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"Chromate treatment before discharge"



2005

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

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


2005

Ted you forgot to raise the pH after reduction

Geoffrey Whitelaw
Geoffrey Whitelaw
- Port Melbourne, Australia
^


2005

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

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

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