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Eh-pH diagram with 2 complexing species

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I try to ceate a Eh-pH diagram for neptunium in the presence of the mineral siderite (and vice versa the diagram if iron in presence of neptunium). Both cations should be able to form complexes with carbonate - and such complexes are within the thermo.dat.

But I can't get Act2 (Version 10.0.4) to manage both carbonate complexations. I attached and example and the carbonato-complexes of neptunium are not taken into account allthough they should be formed as dominant species in the alkaline range then carbonate is present.

Is there a way to inlcude both complexations?


Thanks in advance!





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Hi Frank,


When you diagram iron on an activity diagram, only species containing iron will plot. The iron may complex with various forms of carbon (depending on the Eh and pH), or with chloride, or with any other component that you specify under "in the presence of," but you won't find any carbonate complexes with neptunium on an Eh-pH diagram for iron. By their nature, activity diagrams are simplified versions of chemical systems. I think you'll want to use SpecE8 or React to create a model that accounts for more complex interactions.




Brian Farrell

Aqueous Solutions

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Hi Brian,


thank you for the comment. Actually I have created a model using React and it works fine. I just wanted to create a "nice picture" with Act2.




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