Synthesis of Ca(OH)2 and Na2CO3 through anion exchange between CaCO3 and NaOH: effect of reaction temperature

Abstract

The CO₂ 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 CaCO₃ through reaction with NaOH solutions to produce Ca(OH)₂ at ambient conditions, while sequestrating the process CO₂ in a stable mineral Na₂CO₃·H₂O/Na₂CO₃. 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 Na₂CO₃·H₂O/Na₂CO₃ 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 CaCO₃ : NaOH : H₂O 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.