> My name is Samuel Mutiti with Miami University, Oxfrod Ohio. I am trying to run a simple speciation program using the win version of phreeqc that I downloaded from your website. The problem I am having is that I am not sure of how to write the program. So far I have been using the webphreeq at http://www.ndsu.nodak.edu/webphreeq/. The only problem with this webphreeq is that we are not getting the sulphide phases precipitating when we expect to see sulphides. If you are running only speciation calculations, then there will be no mass transfer of sulfides. Are you getting saturation indices that are not positive? or not getting saturation indices for sulfide minerals? > The other problem is that its limited on what you can enter e.g you cannot enter both sulphide and sulphate concentrations at the same time. I don't trust the our pe values so I would like to let the program compute them using the sulphide/sulphate ratios. I am attaching one of the outputs from for lake Fryxcell (which shows the inputs). I think you are correct that webphreeq does not allow entering S(6)--sulfate and S(-2)--sulfide simultaneously. PHREEQC allows entry of (1) one or both redox states or (2) total sulfur. You simply need to include S(6) xxx S(-2) yyy in the SOLUTION data block, where xxx is sulfate concentration and yyy is sulfide concentration. Note that if the units are mmol, then the "as" field is not used. If you define both redox states, you can use the pe that is calculated to distribute total concentrations of another redox element among its redox states by using -redox S(6)/S(-2) in the solution data block. 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
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