mmontecinos1
-
Posts
6 -
Joined
-
Last visited
Posts posted by mmontecinos1
-
-
Thanks you Brian!
I followed your advice and now my results fits perfectlyBest regards,
Mauricio -
On 01-03-2018 at 8:26 PM, Brian Farrell said:
Hi Mauricio,
I think your surface dataset looks okay. It's possible that your thermo dataset is slightly different from the one used in the original calculations, but I'm not sure how important that is in this case. The paper lists several Cu++ species, including carbonate complexes, that are accounted for in the calculation, but I'm not sure your dataset includes them all. Furthermore, the paper lists a specific Cu++ species, CuOH+, with a log K of formation of -7.29. The dissociation reaction for that species is listed in your thermo dataset with a log K of 7.497. You might try using the "alter" command to set its value to 7.29. If you track down the carbonate complexes, you might consider adding a CO2 buffer to your calculation, but I think the paper mentioned those complexes weren't too important in this calculation, so you might not worry about it.
I think the most important factor is that the "sorbate include" setting has not been applied. In the experiments, the Cu concentration refers to the total amount of Cu in solution and sorbed to the surfaces. In the GWB's default state, the Cu concentration you set on the Basis pane refers only to that in solution (think of sampling water from a well). You can use the "sorbate include" option from the Config -> Iteration dialog to specify that the Cu concentration set on the Basis pane includes sorbed as well as dissolved mass. When I do that, and disable charge balancing and delete the Cl- basis entry, I get results that look very much like those in Figure 2.
For more information, please see React's "sorbate" command in the GWB Command Reference/ Reference Manual.
Hope this helps,
Brian Farrell
Aqueous Solutions LLCDear Brian,
Now I am trying to model the sorption of Cu on Kaolinite through the bidentate model developed by Lund et al (2008) (Fig. 3a, blue line/dots). I created the sorption file using the FeOH.dat as a template for bidentate sorption reactions. However, when I run the program, GWB overestimate the sorption. I used the “sorbate include” option, but the result didn’t improve.
Also, I would like to implement the Bidentate variable charge + ion exchange site model (no Cu sorption on ion exchange site). I created the IonEx.dat file, with the reaction for H exchange, but when I run it in React, nothing happens. I mean, there is no difference between the model with and without ion exchange site model.
I would appreciate any recommendation you could give me to solve these problems.
Best regards,
Mauricio Montecinos2008 - Lund_Fig2a - Bidentate.rea
-
Hi Brian,
I didn't know about the sorbate include option. I followed your instructions and now the model in GWB fits perfectly
Thanks you so much!
Mauricio Montecinos -
Hello everyone,
I am using React program of GWB 9.0 to simulate surface complexation of Copper (Cu++) on Kaolinite. I want to reproduce the modeling results of Lund et al. (2008) (T.J. Lund, C.M. Koretsky, C.J. Landry, M.S. Schaller, S. Das, Surface complexation modeling of Cu(II) adsorption on mixtures of hydrous ferric oxide and kaolinite, Geochem. Trans. 9 (2008) 9). They describe the sorption of copper at a variety of ionic strength using different Double Layer Model (e.g. Monodentate variable charge site, Bidentate variable charge site, among others).I am modeling the sorption for the system with 1E-4 M Cu, 0.01 M NaNO3 and 2 g/L of Kaolinite using a 1-site model (Monodentate) (Fig 2A, blue line in Lund et al. 2008).I created a dataset of surface reaction using file FeOH.dat as a template, but changing basis species, sorbing minerals and surface species. I also modified the thermodynamic database to include minerals and dissolved species of interest.
However, when I run React, GWB underestimate the sorption of Cu for pH > 5.5. I thought it could be due to changes in the Ionic Strenght, but it increase only for low pH (<4). I also tried excluding all other species of Cu, different than Cu++ but the results didn’t improve.
I would appreciate any recommendation to understand the problem.
Best regards,
Mauricio Montecinos -
I am trying to make a surface complexation model for Calcite according to Sø, H. et al, (2008) (Sorption and desorption of arsenate and arsenite on calcite. Geochimica et Cosmochimica Acta, 72(24), 5871).
I am using the thermodynamic database “thermo.dat”, and I have no problems in load the surface data, but when run the sorption model, the program crashes.
The surface database is attached below.
Best regards
Mauricio Montecinos A.
Surface precipitation model
in The Geochemist's Workbench
Posted
Hello everyone,
I am trying to reproduce the surface precipitation model of Cu in HFO y HAO developed by Karthikeyan and Elliott (1999) (Surface Complexation Modeling of Copper Sorption by Hydrous Oxides of Iron and Aluminum, Journal of Colloid and Interface Science 220, 88–95 (1999). I would like to edit FeOH.dat sorption file to include equations [5] to [8] considered by the authors. However, I am not sure how due to these equations consider both sorbed and precipitated species
To include eqs. [5] and [6] I was thinking of include the following species:
>(s)FeOHCu(OH)2H+
charge= 1.0 mole wt.= 171.4228
4 species in reaction
1.000 >(s)FeOH -1.000 H+ 1.000 Cu++
2.000 H2O
log K= -0.7500 dlogK/dT= 0.0000
>(w)FeOHCu(OH)2H+
charge= 1.0 mole wt.= 171.4228
4 species in reaction
1.000 >(w)FeOH -1.000 H+ 1.000 Cu++
2.000 H2O
log K= -0.7500 dlogK/dT= 0.0000
but I am not sure if this is a proper way to represent this model of surface precipitation.
Regarding to eq. [7] and [8], I don’t know how to include it, due to these equations represent the change in Ksp precipitation due to HFO adsorption.
I would appreciate any recommendationBest regards,
Mauricio Montecinos