(1) DATABASE C:\Programme\USGS\PhreeqcI2.3\my_phreeqc.dat ERROR: DATABASE must be the first keyword in the input file. Your input file may have two DATABASE data blocks. The first does not show up in the PhreeqcI editor because PhreeqcI reads the DATABASE line and sets the default database internally. If you can see a DATABASE data block in your input file in PhreeqcI, delete it and one will be included automatically. It also may be that the database file has a DATABASE data block, which it should not. If it does, use WordPad to remove it. If you edited the database file in PhreeqcI, it will have inserted a DATABASE data block. This is probably a bug in PHREEQC. DATABASE data blocks should be ignored as the database file is being read. (2) Checking a book (e.g. Werner Stumm, James J. Morgan, Aquatic Chemistry an Introduction Emphasizing Chemical Equilibria in Natural Waters. John Wiley &Sons, New York Chichester Brisbane Toronto 1981 P245) or some other books, hydroxyapatite has a solubility constant of log K = -57 at 25°C, I=0, i.e. Ca5(PO4)3OH(s) 5Ca2+ + 3PO43- + OH- log K=-57 But according to the calculation result of phreeqc, a datum of logK=-54 must have been used. If it is true, this of course can be understood. But I am not sure whether my judgement is correct. Could you please tell me where people got data when this phreeqc.dat database was written? I think the log K does work out to be in the range of -54 for the same reaction. To check, you need to take the reaction given in the database and add (or subtract) the appropriate aqueous association reactions and their log K's. There is a wide variation in log K for apatite in the literature. The data in phreeqc.dat and wateq4f.dat according to the Wateq4f documentation come from Brown, W.E., 1960, Behavior of slightly soluble calcium phosphates as revealed by phase-equilibrium calculations: Soil Science, v. 90, p. 51-57. David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225
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