different results of the distribution of chemical species with different pH between GWB results and other references

[Cheng]

Dear Jia, 

I have added a new chemical, Tetracyclin, into the thermo-TC_1.tdat, and the detailed equilibrium equations were all prepared in the new thermo data. But the species-pH results were not the same as the reference showed. I have checked by using the Mingteq, the Mingteq results were the same as the reference. I have no idea about this error. Please give us some suggestions or some guide. 

Thanks a lot

Cheng

thermo-TC_1.tdat TC-pH_test1.rea

[Jia Wang]

Hello Cheng,

I took a quick look at your custom thermo dataset and found that your reaction for TC2- log K, 9.3, which did not match the negated value given in your table.  Once I changed the value to 16.57 and reran your calculation, the result seems to match what is shown in your excel plot.

I also noticed that you have loaded a Kd sorption dataset for your React simulation. Perhaps I don't have your customized Kd file for the run, but unless you add the desired species reactions into the surface datasets, the GWB won't perform any sorption reaction. In this case, your React run is not affected by the surface dataset you have loaded. For more information and example for sorbing, please see section "Sorption onto mineral surfaces" in the GWB Essentials User Guide.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

[Cheng]

10 hours ago, Jia Wang said:

Hello Cheng,

I took a quick look at your custom thermo dataset and found that your reaction for TC2- log K, 9.3, which did not match the negated value given in your table.  Once I changed the value to 16.57 and reran your calculation, the result seems to match what is shown in your excel plot.

I also noticed that you have loaded a Kd sorption dataset for your React simulation. Perhaps I don't have your customized Kd file for the run, but unless you add the desired species reactions into the surface datasets, the GWB won't perform any sorption reaction. In this case, your React run is not affected by the surface dataset you have loaded. For more information and example for sorbing, please see section "Sorption onto mineral surfaces" in the GWB Essentials User Guide.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

Hello Jia,

logK 9.3 is really a wrong value, which is the newest change we tried, and the right log K value is really the 16.57.  In addition, we don't need any surface adsorption here, so I give a really small value to the porosity. I think I have control the condition well and they are same as I tried in Mingteq, but I get a wrong result. I can't get the solution from your suggestions. Did there any other problems I have made here? I'm looking forward to hearing from you.

Thank you again,

Cheng Zhang

[Jia Wang]

Hello Cheng,

If you have corrected the log K value for TC--, then it would match the data table you have posted earlier. I am not seeing any particular issue with your GWB input file setup.

I am not sure how your Minteq file is set up, so it would be difficult to know whether your GWB file is set up the exact same way. Is there any additional information from the original reference paper regarding the model set up or software used originally?

If you are using Minteq as a comparison, I think you might consider adding your reactions to thermo_minteq.tdat and use this customized dataset. Thermo_minteq.tdat will use the same activity model as Visual Minteq, whereas thermo.tdat uses the bdot activity model. I don't think this is going to make a huge difference for your calculation. For more information on different activity models, please see the Activity Coefficients chapter in the GWB Essentials Guide.

If you don't intend to simulate adsorption, then you can simply remove the Kd surface dataset loaded. If no surface dataset is loaded, the GWB will not consider sorption reactions. Also, note that loading the Kd surface dataset without providing any mineral mass or inert mineral volume, then no sorption reaction takes place. I don't think this is the reason for the difference between your GWB result and reference figure but it will help to simplify your input file. More information on sorption models in the GWB Essentials Guide. 

Best,
Jia