PhreeqcUsers Discussion Forum

Processes => Surface Complexation => Topic started by: Nlesani75 on April 06, 2022, 07:27:25 AM

Title: surface complex reaction
Post by: Nlesani75 on April 06, 2022, 07:27:25 AM
Hi all
i have question about my code . I believe when i use complex surface reaction it doesn't effect in my run  in comparisons with same case but without surface complex reaction. even I go further and I change my Na or Cl quantity and there is no error from phreeqc that is unbalance and it run like never change. moreover I have same result in both case( with or without surface complex reaction) and it is strange
I use notepad ++ 2020
here my code :
with surface complex:(i comment graph drawing part)
SURFACE_MASTER_SPECIES
    Limsurf_a     Limsurf_aOH 
    Limsurf_c     Limsurf_cH   
SURFACE_SPECIES
Limsurf_aOH = Limsurf_aOH
    log_k     0
Limsurf_aOH = Limsurf_aO- + H+
    log_k     -12
Limsurf_aOH + CO3-2 + H+ = Limsurf_aHCO3 + OH-
    log_k     8.15
   Limsurf_aOH + CO3-2 = Limsurf_aCO3- + OH-
    log_k     1.55
Limsurf_aOH + SO4-2 = Limsurf_aSO4- + OH-
    log_k     -0.1
   Limsurf_cH = Limsurf_cH
    log_k     0
   Limsurf_cH = Limsurf_c- + H+
    log_k     -5.1
   Limsurf_cH + Ca+2 = Limsurf_cCa+ + H+
    log_k     -1.7
   Limsurf_cH + Mg+2 = Limsurf_cMg+ + H+
    log_k     -2


SURFACE 1
    -equilibrate with solution 1
    -sites_units density   
   Limsurf_a    2.5       0.11      0.2
    Limsurf_c    2.5
    -donnan 1e-9
    only_counter_ions false
    KNOBS; -iter 2000


SOLUTION 1 FW
    temp      25
    pH        6.7
    redox     pe
    units     ppm
    density   1
    Alkalinity 1400 as HCO3-
    Ca        14547 as Ca+
    Cl        112943
    K         0
    Mg        739
    Na        56580
    S(6)      1728 as SO4-2
    -water    1 # kg
   
EQUILIBRIUM_PHASES 1
    Calcite   0 15
    ##Dolomite  0 0
    ##Anhydrite 0 0
SAVE solution  1
PHASES
    Fix_H+
    H+ = H+
    -log_k  0

SELECTED_OUTPUT
    -file                 fw3V1.sel
    -reset                 false
without surface complex:
TITLE projectFW
SOLUTION 1 FW
    temp      25
    pH        6.7
    redox     pe
    units     ppm
    density   1
    Alkalinity 1400 as HCO3-
   
    Ca        14547 as Ca+
    Cl        112943
    K         0
    Mg        739
    Na        56580
    S(6)      1728 as SO4-2
    -water    1 # kg
   
EQUILIBRIUM_PHASES 1
    Calcite   0 15
in pH there is no diffrence after equlibrium i wonder why
tnx for your answers i wish you all answer me as soon as possible

Title: Re: surface complex reaction
Post by: dlparkhurst on April 06, 2022, 02:19:16 PM
PHREEQC has some default rules for which reactants to include in a reaction calculation when multiple SOLUTIONs, EQUILIBRIUM_PHASES, and other data blocks are defined between END statements. Rather than explain those rules, I suggest you break up your calculation with multiple END statements and explicitly define reactions with USE statements.

In the following script, each reactant is defined followed by an END. Then two reaction calculations are defined, one including SURFACE and one without SURFACE. The two reaction calculations are quite similar, but slightly different. You can note that the SURFACE composition is slightly different than the original "initial surface calculation", so the surface does indeed react in response to the precipitation of calcite. However, the moles of surface sites is very small (9e-8) so the change in the surface composition makes almost no difference in the solution composition or the amount of calcite that precipitates.

Code: [Select]
SURFACE_MASTER_SPECIES
    Limsurf_a     Limsurf_aOH
    Limsurf_c     Limsurf_cH   
SURFACE_SPECIES
Limsurf_aOH = Limsurf_aOH
    log_k     0
Limsurf_aOH = Limsurf_aO- + H+
    log_k     -12
Limsurf_aOH + CO3-2 + H+ = Limsurf_aHCO3 + OH-
    log_k     8.15
   Limsurf_aOH + CO3-2 = Limsurf_aCO3- + OH-
    log_k     1.55
Limsurf_aOH + SO4-2 = Limsurf_aSO4- + OH-
    log_k     -0.1
   Limsurf_cH = Limsurf_cH
    log_k     0
   Limsurf_cH = Limsurf_c- + H+
    log_k     -5.1
   Limsurf_cH + Ca+2 = Limsurf_cCa+ + H+
    log_k     -1.7
   Limsurf_cH + Mg+2 = Limsurf_cMg+ + H+
    log_k     -2
PHASES
    Fix_H+
    H+ = H+
    -log_k  0
END
SOLUTION 1 FW
    temp      25
    pH        6.7
    redox     pe
    units     ppm
    density   1
    Alkalinity 1400 as HCO3-
    Ca        14547 as Ca+
    Cl        112943
    K         0
    Mg        739
    Na        56580
    S(6)      1728 as SO4-2
    -water    1 # kg
END
SURFACE 1
    -equilibrate with solution 1
    -sites_units density   
   Limsurf_a    2.5       0.11      0.2
    Limsurf_c    2.5
    -donnan 1e-9
    only_counter_ions false
END
#    KNOBS; -iter 2000
 
EQUILIBRIUM_PHASES 1
    Calcite   0 15
    ##Dolomite  0 0
    ##Anhydrite 0 0
END
USE solution 1
USE surface 1
USE equilibrium_phases 1
END
USE solution 1
USE equilibrium_phases 1
END