Precipitation of coarse boehmite from Al-containing acid liquor by high-temperature autohydrolysis

Abstract

In bauxite-scarce China, aluminum extraction from alternative resources via the acid leaching process is promising. However, critical gaps persist: (1) pyrolysis yields lightweight alumina with limited market capacity, and (2) direct electrolytic alumina synthesis from acid leach liquor remains unexplored, especially alumina particle size control. The production of coarse boehmite as an alumina precursor via high-temperature autohydrolysis was investigated in this paper. First, the hydrolysis characteristics of Al³⁺ were revealed by thermodynamic analysis. Subsequently, the experimental parameters and hydrolysate particle size were optimized through a series of experiments. Under optimal conditions, an Al hydrolysis ratio of 82.6 % and a median particle size of 27.1 μm for polycrystalline boehmite were achieved. The morphological evolution of boehmite was revealed by SEM. The hydrolysis path was determined by analyzing the variation of Al-ion species with pH. Kinetics demonstrated that the hydrolysis process followed heterogeneous nucleation and was chemically controlled, with an apparent activation energy of 52.2 kJ/mol. Finally, a novel process for electrolytic Al₂O₃ preparation and simultaneous HNO₃ regeneration using coal gangue and fly ash as raw materials was proposed. This study establishes a technological foundation for producing electrolytic alumina from aluminum-containing solid wastes, providing a novel route for large-scale aluminum resource recovery.