Hydration and carbonation reactions of calcium oxide by weathering: Kinetics and changes in the nanostructure

• Structure changes and mineral phases upon hydration and carbonation were revealed.
• Correlations of nanostructure with hydration and carbonation kinetics were found.
• Carbonation started after completed hydration (300–500 h depending on SBET).
• Full carbonation from atmospheric CO2 was always obtained thanks to nanostructure.
• Random Pore Model provides an empirical description of the weathering reactions.

The weathering reactions of hydration and carbonation of nanostructured calcium oxide with atmospheric moisture and carbon dioxide have been characterized. This work is the first-to-date combined kinetic and nanostructural research on CaO oriented to two key processes for different systems, i.e. hardening of construction materials and carbon mineral sequestration. The evolution of the precipitated crystalline phases was monitored by X-ray diffraction and thermogravimetry, along with structural characterization by nitrogen physisorption, electron microscopy and small-angle scattering. Complete hydration of the samples was always found prior to the onset of carbon sequestration, which depended on the nanostructure of the samples. Hence, carbonation started after 300 h of weathering for samples with a specific surface area of 40 m2/g, whereas carbonation of the samples with 20 m2/g occurred after 550 h. Full carbonation from atmospheric CO2 (100% efficiency) was obtained in all cases. This combined research was completed by developing an empirical description of the weathering reactions in terms of a two-process Random Pore Model. Finally, this work aimed to determine the role of the nanostructure of samples based on industrial wastes as one of the most important factors for developing efficient carbon sequestration technologies.

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