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RE: Release of PHREEQC 2.7 and PhreeqcI 2.7.0.1




> I am trying to use PHREEQC to simulate the formation of green rust (iron
corrosion product). Its formula is considered to be
Fe4Fe2(OH)12SO4------the
first Fe is in 2nd valence and the second Fe is in 3rd valence (So I might
write it as Fe(II)4Fe(III)2(OH)12SO4. But the PHASE data block in PHREEQC
seems only to accept single valent element on left hand side. I thought of
SOLID-SOLUTION but the green rust is not yed considered as any aggregate of
other phases. I don't know if there is any other way to handle this
problem.

> the reaction equation is:

> Fe4Fe2(OH)12SO4 = 5Fe(OH)2 + Fe2+2 + SO4-2 + 1/2O2 + H2O



This equation should be adequate for the PHASE definition. I just did a
little balancing for PHREEQC:

Fe4Fe2(OH)12SO4 = 5Fe(OH)2 + Fe+2 + SO4-2 + 0.5O2 + H2O

If this stoichiometry is added to solution, the iron will be distributed
between +3 and +2 states depending on electron acceptors. With no
additional electron acceptors in the system the ratio of Fe(2):Fe(3) should
be 2:1.

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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