A rich-in- carbonates copper ore was subjected to bioleaching under alkaline pH
conditions by means of different microorganisms or their metabolites. The ore contained 1.40%
copper, 1.94% sulphur, 3.25% iron and 20.3% carbonates, and had a pH of 8.6 and a highly positive
net neutralization potential (325 kg CaCO3/t). Copper was present mainly as different sulphide
minerals (bornite, covellite, chalcopyrite). The leaching was carried out by means of the shake-flask
technique at 32 oC using finely ground (minus 100 μm) ore. The following microorganisms were
used to leach the sample: ammonifying bacteria (related to the genera Bacillus, Acinetocater and
Vibrio); heterotrophic bacteria (Acetobacter and Pseudomonas) and fungi (Asperillus niger and
Penicillium chrysogenum) producing citric acid; heterotrophic bacteria (Micrococcus, Alcaligenes
and Bacillus) producing amino acids (mainly alanine); basophilic chemolithotrophic bacteria
(Thiobacillus thioparus, Hallothiobacillus neapolitanus, Starkeya novella; ”silicate bacteria”
(Bacillus circulans) producing organic acids and exopolysaccharides; bacteria possessing urease
enzymatic activity (Corynebacterium). The best results were achieved by means of a mixed culture
of urease-possessing bacteria, which under certain conditions was able to solubilize 64.4% of the
copper within 30 days of leaching.
