precipitated CaCO3 and an increase in its particle size. Therefore, this method allows for easy control of the whiteness and particle size of CaCO3 by adjusting the pH of the Ca2+-containing glycerol solution through CO2 introduction without the necessity of high-pressure, high-temperature conditions or specialized equipment. This process enhances carbon capture and utilization for CaCO3 production from steelmaking slag.