Fe(III)/Fe(II) reduction-oxidation mechanism and kinetics studies on pyrite surfaces

• Kinetics of Fe(III)/Fe(II) redox reaction on pyrite in acidic sulfate solution is studied.
• The Fe(III)/Fe(II) reaction is isolated from the pyrite oxidation reaction and other side-reactions.
• io of Fe(III)/Fe(II)couple reaction on pyrite is on the order of 10− 5 A cm− 2, higher than that on chalcopyrite.
• Pyrite electrodes with different origins have a common mechanism and different kinetics.
• The unusual ɑc shows a typical n-type semiconductor property.

In this paper, the electrochemical behavior of Fe(III) and Fe(II) couple on the pyrite surface was studied by application of the chronoamperometry technique in acidic solutions at room temperature and atmospheric pressure. The effect of the pyrite origin and the Fe(III) and Fe(II) ion concentration on the electron transfer kinetics of the Fe(III)/Fe(II) reaction was probed. Tafel behavior of the Fe(III)/Fe(II) couple redox reaction under the test conditions was developed. The Fe(III)/Fe(II) reaction on the pyrite electrodes with different origins demonstrated a common mechanism, despite different kinetics. The exchange current densities of the redox reaction had the same magnitude of 10−5 A cm−2 for all samples. The value of cathodic transfer coefficients ranged between 0.4 and 0.5, while the lowest magnitude of anodic transfer coefficients was 0.23. It was shown that an increase of an order of magnitude of iron concentration did not have a significant effect on the Fe(III)/Fe(II) couple redox reaction exchange current density nor on the value of cathodic transfer coefficients of the reaction.