Transforming steel slag into a soil-like matrix via CO2 sequestration: A strategy for simultaneous waste valorization and carbon emission reduction.

Accelerated carbonation of solid waste using CO2 to construct soil-like matrix represents a promising but unexplored pathway for carbon emission reduction and large-scale ecological utilization. However, the feasibility and ecological security of this strategy remain uncertain. This study investigates the reconstruction of a soil-like matrix by simulating the carbonation of steel slag (SS) mediated by flue gas in various solutions. The experimental results demonstrate that NH4Ac significantly enhances the carbonation rate by selectively extracting Ca2+ ions. The optimal kinetic conditions were identified as 60 °C, 0.5 mol L-1 NH4Ac, and 700 rpm. Compared to raw SS, the NH4Ac-mediated carbonated SS exhibits a layered porous calcite structure with a specific surface area of 19.03 m2 g-1, along with significantly improved water retention capacity (175.32%) and cation exchange capacity (116.04%). Meanwhile, the leaching concentrations of heavy metals (Cr, Cu, Zn) decreased by 56.60-83.95%. The plant cultivation experiment further confirmed that the survival rate of ryegrass in the soil-like matrix composed of NH4Ac-mediated carbonated SS and soil exceeded 90%, with no accumulation of heavy metals detected. This study establishes a sustainable paradigm for carbon reduction and large-scale beneficial utilization of solid waste in the steel industry.