Goldman, Patricia J. (goldman@ppg.com)
Mon, 30 Jun 97 12:07:00 PDT

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I was asked a question that I could not give a definitive answer on: Is copper in wastewater chelated
or complexed by phosphates? My first thought is that it is not, that I have not ever heard it to be...,
but I do not have a reference source.

Does anyone out there have a good reference or better answer than my "gut" feeling?

Thanks,

Patty

RSedlak@aol.com
Tue, 1 Jul 1997 09:00:07 -0400 (EDT)

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Maybe in reply to: Goldman, Patricia J.: "Copper and Phosphate"

Ms. Goldman:

It is a pleasure to be able to contribute to a person so knowledgable, as you clearly are.

Let me expound.

There is more than one type of phosphate. The simplest is ortho phophate, and is tbe type that is
in the common phosphoric acid, or household "TSP" (read TriSodium Phosphate), and this animal actually
assists in precipitation of most heavy metals, such as Copper.

The so-called "complex phosphates", which most commonly are pyrophosphate, which is famed in the memory of
most REAL old timers as the electrolyte in the old copper plating baths, and tripoly phophate, which is commonly
found in most laundry detergents, and many/most industrial metal cleaners, are chelates, and will complex heavy
metals quite nicely, and make waste treatment difficult.

And a last comment, the complex phosphates are not totally stable, and their stability is related to pH, the lower the pH,
the less stable, and they decompose into ortho phophates. This means that if somebody is batch waste treating a complex
phosphate containing solution, they can lower the pH to say, 2, or less, and let the bath sit say 24-48 hours, and then
neutralize to pH 9, and all the metals should fall out, some may fall out as the phosphate salt.

More than you ever wanted to know.

Best,

Rudy Sedlak
RD Chemical Company