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adding Sorbing species in X1t


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I moved your post to the front page of the forum. It was posted in the archive of old posts. In the future, please be sure to post to the front page to ensure that it is visible.


It looks like you're trying to use the Dzombak and Morel compilation of surface complexation reactions involving hydrous ferric oxide (FeOOH.nH2O). Most of the information you referenced is already in thermo datasets or surface datasets that come with the software. The thermo dataset thermo.tdat, for example, contains reactions for minerals like Fe(OH)3(ppd), Goethite, and Hematite. Goethite, of course, is FeOOH with no extra waters and has a mole weight of 89 g/mol. The surface dataset FeOH.sdat contains information on sorbing species like >(s)FeOH, surface complexes like >(s)FeOPb+, and the sorbing minerals that contain the sorbing sites: Fe(OH)3(ppd), Goethite, and Hematite. If you look at the entries for these minerals in the surface dataset, you'll see that each has a specific surface area of 600 m2/g. I believe the 89 g/mol value also goes into the calculation of surface site density (moles sites/ mole mineral) that you can find in the surface dataset. All of this information is from the Dzombak and Morel compilation.


If you're trying to model a laboratory experiment or an aquifer, you need to specify how much sorbing mineral you actually have. Unlike the data in the thermo and surface dataset, this information depends on the specific system you're trying to model. In X1t, you would swap a sorbing mineral (Fe(OH)3(ppd), Goethite, or Hematite) into the Basis (the Initial pane) and constrain its mass (I think this is where you're trying to specify g/L). Then, you would load the appropriate surface dataset into the program by going to File - Open - Sorbing Surfaces and browsing for FeOH.sdat.


Hope this helps,


Brian Farrell

Aqueous Solutions

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