In bioleaching processes, gas transfer is often considered as one of the key mechanisms that will influence the leaching efficiency and more precisely the leaching rate. Oxygen can be a limiting factor in bacterial leaching because of its low solubility. One way to overcome this phenomenon consists in increasing the oxygen partial pressure in the gas stream supplied to the leach pulp. The primary objective of this work was to investigate the use of oxygen-enriched gas in bioleaching stirred reactors and its impact on the consortium dynamics. First tests were performed at lab scale in four successive series of 2-L bioreactors alimented either with air or with oxygen enriched gas. The microbial consortium used has proven its efficiency on several ores such as cobaltiferous pyrite and polymetallic ores in former research projects (BioMine, BioShale, ProMine). The community diversity was remarkably reproducible irrespective of the type of gas supply, in each of the successive series of reactors. Only minor changes occurred after subculturing from one batch series to the next one, highlighting the high stability of the established consortium. Different oxygen partial pressures (from 20% to 50%) were then tested in a 20-L continuous reactors pilot experiment. There was no impact on the community diversity, showing the high tolerance to oxygen of the bioleaching strains and their capacity to easily survive 50% oxygen input. The bioleaching efficiency in terms of rate and metal leaching did not seem to be changed. The use of enriched oxygen gas is not detrimental to the bioleaching strains and may be used in order to improve process operation (gas transfer, heat management...).
Growth of Thiobacillus ferrooxidans: a Novel Experimental Design for Batch Growth and Bacterial Leaching Studies.
