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Aluminum sludge build up/removal from caustic tank

I work in an aluminum extrusion plant and I have a concern with our die cleaning caustic solution. The sludge has built up over time, and I am curious if there is a way to run the solution through a filtering or screening process. We keep the tank agitated, but fear of the caustic sludge settling in a tanker has prompted me to wonder of alternatives. Is there a way for us to cycle the caustic and dispose of it in drums, or is draining the only plausible answer?

Dave Goodgame
PROCESS ENGINEER - Bryan, Texas
2003

If aluminum is in the alkaline regime, pH greater than 7, it is going to precipitate out making what you call sludge. You can also strip aluminum from a die using an acid in which case the solution will remain clear, probably not even colored, and will not precipitate. Eventually you will exhaust all the acid and it will be time to change the solution at which time you will add caustic and precipitate it out. If you ever let it dry out, you can make it soluble again by adding acid. There are several weak scids like acetic or citric that might work and not damage your die. If the die is a stainless steel, you can use dilute nitric acid which will passivate the chromium in the SS, protecting it from the acid.

Dave Fairbourn
- Sandy, Utah
2003

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2003

If the Sludge formed over time, there have some possibility of this phenomenon

1. The additive that you used not in proper proportion and if additive is not control in good condition, then the sludge will be formed over time.

2. Agitation of caustic soda [affil links] also can bring same problem to you, I have been in this experience before, stop agitated the caustic soda. The solution that I can suggest to you is using Caustic Recovery System, where you can recycle and filter out the sludge which formed in the caustic soda, at the same time you can save the cost of caustic soda.

Choo Beng, Wong
- Selangor, Malaysia

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I would suggest using a continuous paper gravity filter, Dave. It's a fairly simple device: an open mesh stainless steel conveyor belt slowly runs around two drums; newsprint is drawn in from a roll, over the top of the belt; the solution is pumped onto the paper. The filtrate runs down by gravity into a sump for return to the process tank, and the newsprint with the filtered sludge runs off into a disposal hopper.

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