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"Precipitation of wastewater"


I need suggestion about treatment with chemical precipitation. I have a sample of electroplating wastewater contained of:

Cr 7,09
Cu 37,500
Fe 13,200
Mn 41,6

Can you suggest me what is the best way to precipitate them all? I think I have to reduce the chromium first then doing cyanide destruction and precipitate them all. Can you suggest me the best precipitant? and the best chemical to destruct the cyanide?

Firstly I think, I have to destruct the cyanide content with sodium hypochlorite and reduce the Cr(VI) to Cr(III)with sodium bisulfite. Then I'll precipitate them with pH variation with lime or caustic soda. Anyone have any comment about the chemical that I'll use? Anyone know the pH of minimum solubility for Mn? Do you have any idea of the best stirring velocity (? rpm) and how long is the time to settling down?


Novita Frederika
- Jakarta, Indonesia


You should never mix chrome-bearing waste with cyanide waste. Nor should you mix cyanide waste with any acid due to the possibility of generating poisonous hydrogen cyanide gas. So the first thing you need to do with this mixed batch (you didn't give us the cyanide content) is to treat the cyanide with bleach at a pH of 10.5-11.5. After there is no more free cyanide, reduce the pH to 8.5, adding more bleach to destroy the cyanate resulting from the cyanide oxidation.

Then you can go on to reduce the chrome at a pH of 4.5-5.0 with sodium metabisulfite.

Now you can precipitate the metals with lime. If this doesn't get them all, you need a subsequent treatment of the decantate with sulfide or DTC.

But the very first thing you need to do is get training from an experienced industrial wastewater treatment operator because there are hazards left and right and it's no job for an untrained person.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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