FeAsS.ppi

# predominance diagram for As in the presence of HFO which adsorbs As according to the Dzombak & Morel DL adsorption model

SPECIATION
  calculationType                      ht1
  calculationMethod                    1
  mainSpecies                          As
  xmin                                 2.0                                     # range of pH
  xmax                                 12.0
  ymin                                 -90.0                                   # range of log fO2(g) to control redox
  ymax                                 0.0
  resolution                           500                                      # controls the resolution (big resolution means small step size)

PLOT
  plotTitle                            "Fe-As-S-H<sub>2</sub>O (HFO DLM)"
  xtitle                               pH
  ytitle                               "log <i>f </i>O<sub>2</sub>(g)"
  extratext                            extratextFeAsS.dat 

CHEMISTRY

# simulation 1

include 'ht1.inc'                                                              # standard predominance-calculating file

  SOLUTION 1                                                                   # initial solution calculation
    Temp      20
    pH        1.8
    units     mol/kgw
    Fe(2)     3.5e-1                                                           # total concns
    As        1e-2
    S(6)      1e-2                                                             # sulphide minerals can form but not adsorb
    Na        1e-1
    Cl        1e-1
  END

include 'hfo.inc' 

  KNOBS                                                                        # NB this only applies to this (2nd) simulation
    -convergence_tolerance 1e-10                                               # the default 1e-12 causes a lack of convergence at pH 9.55 and logO2(g) -84.7

# simulation 2
  USE solution 1
  EQUILIBRIUM_PHASES 1
    Fix_H+     -<x_axis> NaOH
      -force_equality true
    O2(g)      <y_axis>            0.1

    As_native                      0 0                                         # most likely minerals given the database
    Orpiment                       0 0                                         # hematite, magnetite removed to make goethite stable
    Realgar                        0 0
    As2S3(am)                      0 0
    Pyrite                         0 0
    Arsenolite                     0 0
    Claudetite                     0 0
    Mackinawite                    0 0
    FeS(ppt)                       0 0
    Sulfur                         0 0
    Fe(OH)3(a)                     0 0
    Greigite                       0 0
    Scorodite                      0 0
    Mirabilite                     0 0
    Melanterite                    0 0
    Thenardite                     0 0
    As2O5(cr)                      0 0
    Jarosite-Na                    0 0
    JarositeH                      0 0
 #   Goethite                       0 0

END