Mn-Fe-S mosaic diagram plot

[Nancy Carman]

Been trying to have alabandite and pyrite on the same diagram. Only way is to swap pyrite for Fe(II) and speciate over x-y. However, by doing this, the program only calculates Fe(II) speciation and it does not include Fe(III) species in the diagram.

 

I think the issue here is that the program calculates speciation of Mn vs complexing ions (i.e. Mn vs sulfur species and Mn vs Fe species) but it doesn't calculate speciation between complexing ions themselves (i.e. sulfur vs Fe species)

Need advice on how to go about creating an Mn-Fe-S mosaic Eh-pH diagram where I have pyrite and MnS in the same graph without the above issues.

[Jia Wang]

Hello,

I am not sure I understand the goal of your activity diagram.  Are you trying to see which sulfur species/mineral (pyrite vs. alabanite) is predominant under varying Eh and Ph conditions? In that case, I would suggest that you use SO4-- as the species you diagram. Set the x and y axes as you have done before. Then in the "in presence of" section, add in the log activity for your Mn++ and Fe++ and select speciate over x-y for both components to allow speciation according to Eh and pH. I think this will be a good starting point for you. If you still have issues with your diagram, please post a complete clear description of the issue along with any input file so we can take a closer look more easily.

Just a general tip for creating activity diagrams. Note that all minerals, aqueous and gas species in the thermodynamic dataset loaded are considered in all calculations. If some of these species in your diagram are not expected in your field site or experiment, you can use the suppress feature to exclude them from the program's calculation. For more information and example on suppress, refer section 4 in the GWB Essentials User Guide and the Command Reference.  

Hope this helps,
Jia Wang
Aqueous Solutions LLC

[Jia Wang]

To follow up with my previous post, the nature of these types of activity diagrams do not account for complexation of the ions with each in the "in presence of" section. If you are interested in more complex phase diagrams, you can try the Phase2 application. Phase2 solves a set of equations to describe the distribution of mass, just like SpecE8 and React, at each node in a 2D grid. You can constrain the composition of a fluid in terms of concentration, rather than activities and set up reaction pathways, along the x and y axis. You can visit the Phase2 web page for information or see examples in the GWB Reaction Modeling User Guide.

Best regards,
Jia

[Nancy Carman]

Thank you for the reply on this post, I'll make another post with a clear intent and add my GWB file.