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: 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: Subject: Iron sulfide's dissolution/precipitation constant 03/25/02 01:50 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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