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

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.