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UO2++ Thermo Data

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Hi Katelyn,


Thank you again for your help!!!. Now, I have a new question!!! :huh:


I am trying to complete a database to simulate a pore water contaminated with U(VI). The cation and anion components present in this porewater are mainly Na, Si, K, HCO3, Al, NO3, Ca, Cl, and UO2++; at a pH between 7 and 8. I will also use the react model to slide the pH to different conditions.


I revised the provided Geochemist's Workbench thermo databases, and I found that the thermo data includes most of my porewater components as well as most of the uranium solid phase that I want to see after my simulation. However, it doesn't include H2SiO4 (to swap with H2SiO4-- to simulate all the polysilicate species) and UO2++. In order to include the missing species; I copied them from the minted data following the next procedure:


1. I renamed the thermo.dat


2. From the minteq data on the basic section, I copied H2SiO4 and UO2++ on the same section of the renamed data.


3. From minteq data on the aqueous species section, I copied +H2SiO4-- and H3SiO4- on the same section of renamed data.


I noted after copying these species that they were saved as a COPY (H2SiO4--_COPY, H3SiO4-_COPY, and UO2++_COPY) since they are included in the thermo data in the redox section.



My questions is if I can remove these species from the redox section without creating any conflict in the data or I should just transfer these species from the redox thermo data to the basic section.


Thank you very much!!!







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Hi Claudia,


I’m a little confused. Can you clarify what species you need that aren’t in the default thermo dataset? Please be sure to include the correct formula and charge for each species.


SiO2 is the basis species for Si in thermo.tdat, while H4SiO4 is the basis species in thermo_minteq.tdat. They are essentially the same in that they both represent uncharged Si, but H4SiO4 has two water molecules included in the formula. Both datasets included the deprotonated species H3SiO4- and H2SiO4(2-) which you were trying to add, so I don’t think you need to modify the default dataset at all.


Since thermo.tdat already has UO2++ as a redox species, I don’t see the need to add it again as a basis species, or to change it to a basis species in the thermo dataset. When you construct your model, simply decouple the UO2++ from the U++++ basis species. That way, UO2++ is treated as a basis species and is thus independent from U++++. To decouple the redox pair go to Config > Redox Couples and select UO2++/U++++. You can read more on Redox couples in Section 7.3 (Redox disequilibrium) in the GWB Essentials Modeling Guide. For even more information on Redox disequilibrium take a look at Chapter 7 in the Geochemical and Biogeochemical Reaction Modeling text.


Kind regards,



Aqueous Solutions

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Dear Katelyn,


Thank you for your guidance and sorry for the confusion.

I want to simulate a synthetic porewater (from my batch experiment) that contains Na2SiO3, Al(NO3)3, KHCO3, CaCl2, and UO2++ (UO2(NO)3)2 as the major components to see which are the uranyl silicates formed.

Thank you, after you explained it to me, I can continue my simulations.



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