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PHREEQC version 2



Dear Dr. Parkhurst,

Having started to use the new version of PHREEQC (version 2) in an inverse
modelling mode, I tried running old models (run on version 1.03 PHREEQCi) to
check the feasible models were the same. Unfortunately I find that the
number of feasible models produced in version 2 is always less. For example,
the phase assemblage;

		Muscovite	dissolve
		Microcline	dissolve
		Quartz	dissolve
		Biotite	dissolve
		Gypsum	dissolve
		Albite(low)	dissolve
		Gibbsite(C)	precipitate
		CO2(g)
		SiO2(am)	precipitate
		Ferrihydrite	precipitate
		Illite	precipitate
		Calcite	dissolve
		Pyrite	dissolve
		O2(g)

in version 1 resulted in 35 models, 8 minimal, but in version 2, only 12
models, 12 minimum, were found. Consideration of the models indicated that
models NOT including pyrite oxidation (i.e. models where pyrite and oxygen
are used and where there are Fe(2) and S(-2) redox transfers) were only
found using version 1, and were not found using version 2. It is these
models that account for the extra feasable models in verson 1.

The input data was copied from the line editor of version 1 to version 2,
thus input solution and phase definition are exactly the same, uncertainties
were the same etc (full input data are pasted below). I tried to select and
de-select the mineral_water identifier to include or exclude water derived
from minerals in the water-balance equation as this seemed the only noteable
difference to the input data file. This made no difference.

Could you let me know why these differences occur?

Many thanks,

Andrew

Andrew Mitchell
Centre for Glaciology / Centre for Research into Environment and Health,
Institute of Geography and Earth Sciences,
University of Wales,
Aberystwyth.
Ceredigion. SY23 3DB

Tel: Direct (+44)(0)1970 622786
     Main Office (+44)(0)1970 622606
     Mobile 07949 406809

SOLUTION 1 supra1/8
	temp	1
	pH	6.67
	pe	7
	redox	pe
	units	mg/kgs
	S(6)	0.0048
	Ca	0.34993
	Mg	0.017703
	Na	0.022
	K	0.032287
	Alkalinity	1.25
	Al	2.838	ppb
	Fe	49.8	ppb
SOLUTION 2 A177(10:00)
	temp	1
	pH	8.21
	pe	7
	redox	pe
	units	mg/kgs
	S(6)	5.716
	Ca	6.726
	Mg	0.364
	Na	0.341
	K	0.369
	Alkalinity	16.35
	Al	21.05	ppb
	Fe	72.72	ppb
INVERSE_MODELING 1
	-solutions 1 2
	-uncertainty 0.1 0.1
	-phases
		Muscovite	dissolve
		Microcline	dissolve
		Quartz	dissolve
		Biotite	dissolve
		Gypsum	dissolve
		Albite(low)	dissolve
		Gibbsite(C)	precipitate
		CO2(g)
		SiO2(am)	precipitate
		Ferrihydrite	precipitate
		Illite	precipitate
		Calcite	dissolve
		Pyrite	dissolve
		O2(g)
	-balances
		Alkalinity	 0.3 0.1
	-range	1000
	-tolerance 1e-07
PHASES 1 # Do not change this number it is used by the program!
Biotite
	KMg3AlSi3O10(OH)2 + 10H+ = K+ + 3Mg+2 + Al+3 + 3H4SiO4
	logk	0
	-check
Illite
	K0.6Mg0.25Al2.3Si3.5O10(OH)2 + 11.2H2O = 0.6K+ + 0.25Mg+2 + 2.3Al(OH)4- +
3.5H4SiO4 + 1.2H+
	logk	0
	delta_h	0 kJ/mol
	-check



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