PhreeqcUsers Discussion Forum

Beginners => PHREEQC basics => Topic started by: Franco Galarce on January 20, 2021, 12:07:43 AM

Title: Adding elements to data base
Post by: Franco Galarce on January 20, 2021, 12:07:43 AM
Hi,

I need to obtain the saturation index of the mineral species that should be present in a geothermal system, asumming the thermodynamic equilibrium. I only have the geothermal fluid data at 260C, and there are certain elements that are not including in the lnll data base. That elements are: SiO2, Rb, Cs, Sb, and As. How can I add them?

I also have doubts about how to get the "pe" parameter from pH value. I chose -5 to test.

This is my input:

SOLUTION 1
    temp      260
    pH        6.98
    pe        -5
    redox     pe
    units     mg/l
    density   1
    Alkalinity 34 as HCO3
    B         273
    Br        10.4
    Ca        543
    Cl        10066
    F         10.9
    K         871
    Li        59
    Mg        0.17
    Na        5182
    S(6)      22
    Sr        13.4
    -water    1
END

Regards!

Franco G.
Title: Re: Adding elements to data base
Post by: dlparkhurst on January 20, 2021, 01:32:35 AM
All of those elements are included in llnl.dat. Check the first line of the output for the database that you are using.

I got an error when I ran your file because of the Alkalinity definition. Apparently there was more alkalinity from B, Si, etc than the defined alkalinity, so the program failed. If you use C(4) instead of Alkalinity, it should work.

As for pe, the main element that it affects is As. If you know the redox state of As, you can define it [As(3), for example].
Title: Re: Adding elements to data base
Post by: Franco Galarce on January 22, 2021, 07:45:11 PM
Hi,

How can I input SiO2? For example, I have 531 mg/l of SiO2, so I have to input the 87,5% of this value as Si?

Regards
Title: Re: Adding elements to data base
Post by: dlparkhurst on January 22, 2021, 09:19:25 PM
The default gram formula weight for converting mass to moles in the llnl.dat database is the gfw of SiO2 (defined in the SOLUTOIN_MASTER_SPECIES data block of the database).

You can also ensure a specific formula or gram formula weight in SOLUTION input

Code: [Select]
SOLUTION
Si  531 as SiO2

Look at the description of SOLUTION in the manual for more details.
Title: Re: Adding elements to data base
Post by: Franco Galarce on January 27, 2021, 11:25:07 PM
Thanks!

I have another question. How can I introduce an equilibrium with andesite-dacite minerals....?
- Plagioclase
- Amphibole
- Biotite
Those minerals are not in the llnl database. There are albite, tremolite, and annite, but I need the solid solutions. I was able to introduce the rest of minerals (Quartz, K-feldespar, etc), but not those.

Regards.
Title: Re: Adding elements to data base
Post by: dlparkhurst on January 28, 2021, 03:15:42 AM
I tend to avoid thermodynamic data issues You can start with the other databases. phreeqc.dat has a K-mica. Databases have data for Albite and Anorthite, so maybe there are some solid solution models to get K for a given composition. I'm not sure how much effort is reasonable because equilibrium may be suspect anyway.

One issue is that llnl.dat uses SiO2(aq) for the master species, whereas the other databases use H4SiO4, so you may have to rewrite the equations for whichever master species you are using.