Question

Purification of aluminum by electrolytic refining is known as ____________________________?

• A. Serpeck's process
• B. Hall's process
• C. Hoope's process
• D. Baeyer's process

Answer 1

The correct option is C

Hoope's process

Explanation for correct answer:-

Correct Option (C)

• The refining of metal by electrolysis is known as electrolytic refining.
• Hoppe's process is used for the purification in the metallurgical isolation of Aluminum, in which we get high purity Aluminum metal from impure aluminum.
• In this process, the bottom of the electrolytic cell is coated with carbon and made up of iron.
• It has three fused layers:-
  Lower layer:- contain an alloy of copper and impure aluminum
  Middle layer :- Contains cryolite $\left(N{a}_{3}Al{F}_6\right)$ and barium fluoride.
  Upper layer:- Contains pure aluminum that acts as the cathode.
• During the process of electrolysis, $A{l}^{3+}$ ions of middle layer mode to the upper layer and reduced to $Al$.
• These pure Aluminum atoms from $99.99\mathrm{\%}$ purity of aluminum metal.

Explanation for Incorrect answer:

Option (A)

• Speck's process is used in the purification of bauxite from Silica.
• In this process, bauxite is heated along with coke and nitrogen gas at a temperature.
• The aluminum forms aluminum nitride and silica reduce to $Si$.
• Upon hydrolysis, aluminum nitride forms aluminum hydroxide which yields pure alumina.
  $A{l}_2{O}_3.2H_{2}O+N_2+3C\stackrel{2000K}{\to }2AlN+3C{O}_2\uparrow +2H_{2}O.$
  $Si{O}_2+2C\to Si\uparrow +2C{O}_2\uparrow$
  $AlN+3H_{2}O\to Al{\left(OH\right)}_3\downarrow +N{H}_3.$
• Therefore, Speck's process is not the process used for the purification of aluminum by electrolytic refining.

Option (B)

• Hall's process is used in the purification of Aluminum.
• It is used as the process of smelting Aluminum on an industrial scale.
• Alumina or aluminum oxide is dissolved in molten cryolite.
• The reaction involved in this process is:-
  $2A{l}_2{O}_3+3C\to 4Al+3C{O}_2.$
• Therefore, this option is incorrect.

Option (D)

• Baeyer's process is used in refining aluminum, which includes industrial refining of Bauxite (are of Aluminum) and producing Alumina.
• Bauxite contains $30-60\mathrm{\%}$ alumina and the rest is Silica oxide, Iron oxides, and titanium dioxide.
• In Baeyer’s process, alumina is converted into sodium aluminate.
  $A{l}_2{O}_2+2NaoH\to 2NaAl{O}_2+H_{2}O$
• Therefore, Baeyer's process is not the process used for the purification of aluminum by electrolytic refining.

Therefore, the purification of aluminum by electrolytic refining is known as Hoope's process.