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Safety Question Concerning Neutralizing Caustic Soap


I hope I am asking this in the correct place.

I need help with an environmental/ safety concern at my company. We use a soap in a ultrasonic bath comprised of Sodium Hydroxide and Potassium Hydroxide, needless to say it is a strongly basic compound with a pH of 14 in pure form and 12.9 in the dilute state. I need to be able to neutralize to at least 12.5 before I am able to drain it into the sanitary sewer system and comply with local regulations. I would like to be able to do this in a safe and cost effective way, and not solidify the compound as that could clog up our system. Does anyone know of an effective method that would work?

I have looked into Spilfyter liquid base neutralizer, but I believe it can release dangerous gas if mixed with the salt compounds in the soap.I have a few potential options in-house. We have HCl, but this is kept locked up and I would rather not have the employees responsible for our sonic maintenance handle it. We also have another pretty benign acidic soap with a pH of 5.5 that works, but it takes a lot of it and it is relatively expensive.

In an ideal world, I would like to be able to find a substance that an operator could pour a cup or so into the tank before draining. At worst, I will set up a tank and have a disposal company handle it- but would only want to do this if there are no other options.

Any help is greatly appreciated.

Thank you!


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2 Replies
Previous Community Member
Not applicable

Re: Safety Question Concerning Neutralizing Caustic Soap

Many companies (i.e. biotech companies) have aqueous holding tanks to automatically adjust the pH of these tanks prior to release into the city's water treatment system.  For increasing pH, soda ash (sodium carbonate) is typically used while for lowering pH either Alum, Citric Acid or Acetic Acid are typically used.

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New Contributor III

Re: Safety Question Concerning Neutralizing Caustic Soap

You could also use dilute sulfuric acid to neutralize your tank.  It is corrosive and will require PPE and good safety procedures.  It has the advantage that the resulting salts are highly soluble in water and it is cheap.

Some other considerations...

1. This tank should be agitated or stirred.

2. You will need some sort of pH measurement

3. You should determine the number of equivalents of acid needed.  This will determine the amount of acid needed which may limit the acid you choose.

4. Neutralization of a "soap" may result in the formation of insolubles.  Even if your tank has a pH of 12, you will get localized areas of much lower pH as you add the acid.  These low pH areas may result in the precipitation of the soap.

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