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Re: Help

> 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

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 Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

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