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  for Metal Finishing since 1989
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Recycling Chromating Wastewater

Dear Sir/Madame,

We do clear & yellow Iridite. We are looking for an inexpensive way to recycle the waste water back into the system. For the time being we neutralize the nitric acid and reduce the hexa-chromium.

thank you.

Adel [surname deleted for privacy by Editor]
- nepeab, Ontario Canada
2000

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At today's cost structures, there may be no "inexpensive" way.

I have seen systems that employ ion-exchange to get the chromates out of the rinse water so that rinse water can be returned; they are fine but they only increase the overall chemical use compared to end-of-pipe neutralization.

Unfortunately, chromates--unlike most plating solutions--are not equilibrium processes wherein you can just add anodes and brighteners and keep things in balance. Rather, the chromates chemically react with the surface, and having done so they become exhausted contaminants which should not be returned to the tank, whereby they only would spoil it that much sooner.

I have seen more exotic and expensive systems where the regenerant and backwash from the ion-exchange systems goes into an electrolytic membrane separation system for regeneration, and it's probably a fine idea. But when you say "inexpensive", uh, I don't think so.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2000