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Cation exchange reaction


chance
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Hi Chans,

 

GWB can certainly model ion exchange reactions. The dataset IonEx.dat, supplied with the software, provides an example of how to set up a surface reaction dataset. You'll need to add to/ modify the dataset to fit your specific application by searching through the literature for selectivity coefficients (basically equilibrium constants for the mass action equations corresponding to each exchange reaction). IonEx.dat describes the different conventions used to model ion exchange reactions and explains how the dataset should be formatted. You should check Section 2.5.4 or 7.5.2 of the GWB Essentials Guide (release 9.0) for more on ion exchange reactions.

 

Hope this helps,

Brian

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  • 2 weeks later...

Hi Brian,

 

I have a question for you again.

I am trying to model the Ca++ exchange reaction on illite surface with H+ ion that is produced from CO2 dissolution in the brine.

I prepared the cation exchange dataset for this reaction according to the example file IonEx that came with the software as you suggested.

First I am using thermo dataset for the CO2 dissolution in the brine under 50 atm. Then,after I got the pH decreased, I changed the dataset to IonEX to model the illite surface exhange reaction between Ca++ and H+.

But I think I am doing something wrong.I dont know the selectivity constant for this echange reaction. So, I am also playing with this parameter.

Can you look at my files?

Thank you.

IonExIllite.datillite_exp.rea

Hi Brain,

 

Thank you for your reply. You helped a lot.

 

 

Regards,

 

Chans

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Hi Chance,

 

The thermo datasets and surface datasets are used differently by the GWB programs. A thermo dataset is always necessary, but a surface dataset is not (only when you want to model surface reactions). You should not replace the thermo dataset with the surface dataset - you simply open a surface dataset in addition to the thermo dataset. This should be done at the beginning of the run, not the end.

 

As for what goes into the surface dataset, I can't help you with your selectivity coefficients. You do need to change the format of your surface dataset, however. I would recommend following convention and using a monovalent ion as the basis species, so >X:H in your case. The surface species, then, would be something like >X2:Ca (no charge on surface species), made up of the species -2H+, 2>X:H, and Ca++. Where you define the surface species, you need to specify the correct number of species needed to form it (3) and make sure that the coefficients are correct to make a balanced reaction (>X2:Ca + 2H+ = Ca++ + 2>X:H).

 

Hope this helps,

Brian

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Thank you Brian. You helped a lot. Now its working. I didnt know that at first, I would open the surface dataset in addition to the thermo dataset.

 

 

Regards,

Chance

 

 

 

 

 

 

 

Hi Chance,

 

The thermo datasets and surface datasets are used differently by the GWB programs. A thermo dataset is always necessary, but a surface dataset is not (only when you want to model surface reactions). You should not replace the thermo dataset with the surface dataset - you simply open a surface dataset in addition to the thermo dataset. This should be done at the beginning of the run, not the end.

 

As for what goes into the surface dataset, I can't help you with your selectivity coefficients. You do need to change the format of your surface dataset, however. I would recommend following convention and using a monovalent ion as the basis species, so >X:H in your case. The surface species, then, would be something like >X2:Ca (no charge on surface species), made up of the species -2H+, 2>X:H, and Ca++. Where you define the surface species, you need to specify the correct number of species needed to form it (3) and make sure that the coefficients are correct to make a balanced reaction (>X2:Ca + 2H+ = Ca++ + 2>X:H).

 

Hope this helps,

Brian

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