surfacechargeFhy.ppi
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# 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
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