Papers by Keyword: CE-SSCP

Abstract: 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...).

Abstract: In the frame of a European project (BioMinE - FP6), a continuous bioleaching operation was carried out in a laboratory-scale unit using a cobaltiferous pyrite. The objective of the work was to use this system to investigate mechanisms of microbial activity and mineral oxidation in continuous stirred bioreactors (1x50L - 3x20L). A combination of scientific and technical approaches (molecular ecology, biochemistry and microscopy) was used and various key operating parameters were tested (temperature, nitrogen source, CO2 availability, designed consortia). An increase of temperature of 10°C (35°C to 45°C) had no major influence on the bioleaching efficiency. When the ammonium source was limiting, there was a negative influence on both bacterial growth and bioleaching efficiency. This result was related to a combination of factors such as less bacterial attachment to the pyrite surface and less precipitate formation. CO2 limitation had a very significant negative effect on the bacterial productivity and consequently on the bioleaching efficiency. Nevertheless, the population composition remained unchanged. An important decrease of EPS (sugar) production was also observed. The bacterial strains, that dominate the culture, originated from the deposit in Uganda. It seems that their bioleaching ability was improved over the time when cultured in continuous mode. The culture composition was very stable. The iron-oxidizer L. ferriphilum was the dominant organism in standard (not limiting) conditions, and was always very well represented during the first 3-4 days of residence time. Sulfobacillus sp. BRGM2 also played an important role in the process. This study gives new insights for the application of this technology, and more specifically on the influence of key operating parameters on bioleaching performances, population dynamics and attachment of bacteria to the solid surfaces.