Forcing minerals in activity diagrams

[Karen Johannesson]

I am wondering if there is a way to "force" a mineral in an activity diagram. For example, in the attached plot that I made with ACT2, I would prefer to include one of the smectite minerals in the thermo.tdat data base instead of the zeolite, Clinoptilolite-Na phase. I have tried to suppress this zeolite to only force another zeolite mordenite-Na to replace it. When I then suppress mordenite-Na, the field is replaced by Albite low, which I don't want to suppress.

Stability diagram.pdf

[Jia Wang]

Hello Karen,

Act2 creates a diagram to show the stability of minerals and the predominance of aqueous species in chemical systems based on all entries available in the thermodynamic database and the constraints for the current calculations. The most stable mineral will be displayed on the diagram and you cannot fix a mineral to be present. When you suppress a species or mineral, the calculation ignores it. Perhaps your thermo dataset has entries that are not representative of the system that you are trying to create a diagram for.

Best regards,
Jia Wang
Aqueous Solutions LLC

[Karen Johannesson]

Hi Jia,

Thank you so much for your response. I guess that is what I thought Act2 does, which is perfectly fine. I don't actually think there has been anyone who has reported the formation of smectites in this aquifer. The major ion chemistry that I have measured would appear to be in agreement with the fact that such minerals haven't been reported. I did try some other databases that come with GWB, and as you mention, the results were a little different. However, most of the waters still plotted in the kaolinite stability field.

Best wishes and Happy Thanksgiving,

Karen

[Jia Wang]

Hello Karen,

You're welcome. I am glad that was helpful.

Hope you had a good Thanksgiving.

Best,
Jia