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"Recycling of sodium hydroxide"

Current question and answers:

May 3, 2021

Q. I have been working over a project since one month. I wonder if anyone implements this system for etching bath (Also it can be implemented for low caustic etch bath and die cleaning by caustic soda). Summary of system: Etching bath solution is transferred by a pump to a crystallization tank where aluminium hydroxide precipitates here by cooling, and caustic soda becomes liberated and it turns back to etching bath. Dissolved aluminium hydroxide is filtered by special filter press and gain "salable product".
So, does this recovery project sound implementable?


Alaattin Tuna
- Sakarya Turkey

May 2021

A. Hi Alaattin. When I started my employment by Lancy Laboratories 50 years ago, the centerpiece of their atrium was a large piece of recovery equipment for aluminum etch solutions which they had already had under development for a few years. So I'm thinking we may have practical fusion energy before we have practical etch bath recycling. By all means, develop what you can -- there is always the possibility of discovering 'the elegant solution' -- but don't believe any glowing reports about how well some technology works until you've checked that the equipment was kept in operation after the grants ran out :-)

Please see also thread 5582, "Remove aluminum from sulfuric acid anodizing & caustic etch"

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

Previous closely related Q&A's, oldest first:


Q. I'm wondering about the possibility of recycling NaOH and sodium aluminate from etching rinse solution of Al by reverse osmosis or diffusion dialysis. I need more details about the technology.

Mohamed A Barakat
CMRDI Institute - Helwan, Cairo, Egypt


A. Diffusion dialysis is probably the only known commercial mechanism. I am currently working on developing a process for a client, but do not have any results. Diffusion dialysis turns out to be very, very expensive, but has been done. You should be able to find the manufacturer through the Metal Finishing Guidebook.

Juzer Jangbarwala
- Brea, California, USA


A. Indeed it's a difficult recovery process. Dr. Leslie Lancy, the pioneer of plating and anodizing wastewater treatment, built a sorption tower for that purpose in the lobby of his laboratories well over 30 years ago but never came up with a truly practical solution. Tom Baker may have something to contribute to this subject.

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


Q. We run an anodising plant in South India. In order to maintain the levels of aluminium below 10 gms per lt we are looking for a solution. Acid purification unit seems one viable option.Can anyone who has used this give me some feedback. Also how effective is regeneration of caustic bath.


P.Jothi Ramalingam
Abhinava Aluminium p ltd - India

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