PHREEQC question

[Annett Sullivan <4as@xxxxxxxx>]

Hi Dr. Parkhurst-

I have a question about the way in which PHREEQC decides mineral
precipitation order.  I have read over the documentation and your
online FAQ, and haven't seen the answer, so I thought I'd send you an
email.

In some of our runs we have different minerals with similar composition
(for instance, iron oxyhydroxides, or calcite/aragonite) that are all
supersaturated, and that we allow to precipitate in EQUILIBRIUM
PHASES.  

How does PHREEQC decide which mineral to precipitate first?  From
working with it, I think that it chooses the mineral that is *most*
supersaturated first, and brings about precipitation to take that
saturation index to 0.  Then in subsequent steps it considers
whether the other (similar-composition minerals) are still
supersaturated, and if so, again chooses to precipitate the mineral with
the highest SI.  And on down the line...  Does this explanation
sound right to you?

Thanks very much, we like PHREEQC a lot!


Annett :)

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Annett B. Sullivan
Environmental Sciences Division
Oak Ridge National Laboratory
P.O. Box 2008, MS-6036
Oak Ridge, TN 37831
phone: 865-574-6367  fax: 865-576-8543
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