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

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.