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Arsenite Sorption Model



Hello Mr. Parkhurst,

  My name is Brian Fitzgerald. I am a masters student
in Environmental Science and Health at the University
of Nevada, Reno. I am working on arsenic sorption in
the groundwaters of Fallon, Nevada (ie- Carson
Desert). I have been able to run an arsenate sorption
model in PHREEQC, but not an arsenite model. My
arsenite "Surface_Species" is from Dzombak and Morel.
My arsenite "Solution_Species" is from Langmuir et al.
My error is:

"ERROR: Could not reduce equation to primary master
species, H3AsO3.
ERROR: Calculations terminating due to input errors.
Stopping."

I wonder whether I have a formatting error or the
program cannot account for the different valence
states. I have attached my input file as well.

Thank you very much for your time.

~Brian


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TITLE Project.--Sorption of As(III) & As(V) on hydrous
                   iron oxides

SOLUTION_MASTER_SPECIES
       As        H3AsO4  -1   74.92  74.92
       As(+5)    H3AsO4  -1   74.92
       As(+3)    H3AsO3   0.0   74.92

SOLUTION_SPECIES
       H3AsO4 = H3AsO4
       log_k  0.

       H3AsO3 = H3AsO3
       log_k   0.

       H3AsO4 = AsO4-3 + 3H+
       log_k  -20.70

       H3AsO4 = HAsO4-2 + 2H+
       log_k   -9.20

       H3AsO4 = H2AsO4- + H+
       log_k   -2.24

       H3AsO3 = H2AsO3- + H+
       log_k   -9.23

       H3AsO3 = HAsO3-2 + 2H+
       log_k    -21.33

       H3AsO3 = AsO3-3 + 3H+
       log_k    -34.74

SURFACE_MASTER_SPECIES
       Hfo_w     Hfo_wOH

SURFACE_SPECIES
       Hfo_wOH  + H+ = Hfo_wOH2+
       log_k  7.18

       Hfo_wOH = Hfo_wO- + H+
       log_k  -8.82

       Hfo_wOH + AsO4-3 + 3H+ = Hfo_wH2AsO4 + H2O
       log_k  29.31

       Hfo_wOH = Hfo_wOH
       log_k   0.0

       Hfo_wOH + AsO4-3 + 2H+ = Hfo_wHAsO4- + H2O
       log_k   23.51

       Hfo_wOH + AsO4-3 = Hfo_wOHAsO4-3
       log_k   10.58

       Hfo_wOH + AsO3-3 + 3H+ = Hfo_wH2AsO3 + H2O
       log_k   5.41

SURFACE 1
       Hfo_wOH        2e-4    600.   0.05

SOLUTION 1
-units ppm
pH 8.304
pe 13.4868
density 1.00
temp 15.0
As 0.0389 gfw 74.92
Na 34.5 charge
Alkalinity 147.9372 as HCO3
S(6) 33.3
O(0) 4.10
SOLUTION 2
-units ppm
pH 8.0
As 0.1
Na 100. charge
C(4) 100.
USE solution none
#
# Model definitions
#
PHASES
Fix_H+
H+ = H+
log_k 0.0
END
#
# As(+5) = 38.9e-3
#
SELECTED_OUTPUT
-file Project.sel
-molalities HAsO4-2 H2AsO4- H3AsO4
-pH
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -5.0 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -5.25 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -5.5 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -5.75 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -6.0 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -6.25 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -6.5 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -6.75 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -7.0 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -7.25 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -7.5 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -7.75 NaOH 10.0
END
USE solution 1
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -8.0 NaOH 10.0
END
#
# As(+5) = 38.9e-2
#
USER_GRAPH
-headings pH HAsO4-2 H2AsO4- H3AsO4
-chart_title "Example 8"
-axis_titles pH MOLALITY
-axis_scale x_axis 5.0 8.0 1 0.25
-axis_scale y_axis -15.0 -5.0 1 1
-connect_simulations true
-start
10 GRAPH_X -LA("H+")
20 GRAPH_Y LOG10(MOL("HAsO4-2")), LOG10(MOL("H2AsO4-")), LOG10(MOL("H3AsO4"))
-end
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -5.0 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -5.25 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -5.5 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -5.75 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -6.0 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -6.25 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -6.5 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -6.75 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -7.0 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -7.25 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -7.5 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -7.75 NaOH 10.0
END
USE solution 2
USE surface 1
EQUILIBRIUM_PHASES 1
Fix_H+ -8.0 NaOH 10.0
END




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Last modified: $Date: 2005-09-13 21:04:21 -0600 (Tue, 13 Sep 2005) $
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