> In the PHREEQC database there is two equations for CaCO3:
This reaction is for the formation of the CaCO3 ion pair:
Ca+2 + CO3-2 = CaCO3
log_k 3.224
This reaction is for the dissolution of calcite:
Calcite
CaCO3 = CO3-2 + Ca+2
log_k -8.480
> Which one of the equilibrium constants is used by PHREEQC to calculate
the
solubility constant?
The second one is for the solid, calcite.
> If both this constants are used doesn't the model became unstable.
You could remove the ion pair (give a small log K = -20), but it should not
cause any instability.
If you are equilibrating with calcite, you need the log K for calcite.
David
David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
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