Kinetics of Ferric-Ferrous Reduction-Oxidation Reactions
on the Pyrite Surfaces
Lin Li*, Ahmad Ghahremaninezhad
The Robert M. Buchan Department of Mining Queen’s University, Kingston, Canada
(lin.li@queensu.ca)
ABSTRACT
Ferric and ferrous couple reaction is an important reaction during the pyrite oxidation process. Ferrous
oxidation by dissolved oxygen is shown to be the rate-limiting step in the pyrite oxidation process.
However, the quantitative kinetics parameters of Fe3+/Fe2+ redox couple during the pyrite oxidation
process rarely has been studied. This is partially due to the complex nature of the redox reaction
mechanism, as along with ferrous oxidation on the pyrite surface, pyrite itself also oxidizes.
In this paper, the kinetics of Fe3+/Fe2+ redox couple reaction on the pyrite surface is studied by the
application of chronoamperometry technique. The effect of the pyrite origin, iron salts concentration,
and temperature have been studied on the electron transfer kinetics of Fe3+/Fe2+ reaction. The results
show that the ferric-ferrous reaction on pyrite electrodes with different origins have a common catalytic
mechanism but a different reaction rate. The measured equilibrium potentials of this study is a constant
value of about 0.68 V vs. SHE. The exchange current densities of the redox reaction have magnitudes of
10-5 A.cm-2. The cathodic transfer coefficients are between 0.4 and 0.5 while the anodic transfer
coefficients are in a wider range, from 0.2 to 0.4. Finally we have shown that increasing the iron
concentration results in increasing of both the exchange current densities and anodic transfer
coefficients.
KEYWORDS
Pyrite; oxidation; Ferric reduction; Kinetics; Exchange current density