Effect of salinity on dissolution of supercritical CO2 in water (PhreeqcRM)

[Mohamadreza]

Dear all,

I want to make the salinity (NaCl) on dissolution dissolution of supercritical CO2 in water. I ran the simulation and obtained pH graph from concentration of H+ but have a problem. The trend of pH first increased then it was decreased. So, it must be not increased, right? what do I do? Is this properties that's right?

Thank you in advance for any help or clarifications.

Most sincerely,

Mohamadreza

========================================
SOLUTION 0 formation water
     units   Mol/L
C  1
temp 150
pH 7
pe 4
redox pe

density 1
Na 1
Cl 1
water 1 # L
END
===========================================

SOLUTION_MASTER_SPECIES
#
#element   species   alk   gfw_formula   element_gfw
#
H      H+   -1.0   H      1.008
H(0)      H2   0   H
H(1)      H+   -1.0   0
E      e-   0   0.0      0
O      H2O   0   O      16.0
O(0)      O2   0   O
O(-2)      H2O   0   0
Na      Na+   0   Na      22.9898
Cl      Cl-   0   Cl      35.453
C      CO3-2   2.0   HCO3      12.0111
C(+4)      CO3-2   2.0   HCO3
Alkalinity   CO3-2   2.0   61.0173    61.0173

SOLUTION_SPECIES
H+ = H+
   -gamma   9.0   0

   -dw    9.31e-9
e- = e-
H2O = H2O
Na+ = Na+
   -gamma   4.0    0.075
   -gamma   4.08 0.082 # halite solubility
   -dw    1.33e-9
   -Vm   2.28  -4.38  -4.1  -0.586  0.09  4  0.3  52  -3.33e-3  0.566 # ref. 1
Cl- = Cl-
   -gamma   3.5     0.015
   -gamma   3.63  0.017 # cf. pitzer.dat
   -dw    2.03e-9
   -Vm  4.465  4.801  4.325  -2.847  1.748  0  -0.331  20.16  0  1 # ref. 1
CO3-2 = CO3-2
   -gamma   5.4   0
   -dw    0.955e-9
   -Vm  5.95  0  0  -5.67  6.85  0  1.37  106  -0.0343  1 # ref. 1
# aqueous species
H2O = OH- + H+
   -analytic  293.29227  0.1360833  -10576.913  -123.73158  0  -6.996455e-5
   -gamma   3.5   0
   -dw    5.27e-9
   -Vm  -9.66  28.5  80.0 -22.9 1.89 0 1.09 0 0 1 # ref. 1
2 H2O = O2 + 4 H+ + 4 e-
   -log_k   -86.08
   -delta_h 134.79 kcal
   -dw    2.35e-9
   -Vm  5.7889  6.3536  3.2528  -3.0417  -0.3943 # supcrt
2 H+ + 2 e- = H2
   -log_k   -3.15
   -delta_h -1.759 kcal
   -dw    5.13e-9
   -Vm 6.52  0.78  0.12 # supcrt
CO3-2 + H+ = HCO3-
   -log_k   10.329
   -delta_h -3.561   kcal
   -analytic   107.8871   0.03252849   -5151.79   -38.92561   563713.9
   -gamma   5.4   0
   -dw    1.18e-9
   -Vm  8.472  0  -11.5  0  1.56  0  0  146  3.16e-3  1 # ref. 1
CO3-2 + 2 H+ = CO2 + H2O
   -log_k   16.681
   -delta_h -5.738   kcal
   -analytic   464.1965   0.09344813   -26986.16   -165.75951   2248628.9
   -dw    1.92e-9
   -Vm   7.29  0.92  2.07  -1.23  -1.60 # ref. 1 + McBride et al. 2015, JCED 60, 171
2CO2 = (CO2)2 # activity correction for CO2 solubility at high P, T
   -log_k -1.8
   -analytical_expression  8.68  -0.0103  -2190
   -Vm   14.58  1.84  4.14  -2.46  -3.20

   -delta_h -0.396   kcal
   -Vm  6.16  0  29.4  0  0.9 # ref. 2
Na+ + OH- = NaOH
   -log_k   -10 # remove this complex
Na+ + CO3-2 = NaCO3-
   -log_k   1.27
   -delta_h 8.91 kcal
   -dw 5.85e-10
   -Vm  3.89  -8.23e-4  20  -9.44  3.02  9.05e-3  3.07  0  0.0233  1 # ref. 1
Na+ + HCO3- = NaHCO3
   -log_k  -0.25
   -delta_h  -1 kcal
   -dw 6.73e-10
   -Vm  0.431 # ref. 1
END

[dlparkhurst]

Are you varying NaCl, temperature, pressure, P(CO2), or some combination of these?

Please explain how you are varying the script to make pH change. Do not include SOLUTION_MASTER_SPECIES or SOLUTION_SPECIES except for any differences from phreeqc.dat.

[Mohamadreza]

I'm use a software (CFD) that it is couple with phreeqc. This software use two file for chemical reaction that it was:
Database of phreeqc
and another that contain solution part:

SOLUTION 0 formation water
     units   Mol/L
C  1
temp 150
pH 7
pe 4
redox pe

density 1
Na 1
Cl 1
water 1 # L
END

Did I apply the salt effect correctly? Or do I need other things?

This software give me the concentration of species in geometry and we can use the concentration of H+ to obtained the pH.

[dlparkhurst]

As far as I know, PhreeqcRM is working correctly.

If you think there is a problem, you will have to generate a Phreeqc script with a reaction that demonstrates the problem.

[dlparkhurst]

Here is a script that shows the solubility of CO2(g) as a function of CO2(g) partial pressure. You can investigate your system by changing temperature and NaCl concentration.

Code: [Select]

SOLUTION 0 formation water
     units   Mol/L
#C  1
temp 150
pH 7
pe 4
redox pe

density 1
Na 1
Cl 1
water 1 # L
END
GAS_PHASE 1
-fixed_volume
CO2(g) 0
END
REACTION 1
CO2 1
10 in 20 steps
END
USE solution 0
USE gas_phase 1
USE reaction 1
USER_GRAPH 1
    -axis_titles            "CO2(g) pressure, atm" "C(4) concentration, molality" ""
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 GRAPH_X PR_P("CO2(g)")
20 GRAPH_Y TOT("C")
  -end
END



[Mohamadreza]

Thanks for your help. Why is solubility of carbon dioxide as a function of CO2(g) partial pressure?
First, We injected CO2 supercritical . So should we not give the pressure and temperature of the CO2? Instead of giving the gas phase. I tried another way that changed the C to 0.05 then the trend of pH is fixed but I still have a problem in trend of pH of pure water. The trend of pH of pure water rapidly down from 7 to 5 in initial time. And I did not understand exactly what this C is and what is its effect?

I have another question. I compared the effect of KCl on pH with the pH of pure water that the pH of KCl solution decreased more compared to pure water. And the same thing happened to MgCl2. And I was investigate the effect of CaCl2 then the phreeqc has error.
I don't know whether I put the reactions correctly or not and whether the initial solution is correct or not. I attached below the reactions and Solution file.

pure water

SOLUTION 0 formation water
     units   Mol/L
C  0.05
temp 150
pH 7
pe 4
redox pe

density 1
water 1 # L

END

data file:
SOLUTION_MASTER_SPECIES
#
#element   species   alk   gfw_formula   element_gfw
#
H      H+   -1.0   H      1.008
H(0)      H2   0   H
H(1)      H+   -1.0   0
E      e-   0   0.0      0
O      H2O   0   O      16.0
O(0)      O2   0   O
O(-2)      H2O   0   0
C      CO3-2   2.0   HCO3      12.0111
C(+4)      CO3-2   2.0   HCO3
Alkalinity   CO3-2   2.0   61.0173    61.0173

SOLUTION_SPECIES
H+ = H+
   -gamma   9.0   0

   -dw    9.31e-9
e- = e-
H2O = H2O
CO3-2 = CO3-2
   -gamma   5.4   0
   -dw    0.955e-9
   -Vm  5.95  0  0  -5.67  6.85  0  1.37  106  -0.0343  1 # ref. 1
# aqueous species
H2O = OH- + H+
   -analytic  293.29227  0.1360833  -10576.913  -123.73158  0  -6.996455e-5
   -gamma   3.5   0
   -dw    5.27e-9
   -Vm  -9.66  28.5  80.0 -22.9 1.89 0 1.09 0 0 1 # ref. 1
2 H2O = O2 + 4 H+ + 4 e-
   -log_k   -86.08
   -delta_h 134.79 kcal
   -dw    2.35e-9
   -Vm  5.7889  6.3536  3.2528  -3.0417  -0.3943 # supcrt
2 H+ + 2 e- = H2
   -log_k   -3.15
   -delta_h -1.759 kcal
   -dw    5.13e-9
   -Vm 6.52  0.78  0.12 # supcrt
CO3-2 + H+ = HCO3-
   -log_k   10.329
   -delta_h -3.561   kcal
   -analytic   107.8871   0.03252849   -5151.79   -38.92561   563713.9
   -gamma   5.4   0
   -dw    1.18e-9
   -Vm  8.472  0  -11.5  0  1.56  0  0  146  3.16e-3  1 # ref. 1
CO3-2 + 2 H+ = CO2 + H2O
   -log_k   16.681
   -delta_h -5.738   kcal
   -analytic   464.1965   0.09344813   -26986.16   -165.75951   2248628.9
   -dw    1.92e-9
   -Vm   7.29  0.92  2.07  -1.23  -1.60 # ref. 1 + McBride et al. 2015, JCED 60, 171
2CO2 = (CO2)2 # activity correction for CO2 solubility at high P, T
   -log_k -1.8
   -analytical_expression  8.68  -0.0103  -2190
   -Vm   14.58  1.84  4.14  -2.46  -3.20

   -delta_h -0.396   kcal
   -Vm  6.16  0  29.4  0  0.9 # ref. 2
END
==============================================================
Nacl effect
SOLUTION 0 formation water
     units   Mol/L
C  0.05
temp 150
pH 7
pe 4
redox pe

density 1
Na 5
Cl 5
water 1 # L
END

data file:
SOLUTION_SPECIES
H+ = H+
   -gamma   9.0   0

   -dw    9.31e-9
e- = e-
H2O = H2O
Na+ = Na+
   -gamma   4.0    0.075
   -gamma   4.08 0.082 # halite solubility
   -dw    1.33e-9
   -Vm   2.28  -4.38  -4.1  -0.586  0.09  4  0.3  52  -3.33e-3  0.566 # ref. 1
Cl- = Cl-
   -gamma   3.5     0.015
   -gamma   3.63  0.017 # cf. pitzer.dat
   -dw    2.03e-9
   -Vm  4.465  4.801  4.325  -2.847  1.748  0  -0.331  20.16  0  1 # ref. 1
CO3-2 = CO3-2
   -gamma   5.4   0
   -dw    0.955e-9
   -Vm  5.95  0  0  -5.67  6.85  0  1.37  106  -0.0343  1 # ref. 1
# aqueous species
H2O = OH- + H+
   -analytic  293.29227  0.1360833  -10576.913  -123.73158  0  -6.996455e-5
   -gamma   3.5   0
   -dw    5.27e-9
   -Vm  -9.66  28.5  80.0 -22.9 1.89 0 1.09 0 0 1 # ref. 1
2 H2O = O2 + 4 H+ + 4 e-
   -log_k   -86.08
   -delta_h 134.79 kcal
   -dw    2.35e-9
   -Vm  5.7889  6.3536  3.2528  -3.0417  -0.3943 # supcrt
2 H+ + 2 e- = H2
   -log_k   -3.15
   -delta_h -1.759 kcal
   -dw    5.13e-9
   -Vm 6.52  0.78  0.12 # supcrt
CO3-2 + H+ = HCO3-
   -log_k   10.329
   -delta_h -3.561   kcal
   -analytic   107.8871   0.03252849   -5151.79   -38.92561   563713.9
   -gamma   5.4   0
   -dw    1.18e-9
   -Vm  8.472  0  -11.5  0  1.56  0  0  146  3.16e-3  1 # ref. 1
CO3-2 + 2 H+ = CO2 + H2O
   -log_k   16.681
   -delta_h -5.738   kcal
   -analytic   464.1965   0.09344813   -26986.16   -165.75951   2248628.9
   -dw    1.92e-9
   -Vm   7.29  0.92  2.07  -1.23  -1.60 # ref. 1 + McBride et al. 2015, JCED 60, 171
2CO2 = (CO2)2 # activity correction for CO2 solubility at high P, T
   -log_k -1.8
   -analytical_expression  8.68  -0.0103  -2190
   -Vm   14.58  1.84  4.14  -2.46  -3.20

   -delta_h -0.396   kcal
   -Vm  6.16  0  29.4  0  0.9 # ref. 2
Na+ + OH- = NaOH
   -log_k   -10 # remove this complex
Na+ + CO3-2 = NaCO3-
   -log_k   1.27
   -delta_h 8.91 kcal
   -dw 5.85e-10
   -Vm  3.89  -8.23e-4  20  -9.44  3.02  9.05e-3  3.07  0  0.0233  1 # ref. 1
Na+ + HCO3- = NaHCO3
   -log_k  -0.25
   -delta_h  -1 kcal
   -dw 6.73e-10
   -Vm  0.431 # ref. 1

END
=========================================================
KCl effect

SOLUTION 0 formation water
     units   Mol/L
C  0.05
temp 150
pH 7
pe 4
redox pe

density 1
K 5
Cl 5
water 1 # L
END

data file:
SOLUTION_MASTER_SPECIES
#
#element   species   alk   gfw_formula   element_gfw
#
H      H+   -1.0   H      1.008
H(0)      H2   0   H
H(1)      H+   -1.0   0
E      e-   0   0.0      0
O      H2O   0   O      16.0
O(0)      O2   0   O
O(-2)      H2O   0   0
K      K+   0   K      39.102
Cl      Cl-   0   Cl      35.453
C      CO3-2   2.0   HCO3      12.0111
C(+4)      CO3-2   2.0   HCO3
Alkalinity   CO3-2   2.0   61.0173    61.0173

SOLUTION_SPECIES
H+ = H+
   -gamma   9.0   0

   -dw    9.31e-9
e- = e-
H2O = H2O
K+ = K+
   -gamma   3.5   0.015
   -dw    1.96e-9
   -Vm  3.322  -1.473  6.534  -2.712  9.06e-2  3.5  0  29.7  0  1 # ref. 1
Cl- = Cl-
   -gamma   3.5     0.015
   -gamma   3.63  0.017 # cf. pitzer.dat
   -dw    2.03e-9
   -Vm  4.465  4.801  4.325  -2.847  1.748  0  -0.331  20.16  0  1 # ref. 1
CO3-2 = CO3-2
   -gamma   5.4   0
   -dw    0.955e-9
   -Vm  5.95  0  0  -5.67  6.85  0  1.37  106  -0.0343  1 # ref. 1
# aqueous species
H2O = OH- + H+
   -analytic  293.29227  0.1360833  -10576.913  -123.73158  0  -6.996455e-5
   -gamma   3.5   0
   -dw    5.27e-9
   -Vm  -9.66  28.5  80.0 -22.9 1.89 0 1.09 0 0 1 # ref. 1
2 H2O = O2 + 4 H+ + 4 e-
   -log_k   -86.08
   -delta_h 134.79 kcal
   -dw    2.35e-9
   -Vm  5.7889  6.3536  3.2528  -3.0417  -0.3943 # supcrt
2 H+ + 2 e- = H2
   -log_k   -3.15
   -delta_h -1.759 kcal
   -dw    5.13e-9
   -Vm 6.52  0.78  0.12 # supcrt
CO3-2 + H+ = HCO3-
   -log_k   10.329
   -delta_h -3.561   kcal
   -analytic   107.8871   0.03252849   -5151.79   -38.92561   563713.9
   -gamma   5.4   0
   -dw    1.18e-9
   -Vm  8.472  0  -11.5  0  1.56  0  0  146  3.16e-3  1 # ref. 1
CO3-2 + 2 H+ = CO2 + H2O
   -log_k   16.681
   -delta_h -5.738   kcal
   -analytic   464.1965   0.09344813   -26986.16   -165.75951   2248628.9
   -dw    1.92e-9
   -Vm   7.29  0.92  2.07  -1.23  -1.60 # ref. 1 + McBride et al. 2015, JCED 60, 171
2CO2 = (CO2)2 # activity correction for CO2 solubility at high P, T
   -log_k -1.8
   -analytical_expression  8.68  -0.0103  -2190
   -Vm   14.58  1.84  4.14  -2.46  -3.20

   -delta_h -0.396   kcal
   -Vm  6.16  0  29.4  0  0.9 # ref. 2

K+ + H2O = KOH + H+
log_k           -14.46


END
=========================================================
MgCl2 effect
SOLUTION 0 formation water
     units   Mol/L
C  0.05
temp 150
pH 7
pe 4
redox pe

density 1
Mg 5
Cl 5
water 1 # L
END

data file:

SOLUTION_MASTER_SPECIES
#
#element   species   alk   gfw_formula   element_gfw
#
H      H+   -1.0   H      1.008
H(0)      H2   0   H
H(1)      H+   -1.0   0
E      e-   0   0.0      0
O      H2O   0   O      16.0
O(0)      O2   0   O
O(-2)      H2O   0   0
Mg      Mg+2   0   Mg      24.312
Cl      Cl-   0   Cl      35.453
C      CO3-2   2.0   HCO3      12.0111
C(+4)      CO3-2   2.0   HCO3
Alkalinity   CO3-2   2.0   61.0173    61.0173

SOLUTION_SPECIES
H+ = H+
   -gamma   9.0   0

   -dw    9.31e-9
e- = e-
H2O = H2O
Mg+2 = Mg+2
   -gamma   5.5   0.20
   -dw    0.705e-9
   -Vm  -1.410  -8.6  11.13  -2.39  1.332  5.5  1.29  -32.9  -5.86e-3  1 # ref. 1
Cl- = Cl-
   -gamma   3.5     0.015
   -gamma   3.63  0.017 # cf. pitzer.dat
   -dw    2.03e-9
   -Vm  4.465  4.801  4.325  -2.847  1.748  0  -0.331  20.16  0  1 # ref. 1
CO3-2 = CO3-2
   -gamma   5.4   0
   -dw    0.955e-9
   -Vm  5.95  0  0  -5.67  6.85  0  1.37  106  -0.0343  1 # ref. 1
# aqueous species
H2O = OH- + H+
   -analytic  293.29227  0.1360833  -10576.913  -123.73158  0  -6.996455e-5
   -gamma   3.5   0
   -dw    5.27e-9
   -Vm  -9.66  28.5  80.0 -22.9 1.89 0 1.09 0 0 1 # ref. 1
2 H2O = O2 + 4 H+ + 4 e-
   -log_k   -86.08
   -delta_h 134.79 kcal
   -dw    2.35e-9
   -Vm  5.7889  6.3536  3.2528  -3.0417  -0.3943 # supcrt
2 H+ + 2 e- = H2
   -log_k   -3.15
   -delta_h -1.759 kcal
   -dw    5.13e-9
   -Vm 6.52  0.78  0.12 # supcrt
CO3-2 + H+ = HCO3-
   -log_k   10.329
   -delta_h -3.561   kcal
   -analytic   107.8871   0.03252849   -5151.79   -38.92561   563713.9
   -gamma   5.4   0
   -dw    1.18e-9
   -Vm  8.472  0  -11.5  0  1.56  0  0  146  3.16e-3  1 # ref. 1
CO3-2 + 2 H+ = CO2 + H2O
   -log_k   16.681
   -delta_h -5.738   kcal
   -analytic   464.1965   0.09344813   -26986.16   -165.75951   2248628.9
   -dw    1.92e-9
   -Vm   7.29  0.92  2.07  -1.23  -1.60 # ref. 1 + McBride et al. 2015, JCED 60, 171
2CO2 = (CO2)2 # activity correction for CO2 solubility at high P, T
   -log_k -1.8
   -analytical_expression  8.68  -0.0103  -2190
   -Vm   14.58  1.84  4.14  -2.46  -3.20

   -delta_h -0.396   kcal
   -Vm  6.16  0  29.4  0  0.9 # ref. 2
Mg+2 + H2O = MgOH+ + H+
   -log_k   -11.44
   -delta_h 15.952 kcal
   -gamma   6.5   0
Mg+2 + CO3-2 = MgCO3
   -log_k   2.98
   -delta_h 2.713   kcal
   -analytic   0.9910   0.00667
   -dw 4.21e-10
   -Vm  -.5837  -9.2067  9.3687  -2.3984  -.0300 # supcrt
Mg+2 + H+ + CO3-2 = MgHCO3+
   -log_k   11.399
   -delta_h -2.771   kcal
   -analytic   48.6721   0.03252849   -2614.335   -18.00263   563713.9
   -gamma   4.0   0
   -dw 4.78e-10
   -Vm  2.7171  -1.1469  6.2008  -2.7316  .5985 4 # supcrt
END

==============================================================

CaCl2 effect
SOLUTION 0 formation water
     units   Mol/L
C  0.05
temp 150
pH 7
pe 4
redox pe

density 1
Ca 5
Cl 5
water 1 # L
END

data file:
SOLUTION_MASTER_SPECIES
#
#element   species   alk   gfw_formula   element_gfw
#
H      H+   -1.0   H      1.008
H(0)      H2   0   H
H(1)      H+   -1.0   0
E      e-   0   0.0      0
O      H2O   0   O      16.0
O(0)      O2   0   O
O(-2)      H2O   0   0
Ca      Ca+2   0   Ca      40.08
Cl      Cl-   0   Cl      35.453
C      CO3-2   2.0   HCO3      12.0111
C(+4)      CO3-2   2.0   HCO3
Alkalinity   CO3-2   2.0   61.0173    61.0173

SOLUTION_SPECIES
H+ = H+
   -gamma   9.0   0

   -dw    9.31e-9
e- = e-
H2O = H2O
Ca+2 = Ca+2
   -gamma   5.0   0.1650
   -dw    0.793e-9
   -Vm  -0.3456  -7.252  6.149  -2.479  1.239  5  1.60  -57.1  -6.12e-3  1 # ref. 1
Cl- = Cl-
   -gamma   3.5     0.015
   -gamma   3.63  0.017 # cf. pitzer.dat
   -dw    2.03e-9
   -Vm  4.465  4.801  4.325  -2.847  1.748  0  -0.331  20.16  0  1 # ref. 1
CO3-2 = CO3-2
   -gamma   5.4   0
   -dw    0.955e-9
   -Vm  5.95  0  0  -5.67  6.85  0  1.37  106  -0.0343  1 # ref. 1
# aqueous species
H2O = OH- + H+
   -analytic  293.29227  0.1360833  -10576.913  -123.73158  0  -6.996455e-5
   -gamma   3.5   0
   -dw    5.27e-9
   -Vm  -9.66  28.5  80.0 -22.9 1.89 0 1.09 0 0 1 # ref. 1
2 H2O = O2 + 4 H+ + 4 e-
   -log_k   -86.08
   -delta_h 134.79 kcal
   -dw    2.35e-9
   -Vm  5.7889  6.3536  3.2528  -3.0417  -0.3943 # supcrt
2 H+ + 2 e- = H2
   -log_k   -3.15
   -delta_h -1.759 kcal
   -dw    5.13e-9
   -Vm 6.52  0.78  0.12 # supcrt
CO3-2 + H+ = HCO3-
   -log_k   10.329
   -delta_h -3.561   kcal
   -analytic   107.8871   0.03252849   -5151.79   -38.92561   563713.9
   -gamma   5.4   0
   -dw    1.18e-9
   -Vm  8.472  0  -11.5  0  1.56  0  0  146  3.16e-3  1 # ref. 1
CO3-2 + 2 H+ = CO2 + H2O
   -log_k   16.681
   -delta_h -5.738   kcal
   -analytic   464.1965   0.09344813   -26986.16   -165.75951   2248628.9
   -dw    1.92e-9
   -Vm   7.29  0.92  2.07  -1.23  -1.60 # ref. 1 + McBride et al. 2015, JCED 60, 171
2CO2 = (CO2)2 # activity correction for CO2 solubility at high P, T
   -log_k -1.8
   -analytical_expression  8.68  -0.0103  -2190
   -Vm   14.58  1.84  4.14  -2.46  -3.20

   -delta_h -0.396   kcal
   -Vm  6.16  0  29.4  0  0.9 # ref. 2
Ca+2 + H2O = CaOH+ + H+
   -log_k   -12.78
Ca+2 + CO3-2 = CaCO3
   -log_k   3.224
   -delta_h 3.545   kcal
   -analytic   -1228.732   -0.299440   35512.75   485.818
   -dw 4.46e-10   # complexes: calc'd with the Pikal formula
   -Vm  -.2430  -8.3748  9.0417  -2.4328  -.0300 # supcrt
Ca+2 + CO3-2 + H+ = CaHCO3+
   -log_k   11.435
   -delta_h -0.871   kcal
   -analytic   1317.0071   0.34546894   -39916.84   -517.70761   563713.9
   -gamma   6.0   0
   -dw 5.06e-10
   -Vm  3.1911  .0104  5.7459  -2.7794  .3084 5.4 # supcrt
END

CaCl2 effect have error.

I'm sorry for the long text.
Thank you very much for your time and assistance.

[dlparkhurst]

Use the # button to enter your code.

As I said before, do not include SOLUTION_MASTER_SPECIES or SOLUTION_SPECIES unless they differ from the database.

Addition of salts will increase the ionic strength and will change activity coefficients, which will affect the activities and concentrations of species, including pH.

Dissolution of CO2 will lower the pH.

I have a hard time following your post. To make it easier for me, please ask one question at a time.

[Mohamadreza]

Okay, I'm sorry.
thanks for your help.

For simulate the CO2 dissolution in brine(saline aquifers), CO2 must be at supercritical condition(T>31 C, P>73 atm). So, why was used the CO2(g) in Solution part? we don't have CO2 in gas condition in initial condition. My question is, How do I introduce CO2 at supercritical condition into phreeqc?

[dlparkhurst]

Use CO2(g). The parameters are fit to cover a range of temperature and pressure that includes the supercritical region.

[Mohamadreza]

Thanks.

Can phreeqc software clearly show the effect of different salts on the solubility (dissolution) of carbon dioxide in brine or not? Because I did two simulations with two different salts (NaCl, CaCl2), but it had no effect on carbon dioxide dissolution, and the amount of carbon dioxide dissolution was the same, but its values were different in the order of 10^-4.
I was use 1.2 mol/kgw NaCl for one simulation and for the another simulation was  0.2 mol/kgw CaCl2 then the amount of solubility was approximately the same.

[dlparkhurst]

Solubility of CO2 at a fixed temperature and pressure is mostly a function of ionic strength. If your salts produce different ionic strength, the solubility of CO2 will differ. Here is a script that produces a partial pressure of CO2 of 1 atm in a solution of NaCl and one of CaCl2 (1 mol/kgw each). The solubilities are 2.9e-2 and 2.4e-2 respectively. Higher ionic strength has a larger activity coefficient for CO2 and a lower solubility.

Code: [Select]

SOLUTION
REACTION
NaCl 1
1
EQUILIBRIUM_PHASES
CO2(g) 0 10
END
SOLUTION
REACTION
CaCl2 1
1
EQUILIBRIUM_PHASES
CO2(g) 0 10
END


[Mohamadreza]

Thanks for your help.

How was to define the CO2 injection at fixed pressure and temperature at supercritical condition?

Should I use these two keywords below?

REACTION_TEMPERATURE
REACTION_PRESSURE

[dlparkhurst]

You can either use EQUILIBRIUM_PHASES or GAS_PHASE when modeling CO2.

EQUILIBRIUM_PHASES allows you to specify a partial pressure of CO2 for the solution. You can use REACTION_TEMPERATURE and REACTION_PRESSURE to set the conditions of the solution, but the pressure specified in EQUILIBRIUM_PHASES will be obtained for whatever conditions apply. I suggest you start by using EQUILIBRIUM_PHASES.

GAS_PHASE simulates a gas phase in equilibrium with the solution. A fixed_pressure gas phase will react at the pressure specified in the GAS_PHASE definition (or the pressure defined by REACTION_PRESSURE). The volume of the gas phase will adjust in the equilibration calculation. A fixed_volume gas phase will always have the volume defined in the GAS_PHASE definition, and the pressure of the gas phase will adjust during the equilibrium calculation. A fixed_pressure gas phase may dissolve completely, whereas a fixed_volume gas phase will always exist.

[Mohamadreza]

Thank you very much.

How do I calculate partial pressure of CO2 under any conditions and any temperature without using mole fraction of CO2?

[dlparkhurst]

The fugacity is given for CO2(g) in the Saturation Index section of the output, by -si CO2(g) in SELECTED_OUTPUT, or by the Basic function SI("CO2(g)") in USER_PRINT or USER_PUNCH.

For most databases, the ideal gas law is used, and the fugacity is equal to the partial pressure. The databases pitzer.dat, Amm.dat, and phreeqc.dat use the Peng-Robinson equation of state for gases, and the partial pressure is equal to the fugacity divided by the fugacity coefficient (phi).

[Mohamadreza]

Thank you.
Is there a suitable reference and equation to obtain the partial pressure of carbon dioxide under supercritical conditions?
I searched but did not find a suitable reference that gives the fugacity formula and the fugacity coefficient formula under supercritical conditions.

And I wrote this code according to the code you gave me, only for NaCl, right?

Code: [Select]

SOLUTION 0 formation water
pH 7
pe 4
redox pe
units   mol/kgW
density 1.023
C  1e-2
water 1 # kg

REACTION
NaCl 1.2

EQUILIBRIUM_PHASES
CO2(g) 1.94 10

END

[dlparkhurst]

The calculations are not restricted to NaCl. You can make the PHREEQC calculations with any solution that can be solved by using the pitzer.dat or phreeqc.dat databases. You can use PHREEQC with these databases to calculate the fugacity, pressure, and fugacity coefficients of multicomponent solutions.

Perhaps these references will give you a start in searching the literature: Duan and Li, 2008, GCA 72, 5128; Duan et al., 2006, Mar. Chem. 98, 131.

[Mohamadreza]

Thanks.

I was run the simulation for solubility of CO2 in NaCl solution with this code but the phreeqc get error:

Code: [Select]

SOLUTION 0 formation water
pH 7
pe 4
redox pe
units   mol/kgW
density 1.023
C  1e-2
water 1 # kg

REACTION
NaCl 1.2

EQUILIBRIUM_PHASES
CO2(g) 1.94 10

END

Code: [Select]

ERROR: Numerical method failed on all combinations of convergence parameters, cell/soln/mix 1

ERROR: PhreeqcRM failed.
ERROR: PhreeqcRM::RunCells


ERROR: ERROR:               A(H2O) Activity of water has not converged. Residual: 1.552408e-02

ERROR: Numerical method failed on all combinations of convergence parameters, cell/soln/mix 1

ERROR:               A(H2O) Activity of water has not converged. Residual: 1.552408e-02

ERROR: Numerical method failed on all combinations of convergence parameters, cell/soln/mix 1

ERROR: PhreeqcRM failed.
ERROR: PhreeqcRM::RunCells

Is this code correct?

[dlparkhurst]

The script will run in the graphical user interface PhreeqcI when using the pitzer.dat or phreeqc.dat database.

I do not know how PhreeqcRM is implemented in the code you are using and cannot make comments on the errors that occur when using you CDF code.

[Mohamadreza]

Thanks.

I want to set the pH value of different salt waters in the SOLUTION part of phreeqc.

How do I calculate the pH of different salt waters at different pressure, temperature, and molality?

[dlparkhurst]

Please start another thread. This one is getting way too long.

Also, you have to show me something. Write a script, and ask a specific question.

[Mohamadreza]

I'm sorry. Okay.