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Melika Sharifi

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Everything posted by Melika Sharifi

  1. Dear Maithili, Each thermo dataset in the GWB has a set of basis species, redox species, aqueous species, minerals, oxides, and gases. In any GWB app, only basis species of the loaded thermo dataset are available to add to the basis pane using "Add". However, when the modeler knows, for example, a mineral is in equilibrium with the system or a gas is at a known fugacity in the system, the mineral or gas should be swapped into the basis for one of basis species. By swapping a species (minerals, gases, redox species, aqueous species, or e-) into the basis for a basis species, you are defining chemical constraints for your system. The swapped species must contain in its composition the original basis species being swapped out (you can’t swap lead for gold). For more information, please see sections 2.1, 2.2, and 2.3 in the GWB Essentials Guide that can be accessed from Docs pane of the GWB Dashboard. Bests, Melika Sharifi Aqueous Solutions LLC
  2. Dear Bill, Your assumption is correct. The distribution of species, of course, is affected by the log Ks being used. The bulk composition, on the other hand, should not change when your Basis is defined entirely with bulk constraints. This is quite common, such as when your input is a bulk lab analysis of a fluid. If you look at your Basis pane (after pick-up), though, you will see HCO3-, Nahcolite, and CO2(g) in the basis. The HCO3- is a bulk constraint but the last two entries are free constraints. The software honors the constraints set for the fugacity of CO2 and concentration of free Nahcolite but the log Ks come into play in figuring the bulk composition of the system. Bests, Melika Melika Sharifi Aqueous Solutions LLC
  3. Hi Bill, In isothermal runs in which temperature is set to one of the principal temperatures, the GWB applications take log Ks directly from the tables in the thermo dataset. In a run at 25°C, for example, React takes the second log K entry for each chemical species in the dataset. Where temperature differs from a principal temperature, React fits each table to a polynomial with respect to temperature T, in °C. The polynomial is used at all temperatures in polythermal simulations. Even though both of your post-pickup simulations start at 25°C, the isothermal run uses the log Ks directly from the dataset while the polythermal run uses the polynomial to evaluate the log Ks at each step. You can verify this by setting the printout for “reactions loaded” to long mode. Type the command “printout reaction = long” or go to the Config – Output dialog and click twice in the “reactions loaded” checkbox to completely fill it (you should see a square, indicating long output, instead of the checkmark for short output). Run each model and compare the text output files. You’ll see slightly different log Ks for the initial condition (25°C) for each reaction that’s loaded. To get around this, you might consider running your pre-pickup simulation at a temperature slightly higher or lower than 25°C , such as 25.001°C. That way, you’ll always use the polynomial to evaluate log Ks and your subsequent isothermal and polythermal simulations will have identical initial conditions. There is another complication that doesn’t arise in your particular example, but it can come up when comparing isothermal and polythemal simulations. The GWB apps will only load reactions for species whose thermo data span the temperature range of the simulation. You may have thermo data for a large number of species at 25°C, but data for some of those species may be unavailable at 150°C. In this case, an isothermal run at 25°C will load more species than an isothermal run at 150°C or a polythermal run from 25°C to 150°C. You might wish to use the extrapolate option, which causes React to use the temperature polynomial to estimate log Ks outside the range of known values, to load the entire set of species over your temperature range of interest. Or, you can suppress the species with limited data from your isothermal run at 25°C so that you’re consistently working with a smaller subset of species. You can take a look at the very top of the Results pane to see how many aqueous species are loaded in a simulation. For more information, please see React’s “extrapolate” command in the GWB Reference Manual as well as the Thermo Datasets Appendix to the Reference Manual.
  4. Dear Pavan, The thermo.com.v8.R6 thermo dataset has data for H2SO4(aq) at 25 C. You could either use that dataset, or look into the literature for its log Ks at other temperatures and edit your dataset using TEdit program. You may find some tutorials on editing thermo datasets on our website useful. Please note that unless you are dealing with super acidic conditions (i.e. negative pH), you don't need to worry about H2SO4(aq) data since it becomes important only at very low pH. Bests, Melika Melika Sharifi Aqueous Solutions LLC
  5. Dear Wbourcier, Since you are using a custom-built thermo dataset, please upload your thermo dataset along with your script, so we could open your script to find the problem. Thanks, Melika Melika Sharifi Aqueous Solutions LLC
  6. Dear Ning, By running as an administrator, I meant run the GWB as an administrator. To do so, you need to right-click on the program and open it as "runs as an administrator". Could you, please, confirm you did that? Bests, Melika Melika Sharifi Aqueous Solutions LLC
  7. Dear Wbourcier, Could you, please, attach your React script here? That way we can take a look at it and find the problem. Thanks, Melika Melika Sharifi Aqueous Solutions LLC
  8. Dear Ning, Thanks for posting your question here. Are you running the installer as an administrator? Could you, please, tell us more about your operating system as well? Melika Sharifi Aqueous Solutions LLC
  9. Dear Marco, Thanks for attaching your Act2 script. In future, if you are using a custom-made thermo dataset, you shall attach it along with your script. So people would be able to open your script. Act2 generates predominant diagrams showing the predominance of aqueous species in chemical systems. However, if a mineral is stable in that point, it will be plotted on top of aqueous species. By unchecking "minerals", Act2 will not consider mineral species when it calculates the diagram. Melika Sharifi Aqueous Solutions LLC
  10. Dear Marcos, Thanks for attaching a screenshot of your Act2 script. An easier way would be to use “Attach Files” and attach the script to your post. We looked into your script as well as the graph you are trying to make using Act2, and found a few points worth mentioning: 1. The blue dashed lines are called mosaic bounds showing the speciation of CO32-- with regard to your x-axis (pH). To know what they are, you can double click on the plot, check “mosaic labels” and carbonate species will be shown on the plot. You can get rid of the bounds by double clicking on your plot and uncheck “mosaic bounds”. For more information, please see section 5.3 in the GWB Essentials Guide that can be accessed from the Docs pane of the GWB Dashboard. 2. Reactions required for showing water limits are not included in the thermo_minteq thermo dataset. If you open the thermo.minteq dataset using TEdit app that can be accessed from the Support pane of the GWB Dashboard, you will see the basis species, redox couples, aqueous species, elements, gases, and minerals that are available. You need to add two reactions along with their log Ks into thermo_minteq.tdat : H2(aq) + 0.5O2(aq) à H2O and H2(g)à H2(aq) Sections 9.2.3 and 9.2.4 in the GWB Essentials Guide describe how to add reactions to your thermo dataset using TEdit. You may find logks for those reactions from the reference, or, use other thermo datasets such as thermo.tdat to find the log Ks. This is also true about elemental La. There is no data about elemental La in thermo_minteq. You should look into some references, find a reaction between La+++ (La+++ is the basis species) and La, and add that reaction along with its log Ks at different temperatures, or at least at 25 C, into the thermo_minteq dataset. 3. Act2 and Tact work in terms of species’ activity, which is equal to the molal concentration of a species when its activity coefficient is 1. In the caption of the attached graph, the concentration of La and C is 10^-3 m and 1 m, respectively. Then, you need to put those numbers for La and CO3 2-- in Act2. Hope this helps. Melika Sharifi Aqueous Solutions LLC
  11. Dear Eranvos, Thanks for attaching your script. We looked into your script, and it works fine in our current release, GWB11. A number of improvements to the numerical solution (and the software as a whole) have been made over the years. To get your script working with GWB8, I suggest you set a smaller step size using the “delxi” command. For more information, please see "delxi" in the GWB Reference manual. Bests, Melika Sharifi Aqueous Solutions LLC
  12. Hi Eranvos, Could you, please, attach your React script here? That way we can take a look at it and find the problem. Thanks, Melika Sharifi Aqueous Solutions LLC
  13. Hello Pavan, You could certainly construct a diagram in Act2 with pH and log a H2SO4 axes, but I’m not sure how meaningful it would be. There aren’t any S-bearing smectite minerals that I’m aware of. If you’re interested in predominant Al-species, though, a plot that shows predominance fields of free Al+++ ion and complexes like AlSO4+ could be useful. For smectite stability in general, you might draw a diagram with axes like pH, the activity of species like K+, Ca++, or Mg++, or perhaps an activity ratio. If you look at a reaction like Saponite-Ca + .165 Mg++ = .165 Ca++ + Saponite-Mg, for example, you can see how increasing the activity of Mg++ would favor the forward reaction. Section 5.1, Diagram calculation, in the GWB Essentials Guide has some examples of aluminosilicate stability diagrams that might be useful to you. You can use SpecE8 to determine the saturation state of smectite minerals in a given fluid or figure the composition of a fluid in equilibrium with a particular smectite. If you’d like to simulate reaction processes, though, you’ll need the React program, which is included in the GWB Standard package. And for time-dependent mineral dissolution, you’ll need to set up a kinetic reaction path. For more information, please see section 4.1, Setting kinetic reactions, and 4.2, Kinetics of precipitation and dissolution, in the GWB Reaction Modeling Guide. If you’d like a demo of the Standard package, please write a note to sales@gwb.com. Bests, Melika Sharifi Aqueous Solutions LLC
  14. Dear Roger, To make your diagram, I believe all you need is Cu++ or Cu+ (depending on which thermo dataset you are using) as the main species. However, you can check your simulated environment by going to the “plot” plane à “view results” to see all the reactions and the activity of species in your system. Please let me know if I can help you with anything else. Best Regards, Melika Sharifi Aqueous Solutions LLC Maker of The Geochemist's Workbench
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