titration site of organic matter

[m.gamrani]

Hello

my problem is that I’m trying to define for a single organic material 2 site two site complexation so I’m going to introduce 2 site Humic a carboxylic forte and the other phenolic.
Ha_s strong site
Ha_w low site

here is my titration script of this MO

Code: [Select]

TITLE Titrage potentiométrique d’un AH
SOLUTION_MASTER_SPECIES # on considère deux sites (carboxylique et phénolique)

        Ha_s       Ha_sOH       0.0       2000
        Ha_w       Ha_wOH       0.0       2000

SOLUTION_SPECIES
     
#    strongle site--Ha_s
   
      Ha_sOH = Ha_sOH
log_k  0.0

     
Ha_sOH = Ha_sO- + H+
log_k  -4   

#   weak site--Ha_w

Ha_wOH = Ha_wOH
log_k  0.0



Ha_wOH = Ha_wO- + H+
log_k  -9   


     

               
END
SOLUTION 1
temp 25
water 0.04 kg
        -units  mol/kgw
        pH      9.1
        Cl      0.1
        Na      0.1    charge # se sert de Na pour équilibrer les charges
-units mg/kgw
Ha_s 637
Ha_w 637
REACTION # on ajoute les titrants
KOH 1
1.067e-4 # ajout initial en moles pour monter le pH à 10
-equil 1
END
REACTION
HCl 2.881e-4 # moles in 17 steps
H2O 1.55e-4 # moles
in 17 steps
-equil 1
END
 
EQUILIBRIUM_PHASES
CO2(g) -3.4 10
USER_PRINT
10 PRINT SOLN_VOL * 1000
USER_GRAPH 1
-cHArt_title  "Titration Curve"
 -axis_titles "Acid Added (mL)", "pH"
 -axis_scale x_axis  0 3 0.5
 -axis_scale y_axis 0 12 1
 -start
10 VT=SOLN_VOL*1000
20 V = VT-40
30 pH = -LA("H+")
110 GRAPH_X V
120 GRAPH_Y pH
END
SELECTED_OUTPUT
-file titration HA
-reaction true
-step true
molalities V -LA(H+)
END

[dlparkhurst]

To model surface complexation, you need to define SURFACE_MASTER_SPECIES and SURFACE_SPECIES, not SOLUTION_. You would then define Ha_s and Ha_w in a SURFACE data block, not in SOLUTION. You will need to define the area parameters for the surface. The charge accumulation on Ha will result from both the strong and the weak sites, and there will be a factor exp of psi that accounts for the work to move an ion to the surface. See the 1999 PHREEQC manual and Dzombak and Morel's book for details of diffuse double layer surface complexation.

If you simply want to define dissolved organic acids, then you use the input that you have given, but you need to see the description of the SOLUTION_MASTER_SPECIES data block in the manual for the correct input items.

REACTION does not have a -equil option, but SURFACE does.

I recommend that you define the reactants of a calculation explicitly:

Code: [Select]

END
USE solution 1
USE surface 1
USE equilibrium_phases 1
USE reaction 1
END