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Author: Subject: Bayer process and Hall–Héroult process to produce chromium
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[*] posted on 10-8-2015 at 12:05
Bayer process and Hall–Héroult process to produce chromium


I am interested in whether it would be possible to use the Bayer process to extract chromium oxide from chromite in the same way that aluminum oxide is extracted from bauxite and to use the Hall–Héroult process of electrolytic smelting to produce metallic chromium from chromium oxide in the same way that aluminum metal is produced from aluminum oxide. The chromium metal would be a solid at this temperature unlike aluminum which is a liquid so the chromium would have to plate out onto the overhead electrodes which would be removed periodically.
I believe this would be an improvement over current methods.
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[*] posted on 10-8-2015 at 21:13


By what method do you propose to reduce the melting point of the chromium oxide? As I'm sure you know the Hall–Héroult process uses cryolite to depress the melting point of Alumina to a manageable level, and so presumably a compound should be added to the chromium oxide to produce the same effect.
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[*] posted on 10-8-2015 at 22:00


Cr[3+] + 3e- ---> Cr(s) E°=-0.76
Al[3+] + 3e- ---> Al(s) E°=-1.71

There is a lot of difference between these two. The first is just on the correct side of
2H2O(l) + 2e- ---> H2(g) + 2OH- E°=-0.83

This fact alone means that Chromium reduction is possible in aqueous chemistry. The Chromium plates out in preference to the production of H2. I honestly don't see how you can get anything easier than that. Playing with solids that refuse to melt even at elevated temperatures cannot possibly be a simpler or easier process.
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[*] posted on 11-8-2015 at 10:42


I propose to reduce the melting point with chromium cryolite, Na3CrF6 which has a melting point comparable to aluminum cryolite, about 1000 degrees Centigrade or with lithium chromium fluoride Li3CrF6 which would probably have an even lower melting point, maybe about 850 degrees Centigrade.

Aqueous deposition of chromium is possible, as for many other metals, but for the production of large amounts the heat would quickly boil the water, so it would be preferable to use a non-aqueous system.

I am interested in finding an alternative to the ferrochrome process which is currently in use.
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