Frequently Asked Question

There are 3 models for aqueous systems in Factsage, one uses an ideal solution model to describe the aqueous solution and the two other models describe the aqueous solution by non-ideal solutions models: Pitzer and Helgelson.

Some additional information from the documentation section at http://www.factsage.com:

For ideal dilute solutions there are several hundred aqueous species stored in the FACT compound database. For concentrated solutions there are Pitzer parameters for over 200 species stored in the FACT solution database (FTmisc-PITZ).

The FACT Helgeson database, FThelg, contains infinite dilution properties for over 1400 aqueous solute species taken from the GEOPIG-SUPCRT Helgeson public database and include the Helgelson equation of state for temperatures up to 350ºC and pressures up to 165 bar. The data are stored as 3 aqueous solutions FThelg-AQID, -AQDH, -AQDD. FThelg-AQID assumes an ideal dilute solution and is generally valid up to approx. 0.001 molal. FThelg-AQDH incorporates the Debye-Huckel equation, and is generally valid up to approximately 0.02 molal. FThelg-AQDD incorporates the extended Debye-Huckel (Davies) equation and is generally valid up to 0.5 molal.

You will find also more information under the links below:

https://www.crct.polymtl.ca/fact/factsage/EquiSage.pdf

https://www.crct.polymtl.ca/fact/documentation/ (please search for "Pitzer", under FTmisc)

https://www.crct.polymtl.ca/fact/documentation/ (please search for FThelg)

The non-ideal Pitzer description for the aqueous solution does not contain organic solutes. The ideal and the Helgeson descriptions contain some organic solutes, but I must say that this is not a strength of Factsage.

Considering phase diagrams, there is the possibility of generating not only Pourbaix diagrams in Factsage, but also more general aqueous phase diagrams, including not only stoichiometric reactions but also (non-ideal) aqueous solution phases, in which the different ions in the aqueous solution may interact, please check:

https://www.crct.polymtl.ca/fact/factsage/PhasSage.pdf
(section 19)

but please be aware that for the calculation of phase diagrams, the only databases for aqueous solutions that are available are those that I have already mentioned.