Brian Farrell

Hi Jin, You have two original basis entries (H+ and HCO3-) and two species you can swap in and constrain (set the fugacity of CO2(g) and the mass of Dolomite). The reactions for CO2(g) and Dolomite-ord include both H+ and HCO3-, so it doesn't matter here what gets swapped for what. Here's an example from section 19.4, Dolomitization of a limestone, in Craig Bethke's Geochemical and Biogeochemical Reaction Modeling text. T = 60 swap CO2(g) for H+ swap Dolomite-ord for HCO3- f CO2(g) = 1 1 free mol Dolomite-ord Na+ = .1 molal Cl- = .1 molal Ca++ = .01 molal Mg++ = .01 molal You could alternatively swap the CO2(g) for the HCO3- and the Dolomite-ord for the H+ and arrive at the same results. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi Chen, You can send your custom thermo dataset to support@gwb.com. Please mention that you posted a question to the forum but the dataset was too large to upload to the forum. Regards, Brian Farrell Aqueous Solutions LLC

Hi Zoe, Sorry for the late response. I missed the notification for this reply. I see that your most recent activation was on November 16. Do you still need assistance activating? Thanks, Brian Farrell Aqueous Solutions LLC

Hi, You can go to the Config -> Output dialog and adjust the three-way checkboxes in the "include" section under "print dataset". Looking at mineral saturation, for example, an unfilled box will cause no saturation indices to be written to the print dataset, a checked box will cause saturation indices above -3 to be written out, and the completely filled box will cause all saturation indices to be written. For more information, please see 2.8, Controlling the printout, in the GWB Reaction Modeling Guide. Gtplot can draw a wide variety of plot types from React output. Even if it doesn't have the special charts that you're interested in, Gtplot provdes a very handy method to export numerical values in a format that you can paste directly into a spreadsheet like Excel. This is almost always easier than copying values from the text output file. For example, make an XY plot with mineral saturation on the Y axis, select all the minerals, then go to Edit -> Copy in Gtplot. When you paste into Excel, you'll have a nice table of all your mineral saturation indices. For more information, please see 6.7, Exporting the plot, in the GWB Reaction Modeling Guide. To see a slideshow of how this works, please go to https://www.gwb.com/tutorials.php#USING_GWB and click on the "How do I retrieve numerical data from my plots?" tutorial. Finally, I noticed a pair of warning messages at the bottom of the Results pane. I'd be happy to take a look at them if you attach your script. Regards, Brian Farrell Aqueous Solutions LLC

Hi Denis, I think the only problem is that React doesn’t recognize your amorphsilica.txt file as a basic script file. Once you rename the file so it has a .bas extension, you can edit your React script to look for the updated file. Regards, Brian

Hi Denis, Thanks for attaching the React input and basic scripts. If your custom thermo dataset is too large to upload to the forum, can you please email it to support@gwb.com? You might use a text editor like Notepad or Notepad++ to write your basic script. When you're ready to save it, go to File - Save As, change the "Save as type" to "All Files", then give it a name like MyRateLawScript.bas. Or, you can open the folder containing your text file in Windows Explorer and right-click on the file, then click "Rename". Change the extension from ".txt" to ".bas". Hope this helps, Brian

Hello, Please provide your React script and custom rate law scripts (if they're separate files) so that we can take a look. Thanks, Brian Farrell Aqueous Solutions LLC

Hello BC, You can request a 30-day demo of GWB Professional at https://www.gwb.com/demo.php. Please be sure to mention that you are already a GWB Student Edition user, but you'd like to try out the React program. I hope you enjoy using the software. Regards, Brian Farrell Aqueous Solutions LLC

Hi Joel, We've fixed the problem. The fix will be available in the next maintenance release. Regards, Brian Farrell Aqueous Solutions LLC

Hi Clint, I’m happy to hear that you’re using the GWB again. The problem you’re having with units probably arises because you’re not including the mole weight and charge of your user-defined analytes. As far as I’m aware Total Organic Carbon is reported as the mass of carbon itself – no oxygen, hydrogen, etc are included. In that case, you’d just use 12.011 for the mole weight and 0 for the charge. Does that fix your problem? The built-in Chemical parameter carbonate alkalinity accounts for the HCO3- and CO3-- species in solution. I’m not sure exactly what data you have, but if your bicarbonate and carbonate alkalinity are the individual contributions of the HCO3- and CO3-- ions to a fluid’s total alkalinity, then you can add them together (remembering that CO3--can neutralize twice the acid of the HCO3-) to use for the GWB’s carbonate alkalinity. You can certainly add total alkalinity as a user-defined analyte. And if you want, you can also create separate user-defined bicarbonate alkalinity and user-defined carbonate alkalinity. Please keep in mind that the user-defined analytes are not used in calculations by the GWB. You use the Chemical parameters and the Basis and Redox species to specify the composition of your fluids for any calculations you wish to make, such as determining the concentrations of free species in solution, the fugacity of gases, and the saturation state of minerals. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hello, We have fixed the problem with saving heterogeneous mineral masses. The fix will be available in the next maintenance release. In the meantime, you might consider one of the other options for setting heterogeneity, such as an external Table dataset or an equation. Regards, Brian Farrell Aqueous Solutions LLC

Hello, Thanks for bringing the problem with heterogeneous mineral masses to our attention. We’re looking into it, but I’m pretty sure it has nothing to do with the machine you install the software on. If you send an email to support@gwb.com with your activation code we’ll be able to take care of your activation/ deactivation problem. You should check your current working directory for your results files. Our tutorials webpage has a short slideshow entitled “How do I manage results files?” that explains pretty well the types of output generated, where to find the output, and how to prevent older results from being overwritten by subsequent calculations. Regards, Brian Farrell Aqueous Solutions LLC

Hi Yiran, If you want an Eh-pH diagram, you should set H+ with pH units on the x axis. For the y axis, add O2(aq), swap it out for the e-, and set Eh units. For what you're doing, it's most common to just leave Fe++ as the diagram species and set the activity roughly equal to the molal concentration of Fe++. You'll likely have to suppress stable phases, such as Hematite, to allow a metastable mineral like lepidocrocite to form. Hope this helps, Brian

Hi Yiran, Since you mentioned you were interested in Eh-pH diagrams, I thought you were referring to selecting axes variables that indicate the oxidation state. The introductory section of the Using Act2 chapter in the GWB Essentials Guide illustrates how to set up various types of redox-pH diagrams, including those with log a O2(aq), log f O2(g), Eh, and log a Fe+++/a Fe++ axes. As you can see, they're all quite similar. From your last message, I believe you're referring to something else. Can you please clarify? Thanks, Brian

Hi Yiran, Even though dissolved oxygen might be so low as to be immeasurable in your fluid, O2(aq) activity is still a perfectly valid variable for thermodynamic calculations. If you don't want the program to write reactions in terms of O2(aq), though, you can simply swap it out of the basis. You might swap it out for a variety of species, such as O2(g), the e-, H2(aq), H2(g), or even activity ratios, such as Fe+++/Fe++. Then you'd constrain the activity, fugacity, Eh, pe, or activity ratio. Does this answer your question? As for your second question, you can suppress stable minerals or species that show up on the diagram in order to consider less stable species. To do so, go to the Config - Suppress... dialog in Act2. Within an Act2 run, you can also temporarily modify the log Ks of any reaction(s) by going to the Config - Alter log Ks dialog. For a more permanent solution, you can go into the thermo dataset that you're using and permanently modify the log Ks of any reaction(s), so that your new data will be used in any calculation that you make. And if you need to consider species that aren't in the thermo dataset you're using, you can add reactions and log Ks for your species of interest to the thermo dataset. The TEdit program is very useful for performing such modifications. To prevent confusion, it's always a good idea to save modified datasets with a unique filename, rather than overwriting the datasets we distribute. For more information, please see the suppress and alter commands in the GWB Reference Manual, as well as the TEdit section of the GWB Essentials Guide. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi Dino, After completing a calculation, React produces in its current working directory a text output file (React_output.txt) and a plot output file (React_plot.gtp). Going to the working directory and double-clicking on the former is equivalent to hitting "View Results" and double-clicking on the latter is equivalent to hitting "Plot Results". What happens if you go to the working directory (you should see the directory listed at the very top of React's window) and double-click the text file that's just been generated? Can you change the working directory (go to File - Working Directory and browse to some other folder, like the Desktop), rerun the example, and try to open the text results either by clicking "View Results" or double-clicking on the text file? If you're still having trouble, can you check the file association for .txt files? In Windows 10, find a text output file, right-click on it and select Properties, then look at the program specified after "Opens with". Typically this is Notepad by default. that app works well for the text output, but others, such as Notepad++, will work as well. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi, WordPad apparently limits you to a few file types when using the "Save as" option. Other editors, such as Notepad or Notepad++, let you choose "All files (*.*)" or "All types (*.*)", respectively, which will let you use the ".bas" extension. At any time, however, you can simply right-click on a ".txt" file in Windows Explorer , choose the "Rename" option, then change the file extension. Hope this helps. Brian Farrell Aqueous Solutions LLC

Hi John, You can adjust the number of steps reported in X1t and X2t simulations by using the dxplot command. The "dxplot" command sets the interval in reaction progress (which varies from zero to one in a simulation) between steps in the plot file. In X2t, "dxplot" defaults to a value of 0.1, so you have plot output at Xi = 0 (the start), 0.1 (one tenth of the way through the simulation), 0.2, 0.3, ... 1. Changing "dxplot" to 0.05, for example, would approximately double the number of steps reported in the plot file (0, 0.05, 0.1, 0.15, ... 1). For more information, please see 7.30 "dxplot" in the GWB Reference Manual. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi Dino, The original fluid (H+, SiO2, Na+) is a little weird in that there are no negatively charged components, so a run in which you enforce charge balance is a little tricky. Turning charge balance off to determine approximately how much Na+ would be needed to balance the excess negative charge in the system is a good first step. After that, one strategy is to swap H3SiO4- into the basis for SiO2(aq). Now, your basis includes H+, H3SiO4-, and Na+. An alternative is to swap OH- in for H+ and set the log activity of OH- instead of the pH. In this case your basis includes OH-, SiO2(aq), and Na+. Either way I arrive at the desired solution. As for the sliding activity path, this looks like a phase rule violation. In a sliding activity path, the species whose activity you're adjusting must be in the basis for the entirety of the reaction path. You're asking the impossible, though, when you slide the activity (or log activity) of a species up to the point where a mineral containing that species becomes saturated, and thus needs to be swapped into the basis if it's to precipitate. GWB11 gracefully issues an error 'Phase rule violation: Cannot precipitate supersaturated mineral "Amrph^silica"' and continues the simulation while preventing the mineral from precipitating (as if it's suppressed). Older releases, however, give the "Exit: React stop: passem: bad basloc call" error and crash when they reach this point. You can avoid the issue entirely by adding SiO2(aq) as a simple reactant rather than using a sliding activity path. As a simple reactant, you gradually titrate SiO2(aq) into the system over the course of the path. You're not forcing the SiO2(aq) activity to a certain value, so there's no requirement that SiO2(aq) remain in the basis when amorphous silica needs to be swapped in. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi, You'll first want to verify that the thermo dataset you're using contains all of the species that you're interested in. A quick look in TEdit at thermo.tdat, the default dataset, shows that ClO4- is indeed included (you can quickly filter the species list to show only those containing Cl). After you make your diagram with O2(g) (or some other measure of redox state) on one of the axes, you'll need to go to Plot -> Diagram and uncheck "water limits" to draw Cl- species above the upper stability limit for water. You may need to increase the range of your diagram to find the O2(g) fugacity in which ClO4- predominates. Hope this helps, Brian

Hi John, A distribution coefficient, or Kd, is simply the ratio under specific conditions of the sorbed to the dissolved mass of a contaminant. In other words, the Kd as originally described is an observation; it is determined from measurements at a specific field site or in an experiment. A field or lab-measured Kd is sometimes used in a predictive sense. In the “Kd approach”, you solve, for example, for the amount of an ion sorbed to mineral surfaces given the Kd value and information about how much of the ion is dissolved in the fluid. Such an approach can attempt to predict the retardation of an ion in flowing groundwater. In other words, the Kd is used here as input to a geochemical model. From your description, it sounds like you want a Kd that is valid for a certain environment (known granite composition, temperature, pressure, pH, Eh, etc.) to use in a predictive sense. Unfortunately, the Kd must be measured for the site; it cannot be calculated solely from information about the composition and temperature of the system. I have one final point that isn’t directly related to your question, but I should point it out in case you discover it while searching through the documentation. As I mentioned before, the GWB can create predictive models of sorption in geochemical environments. The predictive models need as input a measure Kd or measured constants for other surface models like the Freundlich or Langmuir isotherms, ion exchange model, or the two-layer surface complexation model (or some combination of multiple sorption models). Just like we can measure a Kd in a real environment, we can measure a Kd in a simulated environment, assuming we have completely described the mineral mass of the system. To have React calculate a Kd based upon the distribution of species and the mineral mass, go to the Config – Iteration dialog and check the “Kd” option. For more information, please see 6.51, Kd, in the GWB Reference Manual. Hope this helps, Brian Farrell Aqueous Solutions LLC

Dear GWB users, We are pleased to announce our latest maintenance release, GWB 11.0.7. The 11.0.7 update includes various improvements and fixes to GSS, especially the undo/redo, hide/expose, SmartMix, and move column/move row features; fixes crash bugs in Gtplot and TEdit; addresses several edge-case issues with sliding, fixed, and kinetic reactants; and resolves all known issues. Update from 11.0 - 11.0.6 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 Support tab of the GWB dashboard. Regards, Brian Farrell Aqueous Solutions

Hi Oleh, You can pick any 8 principal temperatures when creating a new thermo dataset. You cannot use any more than 8, however. Regards, Brian Farrell Aqueous Solutions LLC

Hi Gordon, Thanks for letting us know what release you're using. Prior to GWB11, you can't use a sliding Eh path without setting the Eh of the initial system. Since you're using GWB9, you might consider instead a sliding f O2(g) path, which is allowed. You could also set the initial Eh by swapping the e- in for O2(aq), but you'll run into another error unless you also set the initial pH (instead of the mass of the H+ component). I'd be a little careful with this option, though, because it's generally a good idea to not tinker with "picked up" calculation results, like those you have in your initial system. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi Gordon, Thanks for attaching the files. The commas in your spreadsheet are causing the problem. Remove those and you should be back in business. As for the “0” values, they’ll prevent SpecE8 from converging on a solution. Whether or not they get included in the launch depends on whether or not you check the ‘Treat zero values as “no data”’ option. By the way, I noticed that the basis entries in your spreadsheet are tagged as free constraints, meaning the concentrations you set are for the individual species rather than the total concentration (the mass of the thermodynamic component). For example, 96 free mg/l HCO3- means that you have 96 mg of HCO3- ion, plus an additional amount of CO2(aq), CO3--, NaHCO3, etc. The majority of lab analyses, however, provide bulk composition; the default setting in GSS and the other GWB apps reflect this. If you leave the free setting off, 96 mg/l HCO3- means the sum of all carbonate species sum to 96 mg. Just wanted to check whether this was appropriate for your analyses. Regards, Brian Farrell Aqueous Solutions LLC