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Cu++ species to create [Cu] vs pH diagram??


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I'm trying to make an log activity of Cu++ vs pH chart in act2, and then overlay a scatter plot of sample data onto it.

I'm having trouble because I can't calculate the log activity of Cu++ (only can do Cu+) in geochemists spreadsheet (see first image). I

I also tried just basis swapping Cu+ for Cu++ but that changes the minerals that appear on the activity vs pH diagram, and I want the divalent minerals to appear on the chart.

I am using the minteq database, but also tried some others and actually can't find any that have Cu++ as a species to calculate.

What's going on here?

Any help is appreciated.

 

CuvspH.PNG

CalcSpecE8_Cu.PNG

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Hello,

I suspect the reason that you are not able to calculate the species activity for Cu++ is because the required constraints aren't provided. In thermo_minteq.tdat, Cu++ is a Basis species and Cu+ is a redox species. Assuming that you have added Cu+ to your dataset, you have disabled the redox equilibrium between Cu++/Cu+. In this case, you won't be able to calculate any species involved with the oxidation state of Cu++ unless you also include a concentration for the Cu++ component.

If your concentration entered is the total concentration for all copper species, you can use Cu++ instead of Cu+. In this case, if you also enter a constraint for the oxidation state (e.g. Eh, pe, or O2(aq)) and H+ (or pH), then SpecE8 will be able find the equilibrium mass distribution between all cuprous and cupric species. For more information about redox couples, please see section 2.4 Redox couples and 7.3 Redox disequilibrium in the GWB Essentials User Guide. 

Hope this helps,
Jia Wang
Aqueous Solutions LLC

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