# Reuse sodium hydroxide?



## sjordannc (May 21, 2012)

This is my first post although I've been lurking and using the vast knowledge here to help me process fingers and pins for a while now. Thanks to members, lasersteve's videos, and Hoke, I've had great success so far.

I usually sell off boards and CPU's but I have a hard time parting with anything that has big shiny chunks. I'd like to try recovering from a stack of boards with gold plate underneath the solder mask. I plan on using sodium hydroxide (Rooto) to remove the mask. My question is what should I do with the sodium hydroxide solution when I'm done? Can this be stored and reused or should it be discarded?


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## NobleMetalWorks (May 21, 2012)

I keep my lye (Sodium Hydroxide) in a container that I can put a lid on and store. It has a pressure valve in the lid so that if any pressure does build up it will release it before blowing the top off, unlikely but a safety precaution. If you store Sodium Hydroxide it's best to have a lid, Lye is very friendly with water, and it will soak up the humidity in the air, diluting itself in the process. And also remember to dispose of it properly. After you have used lye to strip soldering masks or other things like paint, or organic material, it becomes more and more unfriendly to the environment. I am lucky, I can just take my Lye waste to my local waste company, they take it. But if you cannot easily dispose of it, you have to figure out what to do with your spent lye stripping solutions before you start creating it. You don't want to have a bunch of 5 gallon buckets of lye just laying around.

If you are wanting to dispose of a lye solution that doesn't have anything else in it, you can pour it in your toilet at about 8 ounces per flush, also adding more water as it flushes. You don't want to dispose of too much at one time because it could corrode your pipes. It is sold as a drain cleaner though, and might actually help your drains unclog. If you are in the country and use a septic tank you don't want to do this because it will kill off the beneficial bacteria in your septic tank, and that would be a really crappy situation to be in. No pun intended.

Scott


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## NobleMetalWorks (May 21, 2012)

Just another thought on the safety issue thing. Anything I have acids or lye in, matter of fact all containers that I have anything in I clearly label, if it's dangerous I print up the right hazardous label and affix it to the container. Same for my lye vat. That way, if there is a fire, or other people have to come into my work area for some reason, whoever it is will know exactly what material they are dealing with.

Scott


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## sjordannc (May 21, 2012)

Thanks Scott! And yes, I keep my shop safe and labeled. I even have a skull and crossbones stencil I use on acid containers. From what I understand, storing this in glass is a bad idea also.

I checked with my local waste company and they will take it. I prefer to re-purpose whatever I can. Maybe I can modify your paint stripper recipe to work with the used solution. 

Scott


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## Geo (May 21, 2012)

glass is ok for cool, diluted or concentrated sodium hydroxide. it reacts with glass when heated to the boiling point of sodium hydroxide.


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## qst42know (May 21, 2012)

Is there some reason you don't use it to neutralize your waste acids after the base metals have been dropped.

The only trouble I had was in using lye used for de-greasing cast iron skillets. It turned a bit soapy when neutralizing the waste acids so I used some to raise the PH part way and then switched to lime to finish the job.


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## NobleMetalWorks (May 21, 2012)

I try to keep the waste metals clean from other contaminants as I drop them out of solution. I feel that if I use Lye that has been polluted with different types of soldering mask and other material, that I will be contaminating the Fe I am dropping out of the waste solution. Also, I don't feel comfortable putting organic and/or other foreign substances into any solution of acid, and these could be included in spent lye solution. Also, if the lye solution has been used until exhaustion, then it might not react in waste solutions well enough to finish off the clean up process. Because I am not very experienced, I try to keep things as simple and uncomplicated as possible.

Scott


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## butcher (May 23, 2012)

The acidic waste solutions already hold a wide variety of dangerous metals, using my caustic solutions help to raise the pH of these solutions, I have no trouble mixing my caustic waste with my acidic waste, when the waste of these two solutions are treated the dangerous metals are separated from the clear salt water solution. This saves me some chemicals to make my acids into salt water, I would only add the caustic waste to solutions after the other metals have been replace from solution, I do not see any problem adding the caustic solution obtained from solder mask removal to you Iron chloride solutions.

I would not add grease to these solutions from cleaning the oven or skillets using caustic soda, (which possibly contains carbon, soap, and food particles), I am not sure what I would have if I did,

Although I do add the salty solution from converting silver, using caustic and Karo syrup method to my waste, I have not noticed any trouble from the carbon in the sugar.


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## lazersteve (May 23, 2012)

I would advise against adding your caustic waste (lye leftovers) to any ammonical (eg: ammonium chloride waste) solutions. If you do you may end up with an unexpected cloud of choking ammonia gas. Otherwise I think it's a great use of the leftover lye solution to add it to my acidic iron chloride wastes.

Steve


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