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Activity V Activity Diagrams.

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Hello Usman,

To create an Activity-Activity diagram in Act2, you will need to know what the predominant species in your system you wish to diagram and the species for the x and y axes. The predominant species is selected for diagramming under ‘diagram species’ and you would need to enter its activity. For example, to make a redox-pH diagram for iron, you would select Fe++ as the diagram species and then on the x and y axis, select the activity for O2(aq) and pH respectively. The diagram will then show you the predominant species of iron base on the pH and activity of O2(aq). I am not exactly sure what you mean by Fe2+ V activity of O2-, can you clarify on the predominant species you wish to diagram for in Act2?

There are a couple of places with good resources to help you get started. Please refer to section 5 Using Act2 in the GWB Essentials Guide for more information regarding calculations and examples. The example I mentioned above is demonstrated in detail in the Stability diagrams lesson at the GWB Academy. Please attach your input file and thermo database file if you want someone to take a further look.

Best regards,
Jia Wang

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Dear Jia Wang,

Thank you so much for your brilliant comments and suggestion. Sir, I am fresh and new user of the GWB. I have already managed and produced my Equilibrium phase diagrams for iron oxide-hydroxide and sulphides. What I want to know is how to produces Activity-Activity diagram to know which minerals are theoretically stable and unstable in relation to my water sample analysis.  Thant why I need guidance on how to start the Activity-Activity digram, e.g Fe2+  -  Activity of O2-, Fe3+ - Activity of O2- or Fe2+ - Activity of SO42-.

Your above explanation is good but you confused me by saying I should provide thermo database file... Therefore, below are part of my inputs files.

Sir, I want to know how to start building the Fe2+ - Activity of SO42. Thank you.

Best regard.






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Hello Usman,

Here are a couple of suggestions that might help. I think you should consider using the SpecE8 app to calculate mineral saturation indices for your fluid. You can input your geochemical data for each of your fluid into the basis pane in SpecE8 and allow it to perform equilibrium calculation. In the Result pane, you can open and view the output file to see a list of mineral saturation indices. For more information and example, please refer to section 7.2 Equilibrium models in the GWB Essentials Guide. Alternatively, you can also calculate mineral saturation for all your fluid at once using a GSS spreadsheet. To do so, you would need to enter your geochemical data into a GSS spreadsheet and select 'Calculate with SpecE8' under '+analyte'. For more information, please refer to section 3.2.5 Calculating analytes in the GWB Essentials Guide. You can also display your data on the Activity diagram you created by using 'Scatter data'. For more information and example, please refer to section 5.6 Scatter data in the Essentials GWB guide. 

Hope this helps,

Jia Wang

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