CO2 sequestration using red gypsum via pH-swing process: Effect of carbonation temperature and NH4HCO3 on the process efficiency

The main purpose of this study is to investigate the effect of reaction temperature and NH4HCO3 on the overall performance of a pH swing mineral carbonation. The overall performance of the pH swing process is investigated in terms of carbonation efficiency and product purity. Initially, 2 M H2SO4 is used for red gypsum dissolution at 70 °C. Then in the second stage, NH4OH is added for increasing the solution pH and removing the impurities from solutions. Finally, CO32- is introduced to calcium rich solution in the form of pure CO2 and NH4HCO3. The experimental results show that using NH4HCO3 improves carbonation efficiency and product purity. Carbonation efficiency attains a maximum value at 75 °C and then decreases gradually with increasing temperature up to 300 °C, with both CO2 and NH4HCO3. In this research, CaCO3 with the maximum purity of 99.05% is produced successfully when NH4HCO3 is used as a CO32- source.