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Brian Farrell

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  1. Hi Sebastian, There’s an example diagram in the React section of GWB.com/diagrams.php entitled Mineral solubility. You can click on the React icon to download the script. It sets a fluid in equilibrium with Kaolinite at pH 3, then scans all the way to pH 9. We’ve shown a plot of the species distribution in the fluid as a function of pH, but you could easily plot the Al+++ Component in the fluid (the sum of the dissolved Al+++ species) to see the total dissolved aluminum. It’ll look like a curve traced just above the highest concentration species at each pH. In this example, the mineral is least soluble at ~pH 5.4, and the solubility increases in either direction from there. You could easily make a similar diagram with a sliding temperature path to figure the effect of temperature on the solubility of an iron mineral. Of course, there are many factors that can control the solubility of minerals, such as pH, oxidation state, ionic strength, the presence of various complexing ligands in different concentrations, and temperature. React (or SpecE8) can calculate the solubility of a mineral in any fluid you specify, but not every fluid, at least in a single calculation. In other words, you can’t determine from a single reaction path the maximum solubility of a mineral considering every possible fluid composition. You can only find the maximum solubility subject to the prescribed conditions. React lets you consider one variable at a time, and Phase2 lets you consider two at a time. Hope this helps, Brian Farrell Aqueous Solutions
  2. Brian Farrell

    My License is disabled

    Hi Raquel, No worries. I'm glad to hear you're up and running now. Cheers, Brian
  3. Brian Farrell

    My License is disabled

    That error message indicates a reboot is required. It's not likely that the software will work in safe mode, though, so I'll return your license from my end so you can activate on your desktop. As for your desktop, you need to return to the GWB Activation Utility, select the block of text "Source: License File ..." and hit Delete. Then click New... and paste in your activation code (GUA12...) and hit Activate. Regards, Brian
  4. Hi, There might be a little wiggle room in how you define open or closed systems, but you should always be able to justify that the software settings you use match your conceptual model. At the most basic level, the program doesn’t add or remove mass unless you tell it to, so by default a simulation is closed. A very simple example of a closed system (with respect to mass) is a fluid that’s heated to determine the effect of temperature on species stability. No mass is added to or removed from the system, so it’s closed. In another example, a bioreactor is filled with oxygenated water, amended with a carbon substrate, and inoculated with aerobic microbes, then sealed off from the atmosphere with a stopper and left to sit for several days (the closed system simulation starts after the inoculation and feeding). The microbes will consume oxygen, causing its concentration in the fluid to decrease. Because it’s sealed, nothing is added or removed, so it’s a closed system. If that bioreactor is left open to the atmosphere, however, O2 will dissolve into the fluid as it’s consumed to maintain a constant fugacity. In the GWB, you’d use a fixed O2 fugacity path to define this type of open system. The program fixes the O2 fugacity at its original value by allowing gas to enter the fluid from an external reservoir (the atmosphere). Thus, it’s an open system. A configuration that depends on your concept of open vs. closed systems is a titration path. Imagine adding an acid to an alkaline fluid, to see how the pH changes. You might add HCl as a simple reactant. In this example, it seems like a pretty straightforward open system, since you’re gradually adding acid to a fluid. Alternatively, consider a water-rock system composed of halite and water. In our conceptual model, the halite is present in the solution, but it hasn’t reacted at all yet. You could add halite as a simple reactant to the fluid, so that’s its entire mass is gradually exposed to the fluid, or you could set a kinetic rate law, by which it dissolves at a certain rate that can change with time. You might conceptualize the “system” as being composed of the fluid and the rock, in this case, so that the system might be said to be closed. It can be helpful to plot the mass of various components in the fluid, the rock (all minerals), the sorbate, the system (all of the above) and so on. In GWB12, you can additionally plot the mass reacted for all types of reactants: simple, sliding, fixed, or kinetic. If the model includes a time span, you can additionally plot reaction rates for any type of reactant. It can be very useful to make plots of these as a function of reaction progress to help verify that your numerical model matches your conceptual model. In the future, please post new topics on the front page of the GWB forum, not in the archive of old posts. Regards, Brian Farrell Aqueous Solutions
  5. Hi Polly, Tact is for making stability diagrams, like those you’ve made in Act2, but with a temperature axis. In other words, Tact makes polythermal calculations while Act2 makes isothermal calculations. The diagrams you’ve shown from the report are isothermal calculations repeated at different temperatures. It looks like React was used to perform the solubility calculations you’ve shown in the report. You can use sliding and fixed activity paths to scan over a range of pe values, while holding pH constant, or to scan over pH values while holding pe constant. As you run these calculations, you should be aware of the stability range of water. If you start or end a calculation far outside the stability range, you may encounter concentrations that don’t seem to make much sense at first glance. It might be helpful to create rough calculations in Act2 to determine the pH or pe ranges where water is stable, and also where the minerals of interest are stable. There’s no point in setting up the React calculation far outside the mineral stability range, especially if you’re leaving the stability range of water. You can plot data from multiple React calculations together in a single plot by exporting the numerical values to Excel. You can also use the exported information to fill your table. For more information, please see 3.5 Buffered paths and 3.6 Sliding activity and fugacity in the GWB Reaction Modeling Guide. Please see as well 6.7 Exporting the plot in the same guide. Again, please post on the front page of the GWB forum, not in the archive of old posts. Regards, Brian
  6. Brian Farrell

    Temperature of Minteq database

    Hi Gustavo, A thermo dataset is a compilation of reactions with log K values at specific temperatures. You cannot simply change the temperature range without replacing the log K values. I'd recommend starting with one of the datasets that goes up to 300 C and adding the specific REE elements, species, and minerals that you need. The TEdit app will be useful for this. In the future, please post on the front page of the main GWB forum, not in the archive of old posts. Regards, Brian Farrell Aqueous Solutions
  7. Brian Farrell

    GWB for Mac

    Hi Jonah, The GWB runs under Windows 10, Windows 8 & 8.1, and Windows 7. You can also run the software on a Mac using virtualization software such as Parallels Desktop or using a dual boot configuration with a program like Boot Camp. Regards, Brian Farrell Aqueous Solutions LLC
  8. Brian Farrell

    My License is disabled

    Hi Raquel, We'll get this straightened out. Would you prefer to keep using the software on your laptop, or on the new desktop? The software doesn't appear to be deactivated from the laptop, so you'll need to actually deactivate it if you want to use it on the desktop. Can you please send a screenshot of the GWB Activation Utility and the GWB dashboard from the laptop, along with any error messages that you receive? Thanks, Brian Farrell Aqueous Solutions
  9. Hi Polly, Like I said, you need to use the “extrapolate” option to match your 80 C plot to the technical report. When set to 80 C, Act2 by default doesn’t load the UO2(OH)3- and UO2(OH)4-- species that you see in the report because they have log Ks only at 25 C. If you extrapolate these log K values to higher temperatures, Act2 will load them, and you’ll get the same diagram. Regards, Brian
  10. Hi Polly, The CO2 fugacity you specify should be unique for your particular calculation. Looking at the figure you’ve provided from the report, no species with carbon predominate, so I’m reasonably certain that’s not the missing link (in this type of calculation, at least). Act2’s Results pane (as well as the “Act2_output.txt” file that you can access by clicking “View Results” from the Plot pane) includes a list of all the species and minerals included in the calculation. If you look there, you’ll notice that UO2(OH)3- and UO2(OH)4--, which predominate in the upper right of the technical report’s diagram, but not yours, are missing. If you look in the thermo dataset, you’ll see they only have log K values specified at 25 C, so they won’t be considered in your 80 C calculation. Act2’s “extrapolate” function can be used to estimate log K values outside their known values. This can be quite dangerous, especially when only a single log K value is known, but I believe that’s what has been done in the report. For more information, please see the Thermo Datasets chapter in the GWB Reference Manual, as well as the extrapolate command in the GWB Command Reference. Regards, Brian Farrell Aqueous Solutions
  11. Brian Farrell

    Regarding activities of diagram species and the presence of anions

    Hi Polly, First, verify that the thermo dataset you’re using matches that used in the technical report. I think a huge difference is that the diagram depicted in the technical report is an example of a “mosaic diagram”. The complexing HCO3- ion, for example, might be allowed to speciate as a function of pH into CO2(aq) or CO3--. To accomplish this, the diagram is divided into several parts in which one of those forms of carbon predominates. Within each subdiagram, reactions are written in terms of the predominant form of the complexing ligand. You can recognize a mosaic diagram by its shape – the slope of the bounding line between a pair of species is normally constant, but in a mosaic diagram it might change abruptly. You can choose to speciate over the conditions of the x axis only (pH here), y axis only (pe), or both. You should check as well the redox coupling and choice of oxidation states in the diagrams. Your analysis specifies only N, not the valence of nitrogen species. Do you know whether all the nitrogen exists in one oxidation state, such as nitrate, or as several? If it’s only nitrate, for example, you would decouple the redox species NO3- from the basis species NH3(aq), then add NO3- (not NH3(aq). In this case, speciate over y would have no effect, because no coupling reactions are enabled for the ligand. You should consider your choice of redox coupling reactions together with the degree of speciation you specify for complexing ligands. Finally, you may need to suppress one or more species that are thermodynamically favored, but may have been excluded from the report. Perhaps the paper, or an appendix, reveals more information about the details of the calculation? For more information, please see 2.4 Redox couples and 5.3 Mosaic diagrams in the GWB Essentials Guide. For information on suppressing species, please see 3.54 Suppress in the GWB Command Reference, as well as the example in 6.2 Solubility diagrams in the GWB Essentials Guide. Please post on the front page of the GWB forum, not the archive of old posts. Regards, Brian Farrell Aqueous Solutions
  12. Brian Farrell

    questions regarding X1T and X2T

    Hi Jason, The potential drop across the length of the domain is the driving force for flow. The program uses it, along with the permeability and viscosity, to calculate flow according to Darcy’s law. A boundary might be open to flow, closed to flow (no flow), or water might be set to enter at a specified value of specific discharge. For more information, please see 2.14 Groundwater flow, 3.2 Setting flow rate, and 4.3 Calculating the flow field in the GWB Reactive Transport Modeling Guide. The program uses a correlation to calculate the log of permeability from the porosity, and optionally, the volume fraction of one or more minerals. Permeability is always a positive number. Log permeability, on the other hand, can be negative. For details of the correlation, please see 2.13 Permeability correlation in the same guide. If you’d like to set permeability directly, the porosity multiplier (A) should be set to 0. In your example, set B to 3.6987 mdarcy (the log of 5000). Yes, you can plot permeability in the x and y directions in Xtplot. It’s a good idea to verify that the permeability the program calculates is what you expect. You can use a combination of equilibrium and kinetic minerals, if necessary, to define the minerals that exist in your system. For a good example, see the Weathering and Steam examples in the Reactive Transport Modeling guide (3.8 Example: weathering in a soil profile and 3.11 Example: steam flood). In the future, please post on the main GWB forum (the front page), not the archive of old posts. Regards, Brian Farrell Aqueous Solutions LLC
  13. Brian Farrell

    Question for using GWB

    Hi, Can you explain more how you'd like to use these compounds? What is the conceptual model for your chemical system? If you want to see the effects of titrating a base like NaOH into an acidic fluid, for example, you don't need to add NaOH specifically. You can equivalently add Na+ and OH- as simple reactants, because the only property of a simple reactant that matters is its composition. For more information, please see 3.1 Titration paths in the GWB Reaction Modeling Guide. More generally, there are a variety of thermo datasets installed with the GWB, so you might try loading a different thermo dataset. Additionally, the species, minerals, and gases included in thermo datasets are fully editable. You can add new reactions to the GWB's datasets if they're missing something that you need. For more information, please see 2.3 Thermodynamic datasets and 9 Using TEdit in the GWB Essentials Guide, as well as the Thermo Datasets chapter in the GWB Reference Manual. Hope this helps, Brian Farrell Aqueous Solutions LLC
  14. Brian Farrell

    X2t query

    Hi Sam, The inlet fluids don’t infiltrate very far into your domain over the timescale of your simulation, let alone by the first step in the plot file. You can plot “pore volumes displaced” or add a conservative tracer to verify this. And looking at the Q/K for Hydroxyapatite, I don’t think it ever gets undersaturated in most of the domain, it just approaches equilibrium – a log Q/K of ~0. The Hydroxyapatite is supersaturated in the initial porewater, and I think it’s just precipitating really quickly, and thus approaching equilibrium very quickly. The undersaturated inlet fluid doesn’t really come into play here. I think it would be a lot easier to troubleshoot a scenario like this with a 1D model in X1t, or even a flush model in React. Hope this helps, Brian Farrell Aqueous Solutions
  15. Hi Abdulaziz, As Melika stated in response to your question, you set the length of a spherical domain with the values of r1 and r2. For example, setting r1 to 1 cm and r2 to 6 cm will prescribe a spherical domain that’s 5 cm long. Such a configuration would not be appropriate for a cylindrical column, however, because the domain’s width is expanding, as you can see in the graphic in X1t’s Domain pane. You could "hack" the model by setting r1 and r2 so that they are very large, like 1001 cm and 1006 cm, thus defining a domain of the same length, but with a geometry much closer to a cylinder. This really defeats the purpose of using a spherical model, however. I'm only saying this so you get an understanding of how the two radius values are used to define the geometry of a spherical domain. For your model, I recommend just using a linear 1D model. In that case, you set the length to 5cm, and you can choose values of deltay and deltaz that will give you the same cross-sectional area as your cylindrical column. You have several options to set the flow field. You can set specific discharge directly. You can solve for the specific discharge by setting a hydraulic potential or hydraulic head drop across the domain, along with the permeability, in which case the program uses Darcy’s law to solve for specific discharge. Alternatively, you can tell the program how much of the initial pore water should be displaced in the time specific for the simulation (the pore volumes option). The specific discharge is a volume flux, with units such as cm3/cm2/s. So, it’s the volume of water passing a cross-sectional area per unit time. You’ll notice that the discharge units can be simplified to velocity units, such as cm/s. The two sets of units can be used interchangeably here. It’s important to keep in mind that the specific discharge is not the groundwater velocity, because water molecules only move through pore space within the column. The velocity is the specific discharge divided by the porosity. You can divide your experimental flowrate by the cross-sectional area of the column to get the specific discharge. Alternatively, you can determine from your injection rate how many times the volume of fluid in your column (the total volume x the porosity) was displaced over the length of your experiment, then set that value for pore_volumes. It’s hard to say for sure, but I doubt you’ll be able to figure a diffusion coefficient from an experiment with such a high flowrate, and with data only at the outlet. When water flows at any appreciable rate, the effects of diffusion are insignificant compare to advection and hydrodynamic dispersion. As a result, changing the value of the diffusion coefficient won’t affect your results in any noticeable way. For that same reason, specifying a precise value for a diffusion coefficient is only useful in modeling systems with little or no flow. I think an experiment without reaction or flow, and with multiple sampling points at multiple times, would be ideal for determining a diffusion coefficient. The rate constant, on the other hand, could possibly be calculated, but it really depends on your experimental setup. Most commonly rate constants are determined in simple batch systems. You’re adding complexity by trying to derive it from a column experiment. For more information, please see sections 3.1 and 3.1 in the GWB Reactive Transport Modeling Guide. Regards, Brian Farrell Aqueous Solutions