PHREEQC questions

["LaRiviere, Daniel" <DLaRiviere@xxxxxxxxxxxxxxxx>]

Hello Dr. Parkhurst,

I am hoping you could shed some light on the capabilities of your program
and maybe provide some insight as to how to evoke the desired results from
PHREEQC.

Question 1:

I have been conducting several respirometry experiments with sediments from
a wetland site under alternative electron accepting conditions. My problem
is that upon termination of these separate experiments I did not acidify the
soil solution to release any aqueous phase CO2 in the form of carbonate and
bicarbonate. If all of the experiments were aerobic this would not be such a
bad thing because I've found these to be acidogenic, dropping the pH to a
relatively low value so that most of the CO2 is actually already released.
However, under sulfate reducing conditions pH was found to become as high as
8.8 units... so that most of the CO2 is in the aqueous phase. 

I know the final pH, final CO2 in the headspace, initial water composition
in terms of Mg and Ca (in case there may be precipitation of carbonates),
and I even know the buffering capacity of the sediments. 

Can I PHREEQC to estimate the microbially evolved CO2 that would be in the
solid and aqueous phases?

Question 2:

Can I use PHREEQC as a model similar to that of Van Capellen and Wang
(referenced in your manual) : a multi-component, 1D, continuity equation? Do
you have any examples of how that is done?

Dan LaRiviere

Daniel LaRiviere
Chemical Engineering Department
Texas A&M University
College Station, TX 77843-3136
phone: 979 845 5854




Daniel LaRiviere
Chemical Engineering Department
Texas A&M University
College Station, TX 77843-3136
phone: 979 845 5854