Thermal Evolution and Leaching Activity of Kaolinite and Boehmite, the Key Al-Containing Minerals in Coal Gangue

Extracting Al from coal gangue has the double benefits of realizing the high-value application of coal gangue and mitigating the scarcity of bauxite resource. The key Al-containing minerals in coal gangue include kaolinite and boehmite, and thermal activation is pivotal for stimulating their reactivity. In this study, kaolinite and boehmite were subjected to thermal activation and acid leaching to explore the intrinsic link between their thermal evolution and leaching activity. Results showed that the phase evolution of kaolinite followed a multi-step sequential process in the order of kaolinite → metakaolinite →  γ -Al 2 O 3  → mullite, and Al V in metakaolinite was highly active. For boehmite, it underwent the transformation of boehmite →  γ -Al 2 O 3  →  δ -Al 2 O 3  →  θ -Al 2 O 3 and α -Al 2 O 3 successively. Their reactivity in descending order was γ -Al 2 O 3  >  δ -Al 2 O 3  > boehmite >  α -Al 2 O 3 . Furthermore, a comparative study of leaching temperature demonstrated that elevated temperature favorably strengthened the thermodynamic driving force and greatly promoted the Al extraction. This study is of some theoretical significance for guiding the thermal activation and acid leaching of coal gangue. Graphical