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Ross McCartney

Anion exchange

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Hi,

Is there any way to model anion exchange using GWB? Ideally I would like to model Cl-SO4 exchange and I tried modifying the Ionex.dat file but got an error message saying 'Expected a cation as adsorbed species in ion exchange model, found "Cl-"'. If it is not possible at present, is this something that might be included in the next release?

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Hi,

Is there any way to model anion exchange using GWB? Ideally I would like to model Cl-SO4 exchange and I tried modifying the Ionex.dat file but got an error message saying 'Expected a cation as adsorbed species in ion exchange model, found "Cl-"'. If it is not possible at present, is this something that might be included in the next release?

Hi Ross:

Page 15 of the GWB Essentials Modeling Guide discusses a simple method for modeling ion exchange reactions on mineral surfaces that involves swapping the activity ratio for two aqueous species into the Basis and prescribing it's value. This method is applicable to anions as well as cations.

The more general method for modeling ion exchange is restricted to cations, as the three methods (Gaines-Thomas, Vanselow and Gapon) that can be invoked for balancing exchange reactions all refer specifically to cations.

I will add this to the list of user-requested features.

I hope that helps,

Tom

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