[OLD] Fe/As redox and sorption

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From: Brian Gibney

Subject: Fe/As redox and sorption

I am modeling the sorption of arsenic to Fe(OH)3 under the following circumstances:

1) Arsenic consistently oxidized, Fe redox slides from reduced to oxidized

2) Fe consistently oxidized, As redox slides from reduced to oxidized

The basis for my reaction has been set up as below:

hematite/Fe+++ = 1 free gram

e-/O2 = 0 Eh

Na = 100 mmolal

Cl- = 100 mmolal (charge balance)

SO4- = 10 mmolal

Ca++ = 10 mmolal

As(OH)4- = 0.1 mmolal

H+ = 7 (pH)

Reactants:

react 1 g Fe(OH)3 ppd

slide Eh to 1

Plots of reactions don't show a decrease in As sorption at low Eh (as iron is reduced), as one would expect. Any suggestions?