Bioleaching of zinc from low-grade complex sulfide ores in an airlift by isolated Leptospirillum ferrooxidans

Bioleaching of low-grade complex sulfide ores from La Silvita and La Resbalosa (Patagonia Argentina) were carried out in a reverse flow airlift reactor by a native strain of Leptospirillum ferrooxidans (Lf-LS04). The reactor was filled with iron free 9K medium pH 1.8, with mineral particle size of – 74 μm, pulp density of 1% and a superficial air velocity of 0.01m s − 1. Zinc recoveries from the two sulfide ores – mainly in the case of La Silvita ore – were higher than those obtained previously with a collection strain of A. ferrooxidans. By applying the shrinking core-product layer diffusion model to sphalerite leaching, diffusion was found to be rate limiting due to the formation of an insoluble product layer (elemental sulfur, anglesite and ferric iron precipitates) as well as to the presence of an unreacted layer of gangue minerals (quartz, feldspar). Even in this case, the indigenous strain of L. ferrooxidans was shown to be highly efficient for processing both complex sulfides in the absence of sulfur-oxidizing bacteria.