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Leaching
of Zinc Sulfide by Thiobacillus ferrooxidans: Applied
and Environmental Microbiology, Oct 1998, p 3570-3575 The
role of Thiobacillus ferrooxidans in bacterial leaching of mineral
sulfides is controversial. Much of the controversy is due to the
fact that the solution conditions, especially the concentrations
of ferric and ferrous ions, change during experiments. The role
of the bacteria would be more easily discernable if the concentrations
of ferric and ferrous ions were maintained at set values throughout
the experimental period. In this paper we report results obtained
by using the constant redox potential apparatus described previously
(P.I Harvey and F.K Crundwell, Appl. Environ.Microbiol.63:2586-2592,
1997). This apparatus is designed to control the redox potential
in the leaching compartment of an electrolytic cell by reduction
or oxidation of dissolved iron. By controlling the redox potential
the apparatus maintains the concentrations of ferrous and ferric
ions at their initial values. Experiments were conducted in the
presence of T.ferrooxidans and under sterile conditions. Analysis
of the conversion of zinc sulfide in the absence of the bacteria
and analysis of the conversion of zinc sulfate in the presence of
bacteria produced the same results. This indicates that the only
role of the bacteria under the conditions used is regeneration of
ferric ions in solution. In this work we found no evidence that
there is a direct mechanism for bacterial leaching.
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