Tom Meuzelaar

Hello: By default, NH4+ is coupled to NO3- as a redox couple- this means that GWB will calculate the concentration of NH4+ in the system based on equilibrium with both NO3- and Oxygen (O2(aq) is the 'master redox species' in GWB). If you want to constrain NH4+ independently, you'll need to decouple it from NO3- via the Config - Redox Couples menu option. I'd recommend reading the information in the user's guides and modeling textbook about redox equilibrium and disequilibrium to help you decide whether it's appropriate to decouple or not. I hope that helps, Tom Meuzelaar RockWare, Inc.

Hi Thomas: The reaction path message simply states that you've only defined a speciation model up to this point- you can add a reaction path model if you'd like (this is usually done in the Reactants tab). One reaction path model that you might try is a sliding pH model, given that you are interested in Vanadium speciation over a pH range. The only way to benchmark one application against another is to be sure that you are using the same thermodynamic dataset. If indeed the two applications do not share a common thermodynamic database, you'll unfortunately need to do the work of formatting one database so that it can be used within the other application. I hope that helps, Tom Meuzelaar RockWare, Inc.

Hi Tommy: Automatic basis swaps are covered in chapter 5 of Craig Bethke's Geochemical and Biogeochemical Reaction Modeling text (or the older "Geochemical Reaction Modeling", better known as the 'green book'). They are necessary over the course of a model if a mineral dissolves away completely or becomes supersaturated and precipitates. Automatic basis swaps may also be necessary in response to numerical considerations- for example, if one of the basis species occurs at extremely small concentrations, which can create numerical instability in the calculation. As far as rules for swapping, you'll also want to take a look at chapter 3 of the text to see how reactions for minerals and species are written in terms of basis components; and take a look in the database at the reactions for Karelianite/H2(aq), Dolomite/HFeO2-, Hydroxylapatite/HCO3-, to get a better idea of what swaps are allowable. The basis swap is not likely to be the cause of instability. It's probably more tied to defining an initial system that is too far out of equilibrium, issues with charge balance etc. Similarly, there's a discussion on free energy minimization vs. mass action techniques in secion 1.1.1 (page 3) of Craig's book. In short, the two methods are computationally and conceptually equivalent. Finally- I'm not an expert on Vanadate phases, but if the phases you desire are not in the database, you'll either want to use a different database, or add the phases to the database you are using. I hope that helps, Tom Meuzelaar RockWare, Inc.

In the first 'step 0', React calculates mineral saturation states but does not allow any supersaturated minerals to precipitate. In the second 'step 0', React iteratively precipitates those mineral phases that are thermodynamically favorable. In your case, a number of carbonate phases have positive log Q/K values (ie. are supersaturated), so React precipitates Dolomite until there are no supersaturated phases. The removal of solutes tied to Dolomite precipitation lowers the system pH. In order to calculate pH, the H+ component must be defined in the system. Since you don't trust your calculated pH, we 'swap' in CO2(g) at 8 mbar (express as log fugacity) which allows React to calculate pH based on atmospheric CO2. The whole business of species vs. components and 'swapping' can be rather confusing and unintuitive when you first start working with GWB. I highly recommend that you read chapter 3 in Craig's book, as this sheds light on the concept of Basis swapping, and the difference between components and species. You can swap ClO4- in as an aqueous species for any of the basis species that make up it's database reaction. In the thermodynamic database, the reaction for ClO4- is written as follows: ClO4- = 1 Cl- + 2 O2(aq) So, you can swap ClO4- in for the chlorine or oxygen component. I've attached a revised example where ClO4- is used to constrain oxygen in the system. However, in this simulation React predicts that it mostly dissociates to free Cl- ion. Have a look at chapter 3- I think it will help you make a bit more sense of all of this! Hope that helps, Tom Meuzelaar RockWare, Inc.

Hello: Attached is one way to do this. It assumes that pH is constrained by equilibrium with pCO2. If you want to model ClO4- speciation, you'll need to include a constraint for oxygen (ie. Eh, D.O. etc.) in the model. I hope that helps, Tom Meuzelaar RockWare, Inc.

Hi Rosario: If the minerals are not present at the beginning of your simulation, add them in the React panel as kinetic minerals with zero mass, a rate constant, surface area, and then specify a nucleus density, which will ensure that they are able to precipitate along the simulation. I hope that helps, Tom Meuzelaar RockWare, Inc.

Hi Mat: That is correct- removing the conf file usually resolves the problem. However, if you are able to recreate the conditions that lead to the Xtplot crash, let me know- I'd like to take a look. Regards, Tom

Dear GWB Users: Due to excess demand, we have opened registration for a second workshop, to be held June 24-25, 2009 on the ANU campus in Canberra, Australia. We still have a few seats available for this course. If you are interested in attending, please contact me directly. Regards, Tom Meuzelaar RockWare, Inc. 303 640 5526 gwb@rockware.com

Hi Mat: Can you attach the X2t scripts that are generating this error (and any custom databases you are using in the script). If you would rather keep these private, email them to me at gwb@rockware.com. Regards, Tom Meuzelaar RockWare, Inc.

This issue was resolved via personal correspondence. Regards, Tom Meuzelaar RockWare, Inc.

Dear GWB Users: We have released GWB 8.0.2 which addresses the following issues: User's Guides are hyperlinked Better support for landscape and color printing from GSS Improved "connect scatter points" feature in Gtplot and Xtplot Show per-kg units in GSS when calculating charge imbalance Fix a problem in multithreaded polythermal runs using Pitzer model Improve label positioning when copying special plots to clipboard Implement control scripts Provide two header files for user DLLs missing in 8.0 install Correct minor problem with report command Fix all known problems with the GUI Resolve all known issues with 8.0 through 8.0.1 Please contact me with any questions. Regards, Tom Meuzelaar RockWare, Inc.

Hi Joel: Can you either attach or email (gwb@rockware.com) the React scripts and database to me? Regards, Tom Meuzelaar RockWare, Inc.

Hi, I think your model is a bit too ambitious. You are titrating a highly alkaline solid into an acidic solute concentration, high CO2 concentration, neutral pH, and no provision for charge balance. Putting this many extremes into a single reaction path model is likely to lead to numerous convergence issues and frustration! I recommend breaking the model into smaller models. Trying reacting less solid, take smaller reaction steps, using small but numerically tenable concentrations (but not e-14), and set pH by charge balance so it's consistent with CO2 fugacity. Regarding the SO2(g) species, the simplest solution would be to use the v8.r6+ database for this simulation. I hope that helps. Regards, Tom Meuzelaar RockWare, Inc.

Dear Jose: Thank you for sending me your script. It looks like there's an issue with species that have a large number of components- in your case, Smectite-high-Fe-Mg. This issue will be addressed in the upcoming patch 8.0.2. Thanks for bringing this to our attention. Apologies for the inconvenience. Regards, Tom Meuzelaar RockWare, Inc.

Thanks for sending me your script. It turns out that the issue is that GWB does not calculate chlorinity when the phreeqc, wateq4f and minteq datasets are used, because of slight formatting differences. There is a simple work-around- in the element list for either of the 3 databases, change the entry for chlorine from: Cl (Cl) mole wt.= 35.4530 to: Chlorine (Cl) mole wt.= 35.4530 You can use the default database (thermo.dat) for reference, since it has the correct formatting. We'll address this issue formally in the upcoming patch 8.0.2. Apologies for the inconvenience, Tom Meuzelaar RockWare, Inc.

Dear Jose: Can you send me the problem script? Regards, Tom Meuzelaar RockWare, Inc.

Glad it works. By the way- in version 8, you can run speciation calculations for multiple samples directly from the new GSS spreadsheet. Regards, Tom

Hi: Would you mind sending me the actual SpecE8 script? If confidential, simply email it to me at gwb@rockware.com Regards, Tom Meuzelaar RockWare,Inc.

Hi Herdis: It looks like the problem is not so much with the order or formatting of your input file. Assuming that you are using the default Multiple Analyses script provided with GWB in the /Program Files/Gwb/Script/Spreadsheet directory (and also listed in the Multiple Analyses appendix in the back of the GWB Reference Manual), the script sends data from the input file to SpecE8 using the following command: $a = [lindex $headers $i] mg/kg The problem is, that when this is applied to the temperature column, the command 25 = T mg/kg is not recognized. If you add another conditional clause to process the temperature column, } elseif {[lindex $headers $i] == "T"} { T = $a then the script works. I've attached a modified script. Regards, Tom

Hi Herdis: The command temperature = 98 should work- have you tried this formulation? If you send me an example input file that is not being recognized by SpecE8, I'd be happy to take a look at it. Regards, Tom Meuzelaar RockWare, Inc.

Dear GWB Users: We have released GWB 8.0.1 which addresses the following issues: Fix a problem in multithreaded polythermal runs using Pitzer model Improve label positioning when copying special plots to clipboard Implement control scripts Provide two header files for user DLLs missing in 8.0 install Correct minor problem with report command Fix all known problems with the GUI Please contact me with any questions. Regards, Tom Meuzelaar RockWare, Inc.

Hi: The attached PDF describes in detail how fluid density is derived from salinity and temperature. Let me know if you have any further questions. Regards, Tom

Hi: I'm going to post a brief response, which is not yet a direct answer to your question- I am in the process of locating the reference that describes the relationship between chlorinity, temperature and fluid density. Below is the notation from the v8 GWB Reference Manual regarding the density command: I'll follow this up with more detail about the actual calculations used. Regards, Tom

Hi Vincent: One of the two Pitzer databases compatible with GWB allows for temperature extrapolation at temperatures above 25C, but not below - this is the PHRQPITZ database (thermo_phrqpitz.dat). The other database, the Harvey-Moller-Weare database (thermo_hmw.dat) contains data at only 25C. So, there's currently no provision for working with Pitzer data below 25C. As to your two questions - both the activity of water and total rock mass are reported in the header section of the text output file that is generated after you finish a React simulation. You can also use the Report command from the Command pane to explore simulation results interactively - have a look at the appendix section on the Report command in the v6 GWB Reference manual. I hope that helps, Tom Meuzelaar RockWare, Inc.

Hi Jono: For v6-7, under the Help menu in the SpecE8 or React module you'll find a set of instructions specific to adding scatter data for that module, including examples of text formatting. It's not listed in the User's Guides as the formatting differs from module to module (Act2, SpecE8, React etc.). Version 8 makes this much simpler, as data can be plotted directly from the new GSS spreadsheet. If you're still having trouble getting it to work, go ahead and send me your script and scatter dataset. I hope that helps, Tom Meuzelaar RockWare, Inc.