Question

By which process impure alumina converts into pure alumina

Answer 1

electrolytic refining

Answer 2

Impure alumina is converted into pure alumina by the process:

--->Bayer's process followed by the Hall–Héroult electrolytic process.

Impure alumina to pure alumina:

Bayer's process:

• it was discovered in the year 1887.
• It is the primary process for extracting alumina from its ore bauxite.
• This process involves three reaction cycles.
• The powdered bauxite ore is concentrated and heated with sodium hydroxide at around 430-440K temperature in a closed container.
• On refining the bauxite ore alumina is obtained, also called aluminium oxide.
• Here, Aluminum oxide in bauxite is converted to sodium aluminate. Reaction equation: Al2O3 + 2NaOH=> 2NaAlO2 + 3H2O
• Excess of water is added for hydrolysis to NaAlO2 since it is water soluble.Sodium aluminate is then hydrolysed with water to obtain aluminum hydroxide. Reaction: NaAlO2 + 3H2O => Al(OH)3 +NaOH
• Then, precipitates of aluminium hydroxide Al(OH)3 is repeatedly washed with water and heated.
• After this process, pure alumina or aluminium hydroxide is obtained.
• Later, the pure alumina is extracted through electrolysis process called the Hall–Héroult electrolysis process.