define hall and heraults process
Answers
Hall–Héroult process is the major industrial process for smelting aluminium. It involves dissolving aluminium oxide (alumina) (obtained most often from bauxite, aluminium's chief ore, through the Bayer process) in molten cryolite, and electrolysing the molten salt bath, typically in a purpose-built cell.
Explanation:
The method to obtain aluminium from alumina by the electrochemical method was invented by Charles Hall and Paul Héroult.
Electric current cannot pass through the solid form of alumina, and the melting point of alumina is also very high. Hence, cryolite is added to alumina in a small amount to carry out electrolysis easily.
This mixture acts as a good conductor of electricity. Addition of feldspar also lowers the melting point of alumina. Thus, a mixture of alumina, cryolite and feldspar is subjected to electrolysis to obtain pure aluminium.
For electrolysis, an iron vessel with an inner layer coated with carbon-layered graphite is used. This acts as a cathode.
The carbon rods are joined with a copper clamp and immersed in an electrolyte. These rods act as the anode.
On passing electric current, molten aluminium is deposited at the cathode and oxygen gas is released at the anode.