In the Hall-Heroult process for the electrometallurgy of Aluminium, purified Alumina () is mixed with Cryolite () and Fluorspar (). What is the exact dual purpose of these specific additives?

Question

In the Hall-Heroult process for the electrometallurgy of Aluminium, purified Alumina ($Al_2O_3$) is mixed with Cryolite ($Na_3AlF_6$) and Fluorspar ($CaF_2$). What is the exact dual purpose of these specific additives?

Prashant Kotian · Accepted Answer

Correct answer: C. Pure alumina has an extremely high melting point and is a very poor electrical conductor in the molten state. Adding cryolite and fluorspar lowers the melting point of the bath to a practical operating temperature and provides mobile ions () to make the melt highly conductive.

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