Letter 37003

Regenerating anodize bath  

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We use a sulfuric acid anodize bath and our current practice is to replace the bath when the aluminum concentration gets too high. Is there any way to regenerate this bath? Could one plate out the aluminum on some temporary cathodes? Any help would be appreciated.

Pat Reid
Consulting - Costa Mesa, CA, USA

You might look at dialysis or electrodialysis as possibilities. The killer is the high initial cost, followed by the extra floor space that it takes up, followed by the tender loving care that the membranes require and the increased waste stream for the byproduct portion. Basically, it is not cost effective in most cases.Try doing a web search using several different key words.

James Watts
- Navarre, Florida

We are doing anodize in a sulfuric acid bath which we are currently getting rid of and making up a new bath when the aluminum content gets too high. Is there a method for regenerating this bath? Could one use alternate cathodes and plate the aluminum out of solution? Would there be any danger in attempting to plate the aluminum out of the bath?

Any help or pointers would be greatly appreciated.

Pat Reid
Consulting - Costa Mesa, CA, USA

You cannot electroplate aluminum from an aqueous solution, so that idea is a non-starter.

James Totter, CEF - Tallahassee, Florida

I have never heard of a successful plate out operation.

James Watts
- Navarre, Florida

The two processes that are used to purify sulfuric acid anodizing solutions are diffusion dialysis (a membrane process) and acid retardation (this process uses ion exchange resin). They both work and the choice between them may depend upon the volume of acid that you need to purify per day to keep up with the rate that aluminum builds up in your bath.

A web search should locate some suppliers.

Lyle Kirman
water treatment systems - Cleveland, Ohio

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