For the most part, the selection of minerals is straightforward--if calcium is in the mineral, then you will only get a saturation index if calcium is in the analysis. It can be a little tricky with redox elements. I'll just give an example with FeS (Mackinawite). If S is defined in the solution, it will be distributed between S(6) (sulfate) and S(-2) (sulfide) and there will be a saturation index calculated for FeS. If S(-2) is defined in the solution, there will be a saturation index calculated for FeS, however, if only S(6) is defined for the solution, there will be no saturation index calculated for FeS. Whether a saturation index is calculated for a mineral with a redox active element depends on the redox state of the element in the mineral. If individual redox states are defined in the solution composition then saturation index for a mineral will be calculated if there is data for the appropriate redox states in the solution (it also depends on the chemical equation used to define the mineral in the PHASES data block). David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled yangli <yang003@xxxxxxxx To: "David L Parkhurst" <dlpark@xxxxxxxx> edu> cc: In-Reply-To: <3DE30A30@xxxxxxxxxxx> Subject: Question about Phreeqc speciation calculation 11/25/02 10:15 PM Dear Dr. Parkhurst: I am Li Yang, a graduate student in the department of Geological Sciences at the University of Alabama.I and My advisor, Dr, Donahoe, are currently working on a project studying the leachability and sequestering mechanisms of heavy metals from power plant ash disposal facilities. We use your geochemical modeling code PHREEQC to set up some simulations for pore water speciation calculation according to our analytical data. In the model output, we get a list of minerals and their saturation indexes (S.I) with respect to the given pore water solution. What puzzles us is that for a series of pore water of very similar chemical composition collected at different depth, we get different list of minerals for each pore water. In the user's manual, it is said that all minerals with their saturation indexes appropriate for the given solution will be listed in the output file. We are interested in what caused such a difference in the simulation output results. How does the program search the database to choose the minerals to be listed for a given solution? Is there a criteria that the program will follow to calculate the S.I of this mineral over another for a given solution? Thanks for your time! We are looking forward to your reply! Li Yang Li Yang Department of Geological Sciences University of Alabama Tel:(205)348-9293 E-mail:yang003@xxxxxxxxxxx
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