The Bayer Process

Aluminum in many shapes and sizes

1. Crushing and Grinding: Bauxite ore is crushed and ground into a fine powder to increase the surface area for the extraction process.

2. Digestion: The ground bauxite is mixed with a hot, concentrated solution of sodium hydroxide (NaOH) in a digester. This mixture is heated under pressure, allowing the sodium hydroxide to dissolve the aluminum oxide (Al₂O₃) present in the bauxite. The impurities, such as iron oxides and silica, remain undissolved.

3. Clarification: The resulting slurry is allowed to settle in a clarifier. The undissolved impurities, known as red mud, settle to the bottom, while the clear sodium aluminate solution remains on top.

4. Precipitation: The clear solution is then cooled and seeded with aluminum hydroxide crystals. This causes aluminum hydroxide to precipitate out of the solution.

5. Separation: The precipitated aluminum hydroxide is separated from the red mud through filtration.

6. Calcination: The aluminum hydroxide is then heated in rotary kilns or fluidized bed calciners at temperatures around 1000-1100°C to remove the chemically bonded water, resulting in anhydrous aluminum oxide (Al₂O₃).

7. Electrolysis: The final step involves the Hall-Héroult process, where aluminum oxide is dissolved in molten cryolite (Na₃AlF₆) in an electrolytic cell. An electric current is passed through the cell, causing the aluminum ions to migrate to the cathode, where they gain electrons and are reduced to aluminum metal, which sinks to the bottom of the cell. Oxygen is released at the anode as a byproduct.

8. Tapping: The molten aluminum is periodically tapped from the cell and can be cast into ingots or other forms for further processing.

This entire process is energy-intensive and requires careful management of materials, but it is the most effective way to extract aluminum from bauxite ore.