Metal finishing Q&As since 1989

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Waste treatment of zincate solution

 

Can anybody offer any advice on a suitable treatment of used zincate solutions (containing a small amount of cyanide) prior to disposal of into a municipal waste water system? Are there any other alternatives which are "greener"?

Geoff Slater
- Auburn, Alabama

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Alkaline chlorination followed by reducing the pH for precipitation should do it. Try it in a lab beaker [beakers on eBay or Amazon] because you may need to reduce the pH to the acidic side and add ferric chloride [on eBay or Amazon] before neutralization, or polish with DTC, depending on the concentration and the discharge standards.

I don't know of a reliable alternative to zincating and its variants. I have heard (book knowledge only) of the possibility of phosphoric acid anodizing before plating as an alternative to zincating, but it would need a lot of development effort before you could have any confidence in it.

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

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We have had good success utilizing ozone at specific adjustment points in some piloting that we did for a recent client. The low levels of CN make using ozone a good alternative to the use of the less environmentally friendly chlorine, and is effective in also turning the zinc into metal oxide based solids that reduce the volume of sludge created, easily dewater, and are useful for recycling.

Tom Baker
wastewater treatment specialist - Warminster, Pennsylvania