P. Tedesco

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

Abstract A high level of covellite (CuS) dissolution was observed in systems containing Thiobacillus thiooxidans and iron. This activity was higher than with Thiobacillus ferrooxidans in the same medium and lower than that with T. ferrooxidans in the absence of iron. In mixed cultures, covellite dissolution appeared to be associated with T. ferrooxidans in the presence of iron and sulphur but with T. thiooxidans when these were absent.

Effect of iron (III) and its hydrolysis products (jarosites) onThiobacillus ferrooxidans growth and on bacterial leaching

SummaryThere is a significant inhibition of the growth ofThiobacillus ferrooxidans in the presence of iron (III), but this does not affect bacterial leaching. Moreover, the insoluble hydrolytic products (jarosites) have no influence, except from a mechanical point of view when they are generated ‘in situ’.

A need for direct contact with particle surfaces in the bacterial oxidation of covellite in the absence of a chemical lixiviant

SummaryFor bio-leaching, direct contact is needed between Thiobacillus ferrooxidans and covellite (CuS) which oxidizes by a direct mechanism.

Combined degradation of covellite by Thiobacillus thiooxidans and Thiobacillus ferrooxidans

SummaryIn the presence of iron, which is always associated with natural sulphide ores, the percentages of copper dissolution in the bioleaching of covellite were 34 and 45 % when Thiobacillus thiooxidans and Thiobacillus ferrooxidans were used together and when an indirect bioleaching with attached bacteria was performed respectively. In the latter, the percentage of copper dissolution was still higher than the percentages obtained with pure cultures (36 % with a T. thiooxidans culture and 40 % with a T. ferrooxidans culture).

Direct zinc sulphide bioleaching by Thiobacillus ferrooxidans and Thiobacillus thiooxidans

SummaryDirect bioleaching (no iron(II) present) by Thiobacillus ferrooxidans mainly occurs on the surface of the very insoluble sulphides but is more important in solution when the sulphides are more soluble. In this case, Thiobacillus thiooxidans, normally not able to leach directly insoluble sulphides, has an effective leaching action.

Direct and indirect mechanisms in the bacterial leaching of covellite

SummaryBacterial leachings of sample of covellite using a strain of Thiobacillus ferrooxidans in 9 K medium with and without iron were made at several pulp densities. Rates of solubilization with and without iron correspond to total and to direct mechanism respectively. Orders of reaction (at each pulp density) for each mechanism at two temperatures were calculated.

Bioleaching of manganese (IV) oxide and application to its recovery from ores

SummaryBioleaching of manganese (IV) oxide with Thiobacillus thiooxidans has been studied in media with and without sulfur, ferrous sulfide and ferrous sulfate. The knowledge of the role played by the bacteria and the reducing substances suggest that the leaching of manganese (IV) ores through the use of thiobacteria is only justified when suitable amounts of sulfur or metal sulfides are present.

Analysis of molybdenite bioleaching by Thiobacillus ferrooxidans in the absence of iron (II)

SummaryThiobacillus ferrooxidans attachment on MoS2 and Mo dissolution are increased by the addition of the tensioactive agent Tween 80 in absence of iron(II), which suggests that the poor bioleaching of MoS2 is caused by its hydrophobic character. Additionally, inhibition ofThiobacillus ferrooxidans growth by the presence of MoO42− and the effect of variable amounts of Tween 80 on bacteria growth and on MoS2 bioleaching are considered in this paper. Data confirm the need of bacterial attachment to insoluble substrate for bioleaching by the direct mechanism.

Use of packed bed bioreactors application to ores bioleaching

SummaryThe behaviour of glass beads, silicagel and activated carbon particles as bacteria supports for using in backed bed bioreactor has been compared. No important difference was found. Additionally the performance of a bioreactor with glass beads was compared with that of a conventional percolating column in the bioleaching of a copper sulphide ore. Results showed higher copper extraction using the bioreactor.