surfacechargeFhy.ppi

# Calculation of the surface charge-pH curve for ferrihydrite using the CD-MUSIC model
# of Hiemstra & van Riemsdijk (2009) Geochim. Cosmochim. Acta 73, 4423-4436.
# see their Fig. 4

SPECIATION
xmin                         5
xmax                         10
resolution                   51

loopmin                      -1
loopmax                      -3
loopint                      1
looplogvar                   1     # 1 = substitute 10^z not z

numericTags                  <mass> = 10

PLOT

plotTitle                    "Primary charging of ferrihydrite<br>CD-MUSIC model"
pxmin                        5
pxmax                        10
ytitle                       "Charge C/g"
customxcolumn                pH
lines                        charge0(EDL)                 # from selected output
changeColor                  T
labels                       "0.1 M" "0.01 M" "0.001 M"   # in order plotted
labelSize                    0                            # omit in-plot labels
extraText                    extratextsurfacechargeFhy.dat 


CHEMISTRY

# database wateq4f.dat

# import adsorption database
include cdmusic_hiemstra.dat 

# first simulation contains fixed things

SELECTED_OUTPUT
 -reset FALSE
 -high_precision TRUE

USER_PUNCH; -headings pH charge0 charge0(EDL) psi0
10 if step_no = 0 then goto 100
20 F = 96485.3415
# calculate the primary surface charge in two ways
# work out the contribution of each species
# charge/mol * mol for the 0-plane  NB the 'charge' (including sign) refers to the charge in the 0-plane only
30 s = 0.5*mol("Fhy_triOH+0.5")   - 0.5*mol("Fhy_triO-0.5")   + 0.5*mol("Fhy_triOHNO3-0.5")   - 0.5*mol("Fhy_triONa+0.5") \
     + 0.5*mol("Fhy_unicOH2+0.5") - 0.5*mol("Fhy_unicOH-0.5") + 0.5*mol("Fhy_unicOH2NO3-0.5") - 0.5*mol("Fhy_unicOHNa+0.5") \
     + 0.5*mol("Fhy_unieOH2+0.5") - 0.5*mol("Fhy_unieOH-0.5") + 0.5*mol("Fhy_unieOH2NO3-0.5") - 0.5*mol("Fhy_unieOHNa+0.5")
# convert eq to C/g
40 charge0 = s*F/<mass>
# EDL(,) provides an equivalent shortcut to calculate the primary charge... as well as other things including properties of other planes
50 punch -la("H+"), charge0, EDL("charge","Fhy")*F/<mass>, EDL("psi","Fhy")
100 end

END


# second simulation contains variable things - loop here

SOLUTION 1
-units mol/kgw
pH   <x_axis>
Na   <loop>
N(5) <loop>

SURFACE 1
  Fhy_unicOHH0.5 3.5  650 <mass>     # sites/nm2  m2/g  g
  Fhy_unieOHH0.5 2.5
  Fhy_triOH0.5   1.2
    -cap   1.15  0.9              # C1  C2  (in F/m2)
    -cd_music
    -sites_units density
-cd_music
-equilibrate 1
END