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Polly Tsai

Regarding UO2 (uraninite) mineral solubility chart at temperatures of 25, 32 and 80C and under constant pH or pe conditions using Tact

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Dear Brian,

I would like to plot the uraninite (UO2) solubility chart with the function of pH or pe at temperatures of 25, 32 and 80°C, just like the examples in Figs. 1 and 2 captured in the technical report. When the plots have been done, the raw data should be summarized in the Table 1. Please refer to the attachment. Should I use the Tact module to perform them? Please also refer to the script of Tact.

 

Thanks for your kind instruction.

 

Best regards,

Polly

Regarding mineral solubility calculation_to Brian 20190609.docx

Solubility of uraninite.tac

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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
 

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Dear Brian,

Thanks for your instruction.  Based on your previous reply, the calculation result of UO2 solubility and input parameters (i.e., field data) of the groundwater conditions were shown in the attached script of React module. However, I still have the following questions.

1. The total concentration of uranium is 9.923e-07 M at the bottom of view results. Is it also a solubility value?

2. I can not see the trend chart of solubility v.s pH or pe (examples of Figs.1 and 2 in the word file) in this case.

3. The result seems significant difference, 9.923e-07 M for UO2 compared to the table 1 in the attached word file.

Could you please let me know what's wrong in this case?

Thanks for your further response.

 

Polly

UO2 solubility_32C.rea

Regarding mineral solubility calculation_to Brian 20190609.docx

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Hi Polly,

You asked me in another post if certain values were arbitrary, like a CO2 fugacity or the activity of a main species in an activity diagram. I responded that they were not. I didn’t say that you should always include a complete analysis of your fluid in all your calculations, especially for general diagrams like those in the report. As you might recall, I told you I didn’t believe a value for CO2 fugacity was even required to reproduce a particular diagram from your report. I really can’t say for sure how the rest of the diagrams in the report were constructed. You really need to consult the authors for that information. I can’t keep guessing.

As for your latest questions:

1.    Each of these calculations are done at many steps (many pe values, or many pH values). The information you see at the bottom of React’s text output file is simply output from the last step in the calculation. The information in the table you’re referencing is simply information drawn from various points in different calculations. You need to look in your output files (text or plot) for the specific conditions to fill each cell in the table. 

2.    Figures 1 and 2 are from two different types of React calculations. Figure 1 is a from a sliding pe path in React, with pH fixed at 8.6. I believe there is a unique calculation for each mineral, but I’m not sure. It is repeated at two different temperatures. So, I think it’s created from eight different simulations. Figure 2 is from a sliding pH path in React, with pe fixed at -5.73. Like Figure 1, there are four minerals and two temperatures, so possibly eight different simulations. You can use Gtplot to make plots like those you’ve shown.

In your script, you added Uraninite as a simple Reactant. You shouldn’t do that. It’s common to swap the mineral of interest into the Basis (the initial system) in diagrams like this, as described in below. You of course need to ensure that other minerals don’t precipitate later in its place. There’s an example solubility 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 we could have alternatively plotted 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. You could easily make similar calculations to figure the solubility of your minerals as a function of pH or pe.

3.    Your calculation doesn’t look correct at the moment. When you do get it set up, you’ll need to make sure you retrieve the information from the correct points.

Regards,
Brian

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