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Re: comparing PHREEQC




> Estimation of rates of formation of phases is not possible with Phreeqc.

I'm not sure what you want here. PHREEQC has a kinetics module that allows
kinetic reactions to be modeled either in batch or a 1D transport
environment. There is no direct estimation of reaction rates, but rates of
reactions can be modeled by parameter estimation in a 1D column, provided
flow velocities are known. The program PHAST is on the web
(http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phast) which allows for 3D
modeling of flow, transport, and reactions and has all of the chemical
capabilities of PHREEQC.


> And formation of silicates in brines (the saline groundwaters are very
old and
silicate concentrations are high: up to 50 mg/L Si) is not handled by
Phrqpitz. Would you know whether Solmineq and GAMSpath do things that
Phreeqc does not.

To my knowledge, the Pitzer parameterization for aqueous silica (or
aluminum) species does not exist. Thus, I do not think any of the models
that use the Pitzer specific-interaction approach have the capability to
model silicate reactions. I'm not familiar with GAMSpath, but I suspect it
is Solmineq with some kinetics added on top. The advantage of this program
may be that you can model kinetic reactions with the Pitzer approach,
whereas PHREEQC is limited to the ion-association approach. They also claim
to have kinetic expressions for all minerals in their database, but I am
dubious that this information would be adequate for a field investigation.
The advantages of PHREEQC are more types of reactions that can be modeled,
more general kinetics, and advection-dispersion-reaction modeling (3D with
PHAST).


David


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


                                                                                                                               
                      "RG&AJ Gerritse"                                                                                         
                      <geoprocc@xxxxxx         To:      "david parkhurst" <dlpark@xxxxxxxx>                                    
                      net.au>                  cc:      "Tony Appelo" <appt@xxxxxxxxx>                                         
In-Reply-To: <000c01c0b8df$626cf720$b165a8ca@xxxxxxxxxxx>
                                               Subject: comparing Preeqc                                                       
                      03/29/01 06:33                                                                                           
                      PM                                                                                                       
                                                                                                                               
                                                                                                                               



Dear David and Tony,
I hope you don't mind me asking you a question on how Prheeqc compares with
Solmineq and GAMSpath. I regularly use Phreeqc (and Phrqpitz) for modelling
alkaline contaminated and calcitic groundwaters under mine sites and highly
saline groundwaters in the SW of Western Austr. (used in gold mining).
Estimation of rates of formation of phases is not possible with Phreeqc.
And
formation of silicates in brines (the saline groundwaters are very old and
silicate concentrations are high: up to 50 mg/L Si) is not handled by
Phrqpitz. Would you know whether Solmineq and GAMSpath do things that
Phreeqc does not.
Thanks
regards
dr Robert Gerritse
Geoprocc Pty Ltd
64 Hamer Ave
Wembley Downs
Australia WA 6019







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