Stability and solubility fields with respect to Ion products and pH

[BC_IITB]

Hello,

 

I am studying stability and solubility of uranium ore mineral 'carnotite' as a function of pH and the product of ionic concentrations of the constituent elements.

In case of carnotite the ionic species involved are uranium, vanadium and potassium. So I want to create a plot of ion product of uranium, vanadium and potassium on the Y axis against the pH values on the X-axis.

I have used ACT2 module to create the Eh-pH diagrams and demarcate the stability field of carnotite. In this case the x-axis was pH and y-axis was Eh, and the other species were added in the box stating "in the presence of";

But now I want to add multiple species along the Y axis, so that the ion product plots on y-axis as the function of pH. Is there a way to add multiple ions along the y-axis and the pH on x-axis in ACT2?

 

I have attached the figure that I am trying to recreate

 

Any help would be highly appreciated.

 

 

 

[Brian Farrell]

Hi,

 

The GWB doesn't draw diagrams exactly like that, but a solubility diagram made with Act2 should be useful. In a solubility diagram you don't set the activity of the main species to a fixed value like you do in an Eh-pH diagram. You instead set its activity to vary by making it one of the axis variables. The other species, which you set in the "in the presence of" section, are set to fixed composition. In this way you're still considering a range of ion products, but you're only adjusting the activity of one of the species composing the product at a time.

 

To make a diagram, I started by decoupling all the oxidation states of vanadium and uranium. Then, I set VO4--- as the main species and as the y axis variable. I set H+ with pH units as the x axis variable. Finally, I added UO2++ and K+ to the "in the presence of" section and set them to " speciate over x".

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC