Biological Leaching of Non-Ferrous Metals From Copper Slag Using a Strain of Silicate-Solubilising Bacteria

This study aims at the recovery of non-ferrous metals from pyrometallurgy copper slag enriched in diopside, fayalite, and protomangano-ferro-anthophyllite and containing 0.36 % copper, 1.93 % zinc, and 0.09 % cobalt by bioleaching with silicate-solubilising strain Bacillus megaterium CCM 3360. Two techniques of bioleaching were applied: (i) direct one-step bioleaching, where the bacterial strain was cultivated in an Ashby medium and the presence of copper slag; (ii) indirect bioleaching of copper slag with spent medium obtained after separation of the bacterial cells. The results revealed that 5 % pulp density was the optimal out of the tested pulp densities (5-10%), as 15 days was the optimal duration for the direct bioleaching and 3 days for the indirect technique. The formation of biofilm on the surface of copper slag particles was the primary mechanism of the leaching of non-ferrous metals, and their recovery was between 41.7-48.7%. Indirect leaching with bacterial metabolites played a secondary role in base metals leaching.