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Failing to plot equilibrium boundaries in Act2


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Hello,

 

I am learning how to use Act2 for plotting activity-activity diagrams and for the most part it is pretty straight forward. However, when I swap out a diagram species for another mineral phase (i.e., illite(IMt2) for illite(Al)), sometimes it will plot without the other mineral species and equilibrium boundaries. I will get a single field (i.e. illite(IMt2)) with no other mineral species, while previous mineral species plotted normally with various mineral. All the parameters are the same between the two plots, expect the main mineral species.

 

I get the impression it is a simple fix, but where do I begin? Is this a bug in the program or is there something wrong with the database? I have looked at the database, but nothing stands out to be wrong.

 

I have attached the plot with a single mineral field and the illite data from the database used.

 

Thanks for the help!!

mchesh9973

Image_2.pdf

Illites.txt

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Hi mchesh9973,

 

Have you tried adding additional Basis species to your system using the "in the presence of field"? I tried adding Na+, Mg++, Fe++, and Fe+++ (after decoupling the Fe++/Fe+++ redox pair, or you could add Fe+++ and O2(aq) instead) and was able to generate a stability diagram with more than just Illite(IMt2).

 

Try taking a look at the printed output (click "View Results") to get a better idea of how Act2 works. Pay attention to the "Basis species" section (which will include your main species, water, species on the axes, and the ligand species) and the "Species and minerals in main system" section. This shows the different species or minerals that the main species (Illite(IMt2) in your case) can become based on the Basis you've specified.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC

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Hi Brian,

 

I added the other basis species (Fe2+/3+, Mg, Ca, Na) and replotted. The same result occurs. With Illite(IMt2) a single field and with Illite(Al) multiple mineral fields. I have attached the output files you mentioned. It is weird that in the Illite(IMt2) output it shows the only reaction is illite to illite having a Log K of 0.0. I am assuming this is the problem, but how can it be fixed.

 

By they way, I have been using GWB 8.0.8 and just upgraded to the 8.0.12 version to see if it would help. Same result as above.

 

Thanks,

Mchesh9973

K-H_H4SiO4_IMt2_example_output.txt

K-H_H4SiO4_Al_example_output.txt

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Hi,

 

I forgot to add H+ to the list of Basis species you'll need. You'll need that for other species or minerals to be considered (to show up in the "Species and minerals in main system" section) when Illite(IMt2) is chosen as the main species. Whether they actually plot on your diagram depends on the chemical conditions you specify. Changing the temperature, or the activity of various Basis species, can alter your diagram.

 

Hope this helps,

Brian

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