Investigation on Sweetening Process for Enhanced Digestion of Boehmitic Bauxite

This study addresses the core scientific question of how to coordinate digestion conditions and the sweetening-stage bauxite addition to simultaneously improve alumina dissolution, leach-liquor quality (A/S), red-mud settling-compression performance, and overall energy consumption when processing imported gibbsite bauxite in the Bayer process. Using imported gibbsite bauxite as the feedstock, we systematically examine how caustic alkali concentration, temperature, digestion residence time, proportion of sweetening bauxite, and related parameters affect digestion behavior and settling performance in the sweetening stage. A slightly lower sweetening bauxite ratio (13%) can reduce within the investigated range, and digestion efficiency is only weakly dependent on reaction temperature and time but increases slightly as the caustic alkali concentration rises. The alumina-to-silica (A/S) ratio of the leach liquor decreases with increasing caustic concentration yet increases with higher temperature and longer digestion time. The settling behavior of red mud is improved as the fraction of sweetening bauxite is increased. Under the optimized conditionscaustic alkali concentration of 190 g/L, temperature of 170 °C, digestion time of 10 min, and a sweetening bauxite ratio of 15%the alumina digestion efficiency reaches 86.5%, the A/S ratio of the leach liquor is 130, the red mud settling velocity is 58 mm/min, and the liquid-to-solid ratio after 5 min of compression is 1.6. SysCAD simulations further indicate that a slightly lower sweetening bauxite ratio (13%) can reduce high-pressure steam consumption by 8.5%, and the energy consumption of the Bayer process decreases by 4.5%. Industrial application has confirmed that this technology can increase annual alumina production by more than 100,000 tons, reduce steam consumption per ton of alumina by about 10%, and lower overall energy consumption by approximately 5%.