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 appreciated. 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. David SOLUTION_MASTER_SPECIES Ngas Ngas2 0 Ngas2 14 SOLUTION_SPECIES Ngas2 = Ngas2 LogK 0.0 PHASES Ngas Ngas2 = Ngas2 log_k -3.260 delta_h -1.358 kcal SOLUTION units mg/l U 1 EQUILIBRIUM_PHASES 1 CO2(g) -3.5 O2(g) -0.69897 Ngas -0.1079 REACTION 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
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