I used the following solution to calculate SI,
SOLUTION 0
temp 27.10
pH 7.51
pe 4
redox pe
units ppm
density 1
As 0.000 ppb
Fe 0.8
Hg 0.002 ppb
N 17.64
P 0.09
-water 1 # kg
Results show positive SI values in the following,
Strengite 1.34
Ferrihydrite 3.14
Goethite 7.60
Hematite 20.23
Fe3(OH)8 5.34
Lepidocrocite 6.66
Maghemite 9.67
Magnetite 22.08
I want to calculate the dissolved Fe concentration after allowing precipitation if present. Which compound or compounds should I use in EQUILIBRIUM_PHASES.
Thermodynamically speaking, you should include in EQUILIBRIUM_PHASES all the phases with SI > 0. However, for practical modeling of direct precipitation of iron salts, I would include only ferryhydrite and strengtite. From the list you shown, these are the only minerals for which direct precipitation is reasonable. The other iron-oxides require special conditions such as high temperature or long ageing periods to form.
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