Understanding CO2 Adsorption in Steel Slag: A Multi-Scale Simulation Study of CaO, MgO, FeO, and β-Ca2SiO4 Surfaces with the Effect of Water

Abstract

Understanding the molecular mechanisms of CO2 adsorption on steel slag is critical for advancing carbon capture technologies. In this study, a comprehensive multiscale simulation approach combining Grand Canonical Monte Carlo (GCMC), Molecular Dynamics (MD), and Density Functional Theory (DFT) was employed to investigate CO2 adsorption on representative steel slag surfaces, including CaO, MgO, FeO, and β-Ca2SiO4. The effects of temperature, pressure, and moisture content (2-10 wt% H2O) were systematically examined. β-Ca2SiO4 exhibited superior CO2 uptake at low pressure due to heterogeneous high-energy adsorption sites, whereas MgO and CaO showed enhanced adsorption at high pressure through multilayer packing. In contrast, FeO consistently exhibited weak CO2 affinity. The presence of H2O induced strong competitive adsorption, particularly on β-Ca2SiO4, blocking active sites at low pressures while having diminished effects at high pressures. DFT and Hirshfeld charge analyses revealed that the stronger polarity and surface binding of H2O relative to CO2 drive these competitive interactions. This multiscale study provides molecular-level insight into the role of surface chemistry and moisture in steel slag-based CO2 capture and offers guidance for optimizing industrial carbon sequestration processes.