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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
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  phone: 865-574-6398
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