Bioleaching of covellite using pure and mixed cultures of Thiobacillus ferrooxidans and Thiobacillus thiooxidans

ABSTRACT Seven strains of heterotrophic iron-oxidizing acidophilic bacteria were examined to determine their abilities to promote oxidative dissolution of pyrite (FeS2) when they were grown in pure cultures and in mixed cultures with sulfur-oxidizingThiobacillus spp. Only one of the isolates (strain T-24) oxidized pyrite when it was grown in pyrite-basal salts medium. However, when pyrite-containing cultures were supplemented with 0.02% (wt/vol) yeast extract, most of the isolates oxidized pyrite, and one (strain T-24) promoted rates of mineral dissolution similar to the rates observed with the iron-oxidizing autotroph Thiobacillus ferrooxidans. Pyrite oxidation by another isolate (strain T-21) occurred in cultures containing between 0.005 and 0.05% (wt/vol) yeast extract but was completely inhibited in cultures containing 0.5% yeast extract. Ferrous iron was also needed for mineral dissolution by the iron-oxidizing heterotrophs, indicating that these organisms oxidize pyrite via the “indirect” mechanism. Mixed cultures of three isolates (strains T-21, T-23, and T-24) and the sulfur-oxidizing autotroph Thiobacillus thiooxidans promoted pyrite dissolution; since neither strains T-21 and T-23 nor T. thiooxidans could oxidize this mineral in yeast extract-free media, this was a novel example of bacterial synergism. Mixed cultures of strains T-21 and T-23 and the sulfur-oxidizing mixotrophThiobacillus acidophilus also oxidized pyrite but to a lesser extent than did mixed cultures containing T. thiooxidans. Pyrite leaching by strain T-23 grown in an organic compound-rich medium and incubated either shaken or unshaken was also assessed. The potential environmental significance of iron-oxidizing heterotrophs in accelerating pyrite oxidation is discussed.

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Oxidation of galena by Thiobacillus ferrooxidans and Thiobacillus thiooxidans

Canadian Journal of Microbiology ◽

10.1139/m95-067 ◽

1995 ◽

Vol 41 (6) ◽

pp. 508-514 ◽

Cited By ~ 29

Author(s):

Oswaldo Garcia Jr. ◽

Olli H. Tuovinen ◽

Jerry M. Bigham

Keyword(s):

Ferrous Sulfate ◽

Thiobacillus Ferrooxidans ◽

Solid Phase ◽

Sulfide Oxidation ◽

Initial Increase ◽

X Ray Diffraction ◽

Ph Change ◽

Thiobacillus Thiooxidans ◽

X Ray ◽

Abiotic Control

The objective of this work was to determine solution- and solid-phase alterations associated with galena (PbS) oxidation by Thiobacillus ferrooxidans and Thiobacillus thiooxidans. In T. ferrooxidans experiments with 2.5–5% (w/v) galena, the pH remained almost constant at pH 2, whereas the pH increased in uninoculated controls. In T. thiooxidans cultures, the pH initially increased from 2 to 4. This initial increase was comparable to the pH change in an abiotic control, but the oxidation reaction in T. thiooxidans cultures subsequently became acid producing. Anglesite (PbSO4) was detected by X-ray diffraction as a solid-phase product of galena decomposition in both abiotic and inoculated experiments. When ferrous sulfate was added as a supplementary energy source for T. ferrooxidans, jarosite (MFe3(SO4)(OH)6) was detected as a new solid phase. Elemental S was not detected in the residues.Key words: anglesite, bioleaching of galena, galena oxidation, jarosite, lead sulfide oxidation, Thiobacillus ferrooxidans, Thiobacillus thiooxidans.

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