Extraction of Aluminium:

Important ores of Aluminium:

(1) Corundum (Al₂O₃)

(2) Diaspore (Al₂O₃.H₂O)

(3) Bauxite (Al₂O₃.2H₂O)

(4) Gibbsite (Al₂O₃.3H₂O)

(5) Cryolite (AlF₃.3NaF) or Na₃AlF₆

(4) Alunite (K₂SO₄.Al₂(SO₄)₃.4Al(OH)₃

(5) Spinel (MgOAl₂O₃)

(6) Felspar (K₂O.Al₂O₃.6SiO₃) or KAlSi₃O₈

(7) China Clay or Kaoline [Al₂O₃.2SiO₂.2H₂O]

(A) Leaching of Bauxide ore:

(B) Purification of Bauxite:

(1) Baeyer’s Process: By Bayer’s process commercially it is being carried out (for red bauxite) In other words this process is applied to the bauxite ore containing ferric oxide (red bauxite Fe₂O₃) as chief impurity. Ore roasted to convert ferrous oxide to ferric oxide.

(2) Hall’s Process: This process is also applied to the bauxite ore containing ferric oxide (red bauxite Fe₂O₃) as major impurity. This process ore is fused with Na₂CO₃.

(3) Serpeck’s Process: This process is applied to the bauxite ore containing Silica (White bauxite SiO₂) as major impurity.

 NOTE:Silicone Volatile at this temperature and removed easily.

Electrolytic reduction of Al₂O₃:

Electrolysis of molten mixture: HALL HEROULT PROCESS:

Cathode           :           Iron-tank lined with bricks Carbon

Anode              :           Graphite rods (Carbon)

Electrolyte       :           Molten [Al₂O₃ (5%), Na₃AlF₆ (85 %), CaF₂ (5%), AlF₃ (5%) ]

Temperature    :          900 degree centigrade 

Reactions at Electrodes:

According to the first theory the following reaction occurs:

As Cryolite has greater electrochemical stability it does not dissociate. It only increases the dissociation of  Al₂O₃  But the second theory states that, Cryolite undergoes electrolytic dissociation first then Al⁺³  goes to the cathode, produced F₂ at anode then reacts with Al₂O₃   produces .