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Re: Iron sulfide's dissolution/precipitation constant





>   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.

The data are from the compilation of WATEQ4F (Ball, J.W., and Nordstrom,
D.K., 1991, User's manual for WATEQ4F, with revised thermodynamic data base
and test cases for calculating speciation of major, trace, and redox
elements in natural waters, U.S. Geological Survey Open-File Report
91-183). The reference for the data are listed as: Berner, R.A., 1967,
Comparative dissolution characteristics of carbonate minerals in the
presence and absence of aqueous magnesium ion: American Journal of Science,
v. 265, p. 45-70. Note that Mackinawite is given a log K of  -4.648 for the
same reaction. There is almost certainly a range of log K values from fresh
precipitation, to more crystalline mackinawite, and ultimately to pyrite.
The log K you choose for modeling depends on the time scale at which you
are working. The value of -3 may be appropriate for fresh precipitate, but
it is less stable (more soluble) than all of the K's that are in the
databases for PHREEQC.

Data from Lawrence Livermore National Lab(data0.com.V8.R5 and llnl.dat)
lists Pyrrhotite with log K -3.7;  and Troilite -3.8 for the same reaction.
The references are given as

92joh/oel
Johnson, J.W., Oelkers, E.H., and Helgeson, H.C., 1992, SUPCRT92: A
software package for calculating the standard molal thermodynamic
properties of minerals, gases, aqueous species, and reactions from 1 to
5000 bar and 0 to 1000degC:  Computers Geosci., 18, 899-947.

78hel/del
Helgeson, H.C., Delany, J.M., Nesbitt, H.W., and Bird, D.K., 1978, Summary
and critique of the thermodynamic properties of rock-forming minerals:
Amer. J. Sci., 278a, 229p.

David


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


                                                                                                         
                      h2osoft                                                                            
                      Sent by: Kathleen        To:      alfalf@xxxxxxxxxxxxx, David L                    
                      M Flynn                  Parkhurst/WRD/USGS/DOI@xxxx                               
                                               cc:      Diane E Brittle/NMD/USGS/DOI@xxxx,               
                                               h2osoft@xxxxxxxx, ask@xxxxxxxx, William M                 
                      03/25/02 09:06 AM        Alley/WRD/USGS/DOI@xxxx                                   
In-Reply-To: <OF840BACB3.9AEC2338-ON85256B87.00580441@xxxxxxxx>
                                               Subject: Re: Iron sulfide's dissolution/precipitation     
                                               constant(Document link: David L Parkhurst)                
                                                                                                         




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
records.)




                                                                                                         
                      ask                                                                                
                      Sent by: Diane E         To:      "Alf" <alfalf@xxxxxxxxxxxxx>, h2osoft@xxxxxxxx   
                      Brittle                  cc:                                                       
In-Reply-To: <OF840BACB3.9AEC2338-ON85256B87.00580441@xxxxxxxx>
                                               Subject: Re: Iron sulfide's dissolution/precipitation     
                                               constant(Document link: h2osoft)                          
                      03/25/2002 10:28                                                                   
                      AM                                                                                 
                                                                                                         
                                                                                                         




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
USGS
"ASK@xxxxxxxx"




                                                                                                         
                      "Alf"                                                                              
                      <alfalf@xxxxxxxx         To:      <ask@xxxxxxxx>                                   
                      t.net>                   cc:                                                       
In-Reply-To: <OF840BACB3.9AEC2338-ON85256B87.00580441@xxxxxxxx>
                                               Subject: Iron sulfide's dissolution/precipitation         
                      03/25/02 01:50           constant                                                  
                      PM                                                                                 
                                                                                                         
                                                                                                         



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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