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Helge

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Everything posted by Helge

  1. 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
  2. eq3/6 pitzer database

    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
  3. eq3/6 pitzer database

    To my best knowledge: No. However, if you are interested in Pitzer databases formatted for GWB, look out for www.thereda.de Regards, Helge
  4. 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
  5. 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
  6. H2(g) as basis species

    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
  7. 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
  8. 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
  9. 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
  10. Different Eh-reaction

    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
  11. Different Eh-reaction

    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
  12. Different Eh-reaction

    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
  13. Quartz Solubility

    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
  14. Different Eh-reaction

    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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