Mineral occurrence and acid leaching characteristic of aluminum for coal gangue in Shanxi Province

Shanxi Province, a major coal-producing region in China, generates a substantial amount of industrial waste (such as coal gangue) during coal mining and washing processes. Recovering aluminum from coal gangue represents a significant method for its high-value utilization. The content, mineralogical occurrence and spatial distribution characteristics of aluminum for coal gangue from major coalfields in Shanxi was measured by X-ray fluorescence spectroscopy, X-ray diffraction spectroscopy, and scanning electron microscopy-energy dispersive spectroscopy to analyze. Furthermore, the effect of chemical compositions on the leaching characteristics of aluminum from coal gangue treated with calcination and acid leaching was analyzed using multiple linear regression. The resulted indicated that the Al2O3 content in Shanxi’s coal gangue ranges from 13.9% to 42.5%, predominantly existing in the form of aluminosilicate minerals such as kaolinite, illite and muscovite. Notably, due to unique paleo-geological formations, the northern region of Shanxi produces the aluminum-rich coal gangue with Al2O3 content exceeding 30%. The calcination temperature significantly influences the activation efficiency of coal gangue, and the optimal temperature ranges between 700 ℃ and 850 ℃. The aluminum leaching amount is primarily related to the Al2O3 content of coal gangue, with a correlation coefficient exceeding 0.97. It indicate that the higher aluminum leaching amounts with higher Al2O3 content of coal gangue. Additionally, the aluminum leaching amount also shows correlations with the contents of SiO2, K2O, and C of coal gangue. A strong negative correlation exists between aluminum leaching amount and SiO2 content and a weaker negative correlation with K2O content. In comparison, there is a complex relationship between C content and aluminum leaching amount, which change from negative to positive correlation as the increasing of C content. This may be attributed to the intrinsic elemental characteristics of the coal gangue, differences in activation temperatures of various minerals and changes in the solid-liquid contact area during the leaching process.