Extraction of Aluminum from Coal Fly Ash Using Pressurized Sulfuric Acid Leaching with Emphasis on Optimization and Mechanism

Coal fly ash, commonly produced from thermal power plants, is not only an industrial waste but an aluminum-rich resource that needs to be disposed of properly. This study aims to extract aluminum from coal fly ash using pressurized sulfuric acid (H2SO4) leaching and to investigate the dissolution mechanism during the leaching process. The effects of initial concentration of H2SO4, reaction temperature and time on the extraction of aluminum were investigated. Under optimized conditions (3 mol/l H2SO4, 220°C and 180 min), the extraction of aluminum reached 82.51%. It was found that mullite (3Al2O3·2SiO2) contained in coal fly ash was completely dissolved during the leaching, while the dissolution of silica-alumina glass beads was at a limited degree. The un-leached aluminum was found to be locked inside the glass beads which H2SO4 was unable to access.