Fundamental Research on Fluidized Calcination Activation and Atmospheric Acid Leaching for Preparing High−Purity Alumina from High−Alumina Coal Gangue

To overcome the high energy consumption, severe equipment corrosion, and low activation efficiency associated with high−pressure leaching in alumina extraction from high−alumina coal gangue, a synergistic process combining fluidized calcination activation and atmospheric acid leaching is proposed. High−alumina coal gangue from Inner Mongolia (Al₂O₃ = 37.05%) was used as the raw material. The gas−solid efficiently mixed fluidized calcination process eliminates the heat−transfer limitations caused by particle stacking in conventional static calcination, enabling rapid particle dispersion and uniform heating. The calcined product was dynamically quenched to below 100 ℃ to prevent deactivation caused by over−calcination. Results show that 850 ℃ is the optimal calcination temperature, at which the amorphous phase content exceeds 92%, while 98.56% of coal−derived organics and structural water are removed, producing a highly pure and highly reactive powder. Based on this high activity product, a novel atmospheric acid leaching process was developed. Under 90 ℃ and atmospheric pressure, the alumina leaching efficiency reaches 89%, comparable to that of the subcritical leaching process conducted at 120 ℃ and 0.25 MPa. Mechanistic analysis indicates that the rapid quenching effect during fluidized calcination generates a high density of surface defects and promotes the transformation of aluminum coordination from octahedral to tetrahedral structures. These structural changes significantly reduce the activation energy required for acid dissolution, thereby enabling efficient alumina extraction under mild conditions. This technology shifts the process from subcritical conditions to low−temperature atmospheric operation, reducing leaching energy consumption by 31.6% while avoiding equipment corrosion risks. The process offers a low−cost, low−energy, and environmentally friendly pathway for the high−value utilization of coal gangue and green alumina production, with important implications for national aluminum resource security.