Role of intercalated water in calcium hydroxide interlayers for carbonation reaction

Carbonation of calcium hydroxide (Ca(OH)2) is an indispensable process with applications in the stable storage of CO2, geological disposal of radioactive waste, and cement manufacture for the construction industry. In the carbonation reaction of Ca(OH)2, water plays an important role in the conversion of CO2 and increases the thermodynamic stability of calcium carbonate. Therefore, understanding the interaction between water and Ca (OH)2 is essential for controlling the kinetics and thermodynamics of the carbonation reaction of Ca(OH)2. In this study, changes in the physical and chemical properties of Ca(OH)2 that appear before the carbonation of hydrated Ca(OH)2 were observed through XRD and NMR analyses. Through XRD analysis, the interplanar distance of hydrated Ca(OH)2 increased by approximately 0.39% compared to that of the pristine Ca(OH)2. Furthermore, we quantified the intercalated water through NMR analysis based on water signal appearing around 0.9 ppm, which was approximately 3.0-7.0 wt% of Ca(OH)2. Through theoretical calculations, the hydrated Ca(OH)2 formed a stable structure with intercalated water molecules, resulting in lower reaction barrier and heat of reaction of the Ca(OH)2 carbonation. For the first time, the intercalation of water between the Ca(OH)2 interlayers is observed, and its importance in the carbonation reaction is established.