The ferric leaching of pyrite

Master Thesis


Permanent link to this Item
Journal Title
Link to Journal
Journal ISSN
Volume Title

University of Cape Town

The bioleaching of pyrite has been found to occur via an indirect mechanism. Ferric iron leaches the pyrite, and is reduced to ferrous iron. Bacteria such as Thiobacillus ferrooxidans oxidise the ferrous iron to ferric iron, thus maintaining a high redox potential. In this thesis, the effect of the redox potential on the ferric leach rate was investigated by examining previously published data and by developing an experimental technique where dynamic redox potential measurements were used to study the kinetics of the sub-process. The ferric leach rate of pyrite was found to be of the order of 5 x 10⁻⁷ moles pyrite per mole pyrite per second, which is of the same order of magnitude as rates reported for the bioleaching of pyrite over similar ranges of redox potential. The rate decreased as the redox potential decreased, in what appeared to be a Butler-Volmer-like manner. This, along with the observation that there was no significant effect of the total iron concentration, suggested the likelihood of an electrochemical mechanism being operative, with charge transfer at the pyrite surface being rate limiting.

Bibliography: pages 82-90.