Dear Dr. Parkhurst, Having started to use the new version of PHREEQC (version 2) in an inverse modelling mode, I tried running old models (run on version 1.03 PHREEQCi) to check the feasible models were the same. Unfortunately I find that the number of feasible models produced in version 2 is always less. For example, the phase assemblage; Muscovite dissolve Microcline dissolve Quartz dissolve Biotite dissolve Gypsum dissolve Albite(low) dissolve Gibbsite(C) precipitate CO2(g) SiO2(am) precipitate Ferrihydrite precipitate Illite precipitate Calcite dissolve Pyrite dissolve O2(g) in version 1 resulted in 35 models, 8 minimal, but in version 2, only 12 models, 12 minimum, were found. Consideration of the models indicated that models NOT including pyrite oxidation (i.e. models where pyrite and oxygen are used and where there are Fe(2) and S(-2) redox transfers) were only found using version 1, and were not found using version 2. It is these models that account for the extra feasable models in verson 1. The input data was copied from the line editor of version 1 to version 2, thus input solution and phase definition are exactly the same, uncertainties were the same etc (full input data are pasted below). I tried to select and de-select the mineral_water identifier to include or exclude water derived from minerals in the water-balance equation as this seemed the only noteable difference to the input data file. This made no difference. Could you let me know why these differences occur? Many thanks, Andrew Andrew Mitchell Centre for Glaciology / Centre for Research into Environment and Health, Institute of Geography and Earth Sciences, University of Wales, Aberystwyth. Ceredigion. SY23 3DB Tel: Direct (+44)(0)1970 622786 Main Office (+44)(0)1970 622606 Mobile 07949 406809 SOLUTION 1 supra1/8 temp 1 pH 6.67 pe 7 redox pe units mg/kgs S(6) 0.0048 Ca 0.34993 Mg 0.017703 Na 0.022 K 0.032287 Alkalinity 1.25 Al 2.838 ppb Fe 49.8 ppb SOLUTION 2 A177(10:00) temp 1 pH 8.21 pe 7 redox pe units mg/kgs S(6) 5.716 Ca 6.726 Mg 0.364 Na 0.341 K 0.369 Alkalinity 16.35 Al 21.05 ppb Fe 72.72 ppb INVERSE_MODELING 1 -solutions 1 2 -uncertainty 0.1 0.1 -phases Muscovite dissolve Microcline dissolve Quartz dissolve Biotite dissolve Gypsum dissolve Albite(low) dissolve Gibbsite(C) precipitate CO2(g) SiO2(am) precipitate Ferrihydrite precipitate Illite precipitate Calcite dissolve Pyrite dissolve O2(g) -balances Alkalinity 0.3 0.1 -range 1000 -tolerance 1e-07 PHASES 1 # Do not change this number it is used by the program! Biotite KMg3AlSi3O10(OH)2 + 10H+ = K+ + 3Mg+2 + Al+3 + 3H4SiO4 logk 0 -check Illite K0.6Mg0.25Al2.3Si3.5O10(OH)2 + 11.2H2O = 0.6K+ + 0.25Mg+2 + 2.3Al(OH)4- + 3.5H4SiO4 + 1.2H+ logk 0 delta_h 0 kJ/mol -check
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