Home >
Community >
Alumina solubility in cryolite (Hall-Heroult process)
Upvote
VOTE
Downvote
+ Electrolysis
+ Chemistry
+ Electrochemistry
Posted by
Mike Mccall
Alumina solubility in cryolite (Hall-Heroult process)
Most of the bath is cryolite ($\ce{Na3AlF6}$) and not alumina ($\ce{Al2O3}$) because for electrolytic reduction, we do not use an aqueous solution, we have to use melt alumina. But alumina melts at a very high temperature ($\pu{2072 ^\circ{}C}$).
So we use cryolite which serves two purposes:
Cryolite acts as a solvent for alumina and dissolves it.
It increases the conductivity of the melt and decreases the melting point of alumina to about $\approx \pu{950 ^\circ{}C}$
Thus a suitable composition of the bath is required to make the process possible and feasible.
Most of the bath is cryolite ($\ce{Na3AlF6}$) and not alumina ($\ce{Al2O3}$) because for electrolytic reduction, we do not use an aqueous solution, we have to use melt alumina. But alumina melts at a very high temperature ($\pu{2072 ^\circ{}C}$).So we use cryolite which serves two purposes:
Cryolite acts as a solvent for alumina and dissolves it.
It increases the conductivity of the melt and decreases the melting point of alumina to about $\approx \pu{950 ^\circ{}C}$
Thus a suitable composition of the bath is required to make the process possible and feasible.
I do know that cryolite bath should dissolve alumina, but what would be the advantage of having say 15% solubility instead of 1% solubility of alumina in the bath? Whenever the flux is untouched by the applied voltage we only need to dissolve SOME fraction of Al2O3 and we can run the cell while adding new Al2O3 from the feeder to keep this fraction constant. Why should I want to dissolve more % of alumina? What is the effect of alumina concentration in the bath?More
Most of the bath is cryolite ($\ce{Na3AlF6}$) and not alumina ($\ce{Al2O3}$) because for electrolytic reduction, we do not use an aqueous solution, we have to use melt alumina. But alumina melts at a very high temperature ($\pu{2072 ^\circ{}C}$). So we use cryolite which serves two purposes:
Thus a suitable composition of the bath is required to make the process possible and feasible.
Most of the bath is cryolite ($\ce{Na3AlF6}$) and not alumina ($\ce{Al2O3}$) because for electrolytic reduction, we do not use an aqueous solution, we have to use melt alumina. But alumina melts at a very high temperature ($\pu{2072 ^\circ{}C}$).So we use cryolite which serves two purposes:
Thus a suitable composition of the bath is required to make the process possible and feasible.
More
VOTE
1