Question

In the commercial electrochemical process for Aluminium extraction, the electrolyte used is:

• A. $Al(OH{)}_3$ in NaOH
• B. An aqueous solution of $A{l}_2(S{O}_4{)}_3$
• C. A molten mixture of $A{l}_2{O}_3$ & $N{a}_{3}Al{F}_6$
• D. A molten mixture of $A{l}_2{O}_3$ & $Al(OH{)}_3$

Answer 1

The correct option is C

A molten mixture of $A{l}_2{O}_3$ & $N{a}_{3}Al{F}_6$

In the electrolytic extraction of Aluminium, purified alumina is mixed with $N{a}_{3}Al{F}_6$ and $Ca{F}_2$. Cryolite $\left(N{a}_{3}Al{F}_6\right)$ helps dissolve Alumina and lowers the melting point of this mix to about 1050 ${}^{\circ }C$. Pure Alumina melts at about 2100 ${}^{\circ }C$. $Ca{F}_2$ is added to enhance the conductivity.

As shown in the above image, the surface on the inside of the steel case is coated with a graphite lining, which acts as the cathode. The electrolyte is a molten mixture of cryolite, molten Alumina and $Ca{F}_2$.