Re: Phreeqci 2.6 charge balance question

["David L Parkhurst" <dlpark@xxxxxxxx>]

> 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