Molecular Dynamics Investigation of Ca Carbonation in NH -Cl-H O Systems.

The steelmaking industry confronts dual challenges of CO emission mitigation and steel slag (SS) utilization. A promising strategy lies in the synergistic waste treatment through Ca extraction from SS for subsequent CO sequestration. Ammonium chloride (NHCl) solution has become an effective leaching medium due to its optimal acidity and recyclability. However, the ion association dynamics and crystallization pathways during carbonation in NH -Cl-HO systems remain poorly understood at the atomic scale. This study presents the first molecular dynamics simulation of Ca carbonation in NH -Cl-HO solutions, revealing the effects of temperature (20-80 °C) and CO concentration (15-25 vol % in the gas phase) on CaCO crystallization kinetics, binding energies, mean square displacements (MSDs), and diffusion coefficients. Microstructural evolution, bonding configurations, and particle distribution patterns were further characterized through a trajectory analysis. Results demonstrate that elevated temperatures and increased CO concentrations synergistically enhance Ca-CO binding affinity and diffusion coefficients, thereby accelerating CaCO cluster formation. The study on steel slag carbonation experiments found that with the increase of the reaction temperature and CO concentration, CaSiO in the steel slag undergoes continuous carbonation during the reaction process, leading to an increased degree of carbonation of the steel slag. This conclusion is consistent with the findings from the aforementioned CaCO crystallization kinetics simulation. Notably, the Ca-CO binding distance remained stable at 4.05 Å across all tested conditions, suggesting minimal structural dependence on environmental variables.