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citric acid Passivation rinse waters

We have been asked about citric acid passivation and specifically, the treatment of the waste rinse waters. The citric acid rinses can pose a problem with normal waste water precipitation treatment processes. Is there any way to recover the waste citric acid solution?

Paul Pastor
Chemist - Ravenna, Ohio
2004

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There are two issues to questions like yours, Paul. One is the practicality of recovering unconsumed chemicals and getting them back into the loop. But the other question, which is sometimes unappreciated, is that the beneficial properties of chemicals are consumed in the chemical reaction. The reaction product of citric acid and stainless steel is not citric acid , it is a waste product which it might prove foolish to try to turn back into citric acid and stainless steel.

A general rule is to try to use counterflow rinsing to get dragged out chemicals back into the process tank, understanding that even when you do, the consumed portion of the chemical must be bled out to waste, separated out first if there is a technology to do that, or taking with it some good product if no separation technology exists. But whether prolonged exposure to air in the rinse tanks will degrade the citric acid to a point where this is not actually a good idea, I don't personally know. I would bet that Lee Kremer of Stellar Solutions [a finishing.com supporting advertiser] has some real hands-on knowledge of this that you can benefit from. I am not aware of ion exchange or membrane technology being used on citric acid to separate the good product from the waste, but I'd like to hear about it if it has been applied.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003