H. S. Santos, H. Nguyen, M. J. Bojdys, P. Esmaeili, J. A. Sirviö, P. Kinnunen, Phys. Chem. Chem. Phys., 2025, 27, 16671–16684. DOI: 10.1039/D5CP01372K

Key Findings

• Nitrate salts (NaNO₃, KNO₃) catalyze magnesite nucleation by lowering brucite dehydroxylation temperatures, stabilizing Mg²⁺–CO₃²⁻ ion pairs, and acting as structural templates.
• Water nanolayers, regenerated during brucite decomposition, serve as 2D diffusion pathways for carbonate ions, enabling crystallization below the salts’ melting points.
• Revised mechanism challenges previous phase-transfer and interfacial-diffusion models, emphasizing heterogeneous nucleation via nitrate salt templating.

The direct carbonation of magnesium-based feedstocks offers a permanent CO₂ storage pathway, but the slow crystallization of anhydrous MgCO₃ (magnesite) has limited its deployment. This study resolves long-standing discrepancies on the catalytic role of alkali nitrate salts in promoting MgCO₃ formation. Using a simplified wet-mixing preparation, in situ TG–DSC measurements, and structural characterization, the authors show that nitrate salts accelerate brucite (Mg(OH)₂) dehydroxylation, stabilize reactive ion pairs, and provide crystallographic nucleation sites due to symmetry matching with magnesite. The reaction proceeds through water-mediated carbonate ion diffusion rather than molten-salt phase transfer, enabling magnesite precipitation at ∼300 °C. These insights refine mechanistic models for salt-promoted carbonation, opening avenues for energy-efficient CO₂ mineralization and potential integration into low-carbon construction materials.