Conceptual Models > Equilibrium assumptions

model with SI H2S:0

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joserevueltas94:
 I want to create this modeling but  I cant find result  with SI H2S: 0                                                                                                                             Modeling in Phreeqc:
I Use the composition of Manatial Nuevo (the neutral salty spring), determine the amount of CO₂ and H₂S that can dissolve until the saturation index of these two gases equals 1 (incremental reaction), and repeat the model at different pressures between 1 and 250 atm. The spring compositions and additional notes are provided: example p100
    SOLUTION 1
    temp      100
    pH        8.1
    pe        4
    redox     pe
    units     mmol/kgw
    density   1
    Ca        0
    Cl        1356
    K         101
    Mg        78
    Na        1477
    S(6)      41
    Si        155
    Alkalinity 950
    -water    1 # kg

GAS_PHASE 1
    -fixed_pressure
    -pressure 100
    -volume 1
    -temperature 200
    CO2(g)    1
    H2S(g)    0.048


Thermal Camera Images:
Most fumaroles recorded temperatures between 86 and 89 ?C, exceeding 89.7 ?C (the boiling point of water at Tacan?); this data will be considered in thermodynamic analyses.

Thermodynamic Interpretations:
The Henry?s constant of H₂S is two to three times higher than that of CO₂.

dlparkhurst:
I am sorry, but I do not understand your question. The point where the sum of the partial pressures of the gases is 1.0 would be the point at which a bubble would form at 1 atmosphere pressure. But you are working at a pressure of 100 atm, so I am not sure what is relevant about the bubble point at 1 atm.

I also don't think the question is well posed. The partial pressure of CO2 will dominate, so if you want a total pressure of 1 atm, you could simply ignore H2S. CO2 will be close to 1 atm, but H2S could be any small number. You give a ratio of 1.0 to 0.048 for CO2 to H2S in the gas phase. Is that a measurement of the exsolved gases at a given temperature and 1 atm pressure?

Are you trying to recreate the composition of a solution at high pressure from measurements at 1 atm? Seems like you need to know the volume as well as the composition of the gas that evolves from a known volume of solution.

joserevueltas94:
I would like to model, as a function of pressure, the gas composition in equilibrium with a boiling hydrothermal aquifer that contains dissolved H2S and CO2 at the point of saturation. I don't know exactly the composition of the aquifer
The Henry's constant of CO2 in water is higher than H2S, so I suppose that a deeper boiling fluid should produce a gas phase that is enriched in CO2 over H2S. But I would like to use phreeqc to model that quantitatively and compare it to the measurements of this gas that I made at the surface (assuming that their transfer from depth to surface is conservative).

dlparkhurst:
It might take us a couple iterations to develop a script that does what you want. Here is a script that calculates the solubility of CO2 at 100 atm and 100 C in your solution. Assuming H2S is a minor component, there is no constraint on its partial pressure. I simply used the ratio that you gave in your GAS_PHASE composition 1:0.048.

You can pose another question if this script is not what you needed.


--- Code: ---SOLUTION 1
    -temp      100
    -pressure 100
    pH        8.1
    pe        4
    redox     pe
    units     mmol/kgw
    density   1
    Ca        0
    Cl        1356
    K         101
    Mg        78
    Na        1477
    S(6)      41
    Si        155
    Alkalinity 950
    -water    1 # kg
EQUILIBRIUM_PHASES
CO2(g) 2 10
H2S(g) 0.68 10 # log10(4.8)
END

--- End code ---

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