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Chromate treatment before discharge

Dear sir,
I am currently using chromate solutions for different plating processes including Alodining of aluminium,and post treatments after zinc and cadmium plating. My query is how I can treat these plating solutions before discharge, and what is permissible ranges of chromium contents of these solutions before discharge?

Mahboob Alam
- Islamambad, Pakistan
2005

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In most places effluent limitations are a matter of law rather than opinion. But in terms of good citizenship, it should be relatively easy to obtain a discharge below 7 ppm of chrome through simple chemical precipitation by adding sodium metabisulfite to the effluent, and enough sulfuric acid to get the pH down to, say, 3.5 depending on how much reaction time you have available. Then you use a clarifier and a filter press. It's all been done thousands of times, but the chemicals are dangerous so you should hire a consultant to train you and get you started.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

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Ted you forgot to raise the pH after reduction

Geoffrey Whitelaw
- Port Melbourne, Australia
2005

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You're certainly right on that, Geoff. Thanks.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005