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I think the problem is that the ammonia and nitrate will react to form
N2(aq), a reaction that you do not want to occur. The fix is to separate
NH3 from NO3 in the database so that they act as separate "elements".  In
the attached file, Tony Appelo has replaced N(-3) with Amm. You should be
able to merge the Amm definitions into your input file and replaces the
N(-3) with Amm in the SOLUTION definition.Alternatively, you could use
another ion in the calculation in place of NO3 (say Cl-) without any
significant change in the chemistry.


(See attached file: tony.dat)

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

                      "Scott C. Brooks"                                                                 
                      <brookssc@xxxxxxx        To:       dlpark@xxxxxxxx                                
                      v>                       cc:                                                      
                      09/15/2003 03:17                                                                  


I have a question regarding Phreeqc for Windows.  I am using v. 1.5.09 on a

machine running Windows 2000.

I am trying to simulate a laboratory metal-chelate titration.  Solution 1
contains Cd in NaNO3 and an NH3/NH4+ buffer at pH 10.23.  Solution 2
contains NaH2EDTA at pH 4.08.  I save both solutions and get the
anticipated result for each but when I mix the two solutions, the resultant

pH is 12.8.  I anticipate a negligible drop in pH, and lab data confirm
this.  The output indicates that the pH is used to charge balance
regardless of any instructions I give otherwise.  I have appended and
example of the input file.  I am using a slightly modified version of the
llnl database to which I have added Edta and the corresponding protonation
and complexation reactions.  The results of other simulations with the
database suggest that the problem does not lie within the amended
database.  Do you have any suggestions for the correct way to set this up?

Thanks in advance for your time and consideration,

DATABASE C:\Program Files\Phreeqc\llnl-scb.dat

TITLE Test my modified llnl.dat = llnl-scb.dat

units mmol/kgw
pH 10.23
Na 100
N(+5) 110 charge
Cd 5.0
N(-3)        179.3

units mmol/kgw
pH 4.08
Na           200
Edta         100

1            0.100
2            0.001



   Scott Brooks
   Environmental Sciences Division
   Oak Ridge National Laboratory
   P.O. Box 2008, MS 6038
   Oak Ridge, TN  37831-6038

   phone: 865-574-6398
   fax: 865-576-8646

   For FedEx and other couriers
   swap "Bethel Valley Road" for the
   P.O. Box


Attachment: tony.dat
Description: Binary data

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