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An experimental plot consisting of alkaline soil heavily polluted with heavy metals (copper, zinc, cadmium) was treated in situ by stimulating the activity of the indigenous soil microflora, which contained different metal-solubilizing microorganisms. This was achieved by adding to the soil solid biodegradable organic substrates (cow manure, plant compost, straw), zeolite saturated with ammonium phosphate and aqueous solution containing acetate, lactate and magnesium chloride. An efficient removal of the above-mentioned heavy metals was achieved via the drainage water and their residual contents in the soil decreased to below the relevant permissible levels within 18 months of treatment. The metals were solubilized mainly as complexes with the organic acids added by the irrigating water solutions or secreted by the indigenous heterotrophic microorganisms. The effluents containing dissolved metals were efficiently treated by means of a wetland constructed near to the experimental plot.

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.