How to enter AlF3 in the equilibrium phase block with a target SI

[atoumari]

Hi

I am running a batch reaction involving aluminum, fluoride, sodium, and chloride ions with solid calcite. I'd like to know whether aluminum fluoride precipitates. So, I'd like to define AlF3 under equilibrium phases block with a target SI. However, AlF3 it is not defined in the "defined phases" database. If I leave it out of the equilibrium phase block, AlF3 appears in the output as (aqueous) species, and PHREEQC does not calculate a saturation index for it. Does PHREEQC consider aluminum fluoride a dissolve complex and not a solid? Any help clarifying this would be appreciate it.

Arman   

[John Mahoney]

I suggest you look at other databases.

the LLNL.dat database includes:

AlF3
       AlF3  =  + 1.0000 Al+++ + 3.0000 F-
        log_k           -17.2089
   -delta_H   -34.0441   kJ/mol   # Calculated enthalpy of reaction   AlF3
#   Enthalpy of formation:   -1510.4 kJ/mol
        -analytic -3.9865e+002 -1.3388e-001 1.0211e+004 1.5642e+002 1.5945e+002
#       -Range:  0-300

If you have a preferred database that you always use, you can drop this phase into the pqi file by using a PHASES block,  and then include it in EQUILIBRIUM_PHASES.     

I would look into internal consistency between the two databases.  Does your database have essentially the same SOLUTION_SPECIES reactions for Al - F complexes  (also the Al-OH complexes should be similar) with similar log_k values?  Otherwise using LLNL.dat as your database might be best, at least for a start. Or you could replace the Al-F species reactions with the LLNL.dat reactions using SOLUTION_SPECIES in your input file. 

 

[atoumari]

Got it. Thank you very much!