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Practical 1: Modelling Aqueous Solutions with PHREEQC
1. Calculate the solubility of anhydrite as a function of temperature. Set up the
phreeqe file with vi or some other text editor..
TITLE Solubility of anhydrite
SOLUTION 1
units mol/kgw
pH 4.00
temp 300.0
EQUILIBRIUM_PHASES
Anhydrite
END
Note that temperature in PHREEQC is input in ºC. Edit the input file to cover a
range of temperatures from 25 to 300 ºC. USE THE llnl.dat DATABASE FILE
SINCE THAT HAS THE Cp INFO etc.
In the output, you'll find
--------------Distribution of species--------------------
Log Log Log
Species Molality Activity Molality Activity Gamma
H+ 2.790e-05 2.685e-05 -4.554 -4.571 -0.017
OH- 2.010e-07 1.932e-07 -6.697 -6.714 -0.017
H2O 5.553e+01 1.000e+00 1.744 -0.000 0.000
Ca 9.391e-05
Ca+2 7.637e-05 6.531e-05 -4.117 -4.185 -0.068
CaSO4 1.753e-05 1.753e-05 -4.756 -4.756 0.000
CaOH+ 3.575e-13 3.436e-13 -12.447 -12.464 -0.017
The "solubility of anhydrite" can be taken as the concentration of Ca. The line
Ca 9.391e-05
means that the total Ca concentration is 9.39x10-5 molal. Anhydrite has a
"retrograde solubility". What might that mean?
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