Boehmite (γ-AlO(OH)) is an aluminium oxyhydroxide mineral and one of the three principal aluminium-bearing minerals found in bauxite ores, alongside gibbsite and diaspore. Boehmite-rich bauxite typically occurs in older or thermally altered deposits and plays a significant role in global aluminium production.
Compared to gibbsite, boehmite contains less structural water and more tightly bound hydroxyl groups. As a result, boehmite requires higher digestion temperatures and greater energy input during refining, influencing refinery design and operating costs.
Composition & Mineralogy
| Parameter | Description |
|---|---|
| Chemical Formula | γ-AlO(OH) |
| Mineral Type | Aluminium oxyhydroxide |
| Crystal System | Orthorhombic |
| Structure | Layered double octahedral sheets with hydrogen bonding |
| Occurrence | Disseminated or pisolitic aggregates in bauxite |
Physical Properties
| Property | Typical Description |
|---|---|
| Color | White, pale grey, yellowish, brownish (impurity dependent) |
| Hardness (Mohs) | ~3 – 4 |
| Luster | Vitreous to pearly |
| Streak | White |
| Specific Gravity | ~3.00 – 3.07 |
| Cleavage | Good on certain planes |
| Texture in Ore | Fine-grained aggregates |
Mechanical Properties
Boehmite is not a structural material; however, its mechanical behavior affects ore preparation and refining efficiency.
✔ Moderate hardness increases milling energy compared to gibbsite
✔ Brittle fracture behavior aids comminution
✔ Particle size distribution influences digestion kinetics
Strengthening & Metallurgical Behavior
Boehmite does not directly strengthen metals but plays a critical role in aluminium metallurgy as a major alumina source.
Refining Behavior:
✔ Dissolves in hot NaOH at temperatures typically above 200 °C
✔ Requires autoclave digestion (higher pressure & energy)
✔ Produces sodium aluminate solution for alumina precipitation
✔ Calcination yields Al₂O₃ for aluminium smelting
Because of its thermal stability, boehmite-rich bauxites are more energy-intensive to process than gibbsite-rich ores.
Refining & Processing Properties
Bayer Process Considerations:
✔ Higher digestion temperature and pressure
✔ Slower dissolution kinetics than gibbsite
✔ Use of additives (e.g., lime) to improve reactivity
✔ Higher energy demand balanced by alumina yield
Key Characteristics
✔ Thermally stable aluminium oxyhydroxide
✔ Higher density than gibbsite
✔ Chemically amphoteric (reacts with acids and bases)
✔ Suitable precursor for high-surface-area alumina
✔ Important feedstock for refractory and catalyst-grade aluminas
Available Forms
Natural:
Boehmite-rich bauxite ore
Processed:
Hydrated boehmite mineral
Calcined transitional aluminas (γ-Al₂O₃)
High-surface-area alumina for catalysts & adsorbents
Applications
Primary Uses:
✔ Aluminium production (Bayer process)
✔ Catalyst supports (petrochemical & refining industries)
✔ Refractories & high-temperature ceramics
✔ Abrasives & polishing compounds
✔ Flame retardants & functional fillers
Advantages of Boehmite Bauxite
✔ Reliable alumina source in suitable deposits
✔ Thermally stable mineral phase
✔ Enables production of specialty aluminas
✔ Valuable for advanced industrial materials
✔ Supports both metallurgical and non-metallurgical markets
Why Choose Boehmite Bauxite?
Boehmite bauxite is essential where it forms a major fraction of the ore. Although it requires higher processing temperatures, it delivers consistent alumina yield and enables production of high-performance alumina products for catalysts, ceramics, and refractories.
Boehmite bauxite is a strategically important aluminium ore, balancing higher refining energy with versatile industrial applications across metals, catalysts, and advanced materials.