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From: Paul Barton Subject: Database If I run a very simple system such as 10 mg/kg Al+++, 300 mg/kg SiO2(aq), 300 mg/kg Na+, and 500 mg/kg Cl- and a pH of say 6, using REACT, and with the current best data base (thermo.com.V8.R6.full), the REACT_OUTPUT file tries to tell me that quartz plus (depending on the temperature) either Diaspore or Corundum is stable. That's an absurd outcome. What about Kaolinite, or Pyrophyllite, or Andalusite, etc.? Old data bases do not have this problem, but that is faint praise indeed. I am wondering whether (wherever thermo.com.V8.R6.full gestates in the entrails of LLNL) only a partial reassessment of the consequences of revising Al chemistry by Pokrovskii and Helgeson (1995) has been made. A change in log Ko for Al+++ should impact all Al compounds and species since Al+++ is the basis species. But simply making an adjustment, ( based, for example, on the shifts in log Ko for Corundum ) runs the risk of making extra corrections where they have already been applied. From: Craig Bethke Subject: Re: Database I think you are confusing bigger with better. The V8-R6 database is the largest available, and perhaps this led you to think of it as the “current best data base�. In fact, large thermo databases by nature contain data that range widely in quality, and tend to suffer in terms of internal consistency. This database has important attributes -- a broad range of organic species, for example, and lots a data for radionucleides -- but also some widely appreciated problems. In terms of consistency between aluminous and aluminosilicate species, I think you will find another database such as thermo.dat more suitable. Remember that the thermo dataset is input to a model, and choosing appropriate input data is the user's responsibility. Fortunately, you need never treat a thermo database as a black box, since you can quickly use Act2 to plot the relations among aqueous species, minerals, and gases. In this way, you can verify before you begin modeling that the dataset is adequate in scope and sufficiently consistent to describe your system at the conditions of interest.

From: Yoshida Yasushi Subject: dataset format I have another question for database format. In the top of database there are dataset of he header lines. ----------------------------------------------- dataset of thermodynamic data for gwb programs dataset format: oct94 <<--- activity model: debye-huckel * ----------------------------------------------- I would like to know some rules to set month and year on second line 'dataset format: '. If other data is set in dataset format, GWB code says 'thermo.dat is in wrong format.'. From: Craig Bethke Subject: Re: dataset format You should not change the format identifier. This is the month and year that the format -- in other words, the arrangement of data fields – of the thermo dataset was established. If you want to include information about, for example, when the dataset was last modified, you should do so in a comment line, starting with a “*� in the first character position.

From: Yoshida Yasushi Subject: logK of Eh The data table of GWB database has some logK data for significant reactions. In these data block the reaction between O2 and e- exists. * log k for eh reaction -91.0454 -83.1028 -74.0521 -65.8632 -57.8929 -51.6850 -46.7266 -42.6842 I would like to know this reaction indicates whether 2H2O = O2(aq) + 4H+ + 4e- or 2H2O = O2(g) + 4H+ + 4e-. From: Jan van der Lee Subject: logK of Eh As far as I know, it is the reaction with O2(g). From: Craig Bethke Subject: Re: logK of Eh Jan is correct. For more information, please see page 173 of the Users Guide.

From: Paul Foellbach Subject: adding species into database I like to change the database of GWB, because I want to model a system that consists of Goldchlorids and - hydrosulfides. I have to add the hydrosulfides of gold to the existing database thermo.dat. Can you tell me how I can change the database (thermo.dat) and modify it in the way that I add the hydrosulfides? From: Craig Bethke Subject: Re: adding species into database For instructions on altering the thermo database, see Appendix 3 of the GWB Users Guide. (Remember to edit a copy of the database, not the original.)

From: Barry R. Bickmore Subject: Pitzer Database I am new to GWB, and I am attempting to alter the Pitzer database to include some interaction coefficients I've had to estimate. In the estimation methods I'm using I have to assume only binary interactions between cations and anions, so Beta(0), Beta(1), and Alpha(1) are the only parameters I can use. When I am inputting these data into the database, can I include only the cation-anion interaction sets, or do I need to include blocks for all possible cation-cation, anion-anion, and ternary interactions, setting the coefficients to zero? From: Craig Bethke Subject: Re: Pitzer Database You can simply omit the remaining virial coefficients from your dataset; there is no need to set them to zero. From: Barry R. Bickmore Subject: More Pitzer Problems I have one more issue to deal with before I think I'll be up to speed on the Pitzer database. In the GWB 3.0 manual it gives a certain format for the Pitzer data where each virial coefficient also comes with up to 4 constants one can plug into a polynomial to come up with the temperature dependence. The example in the manual has the constants (c1-c4) for Beta(0) in the Na+ Cl- block listed as 0.008946, -777.03, -4.4706, and -3.3158E-6. However, in the database I'm trying to customize, the block appears as follows: Na+ Cl- beta0 = 0.0765 beta1 = 0.2664 beta2 = 0.0000 alpha1 = 2.0 alpha2 = 0.0 db0/dt = 0.716E-03 d2b0/dt2 = -0.150E-04 db1/dt = 0.700E-03 d2b1/dt2 = 0.214E-03 db2/dt = 0.000E+00 d2b2/dt2 = 0.000E+00 I can't detect any relationship between the constants in the manual, and the derivative values listed in the database. Furthermore, there are a max of 2 coefficients, rather than 4, listed in the database. The db/dt term seems understandable if there is a linear change in the coefficient with temperature, but I'm lost on the second derivative term. Can someone explain to me how to interpret the database values? From: Craig Bethke Subject: Re: More Pitzer Problems It looks like you may not be using the correct dataset as a template. The GWB includes two datasets for the virial model: thermo_hmw.dat and thermo_phrqpitz.dat. These are up-to-date in that they use the current virial formalism. There are also two datasets distributed with the software that have not been supported for quite some time: thermo_pitzer.dat and thermo_hdata.dat (see p. 6 of the GWB manual). These are not recommended for use and are included only for compatibility with very early versions of the GWB. Perhaps you picked up one of the latter?

From: Wang Lian Subject: Cd data in surface dataset Why surface species of cadmium on HFO are disabled from the surface datasets? From: Craig Bethke Subject: Re: Cd data in surface dataset The Cd surface complexes are disabled in FeOH.dat because the default thermo dataset (thermo.dat) does not contain Cd. If you adapt FeOH.dat to another thermo dataset that contains Cd, you can enable these complexes.

From: Paul Foellbach Subject: adding Atacamite to thermo-dataset I would like to add a new mineral (Atacamite) to the basis. The thermodynamic data are from thermo_com-dataset: Atacamite type= formula= Cu4Cl2(OH)6 mole vol.= 56.800 cc mole wt.= 427.1334 g 4 species in reaction -6.0000 H+ 2.0000 Cl- 4.0000 Cu++ 6.0000 H2O 16.4204 14.2836 11.9184 9.9085 8.0526 6.5741 500.0000 500.0000 * gflag = 1 [reported delG0f used] * reference-state data source: 87woo/gar * delG0f = -1341.800 kj/mol * delH0f = -1654.433 kj/mol * S0PrTr = 314.600 j/(mol*K) These data I copied and pasted it into the thermo-dataset of GWB3.0.1. I changed the number of minerals at the headline of minerals, original 624 and after adding 625 minerals. After adding to the thermo-dataset I like to use this script: Reading thermodynamic data from: C:ProgrammeGwb3.01Gtdatathermo.dat Read data for 646 aqueous species, 625 minerals, and 10 gases. show system Initial temperature is 200, final is 300 C Thermo dataset: C:ProgrammeGwb3.01Gtdatathermo.dat Options: Debye-Huckel, no-precip Basis is: H2O 1 kg solvent Atacamite (swapped for Cu+) free gram = 1e-9 O2(aq) total mmolal = 6.81 Na+ total molality = 1 Cl- total molality = 1 H+ pH = 4 SO4-- total molality = 1e-9 show reactants No reactants specified. go Solving for initial system. Loaded: 20 aqueous species, 3 minerals, 5 gases, 0 surface species, 6 elements, 5 oxides. React stop: set_basindex: lost basis species (1) -- Hit any key to quit React. Can anyone tell me what I did wrong in adding Atacamite to the thermo.dataset ? From: Craig Bethke Subject: Re: adding Atacamite to thermo-dataset The problem with this run is that the block of thermo data you inserted for Atacamite has no log K entries at 250°C or 300°C (i.e., the entries are “500�), but your reaction path spans this temperature range.

From: Yoshida Yasushi Subject: GWB database - reaction equation I have one question for the constitution for reaction equation. In the original GWB database, the reaction of species including different redox state from basis species are described using redox couples (for example UO2F+ is described as UO2++ + F- <-> UO2F+), however if the reaction of 2H2O <-> O2 + 4H+ + 4e- is used for reaction equation, the reaction of species including different redox state from basis species are described without redox couples (for UO2F+, U++++ + H2O + F- + 0.5O2 = 2H+ + UO2F+). I would like to know if there is any problem for description for reaction equation including redox without using redox couples. From: Craig Bethke Subject: Re: GWB database - reaction equation You can balance reactions in the database in terms of the primary basis, neglecting the redox species. The only disadvantage to this strategy is that you will not be able to decouple correctly the redox pairs in question.

From: Yoshida Yasushi Subject: ion parameter would like to know the function of ion parameter in GWB database and how to set its values for complicated species. For example, if we added new basis species, redox couples or aqueous species to GWB database, we need set its own value for ion parameter. In the point of view for consistency, ion parameter should be determined by same rule as original database. If the value of ion parameter is not important in GWB calculation, we can set its value as blank or dummy. So, I would like to know how ion parameter used in GWB calculation and how to determine its value in original database. From: Craig Bethke Subject: Re: ion parameter The ion size parameter is used to calculate activity coefficients for aqueous species. You can read about it and the calculation of activity coefficients on pages 109-114 of the "Geochemical Reaction Modeling" text. When adding data to the GWB database, you should chose a value for the ion size parameter consistent with the derivation of the equilibrium constant for the species' reaction. In other words, since an activity coefficient must be assumed in order to specify from experimental data the log K for the reaction to form a species, you should use an ion size parameter consistent with that assumption.

From: Wang Lian Subject: surface data I tried some sorption calculation like what demonstrated on the user's guide, p 109. The surface data, i.e., FeOH.dat does not work in combination with database 'thermo_com_v8_r6.full'. It says: Dataset of surface reactions is corrupt or incomplete! Last line read is line 190: > 1.000 >(w)FeOH 1.000 As(OH)3 -1.000 H2O It works, as shown in the guide, with the default database 'thermo.dat'. How to make the 'full' database work with sorption? From: Craig Bethke Subject: Re: surface data You need to make sure that any surface reaction dataset you read contains reactions balanced in terms of known species -- that is, species contained in the thermo dataset in use. If you use thermo.com.V8.R6.full, you should note that species As(OH)3 is listed as As(OH)3(aq), and B(OH)3 as B(OH)3(aq). Also, mineral Fe(OH)3(ppd) is now Fe(OH)3 (with a revised log K). Some quick editing (remember to edit a copy of the surface dataset) and you should be on your way.

From: Wang Lian Subject: uranium phosphate thermo data The default database 'thermo.dat' associated with the release 3.0 is different from that of Livermore's from the web. The stability constants for Uranium phosphate complexes, e.g., UO2(H2PO4)H3PO4+ and UO2(H2PO4)2 are much higher (40 orders of magnitudes) than those compiled in the 'thermo_com_v8_r6.full'. Is there something wrong? What is the general criteria to 'moderate' the full database to the default one? From: Craig Bethke Subject: Re: uranium phosphate thermo data The default database (thermo.dat) is not a subset of the updated databases available for download from LLNL, but an earlier version. We try not to change thermo.dat, so that users' results don't change when they install a new GWB release. The updated LLNL databases are considerably expanded from thermo.dat, especially for the radioactive elements, and contain a number of corrections. In the case of UO2(H2PO4)H3PO4+, the updated dataset (thermo.com.V8.R6.full) contains data from the Grenthe et al., 1992 compilation for uranium species that was not available when thermo.dat was compiled (1986). As to why the log K's differ by forty orders of magnitude(!), perhaps someone working in U chemistry would like to comment.

From: Allan Treiman Subject: Ksp for Crocoite? Could you help me track down the solubility product for Crocoite, PbCrO4. This ought to be easy, but--- 1. The 1986 thermo0.com data base gives log(Ksp) = -12.73 while the newer thermoRev7b gives log(Ksp) -12.087. Both databases refer to the same paper for these numbers. 2. Literature values range from log(Ksp) = -13.66 through -12.19 (and even higher in older literature). 3. Several sources on the web give a value of log(Ksp) = -13.75, e.g., Ksp = 1.77E-14, but without a citation. Can anyone please 1) refer me to the source of the -13.75 value, and/or 2) aim me at a critical review of the thermochem of PbCrO4?

From: Wang Lian Subject: Adding surface sites I am trying to add some surface sites (for sorption) other than iron oxides into dataset HFO+.dat, e.g., Gibbsite as a sorbing surface. I can't seem to do that as I got error message as: React stop: set_bascomp: lost element -- Hit any key to quit React. From: Craig Bethke Subject: Re: Adding surface sites The solution to this problem is easy: you need to have a separate dataset for each type of surface you want to consider in your simulation. The reason is that React figures the surface area for each surface type separately, by summing over the minerals with that surface type. So split the dataset into two files, one for ferric iron, the other for aluminum. Then open both in your React session, and you're done.

From: Mark J. Logsdon Subject: GWB: Thermo data for Melanterite For an evaluation of uncertainty in low-T modeling, we are trying to track variations in published values of log K {as f(T)} back through the underlying functions in different sources, for reaction: FeSO4.7H2O = Fe2+ + SO42- + 7 H2O Values of log K compiled by our group from different sources and different styles of computation range over orders of magnitude. For the current databases thermo.com and thermo.com.v8.r6.full in GWB, the compilations do not provide delta Go,f and delta Ho,f values. I understand why not, of course, but I wonder if anyone who is familiar with these databases can provide the relevant data (with citations to the original source, if possible): delta Go,f (298.15) delta Ho,f (298.15) Melanterite Fe++ (aq) SO4-- (aq) H2O

From: John P. Kaszuba Subject: SIT database GWB has databases available for Pitzer and HMW, but not SIT. Any SIT plans in the future? Any way I could write a database called "SIT" and have GWB recognize it? Or is there a way to edit an existing database? I have GWB version 3.1.2. My interest is based on the large availability of SIT parameters for actinide elements. From: Craig Bethke Subject: Re: SIT database The SIT model is similar to the “Pitzer equations� in the sense that it contains a Debye-Hückel-like term and a summation accounting for pair-wise ion interactions. It has, however, a considerably simpler formalism than the Pitzer model. (For example, there are no virial coefficients for ion triplets.) The easy route is to consider whether SIT can be implemented by constructing an SIT dataset in the HMW format, by setting various coefficients in the Pitzer equations to zero (or leaving them undefined). The “green book� from Oxford contains the equations used to evaluate the HMW model in the exact form implemented within React, so you should start there. Off the top of my head, the E-theta terms in the HMW model may be hard to reconcile with the SIT equations. If that doesn't work, it may be possible to incorporate SIT in a future release of React. Such a modification would be more likely if you would be willing to assist by preparing a thermo dataset containing the SIT coefficients, and helping us test the code. Also, we'd put a modification like this, which of course would be a considerably commitment of programmer time, at higher priority if there is a reasonable level of interest among the GWB user community.

From: Yoshida Yasushi Subject: PHREEQE to GWB database conversion I have questions for the GWB database. My colleague and I have coded the format conversion program of database from PHREEQE to GWB. Prototype of this conversion program has already been completed, however some GWB calculation using the database converted by this conversion program from PHREEQE to GWB show wrong outputs. We tested calculation of ACT2 and REACT. In the calculation of ACT2 reasonable output is derived by using this database. In the calculation of REACT for some cases error messages are shown and run will be stopped. In REACT calculation, pH is set by following commands, React>pH=<value> or React>log a H+ = -10 then, using converted databse, following error are showed React stop: def_basis: add_basis failed - Hit any key to quit React. In REACT calculation, speciation of Ca+2 and SO4-2 in the pH and Eh controlled by CO2(gas) and O2(gas) condition. React> show system Temperature is 25 C Thermo dataset: D:TDBdevelopgwbjnc-tdb_h11a31dec_gwb.txt Working directory: d:tdbdevelopgwb Options: Debye-Huckel Basis is: H2O 1 kg solvent CO2(G) (swapped for H+) fugacity = .000316227766 O2(g) (swapped for O2(aq)) fugacity = .2 HCO3- (swapped for CO3-2) activity = 1e-5 CA+2 activity = .001 SO4-2 activity = .001 (Charge balancing disabled.) React> go Solving for initial system. Loaded: 24 aqueous species, 8 minerals, 15 gases, 0 surface species, 5 elements, 4 oxides. React stop: update: lost species -- Hit any key to quit React. I would like to know the meaning of error message and which data is wrong in database. I would appreciate it if you could let me know the answer for my question. From: Craig Bethke Subject: Re: PHREEQE to GWB database conversion I think you can resolve this problem by making sure the “H2O� is the first basis species in the database (see Appendix 3 of the User's Guide).

From: Rainer Newberry Subject: Problems w/ Ce in the expanded thermo database Does anyone know what's wrong with or how to fix the Ce entries in the expanded thermo database in gwb? Data for Ce4+, Ce3+, and Ce2+ species are given for 25oC, but when trying to create diagrams using Act2 or Tact, all that shows up is 'Ce++'. At other temperatures (e.g., 24C or 26C) the Ce+++ species plot up nicely, but (due to lack of data) none of the other oxidation states of Ce. If one turns on 'extrapolate' , again all that shows up is 'Ce++'. From: Craig Bethke Subject: Re: problems w/ Ce in the expanded thermo database Well, my cerium chemistry is a little rusty, but I notice the log K for the Ce+++/Ce++ redox couple corresponds to a Nerst Eh of more than 6 volts. So I think you can safely assume that this value is in error. The solution (assuming you don't care about the divalent form) is to decouple the Ce+++/Ce++ reaction. Alternatively, you can check the cited source: Spahiu, K., and Bruno, J., 1995, A selected thermodynamic database for REE to be used in HLNW performance assessment exercises: SKB Tech. Rep. 95-35, 80 p. From: Rainer Newberry Subject: Ce update (a topic obviously near the top of everyone's concerns) As Craig Bethke pointed out, the data for Ce++ in the expanded thermo data set is bogus, and as he pointed out, the way to get around it is to 'decouple Ce++'. It would be useful to keep track of any other problematic data as people encounter them. Has anyone else experienced such? From: Rainer Newberry Subject: Ce update The data for Ce++ in the expanded thermo data set is bogus, and as he pointed out, the way to get around it is to 'decouple Ce++'. It would be useful to keep track of any other problematic data as people encounter them. Has anyone else experienced such?

From: Henry Kerfoot Subject: Sodium citrate, citric acid thermo data Does anyone have any sodium citrate and/or citric acid thermodynamic data? I am mainly interested in the use of sodium citrate (or another citrate salt) as a reducing agent, so complex formation data is not of as much interest to me as delta G and delta H of formation and solution....

From: Scott C. Brooks Subject: Database error? I believe that there is an error in the thermo database available from LLNL as "thermo.com.V8.R6.full". In this database there is a species listed as: ***************************************************************************** Co2(OH)3+ charge= 1.0 ion size= 4.0 A mole wt.= 168.8884 g 3 species in reaction -3.0000 H+ 2.0000 Co++ 3.0000 H2O 500.0000 11.2000 500.0000 500.0000 500.0000 500.0000 500.0000 500.0000 * gflag = 3 [reported logK data used] * logk source = 76bae/mes * logk = -11.2000 * logk reference reaction: * 1.0000 Co2(OH)3+ -3.0000 H2O * -2.0000 Co++ 3.0000 H+ * calculated g-h-s values: * delG0f = -180.784 kcal/mol * delH0f = N/A * S0PrTr = N/A ***************************************************************************** The source of the data is the book The Hydrolysis of Cations by Baes and Mesmer. However in this book, the species is identified as Co2OH+++, Baes and Mesmer do not provide data for Co2(OH)3+. The log K value is correct but the species name, charge, reaction stoichiometry, and mole wt. are obviously incorrect. In the database included with the GWB distribution diskettes is the species Co2(OH)3+ with log K value = 94. From: James W. Johnson Subject: Re: database error? The data block for "Co2(OH)3+" in thermo.com.V8.R6.full (and in thermo.com.V8.R6.230) should be replaced by the following corrected data block for Co2OH+++. ****************************************************************************** Co2OH+++ charge= 3.0 ion size= 5.0 A mole wt.= 134.8737 g 3 species in reaction -1.0000 H+ 2.0000 Co++ 1.0000 H2O 500.0000 11.2000 500.0000 500.0000 500.0000 500.0000 500.0000 500.0000 * gflag = 3 [reported logK data used] * logk source = 76bae/mes * logk = -11.2000 * logk reference reaction: * 1.0000 Co2OH+++ -1.0000 H2O * -2.0000 Co++ 1.0000 H+ * calculated g-h-s values: * delG0f = -67.408 kcal/mol * delH0f = N/A * S0PrTr = N/A ******************************************************************************

From: Donna Cosgrove Subject: Tables and Data Precision I have two GWB questions. 1) Is there a way to direct specific output variables to the output tables? The manual and help files refer to Table3 through Table6, but I have not found a way to direct specific output to those tables. 2) Is there a way to increase the precision on output variables? I am integrating GWB with a parameter estimation code which requires higher data precision. From: Craig Bethke Subject: Re: Tables and Data Precision The React "tables" option is a very old feature that exists primarily because nobody has removed it. There is no provision for controlling the variables in the tables, nor their units or number of significant digits. The functionality of the tables has been replaced by Gtplot's "data table" feature (File -> Save Image... -> Data table), which allows you to interactively control which variables appear in the table, their units, and so on. My guess from the second part of your question, though, is that you are looking for direct output from React, without interactive configuration, so you can run the program directly from your parameter estimation code. This will be easy to do in GWB Release 5, which will include a "remote control" feature especially for uses like this. But that won't be released for a few months or so. In the current release, it seems to me your primary options are to filter the information you need from the React_output.txt or React_plot.dat datasets. If you use the latter, you can get any value at near-machine precision. In this case, it's easiest to do the filtering if you specify output to an ASCII rather than binary format dataset. I think there are some GWB users who have written various filters for retrieving values from React_plot.txt. If you don't want to start from scratch, you might post a request to the users' group.

From: Craig Bethke Subject: Ion exchange model in React We have discovered an error in the ion exchange model in React. If you specify the exchange capacity in eq/g (i.e., in equivalents per gram of rock), the program does not always correctly compute the overall exchange capacity. We will correct this problem in the next release. In the meantime, please use units of "eq" (i.e., total equivalents of exchange capacity in the system), rather than "eq/g", to set exchange capacity when using the ion exchange feature.

From: Ben Rees Subject: Problems running React Attached is a .rea file I have just tried to run within React as I want to assess mineral saturation states. The data is from a laboratory leach experiment of some rock to simulate one-off leaching / rinsing. Chloride was not analysed and so I have set Cl as charge balance. Also, there is no sulphate detected. When I try to run the model it states that O2(aq) needs to be specified and also the programme would still not run as residuals were too large at the 673th iteration. I have tried adding oxygen and balancing on sulphate instead but I still can not get the model to run. # React script, saved Fri May 30 2003 by Ben Rees data = "C:Program FilesGwbGtdatathermo.com.v8.r6+.dat" verify temperature = 25 swap Cr+++ for CrO4-- 1 kg free H2O total mg/l Al+++ = .005 total mg/l Sb(OH)3(aq) = .000425616 total mg/l H2AsO4- = .000752376 total mg/l Ba++ = .00777 total mg/l B(OH)3(aq) = .514606846 total mg/l Ca++ = 17.6 total mg/l Cu++ = .0094 total mg/l Mg++ = 4.2 total mg/l Mn++ = .00847 total mg/l SiO2(aq) = 7.29465646 total mg/l MoO4-- = .000133367 total mg/l Sr++ = .0898 pH = 8.19 total mg/l HCO3- = 77.531 total mg/l Cr+++ = .0019 From: Craig Bethke Subject: Re: Problems running React I assume from the input you attach that your sample contains trivalent instead of hexavalent chromium. In this case, you need to decouple Cr+++ from CrO4--, not swap these species. This eliminates the need to have O2(aq) in the system. Second, your input is overbalanced already with anions, so React cannot charge balance on Cl-. If you balance on HCO3-, the predominant anion, I think your input will converge easily.

From: Ben Rees Subject: Basis swapping I have started using GWB and have just a simple question. I have a water chemistry that includes data for Ti, U, V, Se, Cr, B and Sb. When I try and input these various parameters I have to select a complex which I consider to be the most applicable. Is there a way I can just enter the total concentration and allow the speciation to be determined? Also, if I have to enter B as B(OH)3(aq) for instance, must I multiply my elemental B analysis in mg/l by the relevant factor? From: Craig Bethke Subject: Re: Basis swapping The answers are yes and yes. React expects you to enter a total concentration and will do the speciation automatically. Occasionally, you may need to swap an appropriate species in for the default species, to help the program converge. For example, if you have a very reduced solution containing sulfide but no sulfate, consider swapping H2S(aq) for SO4-- as the basis entry for sulfur, if the program fails to converge. But convergence due to such issues is rarely a problem. And you do need to convert analyses in mass units to reflect the mole weight of the basis entry. Your example of B and B(OH)3 is a good one, since B is so light.

From: Andy Wilde Subject: Odd model results I am attempting to simulate the formation of copper ores in shale at 250C, from a relatively reduced brine. The input file is attached. I am using GWB 4.0.2 and Win 98. The input gives what appears to be reasonable results except for a major "glitch" early in the reaction path for stage 2 - the FLUSH step. There is a major fluctuation in the system marked by massive drop in the mass of solution present, increase in mCl- and order of magnitude shift in pH. I have not been able to pinpoint the cause of this glitch, and your help would be much appreciated. Also attached the thermodynamic data (from the UNITHERM compilation, at 500 bars) and the graphical output of the run. From: Craig Bethke Subject: Re: Odd model results In your run, the system contains a large amount of minerals (about 30 kg) and a small mass of fluid (about 2/3 kg). As the minerals react, the amount of water consumed and liberated can be large compared to the amount in the fluid. For example, the hydration reaction to produce chlorite consumes a significant fraction of the fluid present, leading to the results you observe.

From: Larry Hull Subject: Creation of Nitrate from nowhere I am attempting to simulate the leaching of gypsum and nitrate from soil during infiltration. I have suction lysimeters at two levels in the soil, and have input and output concentrations. I am treating the soil as a well mixed batch reactor to simulate a LiBr tracer test. Admittedly not the best approach, but a simple first approximation. There is a net increase in nitrate in the water as it infiltrates. I am attempting to simulate this as a kinetic dissolution reaction of Ca(NO3)2. However, even if I remove the mineral Ca(NO3)2 from the system, I get an increase in nitrate. I don't know where the nitrate is coming from. The input (ie the reaction moles of NO3-) are also lower than the output NO3-. The script and the databases needed to run the script are attached. Note- thermo.dat has been modified by adding Ca(NO3)2 as a mineral. From: Craig Bethke Subject: Re: Creation of Nitrate from nowhere That's an interesting question with an answer that may surprise you. You set up a flush model that includes a number of sorbing surfaces. Nitrate accumulates in the system because as fluid passes through it, nitrate becomes associated with charged surfaces. Although nitrate doesn't specifically sorb on any of the surfaces, it accumulates in the ionic diffuse layer that counterbalances surface charge. In this case, net surface charge is positive, and anions -- nitrate in this case -- accumulate in the diffuse layer. With time, therefore, the amount of nitrate in the system increases, even though the concentration in the input fluid is less than the concentration in the initial fluid. Is this result realistic? That's hard to say. Construction of the diffuse layer is a problem that has long vexed reactive transport modelers: it must be included in the model in order to maintain charge balance as fluid passes through the system, but surface complexation theory gives no guidance as to the layer's specific composition. Given this ambiguity, all reactive transport (and reaction models in a flush configuration) must make up a diffuse layer in a somewhat ad hoc manner. React does this simply by using abundant ions of charge opposite that of the surface.