Impact of organics

[Alexey]

My solutions have some unknown organic molecules. I need to calculate saturation indices for few minerals. In theory the charged organic molecules can impact to the ionic strength of solution. I can’t determine the type and possible charge of organics, but need to estimate the impact of those molecules to saturation indices. Can I input the possible range of ionic strength into the phreeqc calculations?

[dlparkhurst]

If you simply want to consider the range of ionic strength, you could increase or decrease the concentrations of ions, say Na and Cl.

If you want to consider the complexing capacity of the organic matter, then wateq4f.dat has definitions for ligands Humate and Fulvate you could consider. I am not sure how comprehensive the definitions are. llnl.dat and minteq.v4.dat also have definitions of several organic ligands. It might be tedious, but you could consider different concentrations of several/all of those ligands to consider the possible effects of organic ligands on the SIs.

There are some databases for PHREEQC that implement the WHAM model, for example, http://www.hydrochemistry.eu/a&p/7/T_H.DAT, that could also be used to consider ion interactions with organic ligands.

[Alexey]

Thank you! I use fulvate.