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react calculation

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I wang to calculate the dominant species in As-Fe-S-H2O system using react program. However, after I input the parameters and press the run botton, the program reminds of me with " -- Error: System needs to contain: O2(aq)". I don't know the activity of O2 in the system. How should I do.

Please see the attchment for my input.





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Hi Shaofeng,


Do you have any clue about the redox state of your system? Do you know whether you have As(V) or As(III) in your system, or maybe both? An Eh measurement perhaps? Do you have measurements for both oxidized and reduced sulfur? Is your system open to the atmosphere? Do you observe any minerals which might buffer the oxidation state? If the answer to any of these questions is yes, you can perform a basis swap. That is, you'll replace O2(aq) in the basis with something that is more convenient for your particular system, such as the Eh or the ratio of SO4-- to H2S.


There are a few modifications to your existing example I could suggest, but it might be best to hear more about your system first. Have you made a satisfactory redox-pH diagram yet? In such a diagram the O2(aq) activity is an axis variable, which allows you to determine the effect of the redox state on As speciation. Section 5.3 in the GWB Essentials Modeling Guide might be useful to you.




Brian Farrell

Aqueous Solutions LLC

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