Directed synthesis of aragonite through semi-continuous seeded crystallization methods for CO2 utilization

Abstract

The synthesis of high-purity precipitated calcium carbonate (PCC) is responsible for approximately 30% of the global annual production of calcium carbonates. As increasing carbon capture utilization and storage (CCUS) facilities come online to mitigate anthropogenic emissions, PCC production is expected to grow through carbon mineralization production pathways. Tuning the PCC morphological and crystal structure properties will largely dictate the potential downstream uses of the carbonate products; thus, increased research is needed into process design considerations for crystal habit modification of PCC. Of the three anhydrous polymorphic forms of PCC, aragonite shows great promise in applications as a filler material or flow-modifier due to its unique needle-like structure. Synthetic aragonite is generally produced at elevated reaction temperatures (60–80 °C), however alternative crystallization methods can be applied to reduce this energy barrier and better control crystal production. Herein, we compare the crystallization of aragonite in both a batch and semi-continuous crystallizers using a model system (e.g., CaCl₂ and K₂CO₃) to elucidate the effect of mixing and saturation in relation to PCC crystal morphology. Seeding of aragonite is also utilized as a method to better control the PCC production process and lower the required synthesis temperature to 25–40 °C. Finally, these methods are extended to a Ca-rich leachate from waste hydrated cement paste (HCP) for comparison with the model system. The produced aragonite is reincorporated into new cement and tested for its potential hydration and rheological advantages. Overall, this work motivates the use of alternative crystallization methods to promote polymorph control for niche CCUS applications, especially cement decarbonization.