Macroscopic-to-Atomic Mechanism of Zinc Effects on CaO Carbonation

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CaO-based materials are promising sorbents for CO2 capture and represent the dominant reactive phase in Ca-rich alkaline industrial residues. Zinc is one of the most common metal impurities in CaO-based sorbents, yet its influence on the carbonation behavior of CaO remains less understood. Thus, this study investigates the effect of Zn (0–50,000 mg·kg–1) on CaO carbonation, combining phase evolution, structure–property relationships, surface chemistry, carbonate distribution, and density functional theory calculations, to establish a mechanistic framework linking atomic-scale CO2 activation to macroscopic carbonation behavior. Results showed that increasing Zn concentration progressively suppressed the carbonation reactivity of CaO. The CO2 uptake decreased from 0.528 to 0.478 gCO2·gsorbent–1 at 120 min, corresponding to a 9.4% reduction, while the initial carbonation during the chemically controlled stage was inhibited by approximately 30%. At a high Zn concentration (50,000 mg·kg–1), calcium zincate hydrate and zinc hydroxycarbonate formed, and carbonate crystallization shifted from continuous surface precipitation to discontinuous crystal growth, producing fewer but coarser carbonate crystallites. Zn delayed the hydroxyl-to-carbonate interfacial transformation and produced spatially heterogeneous carbonation domains. The weakened interaction between surface O 2p states and CO2-derived C 2p states reduced the electronic coupling at the adsorption interface and lowered the thermodynamic stability of adsorbed CO2. Thus, Zn-affected CaO carbonation through Zn-bearing secondary-phase formation, pore-network reconstruction, spatially heterogeneous interfacial conversion, and local electronic perturbation. This study provides mechanistic insights into Zn-affected gas–solid reactions and a theoretical basis for evaluating Zn-contaminated Ca-rich industrial residues for CO2 capture.