procedure to extract aluminium from bauxite

The extraction of aluminum from bauxite involves several key steps, primarily through the Bayer Process (for refining bauxite into alumina) and the Hall-Héroult Process (for smelting alumina into aluminum). Here’s a detailed breakdown:

—

1. Bayer Process: Refining Bauxite to Alumina (Al₂O₃)
# Steps:
1. Crushing and Grinding:
– Bauxite ore is crushed and ground into fine particles (<100 μm).

2. Digestion:
– The powdered bauxite is mixed with a hot (140–300°C) concentrated sodium hydroxide (NaOH) solution under pressure.
– This dissolves aluminum hydroxide/oxide while leaving impurities (e.g., silica, iron oxides) as solid "red mud."
\[
\text{Al}_2\text{O}_3\cdot\text{H}_2\text{O} + 2\text{NaOH} \rightarrow 2\text{NaAlO}_2 + \text{H}_2\text{O}
\]

3. Clarification:
– The mixture is filtered to separate soluble sodium aluminate (NaAlO₂) from insoluble red mud.

4. Precipitation:
– The filtered solution is cooled and seeded with fine crystals of aluminum hydroxide (Al(OH)₃) to precipitate pure Al(OH)₃:
\[
\text{NaAlO}_2 + 2\text{H}_2\text{O} \rightarrow \text{Al(OH)}_3 + \text{NaOH}
\]

5. Calcination:
– Al(OH)₃ is heated at ~1200°C to produce anhydrous alumina (Al₂O₃):
\[
2\text{Al(}_3 \rightarrow \text{Al}_2\text{O}_3 + 3\text{H}_2\text{O}
\]

—

2. Hall-Héroult Process: Smelting Alumina to Aluminum
# Steps:
1. Electrolytic Cell Setup:
– A reduction cell (lined with carbon cathodes) contains molten cryolite (Na₃AlF₆) at ~950°C, which dissolves alumina (~5–10%).

2. Electrolysis:
– A direct current (~4–5 V, 150–300 kA) is passed