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Tom Meuzelaar

SpecE8 output files and FeOH.dat

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[admin note: this post represents recovered forum content after a critical hard drive failure - it is not in it's original form]

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Posted by: jhodgkinson Feb 21 2007, 05:03 PM

I am modelling surface processes using SpecE8 and have some issues with terminology. The output file specifies surface species as (w) or (s), does this refer to inner and outer sphere complexes? At the bottom of the file three sections entitled "original basis", "sorbed" and "elemental composition" state a table of values for moles in fluid, fraction and moles sorbed, there doesn't appear to be a relationship between the totals for moles sorbed and moles in fluid and the overall "total moles" column. In the FeOH.dat file site densities are specified as mol/mol mineral, I am used to using site densities per square nanometre and I'm not sure how to convert my data to the mol/mol values in the file, the surface sorption sites are again refered to as (s) and (w) which presumably relates to the same terms in the output file. I would very much appreciate any help with the above, if there is a file spec sheet for the input/output files that would be a real help.

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Posted by: Tom Meuzelaar Feb 22 2007, 03:59 PM

Hi Jonathan:

The output file specifies surface species as (w) or (s), does this refer to inner and outer sphere complexes?

Answers to this question can be found in this thread.

[admin note: the above thread now longer exists. The (w) and (s) notation for surface species in GWB do not correlate with inner and outer sphere complexes]

At the bottom of the file three sections entitled "original basis", "sorbed" and "elemental composition" state a table of values for moles in fluid, fraction and moles sorbed, there doesn't appear to be a relationship between the totals for moles sorbed and moles in fluid and the overall "total moles" column.

The relationship between the three is as follows: Total moles in original basis * fraction sorbed = moles sorbed.

However, this relationship is somewhat obscured by the fact that the program, by default, does not include sorbed species in figuring the composition of the initial system (you can change this by checking the option under Config-Options-Exclude Sorbed Species). That is, if you set an initial concentration of Ca at 2.4 mg/kg, your initial system contains that amount PLUS an additional amount sorbed onto your mineral surface. I believe the amount listed under "moles sorbed" thus reflects:

(Total moles in original basis * fraction sorbed) PLUS additional moles sorbed onto the mineral surface

If you check the "Exclude Sorbed Species" option, you'll note in the output file that the relationship between the three is as first listed.

In the FeOH.dat file site densities are specified as mol/mol mineral, I am used to using site densities per square nanometre and I'm not sure how to convert my data to the mol/mol values in the file, the surface sorption sites are again refered to as (s) and (w) which presumably relates to the same terms in the output file. I would very much appreciate any help with the above, if there is a file spec sheet for the input/output files that would be a real help.

Not sure about this one- I'm guessing this involves using molar volumes and molecular weights- maybe someone else can chime in here, or perhaps referring to Dzombak and Morel (1990): Dzombak, D.A. and F.M.M. Morel, 1990, Surface Complexation Modeling, Hydrous Ferric Oxide, Wiley, New York, 393 p. will help.

Hope that helps,

Tom

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