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Eh-pH in Act 2

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I have a solution at pH 2 of 10g/L Cu, 10 g/L Al and 20 g/L dissolved in freshwater, seawater and 2 x seawater that simulates an actual saline acid leach of Cu ore. I have used Spec8 to calculate log activity for these solutions. I now want to plot a series of Eh-pH plots (and plot on actual experimental data). Given that there is a wide range of species activities (e.g. SO4 is mostly Al(SO4)2^1- as well is some other complexed forms and as SO4, how do I best represent the Cu speciation on an Eh-pH diagram given i can only use one SO4 or other species per diagram input on the Basis screen?


I have attached a sample Spec8 input file and Act2 Eh-pH diagram file to illustrate the point. Any advice and/or voice(s) of experience appreciated.


Thank you


Kaizen2SW Fe 20.ac2

2 SW pH 2 and Fe 20.sp8

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Hi Kaizen,


There is no one "correct" way to constrain an activity diagram. It's a very simplified, visual interpretation of a chemical system. What you've done, swapping in multiple different SO4-- complexes (SO4--, plus CaSO4 for Ca++, MgSO4 for Mg++, FeSO4+ for Fe++), is fine. Because mass action equations express the relationship between various species, you could just as easily constrain your Basis without any swaps (SO4--, Ca++, Mg++, Fe++) to get the same result. Just make sure you match up the correct activity for each species.


Hope this helps,


Brian Farrell

Aqueous Solutions LLC

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