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July 1997

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Tue, 1 Jul 1997 09:00:07 -0400 (EDT)
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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

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