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. David (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: Subject: 09/15/2003 03:17 PM Dave, 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 SOLUTION 1 units mmol/kgw pH 10.23 Na 100 N(+5) 110 charge Cd 5.0 N(-3) 179.3 SAVE SOLUTION 1 END SOLUTION 2 units mmol/kgw pH 4.08 Na 200 Edta 100 SAVE SOLUTION 2 END MIX 1 1 0.100 2 0.001 END =================================== 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 ===================================
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