Sciencemadness Discussion Board

Recycling chromium sulfate from alcohol oxidation

NaK - 31-3-2020 at 07:34

Is there a good way of recycling the chromium sulfate waste from a potassium dichromate oxidation reaction to chromic oxide again? Considering chromium being somewhat expensive I would like to reuse it and oxidize it to dichromate again.

Converting it to CrOH and performing a thermite like reaction then comes to mind but that would not be very efficient and would also lead to metallic chromium which would have to be oxidised again.

Is there a better way to achieve this?

Amos - 31-3-2020 at 16:03

You can simply take the aqueous waste, assuming all of it has been reduced to chromium(III) and treat it with sodium carbonate solution to precipitate the hydroxide, and I've found this precipitate is more granular/easy to filter than the precipitate formed with the addition of sodium hydroxide. If you heated your mixture significantly during the oxidation you might get a messier result; some chromium won't precipitate and that which does will be more green and sticky. Regardless, these precipitates will readily dissolve in hot hypochlorite to give a pure yellow solution of chromate, which is easy enough to refine into potassium dichromate.

draculic acid69 - 1-4-2020 at 00:30

Thermite with chrome sounds like a really bad idea.

NaK - 1-4-2020 at 03:30

Quote: Originally posted by Amos  
You can simply take the aqueous waste, assuming all of it has been reduced to chromium(III) and treat it with sodium carbonate solution to precipitate the hydroxide, and I've found this precipitate is more granular/easy to filter than the precipitate formed with the addition of sodium hydroxide. If you heated your mixture significantly during the oxidation you might get a messier result; some chromium won't precipitate and that which does will be more green and sticky. Regardless, these precipitates will readily dissolve in hot hypochlorite to give a pure yellow solution of chromate, which is easy enough to refine into potassium dichromate.


great idea, I completely ignored that possibility
Quote: Originally posted by draculic acid69  
Thermite with chrome sounds like a really bad idea.


I think so too