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Kinetic sorption of U to Geothite in React


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I'm trying to model the kinetic diffuse double layer sorption of uranium to geothite. I'm unsure on how to create the V.10 REACT model. I have followed the tutorial "How do I simulate sorption kinetics?" on the GWB website and still have questions. The following error messages pops up for various inputs:


1. Kinetic -> Sorbed species: >Fe-OH

-- Error: Kinetic reactant >Fe-OH is a surface site, not a complex.


2. Kinetic -> All other sorbed species

[Model freezes and I have to kill it]

What can I do to correct the errors?

Do I need to add each individual sorbed species in the "reactants" tab to accurately model sorption kinetics?


I have attached the REACT file and the Sorption file. I would like to attach the thermodynamic database, but it exceeds the max single file size.


Thank you,




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Hi KDanny,


Apologies for the delay. We've been really busy the past few days traveling, teaching a workshop, and exhibiting at the Goldschmidt conference in Prague. I'll be off the next few days and won't be back in the office until next week, but I'd like to give you some tips to get you headed in the right direction.


Regarding the first error message, you can only set a kinetic rate law for the formation or breakdown of surface or aqueous complexes, like >Fe-O(UO2)+ or CaUO2(CO3)3--, but not basis species. The uncomplexed site >Fe-OH is a basis species for the surface reactions, which is why you receive the error.


It's probably possible to set a kinetic rate law for every surface complex, but I'm not sure it's necessary. I recommend first finding out which surface species is most important in a purely equilibrium model.


If you send the thermo dataset to support@gwb.com, I'll be able to take a closer look at your problem next week. For more information than is available in the tutorial, take a look at section 4.4 Kinetics of complexation and sorption, in the Reaction Modeling Guide.


Hope this helps,


Brian Farrell

Aqueous Solutions

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