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Speciate over x-y in Act2


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Hello,

I have a question about the mosaics in Act2 and the "speciate over xy" option. 
 
I cannot find a good explanation about what it is actually doing to the calculation to make the mosaic output. If this exists and I just have not found it, please link!
 
I was making some mosaics and playing around with the speciate option and got a bit confused on what that option actually does.  Does it "take" that element out of the 'soup' to force it to make the most favorable major mineral with that element in concert with the "main minerals"? 
 
For example, I swap Ca for apatite in one example, resulting graph looks the same, speciated or not. I swap the Ca for fluorite, speciated over x-y, the result looks different and I get the fluorite/calcite "sub-field" over the other main mineral fields. Ca swapped for fluorite UNspeicated over x-y gives a different graph for the main minerals. So the speciate is changing the Ca availability for the main minerals somehow....but I am confused on what is actually happening.
 
Can someone explain what this option does please?
 
Thank you very much,
Danielle
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Guest Melika Sharifi

Dear Danielle,

Could you, please, attach your Act2 scripts? That way, I can explain the difference between when "speciate over..." is on and when it is off.

Thanks,

Melika Sharifi

Aqueous Solutions LLC

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Guest Melika Sharifi

Hi Danielle,

Thanks for attaching your script. Please attach your custom thermo dataset so I could see all species loaded in your script.

Thanks,

Melika

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Guest Melika Sharifi

Hi Danielle,

Thanks for attaching your script and the thermo dataset, it was very helpful. Act2 creates activity diagrams for the main diagram species (Ce+++ in your case) across the axes ranges you specify (CO3-- and F- in your script). You may add complexing species (e.g. Al+++, Ba++, Ca++, etc.) under "in the presence of” to see the effect of adding additional chemical components using the "add" button. In your example, Al+++, Ba++, Ca++, etc., are added to a system already containing cesium, Fluoride and carbonate. 

When you add a component, for example Ca++, to the "in the presence of" field, Act2 assumes by default that Ca++ is the only stable calcium-containing aqueous species over the entire compositional range represented by the X and Y axis. In other words, Ca++ is the only stable form of calcium within the X-axis and Y-axis ranges described. This, however, may not be true in some geochemical systems if you expect Ca++ will speciate in response to changing pH, Eh, or concentration of X and Y axes species (CO3-- and F- in your script). Therefore, if you know that your complexing species reacts under the axes ranges you have set, you can include that in your graph using the "speciate over x”, “speciate over y”, or “speciate over x-y" options. That way, Act2 will plot activity diagrams (you see them as dashed lines in gray) for those species having "speciate over..." option on. You can also include labels for the sub-fields of the plot. To do so, right click on your diagram, select Edit Appearance and check the mosaic labels box in the Diagram pane. When you speciate additional components in an activity diagram, you are essentially overlaying multiple activity diagrams.

On a different note, the pressure you set in Act2 affects the position of water stability limits and the fugacities assigned to gaseous species, and not mineral or species stability, but you can certainly set the fugacity of gases as you have for O2(g).

Hope this helps.

 

Bests,

Melika Sharifi

Aqueous Solutions LLC

 

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