phreeqc model

[ehsan]

Hi dears

What equations are used in Pاhreeqc model to obtain the activity coefficient?

[dlparkhurst]

Ion-association-model activity coefficients are discussed in the documentation for the SOLUTION_SPECIES data block. Uncharged species have only a "bdot" ionic strength parameter.

llnl activity coefficients for charged species are similar to the other ion-association models, but use only the ion-specific "a" parameter, and no ion-specific "bdot" parameter. Uncharged species have the option for a single "bdot" parameter defined with -co2_llnl_gamma.

Pitzer activity coefficients are defined with many specific interaction parameters. Most types of parameters are discussed here: https://pubs.er.usgs.gov/publication/wri884153.