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Author Topic: P  (Read 2128 times)

AnnaJulIQ

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P
« on: 18/03/21 20:20 »
A
« Last Edit: 09/06/21 14:29 by AnnaJulIQ »
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dlparkhurst

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Re: PHASE BALANCING IN AN ALKALINE PILE
« Reply #1 on: 18/03/21 20:48 »
To include a phase in EQUILIBRIUM_PHASES, it must be defined in a PHASES datablock.
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dlparkhurst

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Re: PHASE BALANCING IN AN ALKALINE PILE
« Reply #2 on: 18/03/21 23:53 »
A few comments.

First, you probably do not need to define SOLUTION_MASTER_SPECIES. If the elements are in the database, then the database contains all the SOLUTION_MASTER_SPECIES definitions that you will need.

Next, I think you are trying to define an aqueous species KOH(aq). The log K you are using is consistent with the log K for KOH(aq) found in llnl.dat. To define the aqueous species you would use the following:

Code: [Select]
SOLUTION_SPECIES
K+ + H2O  =  KOH + H+
        log_k           -14.46

By using EQUILIBRIUM_PHASES, you are considering equilibrium with the solid KOH(s). The solubility of KOH is given as 121 g/ 100 ml. Assuming that corresponds to 1210 g/kg water, the following script shows the log K is about 2.18, when using the minteq.dat database.

Note that the input for EQUILIBRIUM_PHASES is phase name, target saturation index, and moles of phase available to react.

Code: [Select]
SOLUTION_SPECIES
K+ + H2O  =  KOH + H+
        log_k           -14.46
PHASES
KOH(s)
KOH = K+ + OH-
log_k 2.18
END
SOLUTION 1
END
USER_PRINT
10 PRINT "KOH(s) solubility, g/kgw: ", \
               STR_F$(-EQUI_DELTA("KOH(s)") * GFW("KOH"), 10, 0)
USE solution 1
EQUILIBRIUM_PHASES 1
KOH(s) 0 25
END
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dlparkhurst

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Re: PHASE BALANCING IN AN ALKALINE PILE
« Reply #3 on: 21/03/21 14:55 »
Your typing is fine, but you have some conceptual errors.

Again, check the manual for the correct input to EQUILIBRIUM_PHASES. You did not define the target saturation index, zero for equilibrium, which precedes the number of moles of reactant available.

The Basic function LM gives log molality of an aqueous species, that is one defined in SOLUTION_SPECIES; your script does not define legitimate aqueous species for LM. I think you want the number of moles of EQUILIBRIUM_PHASES that have reacted. I have substituted the mole transfers for the reactions using EQUI_DELTA. The functions EQUI, or TOT (for example TOT("Zn") are also possibilities.

Now, you can start to consider what you really want to calculate. You have defined a set of equilibrium phases. The calculation determines the stable phase assemblage that would exist at thermodynamic equilibrium. In this case half of the minerals dissolve completely to form the remaining minerals. This end result is where the system would evolve thermodynamically and with geologic time. You must consider what reactions are likely to happen over time scales of days to years.
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dlparkhurst

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Re: PHASE BALANCING IN AN ALKALINE PILE
« Reply #4 on: 25/03/21 03:06 »
Well, the pH is >20 and the pe is <-20. These are not realistic results. I think the main problem is 400 moles of ZnMetal. The reaction

Code: [Select]
Zn + 2H2O = Zn+2 + 2OH- + H2(aq/g)

causes extremely reducing conditions. The H2(aq) concentration is calculated to be 50 moles per kilogram water, which is also unreasonable. Thermodynamically, Zn metal will reduce water,  such that the addition of a little bit of glucose is insignificant.

If you remove ZnMetal from EQUILIBRIUM_PHASES, you will see manganese oxyhydroxide reduction with oxidation of glucose, and an increase in dissolved manganese, and more plausible pH and pe. Still, I would consider these calculations highly uncertain because of the model limitations at high concentrations and high pH, and because many of the reactions are going to be kinetically controlled.




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