Ammonium buffer in llnl.dat

[fsamm]

Dear Users,

I am using the llnl database to model the Si-species in my experiments. I have a quite simple solution (pH=10.08, T=25°C), which contains Silicon (Si 0.00413866 mol/kgw) and a NH4Cl-NH4OH buffer. My question is how to introduce this ammonia buffer correctly.
I use 0.1 mol/kg NH4Cl salt and 0.35 mol/kg NH3 solution.

I introduced it in the following way:

SOLUTION 1
    temp      25
    pH        10.08
    pe        4
    redox     pe
    units     mol/kgw
    density   1
    Cl        0.100138353
    Si        0.00413866
    N         0.45
    -water    1 # kg

Thank you for your help!

[dlparkhurst]

If you use N, you should define the N as N(-3) to enter it as ammonia species.

You probably do not want the N to oxidize with any reactions, so it may be better to use Amm.dat and define the ammonia as Amm in this database:

Code: [Select]

SOLUTION 1
    temp      25
    pH        10.08
    pe        4
    redox     pe
    units     mol/kgw
    density   1
    Cl        0.100138353
    Si        0.00413866
    Amm       0.45
    -water    1 # kg
END

Another approach is to make the solution by adding NH4Cl and NH3 as follows:

Code: [Select]

SOLUTION 2
REACTION
AmmHCl 0.1
Amm    0.35
1 mol
END

This gives a pH of 9.926 without consideration of the Si.

[fsamm]

Indeed, I dont want the N to oxidize with any reactions. I will try your approach.

Thank you very much for your help.