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Pine Beach, NJ

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Removing excess aluminum from Sulfuric Acid anodizing

I have a bath of sulfuric acid I used for aluminum anodizing. It contains far too much aluminum in concentration from usage. I was wondering if there is any way to recycle this sulfuric acid and remove the excess aluminum so we can use the bath again?

Albert White
Anodizing chemist - Oxford, Connecticut
August 5, 2008

August 6, 2008

Some say control the dissolved aluminum between 5 and 15 gm/L, I say 8 to 12.

1. Resin removal systems are available in the industry. some say they do not work, others say they have held the aluminum under 8 gm/L for several years with proper maintenance of the equipment

2. Aluminum How-To has a work sheet (IRS-like) procedure for calculating how much to dip out and how much to add back. To my regular clients I furnish this on an Excel program whereby you enter alum gm/L as is, alum gm/L desired, free acid as is, free acid desired, tank gallons (that is 5 numbers), then punch one button and the read out displays how much to dip out and how much acid to add back.

3. Electroplating shops use the clean aluminum bearing spent acid for pickling and acid dipping.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

Albert

Check out Eco-Tec on the Environmental Equipment page of this website. They make an "Ano-Pur" unit for the purpose you are looking for. They are quite effective.

Willie Alexander
- Colorado Springs, Colorado
August 6, 2008

Adding a compound with Fluoride in it would precipitate out AlF3. Be careful with fluoride compounds though, they're nasty.

Jason Rothman
- Pomona, California
August 6, 2008

August 7, 2008

There are systems for removing aluminium from anodizing baths based on ion-exchange. But unless you have a very large installation, the cost would be prohibitive. You're left with dumping. Unless you have other significant contaminants, it is best to do a partial dumping rather than a complete one.

You do not quote figures. I wonder if you are keeping the "free" sulfuric acid correctly? Provided that you replace the sulfuric acid then the solubility of aluminium sulphate is very high. It can eventually lead to problems because of high viscosity. Often "drag-out" will keep the aluminium at a satisfactory level.

Harry Parkes
- Birmingham, UK

Dear Albert,
I am a hard anodiser who does sulfuric Acid anodising.
I used a small 'suspended particle remover pump' which is supposed to remove particles up to 5 microns. It has a small filter chamber with a cartridge reusable nylon type thread-wound cartridge, and processes 30L per hr.
It seemed to be doing a good job before the motor copped out and has gone for repairs.Am yet to test the solution in Lab but have to wait for motor to return,after which I have to run it up again for a couple of days.But results on jobs seem to have improved.
Will keep you posted when I actually test it.
Ravi

Ravi Rao
- Belgaum, India
August 18, 2008

Ion Exchange resin is the best method to remove al. from anodizing bath Bibra of Italy are suppling this plant.it can be used to maintain al.content without dumping the thank on large scale

ABOOBAKER CHUDESARA
ANODIZING/POWDER COATING CHEMIST - Lagos
January 17, 2011

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