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

Vaterite is a metastable polymorph of calcium carbonate (CaCO(3)) that can be controllably transformed into aragonite or calcite (i.e., stable CaCO(3) 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 (CO(2)) as reactants, remain a challenge. Here, for the first time, we demonstrate that isopropanol (IPA) enables the direct utilization of a dilute gas-phase CO(2) (∼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 CO(2)) with implications for cement decarbonization, and CO(2) mineralization and utilization.