1. Production Processes
Industrial aluminum sulfate (\(\mathbf{Al_2(SO_4)_3}\)) is mainly produced by bauxite pressure acid leaching (low cost) and aluminum hydroxide neutralization (high purity). Several recycling processes are also applied for comprehensive utilization of raw materials.
1.1 Bauxite Pressure Acid Leaching (Mainstream Process)
Raw materials: Bauxite (\(\mathbf{Al_2O_3 \ge 50\%}\)), 55%–60% industrial sulfuric acidProcedures:
Crushing: Grind bauxite into 60–80 mesh powder.
Acid leaching: React at 120–150 ℃ and 0.3–0.5 MPa for 6–8 hours to obtain crude liquid.
Purification: Sedimentation, filtration, iron removal via hydrogen peroxide, pH adjustment to 3.5–4.0.
Concentration: Vacuum evaporation at 115–120 ℃.
Forming: Cool, solidify, crush and sieve to get flake or lump products.
Reaction formula:\(\mathrm{Al_2O_3 + 3H_2SO_4 = Al_2(SO_4)_3 + 3H_2O}\)
1.2 Aluminum Hydroxide Neutralization (High-purity Grade)
Raw materials: High-purity aluminum hydroxide, 98% concentrated sulfuric acidProcedures: Stir and react at 80–100 ℃ for 2–3 hours, followed by sedimentation, concentration, cooling, solidification and crushing.Features: Purity ≥ 99.5% with low impurities, suitable for food, pharmaceutical and high-end water treatment industries.
Reaction formula:\(\mathrm{2Al(OH)_3 + 3H_2SO_4 = Al_2(SO_4)_3 + 6H_2O}\)
1.3 Other Auxiliary Processes
Kaolin process: Calcinate kaolin at 700–800 ℃, then conduct acid leaching, impurity removal, concentration and crystallization.
Alunite process: Calcination, dissolution with dilute sulfuric acid, separation of potassium alum, and concentration of mother liquor.
Fly ash process: Aluminum extraction by alkali dissolution, acid dissolution, impurity removal and concentration (solid waste recycling).
1.4 Liquid Aluminum Sulfate
Prepared by two routes:
Bauxite acid leaching → purification → concentration (density: 1.2–1.3 g/cm³, \(\mathbf{Al_2O_3}\) content: 8%–10%).
High-purity aluminum hydroxide neutralization and direct blending. No crystallization step required for direct use.
