Chemical kinetic modeling and parameter sensitivity analysis for the carbonation of Ca2 + and Mg2 + under ambient conditions

- A kinetic model for the simultaneous Mg2 + and Ca2 + carbonation was developed.
- The experimental results were used to validate and predict the kinetic parameters.
- This model can predict the formation of MgNCa(1 − N)CO3 and the average value for N.
- A sensitivity analysis showed that presence of Mg2 +, slowed the Ca2 + precipitation.
- Atmospheric CO2 pressure is large enough to precipitate the whole Mg2 + and Ca2 +.

A reaction model was developed to predict kinetic parameters and competition of Mg2 + and Ca2 + ions during carbonation in mild conditions, i.e. ambient temperature and up to 3 atm for the CO2 partial pressure. The experimental carbonation results at different temperatures, Mg2 +/Ca2 + ratios, and atmospheric pressure were used to validate and predict the kinetic parameters of individual reactions in the aqueous phase by applying genetic algorithm and reactor modeling. This model showed a good agreement with experimental results, and satisfactorily predicted the competition between Mg2 + and Ca2 + and the formation of magnesian calcite (MgNCa(1 − N)CO3). In addition, a sensitivity analysis was conducted based on the validated kinetic model to maximize the precipitation rates of Mg2 + and Ca2 +. It was found that the final yield for magnesian calcite is the highest for the Mg2 +/Ca2 + molar ratio of 1, referring to an equal concentration of two cations in the leachate. This suggests the strongest synergy between both cations for their co-precipitation. The optimum ammonia amount used as a pH-swing agent was found to be equal to the amount of ammonia released from the leaching stage in a closed loop leaching-carbonation. This amount of ammonia led to ~ 100% Mg2 + and Ca2 + precipitation along with the highest magnesian calcite precipitation yield.