You should define the phase in a PHASES data block. You should use a "dissociation" reaction with the new phase as the first entity on the left-hand side, all other entities on left and right-hand sides should be aqueous species. The log K is immaterial to inverse modeling, but will affect the saturation indices calculated for initial solutions. That said, H2SiO3 is not a common phase formula. I would use SiO2(a), quartz, or chalcedony (just one). The only difference of these with your phase is a water in the formula, which should make almost no difference in the mole transfers that are calculated. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Elizabeth Bryant <elb46+@xxxxxxxx To: dlpark@xxxxxxxx > cc: In-Reply-To: <14446485.3212477731@xxxxxxxxxxxxxxxxxxxxxxxx> Subject: PHREEQC reaction 10/19/01 08:55 AM Mr. Parkhurst, I am working with PHREEQC and using the LLNL database. I have a reaction SiO2 + H20 = H2SiO3 along with the log k. I tried inputing this information as one of the phoses for inverse modeling, but I got an error message saying that PHREEQC didn't recoginize H2SiO3. I know that LLNL has SiO2 as the master species for Si. I was wondering how to input H2SiO3 as a master species. I tried entering a new master species before, but it seemed like I entered it incorrectly, because the program still didn't recognize it. If you could please help me out with this matter, I would greatly appreciate it. Thank you for your time, Elizabeth Bryant
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