The program “Generate pH-pe-files for PHREEQC” supports the creation of pe-pH-diagrams
(predominance diagrams) with PhreeqC. The initial PhreeqC Input file for calculating
predominance diagrams is simple, besides different species in solution it only contains certain pe
and pH values which have to be changed stepwise in order to cover the pe and pH range
necessary for creating a whole pe-pH-diagram. From the Output file the predominant species (i.e.
the species present in the highest concentration) will be determined for each pair of pe and pH
value.
In order not to be obliged to change pe and pH manually (changing e.g. pH from 0 (acid) to 14
(alkaline) and pe from -10 (reducing) to +20 (oxidizing) only in steps of 1 this would be 15 pHvalues * 31 pe-values = 465 combinations!) this program was established.
The program needs a PhreeqC Input file as master (to be opened with FILE / Input-File) with the
following content:
SOLUTION 1
units mmol/L
pe 4
pH 7
Fe 10
Cl 10
The one job in this master will be copied by the program n-times. For the above mentioned
example of 15 pH values and 31 pe values one would get 465 jobs. Solution number as well as pe
and pH will be changed automatically for every new job. The solution number in the Input-master
has to be 1, the program will automatically number the following solutions from 1 to n. Values
for pe or pH in the master file are arbitrarily assumed. Instead of Fe and Cl any other species of
interest might also be defined.
The desired minimum and maximum pe and pH values have to be defined in the program´s Input
mask as well as the step size, e.g. 1. The smaller the step size is the more jobs will be in the Input
file and the more points the resulting pe-pH-diagram will have. If there are any pe-pH
combinations in your defined range which lay above (O2-H2O) or underneath (H2O-H2) the
stability field of water, they will be automatically removed by the program and the resulting
Output file will have n - x jobs, with n = total number of combinations resulting from defined pepH-range and x = number of combinations outside the stability field of water.
The result is written in an Output-file, which the program is creating and for which a name has to
be defined under FILE / Output-File before running the program. The so created Output-file with
n-jobs can be used in PhreeqC as Input file for modelling the species distribution for each pair of
pe-pH values.
In order to facilitate the search for the predominant species in the resulting PhreeqC Output file
the keyword SELECTED_OUTPUT can be used. It is simply added to the master PhreeqC-Input
file:
SOLUTION 1
units mmol/L
pe 4
pH 7
Fe 10
Cl 10
SELECTED_OUTPUT
-file
1_pepH_Fe.csv
-reset
false
-pH
-pe
-molalities
Fe+2 Fe+3
FeCl+ FeOH+ Fe(OH)2 Fe(OH)3- Fe(OH)2+ Fe(OH)3 FeOH+2
Fe+3 Fe2(OH)2+4 Fe(OH)4- Fe3(OH)4+5 FeCl+2 FeCl2+ FeCl3
The automatical reproduction of different pe-pH-combinations will paste all jobs before the key
word SELECTED_OUTPUT. Since there is no END between the different Solutions, the results
of all pe-pH-combinations will be written into the SELECTED_OUTPUT.