Do you want to use Tipping's humic-ion binding Model VII ? (or the CCM)

[remi_marsac]

Dear colleagues,

If you want to model Humic-ion complexation with Tipping's Model VII, I propose a method (and provide everything to do it in supporting information) in the following article :

R. Marsac, N. L. Banik, J. Lützenkirchen, C. Catrouillet, C. M. Marquardt, K. H. Johannesson (2017) Modeling metal ion-humic substances complexation in highly saline conditions. Appl. Geochem. 79, 52-64.

https://doi.org/10.1016/j.apgeochem.2017.02.004


The original version of Model VII (implemented in the speciation code called WHAM) uses a Constant Capacitance Model (CCM)-like equation to account for electrostatic effects. This model is not explicitely implemented in PHREEQC. But you can play with the equations/parameters to use it: by removing the diffuse layer and one capacitor to the "CD-MUSIC" version of the Three Plane Model (TPM). A procedure is detailled in my paper (and sup. info.).


When implementing previous versions of Tipping's model (Model V and VI) in PHREEQC, researchers (including me in some of my previous papers) used the DLM for the electrostatics. This gave only an approximation of Model V/VI, compared to the original model. Now, by using the CCM, results are exactly the same for WHAM and PHREEQC (provided that aqueous databases are the same).


Feel free to contact me if you need help.

Best regards,

Rémi Marsac
Researcher at Géosciences Rennes, Rennes 1 University, France

[Pak]

Hi,

I think this work is great, but I would like to add just one comment. If you wan to use the CCM in Phreeqc, there is no need to trick the TLM, that obviously is possible and does not require a big amount of work.

Phreeqc incorporates an undocumented CCM (http://phreeqcusers.org/index.php/topic,502.msg1558.html#msg1558).

I gave a try using this input:

Code: [Select]

SOLUTION 1 Brine
units mol/L
pH 8
Na 8.436e-5
Cl 8.330e-5
As 2.5e-8
SURFACE 1
# assumes 1/10 of iron is HFO
SurfOH 0.07 600. 30.
-ccm 0.020983919
END
and this database:

Code: [Select]

SOLUTION_MASTER_SPECIES
    H             H+              -1     H               1.008
    H(0)          H2               0     H             
    H(1)          H+              -1     1             
    E             e-               0     1               1.008
    O             H2O              0     O               16
    O(0)          O2               0     O             
    O(-2)         H2O              0     1             
    As AsO4-3 -1.0 74.9216 74.9216
    Na Na+            0 Na 22.9898
    Cl Cl-            0 Cl 35.453
SOLUTION_SPECIES
H+ = H+
    log_k     0
    -gamma    9 0
    -dw       9.31e-009
e- = e-
    log_k     0
H2O = H2O
    log_k     0
H2O = OH- + H+
    -analytical_expression 293.29227 0.1360833 -10576.913 -123.73158 0 -6.996455e-005
    -gamma    3.5 0
    -dw       5.27e-009
Na+ = Na+
-gamma 4.0 0.075
-gamma 4.08 0.082 # halite solubility
-dw 1.33e-9  122  1.52  3.70
-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  194  1.6  6.9
-Vm  4.465  4.801  4.325  -2.847  1.748  0  -0.331  20.16  0  1 # ref. 1

2H2O = O2 + 4H+ + 4e-
    log_k     -86.08
    delta_h   134.79 kcal
    -dw       2.35e-009
2H+ + 2e- = H2
    log_k     -3.15
    delta_h   -1.759 kcal
    -dw       5.13e-009

Na+ + OH- = NaOH
-log_k -10

AsO4-3 = AsO4-3
    log_k 0.0
AsO4-3 + 3H+ = H3AsO4
    log_k 20.7
H+ + AsO4-3 = HAsO4-2
    log_k 11.50
2H+ + AsO4-3 = H2AsO4-
    log_k 18.46

SURFACE_MASTER_SPECIES
Surf SurfOH
SURFACE_SPECIES
SurfOH = SurfOH
log_k 0.0
SurfOH + H+ = SurfOH2+
log_k 7.29
SurfOH = SurfO- + H+
log_k -8.93
SurfOH + AsO4-3 + 2H+ - OH- = SurfH2AsO4
log_k 29.31
SurfOH + AsO4-3 + H+ - OH- = SurfHAsO4-
log_k 23.51
SurfOH + AsO4-3 = SurfOHAsO4-3
log_k 10.58
And the results were correct for this case, I think it works well, but I have not done an exhaustive study of it.