Phase evolution and silicate network dynamics of coal-derived inorganic slags during high-temperature melting: A multiscale experimental and molecular dynamics investigation

This study investigates the phase evolution and silicate network dynamics of coal-derived inorganic slags under high-temperature melting (1300–1400 °C), combining multiscale experimental characterization with molecular dynamics (MD) simulations. Two representative materials—Shenmu coal (SM) and Beishan coal (BS)—were analyzed to elucidate crystallization-amorphous transformation pathways and their environmental implications. Quantitative analyses revealed: X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) confirmed calcium aluminosilicate-dominated microstructures, with >87 % vitreous phase content and 55–62 % heavy metal immobilization efficiency. Molecular dynamics simulations quantified cation diffusion coefficients (Ca²⁺: ∼1.7 × 10⁻⁹ m²/s > Fe²⁺: ∼9.0 × 10⁻¹⁰ m²/s > O²⁻: ∼7.5 × 10⁻¹⁰ m²/s > Al³⁺: ∼5.0 × 10⁻¹⁰ m²/s > Si⁴⁺: ∼3.0 × 10⁻¹⁰ m²/s), demonstrating the critical role of [SiO₄]⁴⁻ tetrahedral polymerization in governing slag fluidity. The developed SiO₂-Al₂O₃-CaO-FeO quaternary MD model bridged molecular-scale dynamics (Qⁿ distribution, >90 % bridged oxygen content) with macroscopic properties The results revealed that SM has a high degree of polymerization (R = 20.19) and requires further pretreatment to be used as a raw material for the preparation of geopolymers. Compared with BS molten slag, it is more suitable as a raw material for resource utilization due to its low degree of polymerization (R = 7.46) and high vitreous phase content of 100 %.