Dear Researchers,
I want to calculate the saturation index or ratio of galena in high saline solution (20%NaCl). As the ionic strength is high. Would you please guide me which database of geochemist's workbench should I use? the Pitzer data base does not have galena so what can I do?
thermo.tdat or thermo_minteq.tdat or thermo_wateq4f.tdat or thermo_pitzer.tdat
Regards,
Taher
for calculating saturation indices you can use phreeqc software for windows and apply Pitzer aqueous model for solutions with very high ion strength, or specific ion interaction model for solutions with high ion strength.
Hi, Thanks for your comment. But Pitzer database of Phreeqc does not have Galena. Do you know how I can enter galena to the phreeqc database?
Adding species to the database is quite straightforward:
http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/phreeqc3-html/phreeqc3-30.htm
finding the Pitzer parameters for the species you need will be harder
Thanks. would you please guide me what parameters I need to find?
Sorry for asking. I am new in geochemistry modelling calculations.
Basically the ones in lines 1-19 of the second example on that page.
I don't know if you'll find them. If I remember correctly those are calculated from experimentally determined osmotic coefficients. This is a rigorous task, due to the many parameters involved and the difficulty to set up such experiments for certain species. You need to look for publications that calculated/measured the interaction terms for all the species you consider in your model. I never worked on Pb and S systems, so can't tell you were to look.
For galena in 20wt% NaCl, I think specific interaction theory might give you a fair approach. The sit.dat database has galena in it, and I seem to remember that SIT is a reasonable approach up to salinities of 10M.
Maybe someone more experienced with high salinities can add to this.
regards,
Pieter
The database you would like to use depends strongly on the modelling task. For example, in case of modelling CO2 storage in a deep saline aquifer our study revealed, that using the pitzer.dat database did not result in better results (Haase et al. 2013, http://www.sciencedirect.com/science/article/pii/S0883292713000656). But this is only one example. The suitable database that should be used depends on the modelling task.
Could you tell us the ionic strength on a molality basis (not calculated by a numerical code)?
In my opinion, it would be useful to calculate the entire model using all possible thermodynamic databases (at least of the used numerical code, in your case The Geochemist's Workbench). If it is not possible to use all thermodynamic databases, you should calculate at least i.e. the saturation indices of the initial solution for the relevant minerals and compare them. Or you can select another parameter, which seems essential for your model.
Regards,
Christoph
Look at Duan et al. : Accurate Thermodynamic Model for the Calculation of H2S
Solubility in Pure Water and Brines.
in Energy & Fuels 2007, v21, 2056-2065.
They give a set of Pitzer parameters relevant to PbS solubility in brines.
Yours
Thermodynamic data can be found here:
http://www.sciencedirect.com/science/article/pii/0016703788903535
But implementation is not straightforward as you will need to account for H2S speciation and Pb-chloride complexation as well. Data for the latter can be found in
http://www.grs.de/sites/default/files/pdf/GRS-219.pdf
(german only).
At any rate you should compare your model calculations with one the sources given above.
Helge
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