Bioleaching of zinc and nickel from sili

In this work, we investigated the role of bacteria from the genera Bacillus and Pseudomonas and fungi from the genera Aspergillus and Penicillium in the leaching process of two different silicates, calamine and garnierite. Since the results obtained with A. niger were better than those with different bacteria, a more detailed investigation of the leaching process with this microorganism was conducted. Moreover, although it is clear that the citric acid generated by fungi could be an important leaching agent acting in the solubilization of the used silicates, other products of metabolism could be involved. The results obtained with chemical leaching using low concentrations of citric acid lower than 10 mM showed that the respective dissolution of zinc and nickel was much lower when compared to those processes in which cultures or supernatant liquor of A. niger cultures were used. The results obtained also suggest that the type of mineral and the metal present influences the bioleaching process, demonstrating the potential improvement of the leaching process with fungal cells. From a practical point of view, the high yield rate of extracting metals from silicates using supernatant liquors of A. niger cultures is noteworthy, presenting advantages over conventional chemical leaching processes.