Cannot swap in elemental Fe as mineral using REACT/GW9

[Oleh Weres]

I am trying to model corrosion of steel in contact with geothermal brine, but GW9/REACT won't let me swap elemental Fe for Fe++2; Fe(0) doesn't appear on the menu of iron minerals available to swap.

 

This is an important issue to resolve, because it will make GWB a useful tool for corrosion research.

[Brian Farrell]

Hello Oleh,

 

This isn't a limit of the GWB programs, but simply a reflection of the thermodynamic data most commonly used by geochemists.

 

thermo.com.v8.r6+.dat has an entry for the native mineral Fe, so you can create a redox-pH diagram accounting for metallic iron (be sure to turn water limits off). To consider kinetics of redox reactions involving Fe(0), however, you'll need to do a little work editing the thermo data.

 

Basically, you'll have to create a new, fictitious redox species, Fe(aq), to add to the thermo data. Then you'll add a mineral Fe(s) to the minerals section, balanced in terms of Fe(aq). Since thermo.com.v8.r6+ has data for Fe(s), this may be a good place to start editing. A relevant example (redox kinetics involving native sulfur) that you can follow is given in Craig Bethke's Geochemical and Biogeochemical Reaction Modeling text in section 17.5 (Redox kinetics), p. 254.

 

Of course, different forms of iron will likely have different thermodynamic properties, so you'll need to find the appropriate data for your application.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC

 

PS I moved your post from the archive of old posts to the top of the front page to make it more visible.