Converting Dilute CO2 Gas Streams into High-Purity Vaterite via Complementary Organic Additives

Abstract

This study introduces a novel approach for converting gas-phase CO2 (∼5 vol % CO2) into vaterite (≥90 mass %), a metastable CaCO3 polymorph that can serve as a low-carbon cementation agent. Following our previous demonstration of an isopropanol (2-propanol; “IPA”)-mediated vaterite synthesis approach, this study incorporates low concentrations of a weak organic acid in a 20 mass % IPA solvent to selectively form vaterite in an oversaturated Ca(OH)2 mixture. Among the array of organic acids considered, amino acids exhibited the greatest enhancement in vaterite formation and the most pronounced effect on particle morphology (i.e., spherical to ellipsoidal). Detailed investigations of CaCO3 precipitation in these mixed additive systems revealed that the amino acids promoted the formation of an amorphous calcium carbonate during the early stages of carbonation, which rapidly crystallized into vaterite between pH 8 and 9. Despite this delayed crystallization, a high vaterite selectivity (≥90 mass %) and yield (1.23 g vaterite/g Ca(OH)2) were maintained in the serine–IPA mixture even when Ca(OH)2 was present in significant excess (e.g., 12 g Ca(OH)2/kg water). The findings demonstrate that a combinatorial additive approach is an effective strategy for transforming gaseous CO2into high-purity vaterite.