Question: make Kd value dependent on element concentration

[Joaquim Tarín Olivares]

Hi all,

I am working on a model of radionuclide transport, using Kd values to calculate sorption of said RNs. The system in question also studies the degradation of cellulose, and the byproducts of this reaction (namely ISA) are expected to affect the sorption of RNs.

I was wondering if theres is any way for Kd values to be dependent on ISA concentration rather than remain at a constant value. Perhaps an external table to cross-reference ISA concentrations and their corresponding Kd value? If all else fails, I believe creating a reaction sandbox would allow for this dependency, but if possible I would like to remain within the bounds of PFLOTRAN's base capabilities.

Thanks in advance,

Quim.

[Hammond, Glenn E]

Quim,

I've long considered developing a "sorption sandbox" that would allow users to create their own custom equilibrium sorption expressions—this sounds like exactly what you need.

In the meantime, there are a couple of alternatives you might find useful. First, you could simulate sorption as a kinetic process by using an immobile species for the sorbed radionuclide within the reaction sandbox. Alternatively, you could modify the subroutine RTotalSorbDynamicKD, found here:

https://bitbucket.org/pflotran/pflotran/src/6ee92553c9cca7eb8cf670939b6e80e298845ac6/src/pflotran/reaction.F90#lines-5022

Although this option is not advertised, it allows for nonlinear sorption of a species based on the concentration of another. For reference, an example input deck can be found at:

https://bitbucket.org/pflotran/pflotran/src/6ee92553c9cca7eb8cf670939b6e80e298845ac6/regression_tests/default/batch/dynamic_KD.in#lines-37

Regards,

Glenn

From: pflotra...@googlegroups.com <pflotra...@googlegroups.com> on behalf of Joaquim Tarín Olivares <joaquim....@gmail.com>
Date: Tuesday, March 3, 2026 at 5:42 AM
To: pflotran-users <pflotra...@googlegroups.com>
Subject: [pflotran-users: 8691] Question: make Kd value dependent on element concentration

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