Re: Phreeqci 2.6 charge balance question

["Brian Park" <bpark@xxxxxxxxxx>]

Hello,

Thanks for your response below, it was very helpful and I've been able to
run the program successfully since.  However, now I'm trying to use the
ADVECTION keyword to simulate acid mine drainage flow through a bioreactor
using sulfate reducing bacteria.  I've tried a 10 cell simulation with a
simple organic addition rate (as CH2O), with 10 shifts.

What happens is, as the water flows through, various metals are precipitated
as they should (Cu, Zn, Cd as sulfides, Al as hydroxide).  But eventually
towards the end of the reactor the Cu/Zn/Cd concentrations increase slightly
which should not happen - they should either decrease or stay the same, not
increase.  I have the equlibrium phase amounts set to zero, so that they
should not dissolve but can precipitate if supersaturated.  It seems like
during the advection sequence, the phase amounts for those metals get set to
nonzero amounts, so that if conditions dictate they dissolve slightly.

Is there a way to get around that with the advection keyword, to have each
shift contact equilibrium phases with zero amounts?  What I'm trying to do
is predict water quality change as it flows through the reactor.

Thank you,
Brian T. Park, P.E.
Senior Process Engineer
MSE Technology Applications, Inc.
200 Technology Way
P.O. Box 4078
Butte, MT  59702

(406) 494-7415
(406) 494-7230  [fax]


----- Original Message -----
From: "David L Parkhurst" <dlpark@xxxxxxxx>
To: "Brian Park" <bpark@xxxxxxxxxx>
Sent: Tuesday, February 18, 2003 9:25 AM
Subject: Re: Phreeqci 2.6 charge balance question


>
> > As a test case I'm trying to simulate the effects of sulfate reduction
> due to sulfate reducing bacteria on acid mine drainage.  The equation
> sometimes put forth as occurring is
>
> > SO4-2  +  2CH2O  =   2HCO3-  +  HS-  +  H+
>
> >Where the CH2O represents some organic material.  Using the REACTION
> keyword I'm taking out sulfate, and adding bicarbonate, bisulfide, and
> protons.  Since it's a redox reaction that's why I was concerned about
> charge.  If the program ignores charges, then for example if I specify
> sulfur as participating in the reaction, how does it know if I'm talking
> about sulfate or sulfide?  Incidentally, when I do put them in as SO4-2,
> HCO3-, HS-, and H+, it does seem to give reasonable results.
>
> Your REACTION should include the moles of elements that enter or leave the
> aqueous phase. The reaction should only include the organic carbon that is
> reacted into the solution. The sulfur is already in the aqueous phase and
> should not be included in the reaction.
>
> REACTION n
>       CH2O  1.0
>       xxx mmol
>
> Thermodynamics will determing the electron acceptors, the pH, and the
> distribution of the carbonate species.
>
> 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
>
>
>