> QUESTION: I appreciate the role of kinetics. However, assuming that kinetics are not an issue, how can I best apply PHREEQC to determine, at equlibirum, what remains in solution and what (eventually) precipitates - for a given a water quality? You're asking a pretty basic question. The short answer is that the saturation indices (SIs) calculated for a solution indicate the thermodynamic state of the solution relative to minerals. Positive SI indicates the mineral could precipitate, negative, it could dissolve. The key factors for what happens are the minerals present in the system and the rate at which the minerals react. You must decide which minerals will react to equilibrium, in which case, you include them in EQUILIBRIUM_PHASES and react these phases with the SOLUTION. The result is equilibrium between the solution and the selected phases (unless a mineral is undersaturated and has zero moles initially). The long answer is the field of low temperature geochemistry. 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
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