Purposes To enhance the recovery efficiency of valuable metals from coal gangue, in this study, the mechanism and process regulation of sodium roasting are investigated with Na2CO3 as an activator within the temperature range of 200-900 ℃. Methods The phase transformation behavior and structural evolution during roasting were systematically characterized by SEM, FTIR, XRD, XPS, and TG-DSC analyses. Results Results indicate that 800 ℃ is the optimal roasting temperature, at which the dense lamellar structure of coal gangue transforms into a porous amorphous morphology and crystalline nepheline (NaAlSiO4) can be formed. The coordination environment of aluminum changes from octahedral [AlO6] to tetrahedral [AlO4], leading to enhanced reactivity. Kinetic analysis based on the Kissinger model reveals an apparent activation energy of 52.91 kJ·mol-1 for the main reaction stage. Thermodynamic calculations by using HSC Chemistry and FactSage show that the reaction SiO2+NaAlO2→NaAlSiO4 exhibits negative Gibbs free energy across the entire temperature range, indicating its spontaneous behavior. At 800 ℃, the Gibbs free energy reaches equilibrium, consistenting with the experimental results. This study elucidates the structural evolution and thermodynamic stability mechanism of sodium-roasted coal gangue, providing theoretical guidance for the efficient metals extraction and resources utilization of high-alumina solid wastes.
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