Processes > Oxidation and reduction equilibria

Equilibrium phases

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tsnmaster:
Hi, i have a basic question related to equilibrium phases.
I'm trying to know which mineral phases could be present in a confluence of two rivers.
After mixing, many mineral phases have SI>0 so my question is in order to add the equilibrium_phases, which ones of these do i have to add? Do i have to know the kinetics of every mineral phases or do i have to add all of these with SI>0?  I know that in this case i'm considering equilibrium but i'm trying to get to know the overall process.

Thanks a lot

dlparkhurst:
For starters, you could include all the minerals with positive SI; however, you do need to know something about kinetics and which minerals are likely to form. For example, dolomite or magnesite may be supersaturated, but they do not normally precipitate in a river environment.

tsnmaster:
thanks a lot.
For example, considering pH 4 to 5 which mineral phases of Fe would you add?
which book do you recommend to investigate about th

dlparkhurst:
Goethite or Fe(OH)3(a) (or Ferrihydrite). If very supersaturated, Fe(OH)3(a) may be the first phase to form, but goethite will be more stable with time, so a goethite calculation is representative of where equilibrium is headed. Hematite usually does not form directly from solution.

If these are acid drainages, jarosites are potential phases, but usually form at lower pH.

Check out the ferrihydrite or acid mine drainage literature.

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