> I wonder if you can advice about the stability constant used in the PHREEQC.dat database for hydroxyapatite (-3.421). In the data base MINTEQ.dat this constant is much lower (given as -44.333 which corresponds to -7.149 if reaction is written as in PHREEQC.dat). The constant of MINTEQ.dat is similar to the constant given by Lindsay (1979) which is -7.14 (using the same presentation of the dissolution reaction). Data of my research with soils seems to fit well with the constant used in PHREEQC.dat, but I had difficulties to point a reference for this constant. I would appreciate if you could inform me of a reference for this constant. The number comes from wateq4f (Ball and Nordstrom, U.S. Geological Survey Open-File Report 91-183), which lists Brown (1960) as the source of the data (with conversion of the reaction to H+ from OH-). Brown, W.E., 1960, Behaviour of slightly soluble calcium phosphates as revealed by phase-equilibrium calculations: Soil Science, V. 90, p. 51-57. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: http://wwwbrr.cr.usgs.gov/projects/GWC_coupled
Please note that some U.S. Geological Survey (USGS) information accessed through this page may be preliminary in nature and presented prior to final review and approval by the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the sole responsibility of the user.
Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.
The URL of this page is:
Last modified: $Date: 2005-09-13 21:04:21 -0600 (Tue, 13 Sep 2005) $
Visitor number 1049 since Jan 22, 1998.