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Calculation pH and Eh


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Hello Abelo,

GSS uses SpecE8 to calculate the pH and Eh of the system. Unfortunately, there’s not a set equation to calculate these values. If you would like more information on the calculations and the methods used in SpecE8, please refer to the Geochemical and Biogeochemical Reaction Modeling text. 

Best regards,

Jia Wang

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  • 5 months later...


You can calculate the pH of a fluid if you supply SpecE8 with the proper constraints. For example, you can calculate the pH if you know that your fluid is in equilibrium with the atmosphere or a specific mineral. For example, you can swap the H+ ion for CO2 fugacity and charge balance on HCO3-. The program can calculate the pH in a speciation calculation. For more information, please see section 7.2 Equilibrium Models in the GWB Essentials guide.
I think you can set up the same method above to set the pH in equilibrium with an aqueous species as well but it would be something that you need to decide is accurate for your system. I am not sure what your model looks like so it is hard to say for sure if it make sense. If you would like someone to further troubleshoot your issue, please post your input file and your thermo dataset.
Hope this helps,
Jia Wang
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