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Excessive Metal Content in Bath

The chemistry manufacturer did a “metals analysis” of our bath and reported iron content at 1,420 mg/L. Is there any other way of removing the iron other than dumping the bath and making up a new one?

Lyle Gilbert, Contributing Editor

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 Q. We are overhauling our clear E-coat process. The chemistry manufacturer did a “metals analysis” of our bath and reported iron content at 1,420 mg/L. Is there any other way of removing the iron other than dumping the bath and making up a new one?   R.S.

 

 
A. I conferred with my friend and fellow industrial coating consultant, Joe Tirado, about this. Joe was our specialist in the chemistry management part of our operations at MetoKote Corp. He has had a lot of experience working with the acrylic E-coat bath. We had quite an interesting conversation about it. 
 
I had thought the iron content reading sounded quite high, and Joe confirmed that it is extremely high. His target was 50 mg/L, and he became concerned when it reached 150. Your reading of 1,420 mg/L is off the charts! This condition is very likely to adversely affect the UV performance of your clear acrylic coating.
 
There are chemicals available to remove the iron from your bath. They are called chelating agents. However, you must use care in applying them to ensure that the performance of the bath is not adversely affected. Because of that, companies that supply paint formulations are reluctant to suggest their use. The safest option would be to dump the bath and make up a new one. With iron content that high, I think I would strongly consider the dumping option.
 
But, either one of these solutions will be an exercise in futility unless you find and correct what is causing the excessive iron condition. A comprehensive review of the coated product chemistry and process compatibilities to establish the root cause of the iron in your paint bath would certainly be in order.
 

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