Calcination of bauxite is a key process in the production of refractory or metallurgical grade alumina, whereby high temperature treatment removes water of crystallization, increases the aluminum content and improves the physical structure.
Pre-treatment of raw materials
Crushing and screening: raw ore (200-500mm) → jaw crusher → cone crusher → screening (≤30mm)
Ore washing (optional): remove clay (for high-silicon bauxite)
Homogenization: mix different grades of ores to ensure stable composition
Calcination and Cooling
Rotary Kiln Calcination
Rapid cooling (air cooling): prevent the slow conversion of β-Al₂O₃ to α-Al₂O₃
Post-processing
Crushing and grading: after calcination, the clinker is crushed to 0-10mm/1-3mm (refractory grade)
| Parameters | Control range | Impact |
|---|---|---|
| Calcination temperature | 1400-1600℃ (refractory grade) | Too low a temperature → incomplete conversion of Al₂O₃; too high → increase in energy consumption |
| Residence time | 2-4 hours (rotary kiln) | Ensure sufficient dehydration and phase change |
| Atmosphere control | Weakly oxidizing atmosphere (O₂＞5%) | Prevents reduction of Fe₂O₃ to FeO |
| Fuel type | Natural gas/coal powder/heavy oil | Natural gas is the cleanest, low cost of pulverized coal |
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