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Nitric acid changed colour if aluminium sheet dipped overnight for a particular lot.

Q. Dear Sir,
Good Day,
Sir, once again I am here. Recently I took a lot of anodising. This coil job first was cleaned in caustic soda [affil links] . After rinsing it was dipped in dilute nitric acid for neutralising. After overnight dipping (which was by mistake), in the morning I found that the colour of the nitric solution became golden. It is not the same for other lots. Whether there is any particular problem with aluminium sheets we do not know.
Please help. How to retrieve nitric to original.

S. Tambe
Hobbyist - Raipur, Chhattisgarh, India
April 6, 2012

A. Hi, Tambe.

Sorry, but I can't quite be sure whether you are saying that the aluminum became yellow or the dilute nitric acid became yellow. But if it is the nitric acid, your only practical option seems to be to treat and discharge it and replace it.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 6, 2012

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