Can llnl_gamma be used as gamma for adjusting a phreeqc database

[R.Schmidt]

Hello,

im a beginner with PhreeqC and I am currently investigating the databases, because i could not find a database, that included all the elements and reactions I needed. In doing so I found different databases with the llnl_aqueous_model and some that just used the default of PhreeqC. Up until now I understood that both models use the Debye-Hückel approach in some way. I know that llnl_aqueous_model defines the parameters in the database and the equation itself contains a minus.

Now my question is, could I convert llnl_gamma informations into gamma informations and vise versa? As far as I understood it, they define closly the same parameter, with gamma having the additional oppotunity to define b (which would be b_dot in llnl_aqueous_model). Am I right about the thought process? Is a convertion even needed? Or would PhreeqC calculate with default calculations if gamma is defined for a species even tho LLNL_AQUEOUS_MODEL_PARAMETERS are implemented? Sadly, I could not answer this by my own and didnt find the answer by myself.

Maybe another short question would be, if anyone knows of an usable database for wastewater from the production of semi-conductors or solar modules preferably? Im trying to use PhreeqC to define the wastewater steams of an production line of solar modules.

I would be happy if you could help me with this questions. :)

Best regards,
Robert Schmidt

[dlparkhurst]

Phreeqc.dat and related databases (minteq, wateq) use an activity coefficient formula that allows two parameters (-gamma) for each aqueous species: an ion-size parameter a, and an ionic strength parameter b-dot (see documentation of SOLUTION_SPECIES data block).

llnl.dat and similar databases allow an ion size parameter (-llnl_gamma), but no b-dot except for uncharged species. Uncharged species may be assigned a b-dot (or Setchenow parameter), however, only one parameter value is available (-CO2_llnl_gamma). The one parameter values is defined in the database in the databse LLNL_AQUEOUS_MODEL_PARAMETERS data block.

So essentially, you can convert llnl.dat parameters (ion-size and 0.0 b-dot, for charged species and CO2 bdot for some uncharged species) to phreeqc.dat parameters, but llnl.dat does not have the b-dot option for charged species. Also, the A and B of the Debye Huckel equation are probably slightly different between the two types of databases.

At low ionic strengths, both types of databases probably give similar activity coefficients. At higher ionic strengths, the b-dot parameters will cause the activity coefficients to diverge. Both types of databases become less reliable the higher the ionic strength.