The Hall Héroult process is used to produce what?

1 Answer
Ben G.
Mar 26, 2017

Aluminium.

Explanation:

The Hall-Héroult process is probably the most common method of smelting aluminium industrially.

Alumina (or Aluminium Oxide, #Al_2O_3#), the most common aluminium oxide, undergoes electrolysis hrough the Hall-Héroult process, where alumina is dissolved in molten cryolite (#Na_3AlF_6#) for electrolysis, at around #940^@-980^@# celsius.

At the cathode:
#Al^(3+)+3e^(-) -> Al#

At the anode:
#O^(2-)+C -> CO + 2e^(-)#

Full Equation:
#Al_2O_3 + 3C -> 2Al + 3CO#

As to why the alumina must be dissolved in cryolite rather than just aqueous #Al_2O_3#: hydronium ions in the water will oxidise the elemental aluminium. You may think, "why not use molten alumina?" Well, while this would work, alumina has a melting point of around #2000^@#C. Thus it is dissolved in molten cryolite (MP #~~ 1000^@#C).

PS: natural cryolite is far too rare to be used for electrolysis, so a synthetic version is created from fluorite, a far more common material.

(source)

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