Carbon mineralization using steel slag represents a promising pathway for permanent CO 2 storage; however, the coupled effects of reaction kinetics and transport processes under flow-through conditions remain incompletely constrained. This study evaluates the mechanistic controls and CO 2 removal efficiency of percolation-driven carbonation using one-dimensional reactive transport modelling in PHREEQC. Simulations were performed for a 1 m-tall, packed column (1 m 3 bulk steel slag volume), where infiltrating water equilibrated with CO 2 mixtures (0.1-99 vol%) reacts with larnite-, portlandite-, periclase-, and brucite-bearing phases, promoting alkalinity generation and calcite precipitation. Model results identify three carbonation regimes. At ≤1 vol% CO 2 , carbonation is CO 2 -limited, resulting in shallow reaction fronts and low uptake (≤0.3 t CO 2 per m 3 of steel slag after 500 days). At ≥6 vol% CO 2 , rapid near-surface precipitation induces pore-scale passivation and transport limitation, restricting reaction progress despite high initial rates. Between these end-members, an optimal regime at ∼3-5 vol% CO 2 enables coupled reaction-transport behaviour, sustaining Ca release and promoting deeper carbonation fronts (∼0.5-0.8 m). Under these conditions (∼4 vol% CO 2 ), cumulative CO 2 uptake reaches ∼0.56-0.60 t CO 2 per m 3 of steel slag (bulk volume basis) after one year, increasing to ∼0.68-0.71 t CO 2 per m 3 after 500 days. These values correspond to ∼0.30-0.33 and ∼0.37-0.39 t CO 2 per tonne of slag, respectively, assuming a bulk density of 1.85 t m -3 . Higher CO 2 concentrations (99 vol%) yield greater initial uptake (∼0.94-1.01 t CO 2 per m 3 ), but with diminished long-term efficiency due to transport constraints. Extrapolation to Türkiye’s projected 2025 steel slag production (4.6-5.7 Mt yr -1 ) indicates a theoretical CO 2 removal potential of ∼1.4-2.2 Mt CO 2 yr -1 under optimal conditions. These estimates represent upper bounds and are subject to limitations associated with reaction kinetics, fluid flow, and operational variability. The results provide quantitative constraints on process performance and highlight the importance of balancing reaction and transport processes for effective implementation of slag-based carbon mineralization. • 1-D PHREEQC reactive-transport model simulates CO 2 mineralization in slag columns • Optimum carbonation at ∼3-5 % CO 2 (v/v), aligned with DAC-enriched and flue-gas streams • Up to ∼0.9 t CO 2 m -3 stored in 500 days via calcite growth + bicarbonate export • High-CO 2 (>50 %) reduces efficiency due to permeability decline and reaction imbalance • Annual slag production in Türkiye could store ∼1.4-2.2 Mt CO 2 yr -1 under ∼4 % CO 2 input
Cosgun et al. (Fri,) studied this question.