Modeling missing species

[MAlexanderB]

Hello everyone,

I would like to model Pb-Zn systems under hydrothermal conditions and I am thinking about the question if I have maybe missed some aqueous species. For example: I find thermodynamic data (property data but also log(K) data) for species like Zn(HS)2, Zn(HS)3- and Zn(HS)4-2 (for Pb only Pb(HS)2 and Pb(HS)3-) but none for Zn(HS)+, Pb(HS)+ and Pb(HS)4-2. Okay, maybe they are not stable under a (wide) range of conditions but I cannot believe actually that they never exist and are just not important.
I am fine with the argument/conclusion that they will not be stable or relevant under typical hydrothermal conditions but I would be more satisfied to see that in a simulation where their concentration values are all zero for example. I just would like to be convinced.

Does anybody know if there is an approach that allows to estimate roughly some thermodynamic properties and log(K) data if actually nothing is known about the species of interest but for other similar species instead (for example, no information about Pb(HS)4-2 but there are data available for Pb(HS)2 and Pb(HS)3-)? I am not sure if it is, at least for a rough estimation, reasonable to do a linear regression.

Thank you in advance!

[dlparkhurst]

The real test would be whether the species that are defined are able to reproduce the solubility experiments for ZnS, for example.

I try to let other people deal with thermodynamic data. The compilers of the databases made some choices, although we do not know whether they were good choices. I think your are better off using their compilations, preferably comparing multiple databases, than trying to use some interpolation method. It will be much easier to justify in a paper that you used one of the more standard databases, than if you invented something yourself, unless you have experimental data to back it up.