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Brian Farrell

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  1. Hello, Density of electrolyte solutions is not calculated in most geochemical modeling programs. It's secondary in importance to species distributions, saturation indices, and so on, but it's our opinion that a simple calculation is better than nothing. The Phillips correlation described above, which is the default method for GWB12 and older releases, was designed for geothermal applications, so it works best at higher temperatures and salinities. The correlation is known to be valid for NaCl solutions from 10 < T < 350 °C, 0.25 < m < 5 molal, and P < 50 MPa and greater than the fluid’s vapor pressure. Your fluid is outside (below) the range of valid salinities and very close to the lower T limit. GWB14 by default uses the Batzle-Wang method (Batzle, M. and Z. Wang, 1992, Seismic properties of pore fluids. Geophysics 57, 1396–1408) for calculating density. It was fit over the range 20 < T < 350 °C and 0 < m < 8 molal, so it works better over a range of conditions. I checked a NaCl fluid of the same ionic strength and temperature as your fluid in GWB14.0.1 and calculated a density of 0.998 g/cm3. PHREEQC's method is quite new. It requires a large number of parameters, but it looks interesting. Regards, Brian Farrell Aqueous Solutions
  2. Dear GWB users, We are pleased to announce our latest maintenance release for GWB subscribers, GWB 14.0.1. The 14.0.1 update improves appearance of legend box in scatter data plots; fixes an issue when several ChemPlugin instances share an ion exchange dataset, resolves a reliability issue in pause/resume feature in X1t/X2t, updates Rxn's outblock feature, resolves basis swapping issue when using Davis-Leckie polydentate formalism, and provides fixes for all known issues. Update from 14.0.0 at no charge to ensure you have all the newest features and bug fixes. Existing installations should automatically update to this release, unless auto-update is disabled. In that case, users should update their installations from the Help menu of any GWB app. Regards, Brian Farrell Aqueous Solutions
  3. Dear GWB users, We are pleased to announce our latest maintenance release for GWB12, GWB 12.0.6. The 12.0.6 update improves the appearance of the legend box in scatter data plots; fixes an issue when several ChemPlugin instances share an ion exchange dataset, resolves a reliability issue in pause/resume feature in X1t/X2t, updates Rxn's outblock feature, and provides fixes for all known issues. Update from 12.0.0-12.0.5 at no charge to ensure you have all the newest features and bug fixes. Existing installations should automatically update to this release, unless auto-update is disabled. In that case, users should update their installations from the Help menu of any GWB app. Regards, Brian Farrell Aqueous Solutions
  4. Hi again, This issue was previously fixed with the release of GWB 14.0.0 for GWB subscribers. It is now available in the latest maintenance release for GWB12, 12.0.06. Regards, Brian Farrell Aqueous Solutions LLC
  5. Hi Silvain, As long as you don’t specify “free” or choose a unit that implies a free constraint (e.g. activity or pH), your constraint is for the bulk concentration of a component. To test this out, fire up SpecE8 and enter HCO3- = .001 molal pH = 6 Na+ = 1 molal balance on Cl- go You can look in the text output file to see the concentrations of several carbon species: CO2(aq) has the highest concentration at .0005060 molal, then in decreasing abundance HCO3-, NaHCO3, CO3--, and NaCO3-. Add them up and you’ll find the molal concentrations will sum to .001 molal, which is the bulk constraint you supplied. Scroll down to “Original basis total moles” in the text file and you’ll see HCO3- = .001 moles, which matches your bulk constraint. You can of course look in the plot file as well. The “species concentration” variable type refers to all the individual aqueous species, and the “components in fluid” refers to bulk composition. You could alternatively use the input below and you’d get the same results. swap CO2(aq) for HCO3- CO2(aq) = .001 molal pH = 6 Na+ = 1 molal balance on Cl- go Of course, if you use units like mg/kg you’ll have to account for the mole weight of whatever species is in your basis, or use the “as” setting to specify concentration in terms of mg Carbon, mg CO2, etc. Since we calculated the complete distribution of species, we can take our results from before and test out the “free” constraint setting: swap CO2(aq) for HCO3- CO2(aq) = .0005060 free molal pH = 6 Na+ = 1 molal balance on Cl- go Running this latest version should give equivalent results. For your second question: Act2 calculates the simple type of diagram that geochemists have traditionally drawn by hand. By design, a number of simplifications make the calculation straightforward (but still laborious). For example, you can only have logarithmic axes (log activity, pH, pe or Eh, etc.). There’s no mass balance. You have to work in terms of activity, rather than concentration. The diagrams are in many cases fairly similar, though. If you want a general picture of how chemistry of a particular system works, a traditional calculation might be fine. Certain applications might demand a more rigorous solution. Beyond recreating activity or redox-pH diagrams, though, Phase2 calculates other diagrams that Act2 cannot even contemplate. You can include surface complexes in your calculations, for example. Or, you can diagram how various properties (solubilities, saturation indices, gas pressures, and so on) vary across the diagram using color maps or contours. You can account for isotope fractionation or kinetic reactions. You can plot assemblages (combinations) of stable minerals under different geochemical conditions. Basically, it has all the capabilities of React, so it's almost endlessly configurable. Hope this helps, Brian Farrell Aqueous Solutions LLC
  6. Hi Polly, For the two-layer surface complexation dataset, you need to specify a site density or densities for each sorbing mineral. If you don’t, the program can’t account for the existence of the surface. If Ferrihydrite contains both of the sites you defined, >(w1)SOH and >(w2)SOH, your entry might look like this: Ferrihydrite surface area= 600.0000 m2/g 2 sorption sites >(w1)SOH site density= .0050 mol/mol mineral >(w2)SOH site density= .2000 mol/mol mineral You should, of course, supply values appropriate for your sorbing mineral. In GWB14, by the way, you can alternatively specify site density in sites/nm2, as you sometimes see in the literature. You should also remove the entry for >(w) in the surface species section. I’m not sure if it was intentionally put in the dataset like this, or it was a stub of an entry that you didn’t finish, but there’s no reaction, stability, or mole weight and that’s causing a problem. Finally, the surface dataset has a field where the user specifies the thermo dataset to use with it. The aqueous species that are included in the surface reactions, as well as the sorbing minerals, are drawn from the thermo dataset you specify. If you plan to use this surface dataset with your custom thermo dataset, it might be best to specify that custom thermo dataset within the surface dataset. Note that the sorbing mineral you’ve chosen, Ferrihydite, is not in your custom thermo dataset, so you may need to make further modifications to either your thermo or surface dataset. You’ll probably have to make these modifications in a text editor, like Notepad, since TEdit can’t open the unproperly formatted dataset. As for your thermo dataset, I don’t think you should include SiO2, H4SiO4, and Si(OH)4(aq) as separate basis entries. They all represent essentially the same thing. Pick one and write all reactions in terms of that species. Hope this helps, Brian Farrell Aqueous Solutions
  7. Hi Thomas, I hope you're doing well. I happened to come across this old post and thought you might be interested to know about Phase2, an app introduced with GWB12. The program essentially traces a stacked series of reaction paths, as you'd run in React, to traverse two geochemical variables of interest. You can set up a diagram with sliding log f O2(g) and fixed pH along the y axis, then sliding pH with fixed f O2(g) along the x axis. The basis fluid is defined in terms of total concentrations, as in React, and mass is conserved throughout the calculation. You can also titrate a species into a fluid initially devoid of it to consider a range of total concentrations. By titrating SO4-- in log steps you can make a diagram much like you've envisioned, with the sulfur speciation depending on the y axis variable, log f O2(g). You can render the calculation results in various types of 2D diagrams or in horizontal or vertical cross-sections through the diagram. For the 2D diagrams, you can plot "true predominance" for any basis species or element (the species accounting for the most mass predominates, not the species with the highest activity), mineral assemblage diagrams (which show every stable mineral or combinations of minerals), and render any variable as a color map, mask, or contour. In a log f O2-pH diagram, for example, you can diagram the stable iron minerals under various conditions and contour the concentration of dissolved Fe. Please visit GWB.com/phase2.php to learn more. I'm happy to send a demo if you'd like to try it out. Cheers, Brian Farrell Aqueous Solutions LLC
  8. Hi Polly, Thanks for providing the thermo dataset. I'm taking a look to see if I can offer any suggestions. Regards, Brian
  9. Johan, Some time ago you tried to report the pore volumes displaced from a ChemPlugin instance in GWB12. I’m writing to let you know that GWB14 is now available, and ChemPlugin instances now plot pore volumes displaced and have the value available in the report command. Additionally, React now plots pore volumes displaced from flush and flash models. I hope you enjoy using the software. Cheers, Brian
  10. Dear GWB users, GWB14 is here! A new compute engine makes it a surface chemistry powerhouse. Plus, our latest release features user equations in GSS datasheets, high-temperature Pitzer coefficients, cluster computing, and flexible input for thermo data, just to start. Visit our GWB14 page to learn more. GWB subscribers upgrade automatically. Can’t wait another minute? Click “Check for updates” on your GWB dashboard. Not subscribing yet? Take advantage of one of our flexible plans—fixed or floating, 3 months to 3 years! Or, convert that old GWB license to a modern subscription and a free kick-off period is on us. Contact us today for a quote, or go shopping at our online store and you’ll be up and running in minutes. Sincerely, Brian Farrell Aqueous Solutions LLC
  11. Hi Sanjoy, I’m writing to let you know about a new feature in the GWB14 release. You can control species loading in a calculation by specifying a temperature range over which thermodynamic data should be available. In your case, many species have thermo data available at 25 C, but not other temperatures, so your calculations at 25 C and 26 C loaded a different set of species, which caused your results to differ more than expected. By specifying a temperature range, say 10-150 C, you can ensure that any calculations within that range load the same exact set of species. It’s basically like automatically suppressing a set of species with limited thermo data, simply by setting a temperature range. You can read about the span command in the GWB Command Reference. The new release has many more new features as well. Please let us know if you’re interested in trying GWB14. I’m happy to send you a demo. Cheers, Brian
  12. Hi Bill, I’m writing to let you know about a new feature available in GWB14. You can control species loading in a calculation by specifying a temperature range over which thermodynamic data should be available. You can additionally force the program to always get log K values by evaluating a polynomial, even when the calculation is isothermal at a principal temperature. In this case, the program would normally use the value directly from the thermo dataset. The difference is small, but it’s why the endpoint of your polythermal path and your isothermal calculation post-pickup were slightly different. You can read about the feature in section 6.92 span in the GWB Command Reference. The new release has many more new features as well. Please let us know if you’re interested in trying GWB14. I’m happy to send you a demo. Cheers, Brian
  13. Hi Mauricio, I’m writing to let you know that GWB 14 is now available. The new release includes support for several different polydentate surface complexation formalisms. You had to convert the log K for a bidentate reaction in your surface dataset to be consistent with the method in GWB9, but now you can choose one of four methods consistent with your log Ks and specify that in your surface dataset. React will read the dataset and evaluate mass action laws according to the convention you specified. In your case, you could set the stoichiometric approach in the dataset’s header and use the original literature reference’s log K value of 4.6. The calculation will reproduce figure 3A in your plot. However, this approach is not satisfactory, as described in the reference above, and it will be in error at other concentrations of the sorbing mineral. The better approach is to convert the log K, as you did before, to use the mole fraction approach, which is entitled Hiemstra-VanRiemsdjik in GWB14. This is the default approach in GWB14, so you can leave the method unspecified in your surface dataset, but to be clear it’s best to set the method in the header. With this approach, changing the amount of the sorbing mineral should still yield reasonable results. Please let us know if you’re interested in trying GWB14. I’m happy to send you a demo. You can read about the feature in section 2.5.8 Polydentate sorption in the GWB Essentials Guide. Regards, Brian
  14. Hi again Dave, Upon closer inspection, you can include a user-defined analyte in a radial plot as long as you put it in the "Components in fluid" category, since this is where the normal basis species plot in Gtplot. If you instead choose a category like "Chemical parameters" and pick Concentration for the dimension, it won't be recognized by the water chemistry plots. Still, if you want to do any thermodynamic calculations including Be, you'll need to use a dataset that includes the relevant reactions. Hope this helps, Brian
  15. Hi Dave, The radial diagram can plot uncharged species when you choose units like mg/l, as you've done. However, the special plots, including the radial plot, only diagram basis and redox species in your spreadsheet. They do not include user-defined analytes. User analytes can only be plotted in xy plots. You might try using a different thermo dataset, like thermo.com.V8.R6+.tdat. That has Be++ as a basis species. Or, you can modify the thermo dataset you're using by adding the element Be and any species that you need, then load that dataset into GSS. Hope this helps, Brian Farrell Aqueous Solutions LLC
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