Minerals supersaturated after defining as equilibrium

[peterwadeuk]

Greetings good persons.

I am simulating the vadose zone of a soil column (excluding organic carbon for now).

Before tackling the kinetics (e.g. albite dissolves slowly), I am attempting to explore the system under the equilibrium assumption.

The input file I prepare is attached, and quoted after this text.

I find that when I run this model some of the minerals input as equilibrium solids do not dissolve, and report as supersaturated.

If I enter the minerals singly, they dissolve and saturation index is zero, as expected. It seems to be the combination of solids that is problematic.

I am clearly doing something wrong.

Please would someone point me in the right direction?

Thank you,
Peter

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TITLE Soil Layer 1 - Vadose zone
#      Uses database file wateq4f.dat

PHASES
K-feldspar
    KAlSi3O8 + 4H+ + 4H2O = Al+3 + 3H4SiO4 + K+
    log_k     0.875
    delta_h   -12.467 kcal
Smectite-high-Fe-Mg
    Ca.025Na.1K.2Fe.5Fe.2Mg1.15Al1.25Si3.5H2O12 + H+  =  3.5 H2SiO4-2 -2 H2O + 0.025 Ca+2 + 0.1 Na+ + 0.2 Fe+3 + 0.2 K+ + 0.5 Fe+2 + 1.15 Mg+2 + 1.25 Al+3
    log_k     -62.94


SOLUTION 1 Pore water from equilibrium with DI water in atmosphere
    temp      25
    pH        7
    pe        4
    redox     pe
    units     mmol/kgw
    density   1
    Ca        0.00958125
    Mg        0.00178985
    Na        0.61334 charge
    Cl        0.66852
    S         0.01175765
    Fe        0.001
    Si        0.001
    K         0.001
    Al        0.001
    -water    1 # kg


EQUILIBRIUM_PHASES 1
    Albite    0 3.37 dissolve_only
    Chlorite14A 0 1.75 dissolve_only
    CO2(g)    -3.5 10 dissolve_only
    Hematite  0 1.11 dissolve_only
    Illite    0 10.68 dissolve_only
    K-feldspar 0 3.18 dissolve_only
    Kaolinite 0 5.68 dissolve_only
    O2(g)     -0.678 10 dissolve_only
    Quartz    0 120.5 dissolve_only
    Smectite-high-Fe-Mg 0 1.97 dissolve_only

SELECTED_OUTPUT
    -file                 phases.csv
    -time                 false
    -step                 true
    -equilibrium_phases   Albite  Chlorite14A  Quartz  Kaolinite
                          Illite  Hematite  K-feldspar  Smectite-high-Fe-Mg
    -saturation_indices   Albite  Chlorite14A  Quartz  Kaolinite
                          Illite  Hematite  K-feldspar  Smectite-high-Fe-Mg

[dlparkhurst]

If some minerals become supersaturated by dissolution of other minerals, you are not allowing the minerals to precipitate, so they are supersaturated. I don't see a problem with the program; it is doing what you asked.

[peterwadeuk]

Thank you David.