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Zinc plating bath draining and storage

A client needs to drain a zinc plating bath (17% caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] )to make repairs and wants to store the bath and pump it back in when work is completed. They have been told that:

A. If the plating bath is stored below 50 degrees, it will solidify and the NaOH will settle out, and

B. This is not the case, and the settling is contaminants and is desirable. Platers often intentionally drain their baths every couple of years during cold weather to let contaminants settle out and the baths can then be re-used minus the contaminants.

Which story, if either, is accurate?

Steve Mallett
- Worthington, Ohio

Put one vote in column B.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.

Put a second vote for B and say that the cooling removes carbonates which has to be done once every so often.

Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England

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