Helge
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Posts posted by Helge
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Hi Brian,
I will be glad to provide you with a polythermal parameter file for GWB, may be next week. Please note that this file will be untested (of course), but you can compare with the results from the benchmark documents when you validate your code for the new temperature function.
Regards,
Helge
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I would like to announce that in the mean time two packages of data were released from the Thermodynamic Reference Database project in Germany (THEREDA). Each package comes with ready-to-use parameter files and with benchmark documents which contain representative test cases including scripts and input files for the tested codes. The data are available free of charge at www.thereda.de.
The second release of data from the THEREDA database (R-02) was issued just before last christmas (2011-12-23) and came with parameter files for the system Na,Mg,Ca,Cl - Am(III), Nd(III), Cm(III) - H2O.
Valid range of temperature: 298.15 K
Supported codes: CHEMAPP, PHREEQC, Geochemist's Workbench
The data have been rigorously tested for simple, ternary subsystems only:
[NaCl or MgCl2 or CaCl2] - [Am(III) or Nd(III) or Cm(III)] - H2O.
This implies that for calculations in higher component systems no quantitative measure for the description quality can be given and no warranty can be accepted for computational results.
As to interactions between Am, Cm, and Nd (R-02) and SO4 or carbonate, data are available but still subject of internal control in the THEREDA-team and can therefore not be released yet.
The responsibility of the data for Am(III), Nd(III), and Cm(III) lies with C. Marquardt from KIT-INE.
On the 21st of February new data were released. This release was denoted as third release (R-03). The new release of data from the THEREDA database came with parameter files for the system Na, Mg, Ca, K - Cl, SO4 - HCO3/CO2(g) - H2O.
Valid range of temperature: 298.15 K
Supported codes: CHEMAPP, PHREEQC, Geochemist's Workbench, EQ3/6 (Version 8.0a)
The data have been rigorously tested for simple, ternary subsystems only, as described in the respective benchmark document. This implies that for calculations in higher component systems no quantitative measure for the description quality can be given and no warranty can be accepted for computational results.
Although no example is given in the benchmark document which contains MgCl2 or MgSO4, agreement between our results and those obtained with the HMW84 database was verified for the solubility of CO2(g) or Nesquehonite in MgCl2 and MgSO4 solutions.
The responsibility of the data in R-03 lies with W. Voigt from TUBAF.
Consistency with earlier releases: the released data are consistent with those for the system of oceanic salts (R-01), calculated for 298.15 K. Thus, with the new parameter files, calculations from the first release (R-01) for 298.15 K can be reproduced.
The first release (R-01) covered the system of oceanic salts (excluding carbonate/CO2) for temperatures between 273.15 and 393.15 K, depending on the particular system. However, this release has not been opened for Geochemist's Workbench yet. For the temperature dependence of equilibrium constants THEREDA uses the expression:
log10(K) = A1 + A2T + A3/T + A4log10(T) + A5/T^2 + A6T^2
For the temperature dependence of Pitzer interaction coefficients THEREDA uses the expression
P = A0 + A1*(1/TK - 1/TR) + A2log(TK/TR) + A3*(TK-TR) + A4*(TK*TK - TR*TR) + A5*(1/(TK*TK) - 1/(TR*TR))
The terms A6T^2 and A5*(1/(TK*TK) - 1/(TR*TR)) are not available with Geochemist's Workbench. The THEREDA team intends to downgrade the first release for GWB users to calculations for 298.15 K only. However, calculations for other temperatures can only be performed with the other supported codes (PHREEQC, CHEMAPP, EQ3/6). This issue had been discussed with Tom who forwarded our request to the developers of GWB about 2010-06-01.
If any questions arise as to the new data, please don't hesitate to initiate a thread in our discussion forum:
http://www.thereda.de > Forum
On behalf of the THEREDA management board
Helge C. Moog
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There is something strange about your diagram. In the medium pH-range, moving from reduced to oxidized conditions, you calculate the predominance of Uranite (UO2, U+IV), then UO2.25 and UO2.333 (both of which are questionable in aqueous equilibrium systems anyway and which represent more oxidized forms of uranium), and then again Soddyite, which is (UO2)2(SiO4)•2 H2O(cr): that is again U+IV phase! This seems to me a hint for a serious bug in your database.
Apart from that you should avoid calculating with uranium phases which contain mole numbers of oxygen which cannot be summed to whole numbers. Depending on the intial boundary conditions issued to GWB, you force the program to introduce charge inbalances by violating the mass balance. Thus, UO2.333 should be transformed to U3O7 (while three times UO2.333 gives U3O6.999 !).
Cheers,
Helge
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Pitzer parameters for iron may be obtained from
(x) Moog, H. C.; Hagemann, S.; Rumyantsev, A. (2004): Isopiestic Investigation of the Systems FeCl2 - (Na, K, Mg, Ca) - Cl - H2O at 298.15 K, Z. Physikal. Chemie 218, 1063-1087.
(x) Rumyantsev, A.;Hagemann, S.; Moog, H. C. (2004): Isopiestic Investigation of the Systems Fe2(SO4)3 - H2SO4 - H2O, FeCl3 - H2O, and Fe(III) - (Na, K, Mg, Ca)Cln – H2O at 298.15 K, Z. Physikal. Chemie 218, 1089-1127.
(x) Moog, H. C.; Hagemann, S. (2004): Thermodynamische Modellierung hochsalinarer Lösungen: Gewinnung von Daten für Fe(II), Fe(III) und S(-II) und Entwicklung eines Programms zur Modellierung des reaktiven Stofftransports im Nahfeld eines Endlagers, GRS-195, Abschlußbericht zu einem aus Mitteln des Bundesministeriums für Wirtschaft und Technologie (BMWA) geförderten Vorhaben, Fördernummer 02 E 9138 4, ISBN 3-931995-63-1, 224 Seiten.
The last one contains a comprehensive set for the whole system of oceanic salts, while the first two refer to chloride systems only. A publication in a peer-reviewed journal is in preparation. Implementation in THEREDA is envisaged.
Regards,
Helge
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To my best knowledge: No.
However, if you are interested in Pitzer databases formatted for GWB, look out for www.thereda.de
Regards,
Helge
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The O2 data is normally the same as the values in the gases section, but does not need to be.
If not, the parameter file is inconsistent.
To us it means that we have to enter precisely the same data in both sections, even though GWB doesn't require this.
Thank you for having made this clear.
Regards,
Helge
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First note that the GWB v8 Reference manual (p. 248) says that of the O2(g), H2(g) and N2(g) solubility equations in the header file of thermo.dat, only the values for O2(g) are currently used. I'm not exactly sure how (I will find out), but note that the equilibrium constants for O2(g) in the header file:
* log k for o2 gas solubility
-2.6610 -2.8990 -3.0580 -3.1250
-3.0630 -2.9140 -2.6600 -2.4100
..are exactly the same as the constants for the O2(g) reaction in the Gases section:
O2(g)
mole wt.= 31.9988 g
1 species in reaction
1.000 O2(aq)
-2.6610 -2.8990 -3.0580 -3.1250
-3.0630 -2.9140 -2.6600 -2.4100
The latter is based on the mass action equation for the reaction: O2(g) = O2(aq)
Given the case, that in the lower block other data for solubility are entered than in the upper block: which data are used by GWB?
Regards,
Helge
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Hello,
is it possible to have H2(g) as basis species in the parameterfile? From what we have it appears, that aqueous species only are permitted as basis species.
Background is that in our database redox reactions are defined in terms of H2(g) instead of with O2(aq).
Regards,
Helge
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For some ideas about how to improve your database you may want to read this:
http://www.netl.doe.gov/publications/proceedings/05/carbon-seq/Tech%20Session%20Paper%20101.pdf
Water chemistry can be easily deduced from your mineralogical composition and thermodynamic equilibrium modeling - however, what you get is very likely to be completely different from lab results. With Si, Al, and Fe you run into problems related to colloids leading to much too high analytical concentrations. Another important factor is cation exhange wich cannot be predicted from remote. For a composite methodology about how to determine pore water chemistry you may find the following interesting:
Pearson, F. J.; Waber, H. N. (2006): Mont Terri Project, Technical Note 2006-26, Diffusion and Retention (DR) Experiment: Experimental Water Chemistry, Report.
Bradbury, M. H.; Baeyens, B. (1998): A physicochemical characterisation and geochemical modelling approach for determining porewater chemistries in argillaceous rocks, Geochim. Cosmochim. Acta (62,5), 783-795.
Motellier, S.; Ly, J.; Gorgeon, L.; Charles, Y.; Hainos, D.; Meier, P.; Page, J. (2003): Modelling of the ion-exchange properties and indirect determination of the interstitial water composition of an argillaceous rock. Application to the Callovo-Oxfordian low-water-content formation, Appl. Geochem. (18), 1517-1530.
Regards,
Helge
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Dear Tom,
sorry, I should have looked into our gwb parameter files on my own, but somehow I took it for granted, that your data are valid from 25C upwards only.
But anyway, is there anybody who has actually tested your data for such calculations?
There is another program called FREZCHEM, where data are part of the source code
. Regards,
Helge
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Hello,
does anybody use GWB for calculations at temperatures below 25°C? If yes: which parameter file do you use? Is there any parameter file for such conditions provided by Rockware?
Best regards,
Helge
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Hi Tom,
I am well aware that GWB can swap H2(g) for O2(aq). The point is: GWB cannot process a datafile that originally builds on H2(g) as primary redox species. The datafile itself builds on O2(aq), which is quite uncommon and not in comliance of standards set up by the IUPAC where redox reactions are written in terms of H2(g).
In the project a hot discussion is going on on the question whether redox reactions should be written in terms of O2(g) or H2(g). When we produce a GWB-datafile with redox reactions based on H2(g), GWB - we fear - will not be able to process that file.
Cheers,
Helge
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Hi Tom,
having thougth this over and over I still think this is a severe constraint for the use of GWB as soon as one is interested in producing own parameter files (as we are currently doing within the THEREDA-project in Germany). No problem with EQ3/6, PHREEQC or CHEMAPP, only with GWB!
I therefore dare to ask: do you see any possibility to make GWB flexible in this point, to have other redox-controlling species instead?
Cheers,
Helge
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NaCl = 0.5 molal is well beyond Debye-Hückel and Davies should be used instead.
Thermodynamic modeling of the solubility of an anhydrous oxide phase might lead to results significantly (even orders or magnitude) lower concentrations than are experimentally obtained. This is because the phase that is actually controlling solubility is a hydrous metastable phase on the surface of the oxide. In the case reported this might be something like "Si(OH)4(am)". logK for this "phase" would be quite different.
A (Pitzer-) model for calculations of Si-containing solutions in brines can be found in Reardon, E. J. (1990): An ion interaction model for the determination of chemical equilibria in cement/water systems, Cement and Concrete Research (20), 175-192.
Helge
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Hi Tom,
this is my output from the attached .rxn file:
O2(aq) + 4 e- + 4 H+ = 2 H2O
Log K's:
0 °C: 93.7064 150 °C: 60.9559
25 °C: 86.0018 200 °C: 54.5990
60 °C: 77.1101 250 °C: 49.3866
100 °C: 68.9882 300 °C: 45.0942
Polynomial fit:
log K = 93.7 - .3318 × T + .001056 × T^2 - 2.34e-6 × T^3 + 2.363e-9 × T^4
Equilibrium equation:
log K = - log a[O2(aq)] - 4 × log a[e-] + 2 × log a[H2O]
- 4 × log a[H+]
At 25°C it says that logK = 86.0018
In thermo.dat it is logK = 83.1028
* log k for eh reaction
-91.0454 -83.1028 -74.0521 -65.8632
-57.8929 -51.6850 -46.7266 -42.6842
In Craigs Book, refering to eq. (3.40), logK (25°C) is given as 25.5; multiplied with 4 this gives 102.
Second question is: when I add to your half-cell reaction the half-cell reaction of the standard hydrogen electrode
H<+> + e<-> --> 1/2 H2(g)
I end up with a standard Eh-reaction which involves H2(g):
H2O <--> H2(g) + O2(g)
The background of my question is: when we produce own parameterfiles for GWB, are we fixed on the Eh-reaction given in Craigs book or may we decide to use H2(g) as basis species for redox reactions? If you say, that the Eh-reaction is fixed, we know how to proceed.
Is it possible, to have O2(g) as basis species and recalculate the Eh-reaction accordingly?
Regards,
Helge
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Hallo,
a logK for Eh-reaction is given in each parameter file for Geochemist's Workbench. Further below O2(aq) is entered as basis species. All redox species to follow are defined using O2(aq). My first question is, how the Eh-reaction as entered in the parameter files relates to equation 3.40 in Craigs book: e- + 1/4 O2(aq) + H+ <-> 1/2 H2O (logK = 25.5 at 25°C).
Second question is: is it possible to choose a different Eh-reaction and use H2(g) instead of O2(aq)? I suppose I would have to enter different logKs in place of those given in the parameter files. But could GWB handle that or is a specific Eh-reaction invariably coded within GWB?
Regards,
Helge
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New parameter files for GWB from THEREDA
in The Geochemist's Workbench
Posted
In the meantime more data packages were release from THEREDA which are available also for GWB:
R-04: System Na, Cl, Np(V) - H2O
R-05: System Cs - Na, Mg, Ca, K - Cl, SO4 - HCO3/CO2(g) - H2O
R-06: System (Si, Al) - Na, Mg, Ca, K - Cl, SO4, CO3, HCO3 - H2O
R-07: System Na, K, Ca, Cl, Th(IV), Np(IV), Pu(IV), HCO3/CO2(g) - H2O
All parameter files are valid for 298.15 K only. Please visit www.thereda.de >> THEREDA Data Query >> Tailored Databases. Any feedback is welcome.
Enjoy!
Helge