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Coralie

Solubility contour

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I am trying to do solubility contours for Pb and Zn (1 ppm and 100 ppm) in an activity-activity diagram and temperature-activity diagram showing the stability fields of iron oxides.

I have no issue doing a diagram that shows the stability fields.

However, is there a way to plot solubility contours on top of this?

Also, I see that all entries have to be activities, is there a way to enter values as ppm and/or moles.

I am new to GWB, so any help would be much appreciated

Coralie

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Hi Coralie,

It sounds like you're using Act2 and Tact for your diagram construction, but I think what you need is Phase2, a new app we developed for GWB12. From the GWB Reaction Modeling Guide:

A Phase2 diagram differs from a simple diagram of the type constructed by Act2 and Tact in that each point in the diagram represents the complete solution to the equations describing the system’s distribution of mass. If you were to use Phase2 to calculate an Eh-pH diagram, for example, you would find that, unlike the result from Act2, the boundary lines are curved, rather than linear. Because of the calculation’s completeness, some Phase2 diagrams differ qualitatively from their Act2 counterparts. For this reason, the diagrams are sometimes referred to as “true” Eh-pH or “true” activity diagrams.

Phase2 diagrams, furthermore, can be plotted over a wide range of variable choices, and in a variety of ways.

You can plot the results of Phase2 calculations as maps of species predominance or mineral assemblages, and you can color map, mask, or contour any variable. You can additionally render cross-sections through the diagrams. Because a Phase2 calculation is conceptually similar to React, you can use any units to constrain your chemical system, and you can choose a variety of axis variables not possible in Act2 or Tact.

For more information, please see our Phase2 webpage and the documentation on Phase2 and P2plot in the GWB Reaction Modeling Guide.

Regards,

Brian Farrell
Aqueous Solutions LLC

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Hi Brian,

Thank you for the reply.

I have tried using Phase2, but so far I am unsuccessful in doing such solubility curves.

In Phase2, I chose fO2 for X axis and pH for Y axis, but when plotting with P2plot, using 2D diagram, I have Rxn progress (x) and (y). 

Is there any tutorial other than the webpage link you sent for using Phase2?

I am trying to reproduce the attached figure on the left. The stability fields I obtain for the Fe oxides is different (see attached), but the most important is I am not able to reproduce the solubility curves for Pb and Zn.

Also, I have tried changing the thermodynamic dataset in the preferences, but to my surprise, the diagram does not change a bit.

Any help with plotting this would be greatly appreciated.

Regards

Coralie

Cooke-et-al-2000_Ec-Geol_Fig3.pdf

logfO2_pH_Fe.ac2

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Hi Coralie,

There are various ways to interact with P2plot and the other plotting apps. You can double-click on a specific plot aspect, like the "Rxn progress (x)" axis variable, to open the "Axis Range and Variables" dialog. Or, you can right-click on "Rxn progress (x)" and pick "X Axis Range" to open the same dialog. Finally, you can use the menubar along the top of P2plot to access the dialogs. Under Format, choose "Axis Range and Variables...". From that dialog, you can pick your axis variables, set linear or log scales, tick increments, units, and so on. You can add contours from Format -> "Contour...". 

I recommend reading the Phase2 and P2plot chapters in the GWB Reaction Modeling Guide, which you can access from the Help menu of any GWB app. At the very least, you should check out the first couple examples (7.8 Example: Speciation diagram and 7.9 Example: Mineral solubility) in the guide to see the process of calculating and rendering the diagrams.

The thermo dataset that you set in the Preferences dialog will become the default dataset every subsequent time you open a GWB app, but it won't load that dataset into an instance of the app that is already open. To do that, you would go to File -> Open -> Thermo Data... You can verify at any time the dataset that is currently loaded by going to File -> File Properties -> Thermo Data.

Hope this helps,

Brian

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Hi Brian,

Thank you for your guidance, I will read those manuals and have another go.

It seems to work better. However, I am assuming I cannot overlay the predominance diagrams and solubility plots using GWB, and will have to use another software. Is that right or can it be done?

Kind regards

Coralie

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Hi Coralie,

You can overlay contours of a single variable on a predominance map in P2plot. Currently you can plot a predominance map of one basis entry or element at a time, however. If you want to overlay the predominance bounds from other basis entries or elements you will need to do so in another program like PowerPoint or Illustrator.

Regards,

Brian

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