Slag carbonation-driven surface activation for simultaneous crystallization of heavy metals: Implications for carbon mineralization and environmental remediation

• Alkali activation enhances slag carbonation through surface activation. • Slag carbonation occurs via coupled silicate dissolution and carbonate precipitation. • Carbonated slags exhibit higher heavy metals removal efficiencies than raw slags. • Carbonated slags improve the stability of immobilized heavy metals against acid and ionic attacks. Carbon dioxide (CO₂) mineralization via enhanced aqueous carbonation of alkaline industrial residues, such as slags, offers dual benefits of carbon sequestration and solid waste utilization. However, a substantial portion of the resulting carbonated materials remains underutilized. In this study, we investigated the potential of alkali-activated slags for improved aqueous carbonation and assessed the capacity of the resulting carbonated products to immobilize heavy metals (HMs), specifically Cd (Ⅱ), Pb (Ⅱ), and Cu (Ⅱ), from aqueous environments. Systematic batch experiments were conducted to evaluate HMs removal efficiencies under varying NaOH pretreatment concentrations (0-4 M), reaction times (0-720 min), initial HMs concentrations (0-1000 ppm), pH levels (4-7), and ionic strengths ([NaCl] from 0 to 10 4 ppm). The results revealed a consistent removal efficiency ranking: carbonated slags > alkali-activated slags > raw slags. Leaching tests further confirmed that carbonated slags exhibited enhanced HMs retention, with greater resistance to acid dissolution and ionic interference. These findings highlight the potential of enhanced aqueous slag carbonation not only for carbon capture and storage but also for HMs remediation, offering an integrated approach to negative emissions and environmental pollution control. A conceptual scheme for integrating enhanced carbonation with heavy metal immobilization using slags.