Quantify how much CO2 is pulled into a solution ex Wollastonite and Calcite?

[peterwadeuk]

Greetings, Sterling persons.

Please pardon the very basic nature of my difficulty.

I am investigating the problems of calculating carbon drawdown into solution from atmospheric. Because I am modelling calcite, there is carbon injected into solution from that source.

So I tried to define a separate carbon, coming in from atmosphere, in the script below, knowing that my unfamiliarity with the definition and modification of the database may catch up with me. Which it did.

I humbly request assistance in my quest for separating the types of carbon, from calcite, and from atmosphere.

TITLE Calcite and Wollastonite dissolution equilibrium
TITLE CO2(atm) in equilibrium
TITLE Wollastonite: CaSiO3 + 2 H+ = Ca+2 + H2O + SiO2


# =========================================== GENERAL MOD DEFAULTS BELOW =========================================

# ------------------------------------------- Solution Definitions ----------------------------------------------------

SOLUTION_MASTER_SPECIES

Catm CatmO3-2 2 61.0173 12.0111
C(+4) CatmO3-2 2 61.0173

SOLUTION_SPECIES

#CO2     could be used instead of H2CO3
        CatmO3-2 + 2 H+ = CatmO2 + H2O
        log_k 16.681
        delta_h -5.738 kcal
        -analytical 464.1965 0.09344813 -26986.16 -165.75951 2248628.9

#HCO3-               68
        H+ + CatmO3-2 = HCatmO3-
        log_k 10.329
        delta_h -3.561 kcal
        -analytical 107.8871 0.03252849 -5151.79 -38.92561 563713.9
        -gamma 5.4 0


# ------------------------------------------- Selected Outputs ----------------------------------------------------

SELECTED_OUTPUT 1
    -file                 250402_1207_Wol-dissn_CO2_no-hum-pH-buff-7_no-Mg-X2.tsv
    -reaction             true
# INCLUDE$ C:\Users\Peter\Documents\Projects\Modelling\Simple-models-CO2-exch-Corg\SELECTED_OUTPUT-2.txt

# ------------------------------------------- Phases Definition ----------------------------------------------------

PHASES
pH_fix # Define pH fixing mineral
H+ = H+; log_k 0 # pH = 10^(-SI)
CO2atm(g)
        CO2atm = CO2atm
        log_k -1.468
        delta_h -4.776 kcal
        -analytical 108.3865 0.01985076 -6919.53 -40.45154 669365


# =========================================== SPECIATION CALCULATIONS BELOW =========================================

SOLUTION 1
             temp     25 # 100
                  Si        1e-9 charge
                  Na        2e-9
             units     mol/kgw
REACTION 1
    Wollastonite 0.5
    Calcite    0.5
    2.5 millimoles in 5 steps
   
EQUILIBRIUM_PHASES 1
CO2atm(g)      -3.7 100 # CO2(g) = 425.40 ppm (Mona Loa)

[dlparkhurst]

I don't think you can have separate equilibria for the two sources of carbon. The saturation indices for calcite and CO2 would not be consistent.

I think all you need to do is to look at the mole transfer of CO2(g). In this script, the amount of C from calcite is specified by the REACTION definition, and the amount of CO2(g) is in the "Phase assemblage". The Basic function EQUI_DELTA("CO2(g)" will also give the mole transfer.

Code: [Select]

-------------------------------Phase assemblage--------------------------------

                                                      Moles in assemblage
Phase               SI  log IAP  log K(T, P)   Initial       Final       Delta

CO2(g)           -3.70   -11.53     -7.83    1.000e+02   1.000e+02  -1.354e-03

Code: [Select]

SOLUTION 1
REACTION 1
    Wollastonite 0.5
    Calcite    0.5
    2.5 millimoles in 5 steps
   
EQUILIBRIUM_PHASES 1
CO2(g)      -3.7 100 # CO2(g) = 425.40 ppm (Mona Loa)
END

[peterwadeuk]

Thank you very much, David, for this elegant solution!