Pitzer Database

[ljcrisc]

Hi All -

I am looking for an updated PITZER database for PHREEQC for salt dome/brine interactions that includes coefficients for the temperature dependence of the Pitzer parameters.

Does anyone know if there are one (or more) of these databases available? I don't think the one packaged with PHREEQC 3 is very complete.

Thanks.

Louise Criscenti

[dlparkhurst]

There is much more information for binary solids. However, for mixed electrolytes, I think most geochemical simulators (including PHREEQC) use some variant of Harvie, Moeller, Weare compilation of Pitzer parameters. Temperature-dependence is available, but inconsistent. , Generally, multiple redox states, aluminum, and to some extent silica are not parameterized.

I did see a model--with similar cations and anions to HMW--extended to 95C by Alai and others (https://link.springer.com/article/10.1186/1467-4866-6-31).

If you find better compilations, please make a post.

[ljcrisc]

Thanks! I have two compilations for EQ3/EQ6; I'll check out the one you suggest also. I'm just starting to look at them to see how different they are. I was hoping not to have to format the database if possible, but I will definitely learn more if I have to!

[ljcrisc]

Hi Again,

I just worked my way through the PHREEQC Pitzer Database again. I'm okay for my system with the Pitzer parameter set provided. However, because I'm new to Pitzer, I was surprised at how few Solution_Species were in the database. I would have expected that each of the cation-anion pairs that have a Pitzer B0 term would also have a log K for an aqueous complex. An example would be CaCl+. Is this block not used when the Pitzer expressions are used?

Thanks for any help you can give me.

Louise Criscenti

[dlparkhurst]

To oversimplify, the Pitzer (Guggenheim) approach uses the parameters B0, B1, B2, C0 (and many others) to account for solution nonideality, whereas ion-association models use ion pairs and complexes to account for nonideality.

[ljcrisc]

Hi Dave -

Is there a way in PHREEQC to have the ion pair (or triplets) molalities and activities included in the output file rather than the distribution of species that are not calculated with the Pitzer expressions in the database.

Thanks.

Louise

[dlparkhurst]

The "Distribution of species" section of the output lists all of the aqueous species for the solution, given the database that is used. With pitzer.dat, typically there are only 1 to 3 species for an element; all activity corrections for all species in the database use the Pitzer formulation. Most interactions between ions are accounted for in the activity coefficients that are calculated with the interaction coefficients for pairs and triples of ions without resorting to explicit aqueous species. Except for carbonate, silicate, and sulfate protonation reactions, MgOH+ and MgCO3 are about the only ion pairs explicitly considered among the major elements.

So, if you are asking to print out a concentration of CaHCO3+ ion pair for the Pitzer approach, there is no such thing. Concentrations are only calculated for the aqueous species listed in the SOLUTION_SPECIES data block of the pitzer.dat database.