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2 more PHREEQuestions



Hi again Dave,

Is there a way to make PHREEQC report output in ppm rather than moles?

Also I'd like to run a simulation which will report the amount of
ferihydrite precipitated from a solution THEN, using that amount of
precipitate, perform sorbtion calculations.  I've been running one
simulation to find the amount of precipitate and then running the sorbtion
reaction in a second simulation where I manually input the amount of
precipitate formed in the first simulation using the Surface block.  Is
there a way to do this automatically in one step?

Thanks again, have a nice weekend.

Shane

----- Original Message -----
From: "David L Parkhurst" <dlpark@xxxxxxxx>
To: "Shane Matolyak" <smatolyak@xxxxxxxxxxx>
Sent: Wednesday, September 25, 2002 7:52 AM
Subject: Re: PHREEQC question


>
> > We're using PHREEQCI for speciation modelling.  When we give the program
> an input solution and then perform a batch reaction the program
> automatically adjusts the pe in the resultant solution.  Presumably this
is
> to maintain charge balance.  Is there a way to over-ride this in order for
> the resultant solution to have a pe which we specify even if there will be
> a charge imbalance?
>
> PHREEQC does not easily allow fixed activities of individual species. In
> part, this is by design because maintaining a fixed pe in your case, while
> allowing pH to vary can move the solution out of the stability field of
> water. You can also implicitly be requiring many moles of mass transfer to
> maintain a fixed activity. Usually, the change in pe from reaction is
> telling you something.
>
> However, although you can not simply specify a constant pe, you can define
> a phase that reacts until you get the pe that you want. Thus, you have to
> explicitly add something to solution to adjust the pe. The following is a
> bit artificial, but organic matter reacts with water, the reaction would
> normally produce methane, CO2, and a very low pe. The phase "Fix_pe" is
> defined in PHASES and required to equilibrate with the solution with
> EQUILIBRIUM_PHASES. However, the definition in EQUILIBRIUM_PHASES
specifies
> that oxygen (O2) be added or removed from the solution until the
saturation
> index of -7 is reached for the mineral. This combination of definitions
> causes oxygen to be added until the pe is 7.0. The oxygen allows all the
> carbon to be CO2 rather than half as methane.
>
> David
>
> SOLUTION 1
>       pe 7
> REACTION
>       CH2O 1
>       1 mmol
> EQUILIBRIUM_PHASES
>       Fix_pe   -7   O2
> PHASES
> Fix_pe
>     e- = e-
>     log_k  0.0
> END
> David Parkhurst (dlpark@xxxxxxxx)
> U.S. Geological Survey
> Box 25046, MS 413
> Denver Federal Center
> Denver, CO 80225
>
> Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled
>
>
>



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