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RE: diolution of Air composition

Dr. Parkhurst:

I am very appreciated of your reply and advisement.

I tried to use the Ngas to simulate the air component disolution in water.
the result is very close (almost the same) to the simulation with only
CO2(g) in pH 2-9.5. I think this may be because the N2 (maybe O2 too) is
just not disoluted in the water  during the blowing process. However there
is no further analysis of the outlet component to verify. But it makes me
feel better that the simulation is somehow very close to the real world.

However after pH increases over 9.5, the total CO2 (as well as CO3-2 and
HCO3-) seems to deviate (decrease sharply) from the "right track". Even
REACTION data block seems ineffective. Attached is the CO2 and carbonate
species distribution in solution.

Any advise on this problem at your convenient time would be very

Have a nice day !

Yong(Young) Wang

Binghamton University
Binghamton, NY 13903

-----Original Message-----
From: David L Parkhurst [mailto:dlpark@xxxxxxxx]
Sent: Monday, August 12, 2002 11:36 AM
To: Yong Wang
In-Reply-To: <FOEMLCJFIJMKLGPCIDHCCEAKCAAA.ywang2@xxxxxxxxxxxxxx>
Subject: Re: diolution of Air composition

The experiment you describe fixes the partial pressures of the gases and
EQUILIBRIUM_PHASES is the right keyword data block to use.

The reason you are having numerical problems is related to the introduction
of N2 and O2. PHREEQC calculates redox equilibrium in reaction calculations
and thermodynamically, N2 and O2 should react to form NO3. Fixing partial
pressures of N2 and O2 generates huge amounts of NO3, and the program fails
to converge. If you assume the N2 is essentially inert, the following input
file will make the calculation without allowing N2 to react to NO3, by
defining a new "element" Ngas, which has only one aqueous species, Ngas2
and the gas component Ngas.


    Ngas          Ngas2            0     Ngas2           14
      Ngas2 = Ngas2
      LogK  0.0
        Ngas2 = Ngas2
        log_k           -3.260
        delta_h -1.358  kcal

      units mg/l
      U     1
             CO2(g)            -3.5
             O2(g)       -0.69897
             Ngas        -0.1079
      NaOH  1
      0 .0000001 .000001 .00001 .0001 .001 .01 .1 1 mol

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

Attachment: question.doc
Description: MS-Word document

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