Studies on the bioleaching of refractory concentrates

The bioleaching of arsenopyrite, the oxidation of arsenate and the precipitation of ferric arsenate are competing reactions, hence their rates depend on the relative concentrations of the respective species, and the activity of the bacterial culture. Bacterial arsenic resistance may be attributed to...

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Bibliographic Details
Published in:Journal of the South African Institute of Mining and Metallurgy 2000-11, Vol.100 (7), p.389-398
Main Author: Breed, A.W., Dempers, C.J.N. & Hansford, G.S.
Format: Article
Language:English
Subjects:
Arsenate minerals
arsenate oxidation
arsenopyrite
Bacteria
bioleaching
Bioreactors
Enzyme inhibition
ferric arsenate
ferric leaching kinetics
ferrous-iron oxidation kinetics
gold leaching
gold recovery
leptospirillum ferrooxidans
Oxidation
Precipitation (chemical)
Pyrites
Rate constants
redox potential
Redox reactions
refractory concentrates
Refractory materials
sulphide minerals
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Summary:The bioleaching of arsenopyrite, the oxidation of arsenate and the precipitation of ferric arsenate are competing reactions, hence their rates depend on the relative concentrations of the respective species, and the activity of the bacterial culture. Bacterial arsenic resistance may be attributed to the Pst+ Pit- mutation and an energy dependent efflux pump. Pst+ Pit- mutations result in a reduced uptake of arsenate. This enables the bacteria to survive in solutions in which the arsenate concentration is significantly higher than the arsenite concentration. However, the excretion of arsenate requires energy. Therefore, in the absence of an energy source or during periods of reduced bacterial activity, the inhibitory effect of arsenate may manifest at concentrations to which the culture has been adapted. The chemical ferric leaching rate of pyrite and arsenopyrite decrease with a decrease in the solution redox and may be descriptionbed using a modified Butler-Volmer equation. The bacterial ferrous-iron oxidation kinetics of L. ferrooxidans also depend on the redox potential, and can be descriptionbed using a Michaelis-Menten type model modified to account for both temperature and pH. A model developed using the independently determined ferric leaching, and ferrous-iron oxidizing kinetics, has been shown to compare well with the experimental data for the continuous bioleaching of pyrite. Keywords: Leptospirillum ferrooxidans, arsenopyrite, bioleaching, sulphide minerals ferrous-iron oxidation kinetics, ferric leaching kinetics, redox potential
ISSN:0038-223X