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React - How to add Fe(total) into basis for modeling

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If you have a bulk concentration of iron, you can enter it as an entry for the basis species for Fe in the basis pane. As long as you don't select the "free" unit, or decouple the redox reactions for various valence species of iron, the software will automatically calculate the equilibrium distribution of total mass across oxidation states.

For example, if you are using thermo.tdat, the basis species for iron is Fe2+. You can add this to the basis and then set your bulk concentration for iron from your analysis. In thermo.tdat, Fe3+ is a redox reaction with Fe2+. When you trigger the calculation to go in React, the total mass of iron specified in the basis will be distributed across the two oxidation states assuming the redox couple is in equilibrium.

If you do have measurements for Fe2+ and Fe3+ concentrations separately, you can decouple the redox reaction and this would allow you to add in both constraints (Fe2+ and Fe3+ bulk concentrations) to the basis.

For more information on configuring the basis, please see sections 2.1-2.2 and 7.1-7.2 in the GWB Essentials User's Guide. For more information regarding decoupling redox couples, please see section 7.3 Redox disequilibrium in the same user guide.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

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