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PHREEQ-C question

Mr. Parkhurst,

I have a question for you about PHREEQ-C: you mention in the manual that the
usage of mole fraction for the activity of surface species instead of
molarity (which sounds reasonable to me) does affect multidentate
complexes - I'd be interested in how this affects bi- or tridentate

In addition, I was wondering if it is possible to include surface
precipitation as well in PHREEQ-C (accounting for the phenomenon that near
the surface concentrations may be high enough for precipitation whereas
overall solution concentrations are too low for precipitation to occur).
I simulated As(V) sorption onto a quartz sand using the diffuse double layer
model, and I had some problems at "higher" As(V) concentrations - at 10^-7
and 10^-8 moles/l As(V) the model works fine, but it underpredicts sorption
at 10^-6 moles/l and I was wondering if that could be due to bidentate
complexes involved (which was observed in other studies) or surface
precipitation with dissolved Fe.

Thanks for you help.

-----Original Message-----
From: David L Parkhurst [mailto:dlpark@xxxxxxxx]
Sent: Thursday, February 13, 2003 4:37 PM
To: Birgit Braun
Subject: Re: PHREEQ-C mailing list

Ok. Your name will be added to the PHREEQC mailing list.

Dipl.-Ing. Birgit Braun, M.S.
Reserach Associate
Colorado School of Mines
Department of Environmental Science and Engineering
Golden, CO 80401
Phone: (303) 384 2116
Email: bbraun@xxxxxxxxx

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