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Sulfuric Acid coagulation issue

2003

Our continuous anodizing line comprised of usually 20-25% tech. grade Sulfuric Acid has had recent issues of coagulation when either the concentration spikes (25-30% sulfuric) or if ambient temp. drops below 70 degrees. The solution turns a iridescent pearl color and looks of oil. Can anyone explain the reason? Solids form at the bottom of the tank and only water or elevated temp. will break it.?

Jason Von Marschner
- Ontario, California, USA

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2003

I'm having a bit of a hard time picturing it, but it sound like you have too much aluminum in the bath and it is precipitating. Decant those solids out of the solution.

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

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2003

Running at 25-30% acid is in my opinion very high. It may be that way because you have a very high Aluminum content. Check the aluminum content out and if it is over 12 oz per gal decant. Also check for copper.

Drew Nosti, CEF
Anodize USA

Ladson, South Carolina