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topic 6368

Recycling of Aluminum Etch Solution


Q. I am an Environmental Engineer trying to reduce the cost/waste from our company's aluminum etching process. We use a caustic cleaner/etch to remove a stearate based lube from aluminum cans, and to etch the surface prior to painting. We overflow the bath to remove foam, and then add caustic to maintain a conductivity of about 12 mS. This is done at 65 C.

I believe we are wasting a lot of caustic. Is there a way to recycle the bath, or control it better to reduce overflow?

Steve Roosz
- Greensburg, Pennsylvania USA


A. I think that electrodialysis is used to recycle aluminum containing solutions but an even better way is to use an acidic etch instead of an alkaline one. The acidic etch for aluminum etches only 10-15% aluminum compared to an alkaline etcher.

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel


A. Electrodialysis would work, I think. The EPA ETV metal finishing center is in the process of verifying one unit being used to remove Al from a chrome anodizing bath.

James Totter
James Totter, CEF
- Tallahassee, Florida


A. Have you considered using alkaline cleaner prior to etching so you don't have to saturate your etch solution with lube?This will mean longer service life and less disposal.

dado macapagal
- Toronto, Ontario, Canada


A. I'm with Mr. Macapagal! Many times I've seen a single alkaline tank doing double duty as both the aluminum cleaner and the etch. It's corner cutting that comes back to bite you as corner-cutting always does.

For example, when you get a batch of parts that needs extra cleaning, you'll automatically get extra etching that you didn't want; then the desmut isn't strong enough to remove the alloying ingredients left behind from etching that much aluminum. And soon you're wondering why you have smut problems, and you're adding extra pickling steps or moving to more toxic pickles :-)

You need to clean the parts in a non-etch cleaner, THEN etch them (and Sara could be right that an acid etch is preferable). Also, this way the organic contaminants are in one tank and the dissolved aluminum is in another and you have at least a fighting chance of prolonging the solution life through some recovery mechanism.

In my experience, almost all of the recovery systems you see written up in the plant write-up articles in the journals were decommissioned in a couple of years or less due to impracticality in actual operation once the grants expired. If you try to remove both organics and dissolved aluminum simultaneously it is all the harder, and I'd be pretty confident you will end up in that "almost all" smiley

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. For cleaning of oily aluminum work pieces we had same problem and received 3 advice as follows:

1- changing lubricant to evaporative or water soluble type.
2- downward streaming to catch 90 percent lube and then cleaning and etching.
3 - using double phase cleaner available in market. in practice we found 2 suitable and cheaper but for you it depends if your lube being not viscose to be dripped.

About cleaning after lube removal, find suitable low attack silicate-free alkaline cleaner.

- Tehran, Iran

December 22, 2008

Q. I am a chemical engineer wants to know the best technique for recover sodium hydroxide and sodium aluminate from aluminum profiles etching tank to reduce both waste and cost.
is it more cost saving to do it chemically or by hydrolysis and by which mean.

Ghada Hosny
chemical engineer - Beirut, Lebanon

January 21, 2009

Q. Dear Reader:

I am asking about the ability of recycling caustic soda [from etching aluminum profiles as a pre-treatment prior anodizing] by precipitating Al via CaO in the presence of sodium gluconate " scale inhibitor "

Dina Joseph
Al Plant employee - Cairo, Egypt

Recycling spent die strip caustic


Q. I have been working on the use of 308A die strip additive to speed up the stripping of dies and the trials were successful. Our consultant further proposed the use of the spent die strip caustic in anodising etch operation, something we are currently pursuing. I would like to know the further additives that we need to use to prevent the adverse effect of the dissolved aluminium carried over from die strip. Currently we are using Almeco plus 2 to hold aluminium ions in solution in our anodising etch, but we are having problems on the accumulation of sludge in the etch tank, which is affecting the heating up of the tank.

Please can you suggest an alternative.

Noah Nyemba
metal industries - Harare, Zimbabwe

May 4, 2013

Q. Have you any knowledge about regeneration and recycling systems for caustic etch and anodizing baths rinses? Or used these systems? We have a some ideas for the systems ... maybe we'll try as a project.

Alaattin Tuna
- Sakarya, Turkey

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