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Tom Meuzelaar

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Everything posted by Tom Meuzelaar

  1. Hi Trevor: Have you read pages 13 (and the top of 14) in the Reactive Transport Modeling Guide? This covers heat transfer across medium boundaries. Hope that helps, Tom Meuzelaar RockWare, Inc.
  2. Hi Kelvin: Equilibrium constants for CuCl3- and CuSO4(aq) are only defined at 25C, thus you should either define solubility data for the temperatures you are working at or turn the extrapolate variable off. Hope that helps, Tom Meuzelaar RockWare, Inc.
  3. Dear GWB users: We are pleased to announce a workshop in Golden, CO for GWB Essentials, Standard and Professional users this fall. The July 7-8, 2011 workshop is designed for: Current users of GWB Essentials, GWB Standard and GWB Professional who wish to become more familiar with the software's interface and features. Those interested in reviewing the basics of geochemical modeling (speciation models, activity models and activity diagrams) Those interested in learning detailed reaction path modeling (using redox disequilibrium, kinetics, and surface complexation) Those interested in
  4. Hi: Absolutely. Just make sure that you include H+ as a component, and constrain it (swapping) with the variable that controls pH. Hope that helps, Tom Meuzelaar RockWare, Inc.
  5. Hi Laurie: Finally getting around to your question. The issue of charge balance calculation differences among the various codes is a significant one that has not been discussed yet on this forum- so I will post it here for reference. There are two very different methods for calculating charge balance, both with an apparently significant following: Imbalance calculated relative to the sum of anionic and cationic charge, popular among water engineers: Charge balance = 100*[((Sum cations-Sum anions)/(Sum cations + Sum anions))/2)] Example reference: Weight, W.D. (2008), Hydrology Field Man
  6. Hi: Apologies for the delay. In your first script, as the error message indicates, you run out of Cl- for charge balance, and it is forced to negative concentrations. You can remedy this by either beginning with a higher anion concentration, or better yet, consider a base titration (NaOH for example), rather than a pH slide, as this avoids negative concentration issues. Unless this is a pure solution, it's a good idea to have some background electrolytes (Na, Cl). The issue with the smaller reaction path steps occurs right when Zincite reaches saturation- you are essentially removing 1/10th
  7. Hi: Please attach the script you are working with, and I'd be happy to take a look. Regards, Tom Meuzelaar RockWare, Inc.
  8. Hello: Can you please attach a script that shows me your results? If you are using a modified thermodynamic database, please includes this also. If the model and data are proprietary, feel free to email them to me. Regards, Tom Meuzelaar RockWare, Inc.
  9. Hi Ale: The alkalinity reported by GWB is carbonate alkalinity, computed as follows: Alk = 50.0445 * 1000 * (m_HCO3 + 2 m_CO3) * (kg_solv/kg_soln) For computing total alkalinity from the above, refer to Craig Bethke's Geochemical and Biogeochemical Reaction Modeling, page 220 (Chapter 15). I hope that helps, Tom Meuzelaar RockWare, Inc.
  10. Hello: If you want to model changing system chemistry over time, you should take a look at the various kinetic options available in GWB. The best place to start is the Reaction Modeling Guide (starting with page 33). I hope that helps, Tom Meuzelaar RockWare, Inc.
  11. Hello: Please email me, and we'll see if we can get this resolved. Regards, Tom Meuzelaar RockWare, Inc.
  12. Hi Elisabeth: The purpose of a flash diagram is to predict scale and mineral saturation state changes that arise when two fluids are mixed in varying proportions. What GWB actually does is remove fluid from the system in the same proportion that new fluid (in your case, end member groundwater) is titrated in. This allows you to see a range of mixing ratios between your end member groundwater fluid and your mixed fluid. So this approach may not work for your inverse model, as you would essentially be removing water of different compositions twice over. Keep in mind that the water you are 'unm
  13. Hi: Try balancing your Basis water on Na- it's the one that is not converging. Your Na/Cl concentrations are extremely low, so you might choose more abundant, nonessential cations and anions for charge balance. Hope that helps, Tom Meuzelaar RockWare, Inc.
  14. Hello: You'll want to use the React module, which is well suited for this: Load the water that you would like to titrate into the React Basis panel Speciate this water (Run) and use the Run - Pickup - Reactants command to load this speciated water into the Reactants tab This water becomes the water that you will mix into your primary water Load your primary water into the Basis tab (Open - React Script) Your mixing model is now set up If you want to experiment with variable mixing ratios, use the Reactants times setting in the Reactants tab Hope that helps. Regards, Tom Meuzelaar
  15. Hello: It looks like you don't have a constraint for the HCO3-, which is necessary for the higher pH range. Some constraints on other dissolved solutes (at a minimum Na and Cl) are going to be helpful as well for maintaining charge balance. Regards, Tom Meuzelaar RockWare, Inc.
  16. Hi Blake: Thanks for your post. Would you mind attaching the script that is generating the singular matrix error so I have a starting point? Regards, Tom Meuzelaar RockWare, Inc.
  17. Dear GWB Users: We have released GWB 8.0.12, which addresses the following issues: Fixes a flaw in React 8.0.11 (but not earlier maintenance releases) introduced by an error in the latest update level of the Intel optimizing compiler; the flaw affected kinetic reaction paths. All current GWB Essentials, Standard and Pro version 8 users can download the GWB 8.0.12 patch here. Please contact me with any questions. Regards, Tom Meuzelaar RockWare, Inc.
  18. Hi Stefan: Attached is an alternate way to set up your problem, which doesn't run into any of the charge balance issues of the first method. Let me know if this is helpful. Regards, Tom Meuzelaar RockWare, Inc. SiO2_test2 - Copy.rea
  19. Dear GWB Users: We have released GWB 8.0.11, which addresses the following issues: corrects a GUI issue in X1t and X2t that can cause the basis panes to freeze or behave oddly. All current GWB Essentials, Standard and Pro version 8 users can download the GWB 8.0.11 patch here. Please contact me with any questions. Regards, Tom Meuzelaar RockWare, Inc.
  20. Hello: Apologies for the late response- I somehow missed notification of your post. Yes, GWB is a great tool for modeling pyrite oxidation. I'd make a couple of changes to your script: You can remove the time constraint, as this is useful only for kinetic modeling, and you do not have a kinetic rate set for pyrite (might be useful to add this to your model...) I would swap Pyrite in for Fe++ in your Basis, and titrate oxygen in from the Reactant panel Those two changes should get you most of the way there. Let me know if you have any further questions. Regards, Tom Meuzelaar RockW
  21. Hi Stefan: In version 8, you can plot charge imbalance error under the System parameters variable type in Gtplot. I wonder if we are looking at different output files- when I run the script you sent me, and look at the last reaction path script in the 'd' output file, charge balance adds up fine. What version are you using? (use the Help - About menu to determine version and sub-version). Regards, Tom
  22. Hi Stefan: The charge imbalance message is not an error, but simply a warning that you are not forcing charge balance. A plot of charge imbalance error shows that your initial system, as you've defined, carries a charge imbalance error of 3.2e-4%. At the end of the simulation, this decreases to 3.2e-5%. Is this significant? Regards, Tom Meuzelaar RockWare, Inc.
  23. Hi: Unfortunately, there is no way to display both the water stability boundaries and show phase stability across your entire axis range. You can do one or the other, but not both. One work-around would simply be to export your second diagram in vector format (using the File - Save image as.. menu option) to a third-party graphics program, and add the water lines in manually. Best regards, Tom Meuzelaar RockWare, Inc.
  24. Hi: Currently there is no provision for sorption kinetics in GWB. However, this functionality is planned for an upcoming release. Regards, Tom Meuzelaar RockWare, Inc.
  25. Hello: The thermo.dat database is configured for work at 1 atm system confining pressure. GWB is able to calculate fugacity values for individual gases in equilibrium with the fluid. In most cases, increasing the confining pressure of your system will have little effect on the equilibrium constants in the database. However, for CO2 this is not the case. To calculate accurate CO2 solubility at higher pressures, I recommend you look at the work of Duan et al., specifically: Duan, Z., and Sun, R. (2003) An improved model calculating CO2 solubility in pure water and aqueous NaCl solutions from
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