Stabilization of Pure Vaterite During Carbon Mineralization: Defining Critical Activities, Additive Concentrations, and Gas Flow Conditions for Carbon Utilization

The use of carbon mineralization to mitigate anthropogenic carbon emissions is an attractive carbon capture and utilization (CCU) method. This is due to the abundance of global Ca-bearing alkaline wastes and minerals and the associated thermodynamic stability of precipitated calcium carbonates (PCC). In order to improve the motivation for CCU mineralization methods, increasing the value and uses of the formed PCC is crucial. The properties of the PCC, namely, the crystalline phase(s) present, will have serious implications regarding the postrecovery uses and the commodity value. Vaterite, a metastable form of calcium carbonate, is a valuable polymorph of PCC due to its spherical shape, solubility, and porosity; its potential uses include the construction, pharmaceutical, and consumables industries. Herein, we examine the practical conditions necessary to produce pure vaterite from a calcium source (i.e., CaCl₂) reacted with carbon in the form of both aqueous carbonates (i.e., K₂CO₃) and gaseous CO₂. Dosage of and the relative bulk concentration of carbon species (e.g., CO₂/CO₃^2-) has implications on the stability of vaterite on reaction time scales. Ionic cofactor additives, such as NH₄⁺ and SO₄^2-, were effective in enhancing the stability of vaterite under ambient conditions, revealing the critical additive ratio to synthesize pure vaterite. Finally, testing showed that vaterite’s effect on cement hydration kinetics is similar to that of calcite, which is currently used in industry, indicating that vaterite can also serve as a filler for concrete production to replace Ordinary Portland cement. Overall, this study provides insights into the engineering of crystallization systems which can easily and selectively produce vaterite, an emerging and valuable PCC product in the context of carbon mineralization activities for CCU.