CO₂ mineralization into different polymorphs of CaCO₃ using an aqueous-CO₂ system

This study examines a sequestration of CO₂ using sterically hindered 2-amino 2-(hydroxymethyl)-1,3-propanediol in the presence and absence of the carbonic anhydrase enzyme to obtain a CaCO₃ with a polymorphic crystal composition that depended on the pH, temperature, or mole ratio of the reactants in the reaction mixture. The CO₂ loading capacity of amine absorbent was 8.5 fold higher than CO₂ saturated in water. The amounts of CO₂ and CaCO₃ precipitated were quantified using ion-selective electrodes and ion chromatography, respectively. Interestingly, each of the three polymorphs of CaCO₃ (calcite, aragonite, and vaterite) were obtained in pure form, regardless of the presence of the enzyme, and reaction parameters, or the presence of additives in the reaction medium. Mg²⁺ was found to promote the formation of one of the polymorphs, aragonite. The purities and characteristics of the three polymorphs were verified and quantified by XRD. The carbonization yield, surface morphologies and specific characteristics of the three phases were revealed by IC, FE-SEM, FT-IR, and XPS studies. This study suggests conversion of absorbed CO₂ to three polymorphs of CaCO₃ could be considered as a potential mineralization process.