Processes > Surface Complexation

Surface Complexation with gas

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dat:
Hi,

I am modelling surface complexation reactions with Quartz, Kaolinite, brine and with hydrogen. How to incorporate my gas phase into surface reactions.

Would it be possible to differentiate the H+ from gas?

I have attached my sample code. Could you please have a look? Appreciate your help.


--- Code: ---SOLUTION 1
units mmol/kgw
Temp 80
ph 6.33
Na 604.61
Cl 685.47
Ca 14.97
Mg 64.17
S(6) 35.60
water 0.02

GAS_PHASE 1
    -fixed_pressure
    -pressure 197
    -volume 1
    -temperature 80
    H2(g)        197

EQUILIBRIUM_PHASES 1
Kaolinite 0 5.42E-07
Quartz 0 1.52E-04
K-feldspar 0 1.33E-06
Dolomite 0 8.13E-07
Albite 0 4.58E-07

SURFACE_MASTER_SPECIES

Surf_al Surf_alOH
Surf_si Surf_siOH
Surf_qs Surf_qsOH


SURFACE_SPECIES

Surf_alOH = Surf_alOH
-cd_music 0 0 0
log_k 0
Surf_siOH = Surf_siOH
-cd_music 0 0 0
log_k 0
Surf_alOH + H+ = Surf_alOH2+
-cd_music 1 0 0
log_k 0.8
Surf_siOH + H+ = Surf_siOH2+
-cd_music 1 0 0
log_k 0.8
Surf_alOH = Surf_alO- + H+
-cd_music -1 0 0
log_k -7
Surf_siOH = Surf_siO- + H+
-cd_music -1 0 0
log_k -7
Surf_alOH + Ca++ = Surf_alOCa+ + H+
-cd_music -1 2 0
log_k -6
Surf_siOH + Ca++ = Surf_siOCa+ + H+
-cd_music -1 2 0
log_k -6
Surf_alOH + Mg++ = Surf_alOMg+ + H+
-cd_music -1 2 0
log_k -5.55
Surf_siOH + Mg++ = Surf_siOMg+ + H+
-cd_music -1 2 0
log_k -5.55
Surf_qsOH = Surf_qsOH
-cd_music 0 0 0
log_k 0
Surf_qsOH + H+ = Surf_qsOH2+
-cd_music 1 0 0
log_k -1.75
Surf_qsOH = Surf_qsO- + H+
-cd_music -1 0 0
log_k -6.75
Surf_qsOH + Ca++ = Surf_qsOCa+ + H+
-cd_music -1 2 0
log_k -5.7
Surf_qsOH + Mg++ = Surf_qsOMg+ + H+
-cd_music -1 2 0
log_k -5.70


SURFACE 1

-sites_units Density
-cd_music
-equilibrate 1
Surf_alOH 5.5
Surf_siOH 5.5
Surf_qsOH 4.6 2.34 0.01
-capacitance 3.098 0.2
END


--- End code ---

dlparkhurst:
If you model equilibrium between H2(g) and your solution, you will either convert all of the carbonate from dolomite to methane, or oxidize all of the H2(g) to water. C(4) and H(0) will not coexist in appreciable amounts at equilibrium.

What you probably need to do is to use Hdg(g) as an unreactive form of H2(g), and then kinetically convert Hdg to H2 to account for abiotic or biotic reactions.

There have been quite a few posts to the forum about H2 storage and reaction. Search the forum for Hdg(g) to find them.

dat:
Hi David,

Thank you for the reply. I will use Hdg.
But I really want to see is how the surface reactions vary with hydrogen. How this affects to the electrostatic forces and etc.

Will this code do that? Also in the -cd music model, (-cd music 1 2 0) do I have add a diffusing charge ( in the third zero) because of hydrogen.
If so, could you please guide me how to do that?

dlparkhurst:
Hdg will have nearly zero effect on the surface complexation reactions.

If you allow Hdg to kinetically react (converting to H2), then you will have a series of reactions with H2 reducing sulfate and (or) carbonate, with consequent pH changes that will affect the surface-complexation reactions.

dat:
Hi David,

Thank you. Do I have to add a charge to the diffuse layer, because of H2?

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