Synthesis of Ca(OH) 2 and Na 2 CO 3 through anion exchange between CaCO 3 and NaOH: effect of reaction temperature

The CO 2 released upon calcination of limestone accounts for the largest portion of the emissions from the cement, lime, and slaked lime manufacturing industries. Our previous works highlighted the possibility for a no-combustion decarbonisation of CaCO 3 through reaction with NaOH solutions to produce Ca(OH) 2 at ambient conditions, while sequestrating the process CO 2 in a stable mineral Na 2 CO 3 ·H 2 O/Na 2 CO 3 . In this study, the effect of temperature was assessed within the range of 45–80 °C, suggesting that the process is robust and only slightly sensitive to temperature fluctuations. The proportioning of the precipitated phases Na 2 CO 3 ·H 2 O/Na 2 CO 3 was also assessed at increasing NaOH molalities and temperatures, with the activity of water playing a crucial role in phase equilibrium. The activation energy ( E a ) of different CaCO 3 : NaOH : H 2 O systems was assessed between 7.8 kJ·mol −1 and 32.1 kJ·mol −1 , which is much lower than the conventional calcination route. A preliminary energy balance revealed that the chemical decarbonisation route might be ∼4 times less intensive with respect to the thermal one. The present work offers a further understanding of the effect of temperature on the process with the potential to minimise the emissions from several energy-intensive manufacturing processes, and correctly assess eventual industrial applicability.