Isopropanol Mediates the Rapid and Selective Synthesis of Vaterite during Ambient Carbonation

Vaterite is a metastable polymorph of calcium carbonate (CaCO₃) that can be controllably transformed into aragonite or calcite (i.e., stable CaCO₃ polymorphs) - via a dissolution-precipitation pathway - thereby enabling cementation. Despite its potential as a low-carbon cementitious material, vaterite's synthesis and stabilization at high yield, particularly when using alkaline calcium solids and gas-phase carbon dioxide (CO₂) as reactants, remain a challenge. Here, for the first time, we demonstrate that isopropanol (IPA) enables the direct utilization of a dilute gas-phase CO₂ (∼5 vol %) stream to rapidly and controllably synthesize vaterite using technical hydrated lime (portlandite: Ca-(OH)₂) as a Ca-source at ambient temperature and pressure. It appears that, in aqueous solution and in the presence of monohydric alcohols, a surface tension less than 30 mN/m and a viscosity greater than 2 mPa·s promote the selective precipitation of vaterite. But, this suggestion was unfounded as these solution properties alone do not explain the exceptional vaterite selectivity (>80 mass %) that was achieved only in IPA-water mixtures. The findings indicate a pioneering approach for the use of IPA to mediate the continuous synthesis of vaterite using technical reagents (hydrated lime and CO₂) with implications for cement decarbonization, and CO₂ mineralization and utilization.