Jia Wang

Dear GWB users, We are pleased to announce our latest maintenance release, GWB 12.0.5. The 12.0.5 update features an important update to Flexera license manager, better user and administrator support for network floating licenses, Python 3 support for the GWB Plugin feature (ChemPlugin already supported Python 3), better ability of the time marching apps to back up and recover convergence failure, tracking and reporting of the number of pore volumes displaced in React, fixes for tab-completion feature in Command pane, and resolution of all known issues arising since the GWB 12.0.4 release. Update from 12.0.0-12.0.4 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, Jia Wang Aqueous Solutions

Dear Usman, The Durov diagram currently cannot be modified to include alternate axes variables, such as Fe concentration. You can alternatively try to use one of the other diagrams such as Ternary, Stiff, or Bar graph. In these types of diagrams, you can select the species on each axis. Please refer to section 3.6 of the Essential Guide for information on plotting your data. To create diagrams with activity ratios as the axis variable, you would simply swap an activity ratio into the basis as described in section 5.1-5.2 in the GWB Essentials Guide. The procedure is essentially the same for K+/H+, Ca++/H+^2, and Mg++/H+^2. You can overlay your data points in GSS data sheet to the Activity diagram. Go to 'File' --> 'Open' --> 'Scatter Data' and select the GSS file with your data. Act2 diagrams are plotted in terms of species’ activities and fugacities, not chemical concentrations. You can calculate activities of your species in GSS directly or supply values as user defined analytes. Please refer for section 5.6 of the GWB Essentials Guide for more information on Scatter Data and section 3.3.4 for Calculated values. Hope this helps. Best, Jia

Dear Misato, I would recommend using the ‘script’ or ‘script file’ option for setting the nucleus density rather than an ‘equation’. Using a script or script file would allow you to set 10 [cm2/cm3] if Time is less than 3000000 seconds and after that, the equation desired. It would look something like this: IF Time < 3000000 THEN 20 ELSE 40 20: nucleus = 10 GOTO 60 40: nucleus = 10*(1/2)^((Time-3e6)/150000) 60: RETURN nucleus As you’ve done, you need to check the “transient” option to evaluate the variable at each time step. Please refer to section 5.2 of the GWB Reaction Modeling Guide and the Heterogeneity Appendix to the GWB Reactive Transport Modeling Guide for more information. Please note that the nucleus density option prescribes a minimum value for a supersaturated mineral’s surface area over the calculation. The program calculates the actual surface area from the mineral’s current mass and specific surface area and uses this whenever it exceeds the nucleus density. Best, Jia Wang

Hello Jeonghwan, Thank you for attaching your script. Suppress is a very useful feature to allow for less thermodynamically favorable minerals or species to form in your system by suppressing the more stable minerals from forming. React consider all minerals available from the database when making calculations unless otherwise specified. You can refer to the GWB Command Guide and the Reaction Modeling guide to learn more about this feature. With regards to your first question, you can certainly suppress AlO2- in your model but does this make sense in the context of the system you’re modeling and your field observations? I am not sure what your system is so it is difficult to determine what would be the most appropriate to suppress. Perhaps your field data will help to give you some suggestions with regards to what is appropriate for suppressing? I also noticed that you have unchecked precipitation in REACT0928.rea. This restricts minerals from precipitating even when they are supersaturated. Is this a constraint you meant to set? As for your second question, I think you mean to ask if your model has a pH of 8.3 at equilibrium? In simple reaction paths, where one or more reactants are gradually added to the system is called a “titration path”. The system’s equilibrium state is calculated as it steps forward in reaction progress. So React actually calculates the equilibrium state of your reaction at every time step. You can refer to chapter 3.1 “Titration paths” for more information. Hope this helps. Best Regards, Jia Wang

Hello Jeonghwan, Thank you for attaching your script. I have looked at your script and noticed a couple of things that might help explain why the pH decreases initially. If you look at the primary dissolution of Montmor-Ca with its default species using Rxn, then you do indeed expect the reaction to consume H+ and consequently for the pH to increase. However, in your React model, the output text file shows that the pre-dominant Al species is AlO2-. When you swap the Al+++ species with AlO2- and recalculate the reaction for Montmor-Ca dissolution in Rxn, you will see H+ is on the right hand side of the equation and thus indicating the production of H+ in your system. Additionally, other minerals precipitating in your React model might also influence the consumption or the production of H+ in your system. For example, you can see that the initial system is saturated with respect to Talc and precipitates in React’s calculation. (For more information about React’s treatment of the initial system , please refer to section 2.3 in the GWB Reaction Modeling Guide.) If you return to the Rxn application, you can balance the reaction with Talc using the predominant species in fluid and see that the precipitation of Talc will increase H+ in solution. Your model subsequently precipitates other minerals such as Diaspore, Saponite-Ca, Stilbite, etc with the addition of Montmor-Ca. I would suggest you check whether the precipitation of these minerals is consuming or producing H+ using Rxn as mentioned above. This will most definitely influence the pH of your system. Lastly, it is rare to constrain the initial H+ concentration in mg/kg. Did you get this from a calculation? Perhaps check if the pH of your field measurements matches with what you entered for the H+ constraint? Hope this helps. Best regards, Jia Wang

Hello Jeonghwan, Here are a couple of suggestions to get you started. You might want to consider checking the equilibrium constants (Log Ks) in the existing database for the minerals of interest against the values used in the Garrels 1984 publication. To do so, use the TEdit app to open the database, in your case it would thermo.com.V8.R6+.tdat, and check the Log K values corresponding to each mineral. You can simply edit the thermo dataset in TEdit to match the values used in literature or make a duplicate to preserve the original values. After you have checked the equilibrium constants in the database, you might also want to try suppressing all minerals except for the ones in the targeted activity diagram so that less stable phases are considered. Hope this helps. Best, Jia Wang

Dear Christophe, The green and the blue lines are from two separate X1t simulations. The blue lines in the plot of your screenshot is the result of Pulse.x1t from the mass transport section, where Pb++ is a non-reacting solute because the change in concentration is not associated with any chemical reactions. To attain the numerical data for this simulation, you can simply run the Pulse.x1t example without sorption. You can view the mass transport section (linked above) for more details. Then plot Pb++ (mmol/kg) on the y-axis and distant along the x-axis. Simply click Edit --> Copy as --> Spreadsheet and the paste the data in an excel spreadsheet. In the case of the green line, the simulation is accounting for sorption of Pb++. In this case, I think you’re referring to the sorbed particulate as the amount of Pb++ that is sorbed based on the distribution coefficient Kd from the database. Therefore, the particulate in solution would be the Pb++ remaining in the dissolved phase. Hope this helps. Best, Jia Wang

Dear Christophe, The maximum sorbed capacity for each metal is calculated outside of React. From Gtplot or the text output file of the simulation, you can see that there are 0.89 mmoles of Fe(OH)3ppd precipitated. Then in the surface dataset (FeOH+.sdat) you can find the sorbing density, which is 0.005 mol of strong sites and 0.2 mol of weak sites per mole of Fe(OH)3ppd. Then you look at each metal and see if they sorb onto weak, strong, or weak and strong sites. To calculate the maximum capacity for each metal, assume that there is only one metal sorbing to the mineral surface at a time. Just multiply the mineral mass by the site density of each appropriate site and convert to mg/kg. For As(OH)4-, it's 0.00089 mol/kg * .2 mol sites/mol * 142.951 g/mol * 1000 g/kg = 25.4 mg/kg. For metals that include strong sites, include those as well. The ‘in solution’ component concentrations are reported directly by React under ‘Components in fluid’. You can select to plot ‘Components in fluid’ vs. pH in the XY Plot Configuration dialog in Gtplot and export the numerical data using the method described in my previous response. Alternatively, you can also open the text output file and look for the concentrations of the desired components at each time step listed under ‘Original basis’ text block in the column ‘in fluid’. Hope this helps. Best, Jia Wang

Dear Christophe, In the React app, the results file output a dataset in tabular form. You can scroll down and see the concentrations of various basis species sorbed and in fluid and more information(e.g. mineral saturation state, reactants, gasses, etc..) at each reaction step. However, another way to retrieve numerical data is to use Gtplot and copy and paste the data onto an excel spreadsheet. You can select ‘Plot Results’ in the Results pane and Gtplot will open up. Double-click in the plot to open the XY Plot Configuration dialog. Select the desired X and Y axis parameters and click apply to modify the plot. For example, you can plot one or many components in fluid as the Y-Axis parameter and Rxn progress on the X-Axis. To obtain numerical data for this data, you can click Edit --> Copy as --> Spreadsheet and the paste the data in an excel spreadsheet. For more detailed instructions, you can refer to the ‘How do I retrieve numerical data from my plots?’ on the GWB Tutorials webpage and section 6.7 in the GWB Reaction Modeling Guide. The number of moles regarding strongly and weakly binding surfaces refers to the sorption site density available on the sorbing mineral. In this case, for every mole of ferric hydroxide precipitated, there is 0.005 moles of strongly binding surface sites and 0.2 moles of weakly binding surface sites available. Hope this helps. Best, Jia Wang

Hi Christophe, You can most certainly change the species for charge balancing. To change to a different species, add the species into the basis pane and in the drop arrow next to the units and select ‘Balance species’. Typically, the balance species chosen has high abundance and low uncertainty. For example, React is setup to use Cl- as the default charge balancing ion since most Cl- is usually abundant and can be calculated from charge balance base on other species concentrations measured in chemical analyses. Hope this helps, Jia Wang

Dear Koitoliver, In the screenshot you provided, the analyte HCO3- is already added to the spreadsheet and therefore you cannot add it again when you select “+ analyte”. The hardness of the fluid sample is a result of calculation; it cannot be used as a constraint. Only the HCO3- concentration (typically the HCO3- component, but you can alternatively constrain the free HCO3- ion) or the carbonate alkalinity can be used as constraints. I quickly did a charge balance calculation with a few of your samples and I am seeing slightly different results from your calculations. The charge imbalance error from my quick calculation did not match the value in your row 1 sample calculation. However, my calculations for the row 19 and row 20 samples did match with your charge imbalance error result. This leads me to believe something is missing (such as a HCO3- constraint) and you haven’t recalculated your analytes for the first group of samples after changing the spreadsheet. To recalculate right click on the charge imbalance column header and select ‘Recalculate Analyte’. Again, is it possible you had HCO3- values entered previously on your old spreadsheet? Maybe the values were accidentally deleted? Did you switch from a different thermo dataset from when you reopened the spreadsheet? The thermo_phreeqc.tdat dataset uses carbonate (CO3--) as a basis species instead of bicarbonate (HCO3-). If you did not allow the substitution of CO3-- for HCO3- when you switched thermo datasets then it will delete the HCO3- component’s column. That could also explain why you can’t find HCO3- in the list of basis entries. With regards to pH, the new GSS spreadsheet defaults to include pH as one of the analytes when a new spreadsheet is created. If it’s already in your spreadsheet, you won’t be able to add it again. Perhaps you hid the analyte? Under the Data menu, you have the option to hide and show analytes or samples. Please try check your spreadsheet according to the suggestions above. If you need further assistance, please attach your script. Best, Jia Wang Aqueous Solutions LLC