Re: Use of Programming for Aqueous GeoChemical Modeling/Phreeqc

["David L Parkhurst" <dlpark@xxxxxxxx>]

> I have a need to learn and apply phase chemistry and mass balances to the
system K, Mg, Na, Cl, SO4, H2O at various temperatures and various %
Saturation's for KCl & NaCl. This includes evaporation schemes to recover
salts from brines. At weaker concentrations I may need to be concerned with
Ca, but most of the work will be done at concentrations where Ca is
essentially insoluble.

> I have experience in simple systems like K-Na-Cl-H2O but the above
complex
system I have difficulty with. With my limited knowledge I believe the
fields I will have interested in will be glaserite(aphthitalite),
schoenite(picromerite), leonite, kainite, and carnallite in addition to the
KCl and NaCl. Will Web-Phreeqc or another commercial version do this work?

PHREEQC uses an ion-association model for the thermodyanamics of aqueous
solutions, and it works best at relatively low ionic strengths. The model
will run for more concentrated solutions, but results will be qualitative
at best. It will tend to work better in sodium-chloride dominated systems.

For the calculations you want to make, you need to use a specific
interaction model, usually termed the Pitzer approach. We have a program
called PHRQPITZ (http://water.usgs.gov/software or
https://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phrqpitz) that implements
this approach, however, it is pretty dated and not very easy to use. There
is a program TEQUIL, that John Weare has written
(http://www.sdsc.edu/TEQUIL) that will make these calculations. To be
honest, I have never gotten the version to work on my computer, but perhaps
you will have better luck. The Geochemist's Workbench (commercial) and
EQ3/6 (Lawrence Livermore National Lab) have implementations of the Pitzer
approach.

David


David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225