gridFeAsS(cd-music).ppi

# predominance diagram for As in the presence of goethite which adsorbs As according to the CD-MUSIC adsorption model

SPECIATION
  calculationType                      grid
  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                           101       # controls the resolution (big resolution means small step size)

PLOT
  plotTitle                            "Fe-As-S-H<sub>2</sub>O (CD-MUSIC)"
  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, also sets -high_precision true

include 'cdmusic_hiemstra.dat'         # CD-MUSIC database, resets convergence criterion, therefore must FOLLOW ht1.inc

  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        8e-1   charge
  END


# 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           # common Fe oxide under oxidising conditions
#   Magnetite                      0 0           # stable below log fO2(g) = -60 but not in cd-music database (yet) so ignore!!

  SURFACE 1
    Goe_uniOH1.5  Goethite 0.049886874 8707.79   # 3.5 sites/nm2,  98 m2/g, MWt = 88.855 g/mol
    Goe_triOH0.5  Goethite 0.039041901 8707.79   # 2.7 sites/nm2
     -cd_music
     -cap    0.85  0.75                          # C1  C2  (in F/m2)
     -equil 1
END