Biological vs Acid Leaching of Industrial Fe-Si Alloys

摘要

Acidophilic iron-oxidising microbial cultures, collected in mining environments and maintained in the laboratory, were employed in the bioleaching of an industrial Fe-Si alloy on a laboratory scale. For this task two cultures isolated from different mining environments and designated as NC_1 and NC_2 were selected for their ability to endure low pH (optimal growth around pH 1.5), to oxidise Fe(II) and to use this substrate for growth. Other factors taken into account for the selection were the possible inhibitory effects of the elements Si and Al which are constituents of the alloy. Thus, cultures acclimatised to ore with high contents of SiO_2 and Al (wastes from Neves-Corvo mine containing 15.95 and 0.2 mass/mass %, respectively) were selected. NC_1 and NC_2 are both mixed cultures (as determined by plating experiments) the second having a slight predominance of heterotrophic/mixotrophic organisms. This culture had been previously evaluated as the best iron oxidiser in an assortment of samples from different origins. In terms of physiology both cultures are exclusively composed of gram negative rod-shaped organisms, as observed by optical microscopy. pH and Eh measurements of aqueous media were performed and the extraction yields of Ca, Fe and Al were calculated from ion concentrations as determined by atomic absorption spectrometry. These values of extraction yields were compared with the results obtained by acid leaching at 102°C with leachants with different HCl and FeCl_3 concentrations.