hfoCax.ppi

# produces a set of predominance diagrams for Ca using the <loop> variable to systematically vary the total Fe in the system
# system contains a reduced Fe mineral

# Ca is present in solution, on an ion exchanger (eg clay), sorbed by Fe(OH)3(a) and potentially in a mineral (calcite)

SPECIATION
  jobTitle                             "Fe-Ca-H2O redox"
  calculationType                      ht1                                     # produce a predominance diagram using the hunt and track approach
  calculationMethod                    1
  mainSpecies                          Ca   Fe                                 # diagram for Ca
  xmin                                 2.0                                     # pH range adjusted through the <x_axis> variable
  xmax                                 10.0
  ymin                                 -80.0                                   # f(O2(g)) range adjusted through the <y_axis> variable
  ymax                                 0.0
  resolution                           50                                      # low resolution - jumps around on a 50 x 50 grid

  loopMin                              0.0                                     # min, max and step size for FeT (the z-loop variable)
  loopMax                              0.1
  loopInt                              5.0E-02

PLOT
  plotTitle                            "Ca-Fe-Na with sorption and ion exchange<br>(includes Fe(OH)2(s) from llnl.dat)"
  xtitle                               pH
  ytitle                               "log <i>f</i> O<sub>2</sub>(g)"
  pxmax                                10.0
  extraText                            "extratextFeOHCa.dat"                   # additional text on the plot

  multipageFile                        F                                       # each plot in a separate file


CHEMISTRY

include 'ht1.inc'                                                              # standard predominance calculating file

PHASES                                                                         # temporarily add this to the database
Fe(OH)2(a)  # from llnl.dat (NB approximate only - not checked for consistency)
       Fe(OH)2 + 2.0000 H+  =  + 1.0000 Fe++ + 2.0000 H2O
        log_k           13.9045
   -delta_H  -95.4089 kJ/mol    # Calculated enthalpy of reaction
   -analytic -8.6666e+001 -1.8440e-002 7.5723e+003 3.2597e+001 1.1818e+002

SOLUTION 1
   temp      25
   pH        1.5
   units     mol/kgw
   Fe(3)     <loop>                                                            # FeT is controlled by the <loop> variable
   Na        1e-2
   Cl        1e-2 charge
   Ca        1e-3                                                              # CaT

EXCHANGE
   -equilibrate 1
   X 0.02                                                                      # 0.02 equiv of an exchanger

EQUILIBRIUM_PHASES 1
  Fix_H+ -<x_axis> NaOH                                                        # x-axis is pH
    -force_equality true
  O2(g)  <y_axis>                                                              # y-axis is log fO2(g)
  CO2(g) -2       0.3                                                          # soil PCO2 - max CO2 supplied is 0.3 mol

  Fe(OH)3(a)      0 0                                                          # possible minerals
  Fe(OH)2(a)      0 0                                                          # ... added to database above
  Calcite         0 0

SURFACE 1
   Hfo_sOH Fe(OH)3(a)   equilibrium_phase 0.005  53300
   Hfo_wOH Fe(OH)3(a)   equilibrium_phase 0.2
END