Investigating the Kinetics of CO2 Mineralization via the Carbonation of CaO in Ammonium Carbonate Solution by Reaction Heat Flow Calorimetry

The utilization of CaO-containing materials in conjunction with ammonium carbonate solution, as a form of captured CO 2 from ammonia scrubbing, presents a promising avenue for achieving accelerated CO 2 mineralization at industrial scales. Understanding the kinetics of this aqueous phase process is pivotal for reactor design and scaling up. Therefore, this study investigates the carbonation of model CaO materials using a reaction heat flow calorimetry. Based on the experimental results, several qualitative and quantitative observations have been made. First, the grain size of CaO does not appear to impact the reaction rates. The carbonation process was found to proceed via three reaction steps: the hydration of CaO to form Ca(OH) 2, its subsequent dissolution, and the eventual precipitation of insoluble CaCO 3 . Accordingly, kinetic measurements were performed for each of the individual reaction steps. First, the hydration reaction was found to consist of two stages, the second of which shows a stronger temperature dependence. Both stages can be described by nucleation and growth mechanism. Dissolution reaction is found to be 0.22th and first order with respect to the mass and concentration driving forces in the solution phase, respectively. The kinetics evolves following a shrinking particle model, while the precipitation reaction exhibits first order kinetics. Although Ca(OH) 2 solubility decreases with temperature, the dissolution reaction was not dependent on temperature owing to the low solubility rates. For the entire mineralization process, the hydration step was found to be rate limiting, especially at higher temperatures when the second dehydration stage dominates. The hydration reaction had apparent activation energies of 6 and 75 kJ mol –1, for the first stage and the second stage, respectively, while the activation energy of the precipitation reaction was found to be 82 kJ mol –1 . Overall, the carbonation of CaO in the aqueous phase exhibits a shrinking core behavior with unreacted Ca(OH) 2 cores enveloped by CaCO 3 shells even after extended reaction times.