Re: how long will premixed sensitizer last?

Tox Gunn (tox@remarque.berkeley.edu)
Wed, 2 Oct 96 11:00:18 PDT

Not flatly, no. I'd have to go back and do more digging in my chem, take pH
readings of the solutions, and run through the formulas for the affinity of
EDTA for Ferrous/Ferric ion at that pH before I'd be quite that blunt. If you
have other minerals in your water that the EDTA has a greater affinty for
than Fe at that pH, then some EDTA is still going to be helpful. But adding
extra EDTA solely to make the FeOX dissolve "faster" doesn't seem to me like
it's truly helping, because at that point a lot of the Fe is going to get
tied up by the EDTA and become unavailable for the rest of the process.

Where this might make some sense is when the other ions in solution have a
strong enough tendency to react with the Fe that it shifts the equilibrium of
the Fe + EDTA <-> FeEDTA reaction substantially. At that point, the EDTA
would act more as a buffering agent for trace metals, similar to sodium
bicarbonate acting as a buffer for pH.

Sorry to get bogged down in the chem. Are there any practicing chemists about
here who feel inclined to crunch all of the formation values?

Tox

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* Tox Gunn .......tox@remarque.berkeley.edu *
* "Your sanity is not my responsibility!" *
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