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, CO₃^2– 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 CO₃^2– source.