The Mechanism and Kinetics of Bioleaching Sulphide Minerals

Abstract

The measurement of oxygen and carbon dioxide consumption rates together with the measurement of redox potentials, has led to the further elucidation of the mechanism of bioleaching of sulphide minerals and enabled the kinetics of the sub-processes involved to be determined separately. This has shown that the primary attack of the sulphide mineral is a chemical ferric leach with the role of the bacteria to re-oxidise the ferrous iron formed back to the ferric form and maintain a high redox potential as well as oxidising the elemental sulphur which is formed in some cases. The kinetics of bacterial ferrous oxidation by Thiobacillus ferrooxidans and Leptospirillum ferrooxidans have been determined over a range of expected operating conditions. Also the chemical ferric leach kinetics of pyrite have been measured under conditions similar to those in bioleach systems. The kinetics have been described as functions of the ferric/ferrous-iron ratio or redox potential which enables the interactions of the two sub-processes to be linked at a particular redox potential through the rate of ferrous iron turn-over. The use of these models in predicting bioleach behaviour for pyrite presented and discussed. The model is able to predict which bacterial species will predominate at a particular redox potential in the presence of a mineral, and which mineral will be preferentially leached. The leach rate and steady state redox potential can be predicted from the bacterial to mineral ratio. The implications of this model on bioleach reactor design and operation are discussed.

Keywords:

• Bioleaching
• sulphide minerals
• kinetics
• mechanism
• bacterial ferrous iron oxidation
• Thiobacillus ferrooxidans
• Leptospirillum ferrooxidans

Notes

*To whom correspondence should be addressed.