Re: PHREEQC

["David L Parkhurst" <dlpark@xxxxxxxx>]

Hello Doug,

> The query I have regards the equations of formation for the aqueous
species. In the HATCHES database these are all written in the form suitable
for PHREEQE i.e. always from the "master species".  As I understand it,
PHREEQC requires the equations to be specified in terms of a particular
oxidation state, in order for the different oxidation states of redox
sensitive elements to be distinguished e.g. Fe+2 species should be written
in terms of Fe+2, Fe+3 species are written in terms of Fe+3 etc.  If this
is not done and, say, Fe+3 species are written in terms of Fe+2, the
species is assumed to be Fe(II).

That's right. If you were to make a PHREEQC database that is the same as
PHREEQE--that is only primary master species are defined (as in PHREEQE),
PHREEQC would work. However, you would loose the ability to input
concentrations of individual redox states, for example Fe(2) or S(-2).
Reaction calculation would actually be no different than having all of the
individual redox states defined because redox equilibrium is always
calculated for reactions.

> For use with PHREEQC, would it be necessary to rewrite the equations for
all aqueous species containing redox sensitive elements ? (or have I got
this wrong ?!!)

I think you have it right. It would be best if you do as you suggest,
although it would be possible to compromise with no secondary master
species. You could reproduce PHREEQE results, but you would loose some of
the capabilities of PHREEQC. Greg Anderson and I translated essentially a
EQ3 database to PHREEQC and most of the reactions came out alright, so
maybe it wouldn't be too hard to just make a PHREEQC database. I'd be glad
to provide assistance if you need it. I'd also be willing to distribute the
database with the code if you would like.

David


David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225


                                                                                                                               
                      "Doug Ilett"                                                                                             
                      <doug.ilett@xxxx         To:      <dlpark@xxxxxxxx>                                                      
                      .co.uk>                  cc:                                                                             
In-Reply-To: <sac0a104.003@xxxxxxxxxxxxxxxxxxxxxxxxxx>
                                               Subject: PHREEQC                                                                
                      03/27/01 05:17                                                                                           
                      AM                                                                                                       
                                                                                                                               
                                                                                                                               



Dear David,

RE: PHREEQC data requirements

I wonder if you could help me with the following query regarding the format
of data for the PHREEQC code ?

I currently manage the HATCHES database - a thermodynamic database for
groundwater modelling which is distributed via the NEA in Paris, France.
The data is currently output in a form suitable for use with the PHREEQE
and EQ3/6 codes.  I am looking at the feasilbility of distributing the data
in a form suitable for use with PHREEQC.

The query I have regards the equations of formation for the aqueous
species. In the HATCHES database these are all written in the form suitable
for PHREEQE i.e. always from the "master species".  As I understand it,
PHREEQC requires the equations to be specified in terms of a particular
oxidation state, in order for the different oxidation states of redox
sensitive elements to be distinguished e.g. Fe+2 species should be written
in terms of Fe+2, Fe+3 species are written in terms of Fe+3 etc.  If this
is not done and, say, Fe+3 species are written in terms of Fe+2, the
species is assumed to be Fe(II).

For use with PHREEQC, would it be necessary to rewrite the equations for
all aqueous species containing redox sensitive elements ? (or have I got
this wrong ?!!)

Thanks for any help,

Best Regards

Doug Ilett
AEA Technology plc
Harwell
UK    +44 (0)1235 433225




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