Hi again Dave, Is there a way to make PHREEQC report output in ppm rather than moles? Also I'd like to run a simulation which will report the amount of ferihydrite precipitated from a solution THEN, using that amount of precipitate, perform sorbtion calculations. I've been running one simulation to find the amount of precipitate and then running the sorbtion reaction in a second simulation where I manually input the amount of precipitate formed in the first simulation using the Surface block. Is there a way to do this automatically in one step? Thanks again, have a nice weekend. Shane ----- Original Message ----- From: "David L Parkhurst" <dlpark@xxxxxxxx> To: "Shane Matolyak" <smatolyak@xxxxxxxxxxx> Sent: Wednesday, September 25, 2002 7:52 AM Subject: Re: PHREEQC question > > > We're using PHREEQCI for speciation modelling. When we give the program > an input solution and then perform a batch reaction the program > automatically adjusts the pe in the resultant solution. Presumably this is > to maintain charge balance. Is there a way to over-ride this in order for > the resultant solution to have a pe which we specify even if there will be > a charge imbalance? > > PHREEQC does not easily allow fixed activities of individual species. In > part, this is by design because maintaining a fixed pe in your case, while > allowing pH to vary can move the solution out of the stability field of > water. You can also implicitly be requiring many moles of mass transfer to > maintain a fixed activity. Usually, the change in pe from reaction is > telling you something. > > However, although you can not simply specify a constant pe, you can define > a phase that reacts until you get the pe that you want. Thus, you have to > explicitly add something to solution to adjust the pe. The following is a > bit artificial, but organic matter reacts with water, the reaction would > normally produce methane, CO2, and a very low pe. The phase "Fix_pe" is > defined in PHASES and required to equilibrate with the solution with > EQUILIBRIUM_PHASES. However, the definition in EQUILIBRIUM_PHASES specifies > that oxygen (O2) be added or removed from the solution until the saturation > index of -7 is reached for the mineral. This combination of definitions > causes oxygen to be added until the pe is 7.0. The oxygen allows all the > carbon to be CO2 rather than half as methane. > > David > > SOLUTION 1 > pe 7 > REACTION > CH2O 1 > 1 mmol > EQUILIBRIUM_PHASES > Fix_pe -7 O2 > PHASES > Fix_pe > e- = e- > log_k 0.0 > END > 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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