Electrolytic Reduction of Pure Alumina

Electrolytic Reduction of Pure Alumina


1 Answers

Sachin Tyagi
31 Points
13 years ago

Electrolytic Reduction of Pure Alumina:- The electrolysis of pure alumina involves two difficulties:-

i)             Pure alumina is a bad conductor of electricity

ii)           The fusion temperature of pure alumina is about 2000oC and at this temperature when the electrolysis is carried of fused mass, the metal formed vapourises. The above difficulties are overcome by using a mixture containing alumina, cryolite and fluorspar which reduces the fusion temperature to 900oC and makes it good conductor of electricity.

The electrolysis is carried out in an iron box lined inside with gas carbon which acts as cathode. The anode consists of carbon rods dipped in the fused mixture of the electrolyte. The fused electrolyte is covered with a layer of coke.

The current passed through of cell is used in heating of the electrolyte, electrolysis. On passing current aluminum is discharged at cathode. Aluminum being heavier than electrolyte settled down at bottom and is tapped out periodically from tapping hole. Oxygen is liberated at anode. It attacks carbon rods forming CO and CO2. When the concentration of the electrolyte decreases, the resistance of the cell increases. This is indicated by the glowing of lamp placed in parallel. At this stage more of alumina is added.

The exact mechanism of the electrolysis is not yet known.

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