You do not need to define "Lye". You need to define your second solution to contain the appropriate amount of sodium and then either fix the pH at your given value (which will result in a charge imbalance, although it should not cause a problem) or allow the pH to vary to produce charge balance for solution 2. The latter is probably better because it will generate the appropriate molality of OH. Note your input is mol/L, so the density may be important. PHREEQC will use the density to converting to mol/kgw, which are the units used for all internal calculations (and all printout). Right now the density is 1.0. Finally, I would use mixing fractions that sum to 1--0.998 and 0.002. It is not required but it is better to keep approximately 1 kg water in the reaction solution, especially if concentrations are extreme, as in your case. Note that the lye solution speciation is probably not very good because it is well beyond the range of the ion-association model. It is not really a problem because you are only interested in adding the appropriate amount of NaOH to the mixture and are not really interested in the lye solution itself. You could also use REACTION form this simulation, without explicitly generating the lye solution. David 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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