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Re: Iron sulfide's dissolution/precipitation constant

With this message, I am forwarding your question to Dave Parkhurst, one of
the authors of PHREEQC (Dave-with your response, please include a cc to
h2osoft@xxxxxxxx for the e-mail archive and to ask@xxxxxxxx for their

                      Sent by: Diane E         To:      "Alf" <alfalf@xxxxxxxxxxxxx>, h2osoft@xxxxxxxx                  
                      Brittle                  cc:                                                                      
                                               Subject: Re: Iron sulfide's dissolution/precipitation constant(Document  
                                               link: h2osoft)                                                           
                      03/25/2002 10:28                                                                                  

March 25, 2002
>From USGS:

I have forwarded this message to the following USGS office, which is
identified on the PHREEQC home web page as the technical contact for your
question.  You should receive a separate response from them.

U.S. Geological Survey
Hydrologic Analysis Software Support Program
437 National Center
Reston, VA 20192
(electronic mail: h2osoft@xxxxxxxx)

To the "H2OSOFT" team - please make your response to
"Alf" <alfalf@xxxxxxxxxxxxx>

We would appreciate a CC sent to "Ask@xxxxxxxx".
Thank you,
Diane Brittle

                      <alfalf@xxxxxxxx         To:      <ask@xxxxxxxx>                                                  
                      t.net>                   cc:                                                                      
                                               Subject: Iron sulfide's dissolution/precipitation constant               
                      03/25/02 01:50                                                                                    

Dear sir:
   I have a question about the PHREEQC. Refer to a report: User's guide to
PHREEQC - a computer program for
speciation, reaction-path advective-transport, and inverse geochemical
calculations. by David L. Parkhurst, 1995,
USGS Water -resources investigations report 95-4227.
   My question is about the dissolution/precipitation equilibrium constant
of iron sulfide (FeS).  In the PHREEQC's
database- phreeqc.dat and waterq4f.dat,  FeS(ppt)    FeS + H+ = Fe+2 + HS-,
logK = -3.915. Can you tell me where
the value come from?
   According to Morse et al.(1987, The chemistry of the hydrogen sulfide
and iron sulfide systems in natural waters,
Earth-science reviews, 24, 1-42.)  and Davison (1991, solubility of iron
sulfide, Aqut.Sci, 53, 309-329) logK = -2.95.
In my own data (in PhD thesis of National Taiwan University), I survey over
100 data from wells and references,
show logK is about -2.9 ~ -3.0.  Because my data against USGS's phreeqc
database, my adivser asked me why the
USGS's phreeqc.dat (1995) didn't follow the results from Morse et al.(1987)
and Davison(1991). And where the data
logK = -3.915 come from.
    Thank you very much
Wen-fu Chen
National Taiwan University

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