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Polly Tsai

Regarding solubility calculation using REACT module of GWB

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Dear Brian,

Recently, I calculated the solubility limits of nuclides and compared the results with simple function of Excel by SKB. However, there was a significant difference (~3 orders) for Se (selenium). Please refer to the ppt file (Solubility calculation_20191022). The species and chemical reactions with log k values (25C) in the Excel file (simple functions_atrisk_goethite_magnetite_temperate_fix_GW_110209, please refer to the link: https://drive.google.com/open?id=1ZoDivTdFTa7RzS1I1-SHCXzBM4_r9Kas) that I used and I also edited all of them in the thermo data file using Phreeqc template of TEdit. Please refer to the file (thermo_phreeqc_Polly). The script of React module was also attached and please refer to the file (U, Sr, Pa, Zr, Nb, Ra,Tc, Ni, Pd, Sn, Se, Th, Np, Pu, Am, Cm, Pb solubility_25C_SKB.rea). The overall calculation results were summarized compared with SKB (simple function) in the ppt file (Solubility calculation_20191022). The value marked as red color indicated “Big difference” and the values marked as blue color meant 2-3 folds difference between GWB (INER) and Simple function (SKB). I don’t know why there were some differences between them even I used the same thermo database as SKB. In addition, in the basis pane, why very trace amount of nuclide concentrations need to be input in the initial condition? The water compositions in the initial conditions were used as input parameters by following the SKB data (in the DON’T TOUCH spreadsheet of Excel file) and the reactants were selected using amorphous solid phases shown as blue color of solubility limits in each element spreadsheet of Excel file.

 

 

Thanks for your kind response to answer my questions in advance!!

 

 

Polly

Solubility calculation_20191022.pptx thermo_phreeqc_Polly.lnk U, Sr, Pa, Zr, Nb, Ra,Tc, Ni, Pd, Sn, Se, Th, Np, Pu, Am,Cm, Pb solubility_25C_SKB.rea

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Hi Polly,

You attached a .lnk file (a shortcut), not your actual GWB thermo dataset, which should be a .tdat file. For one thing, you should check to ensure that your dataset and your spreadsheet are using the same exact set of reactions and log K values. 

I looked at how you set up your script, but I couldn’t run it because I don’t have the thermo dataset. In any case, it doesn’t look like you took my advice. Can you explain why you’ve set your calculation up with trace quantities of all your basis entries, then titrated large amounts of all your minerals of interest? 

As I mentioned before, a common way to find solubility is to swap your mineral of interest into the basis, then find the total dissolved concentration of the constituent of interest. In my example to find the solubility of Kaolinite, the mineral was swapped into the basis and the concentration of the Al+++ component in the fluid was determined. The sliding pH part is a convenient method to make a type of solubility diagram, to see how the solubility changes with pH, but if you don’t care about that part, you can certainly omit it to look at solubility under a single condition – your groundwater of interest. 

I would repeat the calculation for each mineral of interest. Swap a mineral like Pd(OH)2(s) into the basis in place of Pd++, but use the measured concentrations for all of your other ions.  Find the total concentration of Pd++ in the fluid in equilibrium with your Pd(OH2(s). Then move on to SnO2(am), swapping that for Sn++++ but leaving all the other ions, like Pd++, at their measured values. It’s likely that your spreadsheet is performing a series of calculations, so I think you need to do the same.

As I also mentioned, you need to look at the output and ensure that your mineral of interest is still present in equilibrium with the fluid. If you swap amorphous silica into the basis to find its solubility, React will precipitate quartz, which is more thermodynamically stable, unless you suppress it or disable precipitation entirely. If you don’t, you’d actually be finding the solubility of quartz, which is lower than the amorphous silica, so it’s important to check your output carefully and adjust your input as necessary. 

Regards,

Brian Farrell
Aqueous Solutions LLC


 

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Dear Brian,

 

Thanks for your kind response. I have already saved as a .tdat file in replace of .lnk file (a shortcut). Please refer to the attachment. Yes, I also ensured that the dataset and spreadsheet were using the same exact set of reactions and log K values.

 

Can you explain why you’ve set your calculation up with trace quantities of all your basis entries, then titrated large amounts of all your minerals of interest? à The trace quantities of radionuclides need to be input in the dialog box as reminder before calculation. Actually, the concentrations of radionuclides within the spent nuclear fuels are quite low in case of copper canister corrosion resulted from the groundwater intrusion. The input values in the basis entries were just hypothetical and indicated very low concentrations of nuclides and “0 (zero)” value was not allowed for solubility calculation.

Thanks for your further understanding.

 

 

Best regards,

 

Polly

thermo_phreeqc_Polly.tdat

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Hi Polly,

Thanks for providing the thermo dataset. I'm taking a look to see if I can offer any suggestions.

Regards,

Brian

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