Computing equilibrium activity ratios

Muscovite and kaolinite

Using the standard GWB database and the component kaolinite instead of Al (using a swap), the reaction has an equilibrium constant at 25C. Assuming a water activity of 1, the equilibrium activity ratio can be computed to be

To perform this calculation using the geochemistry module, a GeochemicalModelDefinition object must be created with the desired mineral species:

[UserObjects]
  [definition]
    type = GeochemicalModelDefinition
    database_file = "../../../database/moose_geochemdb.json"
    basis_species = "H2O K+ Al+++ SiO2(aq) H+"
    equilibrium_minerals = "Muscovite Kaolinite"
    piecewise_linear_interpolation = true # to get exact logK at 25degC with no best-fit interpolation
  []
[]

Then a GeochemicalModelInterrogator must be created which specifies the desired swaps and the interrogation = activity instruction:

[GeochemicalModelInterrogator]
  model_definition = definition
  swap_out_of_basis = "Al+++"
  swap_into_basis = "  Kaolinite"
  activity_species = "H2O"
  activity_values = "1.0"
  equilibrium_species = Muscovite
  interrogation = activity
[]

The final line of the output yields the desired information:

(A_K+)^1 (A_Al+++)^3 (A_SiO2(aq))^3 (A_H+)^-10 = 10^14.56
(A_K+)^1 (A_H+)^-1 = 10^3.421

Muscovite and other minerals

The geochemical database can be manipulated to give the following reactions for muscovite: (at 25C). These yield, respectively

To perform this calculation using the geochemistry module, a GeochemicalModelDefinition object must be created with the desired mineral species:

[UserObjects]
  [definition]
    type = GeochemicalModelDefinition
    database_file = "../../../database/moose_geochemdb.json"
    basis_species = "H2O K+ Al+++ SiO2(aq) H+"
    equilibrium_minerals = "Muscovite Quartz Maximum Tridymite Amrph^silica"
    piecewise_linear_interpolation = true # to get exact logK at 25degC with no best-fit interpolation
  []
[]

Then a GeochemicalModelInterrogator must be created which specifies the desired swaps and the interrogation = activity instruction:

[GeochemicalModelInterrogator]
  model_definition = definition
  swap_out_of_basis = "SiO2(aq) Al+++   Quartz   SiO2(aq)  Tridymite SiO2(aq)"
  swap_into_basis = "  Quartz   Maximum SiO2(aq) Tridymite SiO2(aq)  Amrph^silica"
  equilibrium_species = Muscovite
  interrogation = activity
[]

The output yields the desired information

(A_H2O)^6 (A_K+)^1 (A_Al+++)^3 (A_SiO2(aq))^3 (A_H+)^-10 = 10^14.56
(A_H2O)^6 (A_K+)^1 (A_Al+++)^3 (A_H+)^-10 = 10^26.56
(A_K+)^-2 (A_H+)^2 = 10^-9.681
(A_K+)^-2 (A_SiO2(aq))^-6 (A_H+)^2 = 10^14.31
(A_K+)^-2 (A_H+)^2 = 10^-8.686
(A_K+)^-2 (A_SiO2(aq))^-6 (A_H+)^2 = 10^14.31
(A_K+)^-2 (A_H+)^2 = 10^-1.967

Ca-clinoptilolite, prehnite and quartz

Using the standard GWB database, prehnite instead of Al, quartz instead of SiO(aq) (using swaps), the reaction has an equilibrium constant at 200C. Assuming a water activity of 1, the equilibrium activity ratio can be computed to be

To produce this result using the geochemistry module, a GeochemicalModelDefinition object must be created with the desired mineral species:

[UserObjects]
  [definition]
    type = GeochemicalModelDefinition
    database_file = "../../../database/moose_geochemdb.json"
    basis_species = "H2O Ca++ Al+++ SiO2(aq) H+ K+"
    equilibrium_minerals = "Clinoptil-Ca Prehnite Quartz"
    piecewise_linear_interpolation = true # to get exact logK at 200degC with no best-fit interpolation
  []
[]

Then a GeochemicalModelInterrogator must be created which specifies the desired swaps and the interrogation = activity instruction:

[GeochemicalModelInterrogator]
  model_definition = definition
  swap_out_of_basis = "Al+++    SiO2(aq)"
  swap_into_basis = "  Prehnite Quartz"
  activity_species = "H2O"
  activity_values = "1"
  equilibrium_species = "Clinoptil-Ca"
  temperature = 200
  interrogation = activity
[]

The final line of the output yields the desired information:

(A_Ca++)^1 (A_Al+++)^2 (A_SiO2(aq))^10 (A_H+)^-8 = 10^-13.51
(A_Ca++)^-1 (A_SiO2(aq))^7 (A_H+)^2 = 10^-27.22
(A_Ca++)^-1 (A_H+)^2 = 10^-10.23

References