Using log K values for dissolution of Ferrihydrite and Goethite in model

[Bisesh Joshi]

Hi all, 

I'm adding the mineral precipitation dissolution reaction in my model to simulate Ferric iron in the system for anaerobic ammonium mineralization. Using available log K values in the default pflotran Database is yielding very low values. Are these standard values?  Or is it okay to increase logK values of these minerals to significantly higher values,  for e.g., for Goethite, increasing it from 0.5345 to 15.45?

Please let me know if you have any suggestions.

Thank you 

Best regards,

Bisesh

--

Bisesh Joshi

PhD student

Water Science and Policy

Graduate College

University of Delaware

901-297-6761

[Sam Shaheen]

Hi Bisesh, 

For clarification, this is modeling dissolution/precipitation of ferrihydrite and goethite using mineral kinetics? If so, how confident are you in the rate constant/surface area/initial volume fractions of these minerals in your system? This can all have a major influence on rates as well. You could always compare values across other thermodynamic databases, but my guess is that the parameters in your input script are a better place to start unless you're very confident in those values.

-Sam

[Hammond, Glenn E]

Bisesh,

The logKs in the hanford.dat database originate the EQ3/6 database: https://documentation.pflotran.org/theory_guide/mode_reactive_transport.html#thermodynamic-database. It is possible that newer values are available in the literature. We have other databases that incorporate project-specific logKs generated from experiments.

And I second Sam's advice.

Glenn

From: pflotra...@googlegroups.com <pflotra...@googlegroups.com> on behalf of Sam Shaheen <samuelw...@gmail.com>
Date: Friday, June 27, 2025 at 3:37 PM
To: pflotran-users <pflotra...@googlegroups.com>
Subject: [pflotran-users: 8467] Re: Using log K values for dissolution of Ferrihydrite and Goethite in model

Check twice before you click! This email originated from outside PNNL.

--
You received this message because you are subscribed to the Google Groups "pflotran-users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to pflotran-user...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/pflotran-users/7f46a9f6-e931-4c04-8810-3a08ccac3be5n%40googlegroups.com.