Contributory Roles of pH and Temperature in Phase and Morphology CaCO₃ Formation Using Steamed Ammonia Liquid Waste...

Resource utilization of waste and CO₂ capture are one of the key technologies, and temperature and pH are the key factors that determine the nucleation and crystallization of CaCO₃. Factors such as temperature and pH on CaCO₃ production, polymorphism, and growth processes were studied using steamed ammonia liquid waste as direct carbonation. The resulting CaCO₃ particles were characterized by using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The findings demonstrated that the original CaCl₂ pH and reaction temperature had a synergistic effect on the crystal-phase composition and morphology of CaCO₃. The original CaCl₂ pH has a strong competition on CaCO₃ nucleation, crystallization, and growth process under the 40-60 °C reaction temperature. The mechanism analysis indicated different phases and morphology CaCO₃ formation due to the reaction system. Ca²⁺, CO₂^-3, H⁺, and OH^- concentration; nucleation rate; carbonation rate; calcite dissolution rate; and dissolution critical value of CaCO₃ were changed by the competitive role of reaction temperature and pH. This study successfully demonstrated the selective synthesis of all the anhydrous crystalline polymorphs of CaCO₃ using a unique approach.