Folks

I was hoping someone can help me.  I have been asked for some advice on a caustic soda tank clean project.  The tank is aproximately 15000 litres capacity, however there is a small quantity of crystalised caustic soda which needs to be removed.  (residue)  I would like to avoid entry into the tank where possible.  A colleague has suggested we add a significant amout of water to the tank with the hope to get the crystalised caustic into a solution which can be pumped to a specialist chemical tanker.  My concern is when adding water there is a chemical reaction.  Is there any practioner with chemical experience that could advise me.  Eddy

In its dry state this stuff is a very hazardous dust, so dilution is the way to go.

Depending on what you mean by "small quatity" it might be acceptable to just flush it into the sewer if you dilute it enough.

Maybe not the best Forum for your question.

Starter for 10:

http://www.oxy.com/OurBusinesses/Chemicals/Products/Documents/CausticSoda/caustic.pdf

Do an edit/find on 'cleaning'.

Addition of water to solid NaOH can produce a very significant amount of heat.  I recall from a training video some time ago that this reaction blinded an operator at a soft drinks manufacturer when he was mixing a cleaning solution.  He added water to the dry granules in a container and stirred it - it boiled and he was sprayed in the face with the resulting solution.

We add 25kg of sodium hydroxide to approx 300 litres of water at 20 oC in a cleaning bath.  The temperature rises to 70 oC.

I think when you add the water to the solid you may get localised boiling.  But I don't know if a rapid addition of copious amounts would add cold water which would mix and cool the whole, or just cause a more rapid heat evolution.  You probably need advice from a chemical engineer - sorry.

Ian