Surface Complexation with gas

[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: [Select]

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



[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?

[dlparkhurst]

You have defined the surface complexation reactions; that is all you need. I would include the -donnan option to calculate a diffuse layer, just because it maintains charge balance in the system. I don't think you need any of the more complicated surface transport options.

I don't think surface complexation is even an important issue for you. The main question is how H2 reacts in the system. H2 could be involved in biotic and abiotic reactions that need to be simulated with kinetics. Those are the important processes, and I have no idea how you get at them other than lab and field study.