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About thomasw

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  1. DEar BRian, I have tried that command out, but unfortunately I receive an error message: Act2> activity Gold = 0.4 -- Error: Gold needs to be swapped into the basis -- Error: Can't set activity of Gold I attach for you the act2 script that I am using. The stup is such that Au+ is the diagram species, and pH and O2(g) are the species on axes. I can then set up activities of other aqueous species (in the presence of), in my example that of Cl-, H2O and H2S(aq). However, I CANNOT set up the activity of Gold (solid phase), neither through the GUI nor on the command pane
  2. Dear Brian, thanks for pointing this out. Unfortunately the script that you attached to your posting does not contain any command that would set the activity of quartz to a non-unity value. Could you please add the example that contains the syntax of that command that one would need to enter into the act2 script? Does this approach also work for the diagram species? If I calculate the solubility of gold as function of pH and log(fO2), then I set up Au+ or Au+++ as my diagram species, and then swap in Au(s) for the selected aqueous species. Then I would need to enter a command in the act2 s
  3. Dear all, I typically deal with solubility contours exactly the way Brian described it, and it works well because act2 produces vector graphics output. Having the possibility to use isotopic reactions in activity diagrams would be very helpful I must say, but I understand that implementing this feature just for few potential users that would need is might not be feasible. The most troublesome issue with act2 at the moment IMHO is that one cannot set activities for any solid phases, they are just assumed to be 1. If one wants to display for example the solubility of solid gold, where th
  4. Dear all, The importance of pressure on hydrothermal reaction equilibria would certainly depend on the magnitude of pressure and the P-T region that you are dealing with. For example, at 250 °C, the dissociation constant of water (H2O = H+ + OH-), admittedly the most fundamental aqueous reaction, will be 11.2, 10.9 and 10.7 at Psat, 500 bar and 1000 bar. At 350°C, the values will be 11.8, 11.1 and 10.6 for the same presures. The difference of 1.2 log units translates into 0.6 pH units, certainly not negligible. The statement that pressure does not matter in hydrothermal systems appears to
  5. Dear all, I have created an activity diagram for Fe-S-O minerals using Act2, and it was based on the default database file thermo.dat. Now I would like to update the diagram by loading a customized thermodynamic database file. It loads the file successfully, but when trying to plot the diagram, the following error is displayed: Error: Cant swap H2S(aq) for SO4-- Then it offers to press OK or Quit, and tyring both commonly results in program crash When I use the same thermodynamic data file for plotting a gold solubility diagram, it works no problem. A suspicion I have is that it
  6. Hello, it looks like the suggestion to check out the Theredata website for Pitzer database files is not very useful. I checked this website and there is a lot of stuff like political statements, news, plans, reports from meetings, but actually NO DATA. All links that appear to point to actual data conclude with the statement that this is under construction. Maybe it is worth to check back again in five years or so, eventually they might upload some database files. A more useful thing to do would be to contact Luigi Marini who mentions a modified version of the data0.YPF file in a recen
  7. Hello, when reading the request to add such a complicated 7-term temperature dependence for Pitzer coefficients, I started to wonder whether this is justified in view of the availability of experimental data (measurements of mean acitivities etc.) that could constrain such parameters. In particular, some terms such as the high T powers (this is already a potential issue with T2 terms) might behave very unreasonably outside the calibrated T range where constrained by experiments. There could be inflection points and strong divergence appearing at temperatures well above the calibrated inter
  8. Hello Tom, yes ideally I would like a 3D diagram with pH, log(fO2) and log(aS) as the three axes. Because 3D diagrams are generally difficult to read for people in publications, I am also happy with 2D sections through that 3D space. Two such sections will usually be sufficient to illustrate the effect the three variables have relative to each other. The only point I wanted to make is that if a(H2S,aq) is selected as independent variable along with f(O2,g), then it appears to me that H2S,aq cannnot be speciated. But if you look at the pyrite example scripts that I posted, you will see that
  9. Hello Tom, thanks for the suggestion of that workaround, which makes it at least in principle possible to calculate activity diagrams for mineral activities that are different from unity. But you would certainly agree that having to calculate the log k increments manually from the activity of the mineral every time time, especially when for example you want to contour the mineral activity (e.g. for Au activity in Au-Ag alloy to look at the effect of electrum composition and similar), this is pretty inconvenient and time-consuming. Speaking frankly, my intention in purchasing Gwb was actual
  10. Hello Tom, thanks for your response, and especially for taking into account to add the feature of plotting several solubility contours into one diagram. As said, this task can of course be accomplished by creating several diagrams for different values of the diagram species, and then assembling them in a graphics package. But of course this is much less convenient than doing this right away in act2 before exporting to the graphics package. Regarding my question number (2), I am adding some act2 scripts to illustrate this point. Diagram pyrite1 is a log(fO2) versus pH diagram that shows
  11. Dear all, in some calculations of activity-activity and activity-temperature diagrams it is pretty useful to set the activity of minerals involved into the set of reactions to a value that is different from 1.0. For example, consider that you work on fluid-rock interaction and want to look at the controls on mineral stability in an hydrothermally altered rock. Now you have analyzed for example the chlorite in this rock by electron microprobe and used some composition-activity model (in the simplest case just configurational energy arising from ideal mixing) to calculate the activity of one
  12. Dear all, I have been calculating activity diagrams by hand for many years, and now I have started to work with act2 (and also in tact) to save time. The basic stuff is straightforward and clear, but in addition I would need some special calculation types and plot options and I am not sure where to find them or if this can be done at all with the programs. These would be the following: 1) Solubility contours Is it possible to plot simultaneously (i.e., in one diagram) aqueous species - mineral boundaries (e.g. some metal solubility) for different values of this metal (i.e., the diagra
  13. Hi, as Tom has said, GWB apparently has no provision for solid-solutions. In general, geochemical modeling codes that are based on the law of mass action (LMA) method have difficulties and limitations when dealing with solid-solutions. Some LMA based programs can deal with binary non-ideal solid-solutions, and many can deal with multi-component ideal solid-solutions. There are some workarounds, for example P. Lichtner and coworkers use a so-called disrete composition approach, i.e. they slice each solid-solution into many phases of fixed composition, generate their thermodynamic properties
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