Conceptual Models > Database selection and modification

Modifying Pitzer database with new phase

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spacelover99:
I am trying to modify a pitzer database to include fluorine. I?ve defined it in the SOLUTION_MASTER_SPECIES and also defined a few reactions in SOLUTION_SPECIES (F- = F-, H+ + F- = HF, H+ + 2 F- = HF2-). Finally I?ve included fluorite as a phase and added in some binary reactions based on Weber et al. (1999). However, this does not seem to be working as fluorite won?t precipitate and the F molal values in solution are way undersaturated compared to what I would expect. (I would use llnl.dat, but I want to work with concentrated solutions rather than dilute ones.)

My first question is: for using analytic parameters for fluorite and the SOLUTION_SPECIES additions, is it possible to take these directly from another dataset? I took the analytic parameters for PHASES from iso.dat. Perhaps these values needs to be recalculated?

Second, I wanted to make sure my implementation of the Pitzer parameters from Weber et al. (1999) was accurate.

Below are some of the modifications. Would be glad to get any insights!

SOLUTION_MASTER_SPECIES
F   F-   0.0   F   18.998

SOLUTION_SPECIES
F- = F-
   -dw    1.46e-9
   -Vm   0.928  1.36  6.27  -2.84  1.84  0  0  -0.318  0  1

H+ + F- = HF
   # -log_k   3.18
   # -delta_h 3.18   kcal
   -analytic   -2.033   0.012645   429.01
   -Vm  3.4753  .7042  5.4732  -2.8081  -.0007

H+ + 2 F- = HF2-
   # -log_k   3.76
   # -delta_h 4.550   kcal
   -Vm  5.2263  4.9797  3.7928  -2.9849  1.2934

PHASES
Fluorite
   CaF2 = Ca+2 + 2 F-
   -log_k   -10.6
   # -delta_h   4.69 kcal
   -analytic   66.348   0.0   -4298.2   -25.271
   Vm 15.7


PITZER
-B0   
Na+   F-      0.0330   0   246.83   -0.6728   0 # Weber et al., 1999

-B1
Na+   F-      0.2456   0   2833.0   -9.451   0   0 # Weber et al., 1999

-PSI   
Na+   Cl-   F-   -0.00045   0   0   0   0   0 # Weber et al., 1999
Na+   OH-   F-   -0.0350   0   0   0   0   0 # Weber et al., 1999

dlparkhurst:
Because you have commented the log Ks for the ion pair and complex, by default the log Ks will be zero. With or without these aqueous species , I calculate the solubility of fluorite in pure water of about 0.2 mmol.

In theory, the log K of fluorite should be the same for any database, but is often adjusted as part of the pitzer fitting process.

I do not know if you implemented the aqueous species or Pitzer parameters correctly.


--- Code: ---SOLUTION
EQUILIBRIUM_PHASES
Fluorite 0 10
END

--- End code ---

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