Two-step acid leaching extraction of Fe&Al from karst bauxite and optimization experimental study

Although Bayer process is widely used in bauxite extraction, it challenges karst bauxite with low Al-Si ratio. Therefore, a two-step acid leaching process suitable for karst bauxite was studied based on the engineering strengthening principle, aiming at effectively separating and recovering iron and aluminum. The key parameters affecting extraction efficiency were evaluated by single factor experiments, with emphasis on reaction temperature, ratio of HCl to NH4HSO4 concentration, liquid-solid ratio (L/S) and reaction time. In order to optimize extraction parameters and minimize energy consumption, response surface methodology (RSM) is adopted. The optimized process conditions make the aluminum extraction rate reach 92.92 %, and the energy consumption is the least. In addition, XRD, SEM and EDS were used to characterize the leaching residues, which revealed that unreacted kaolinite and ammonium alum were dominant, and their cluster aggregation partially hindered leaching. The two-step acid leaching process in this study provides valuable insights for the process strengthening strategy of extracting iron and aluminum from karst bauxite.