Arsenite Sorption Model

["Brian Fitzgerald" <bc_faang@xxxxxxxxxxx>]

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