Oxygen Mass Transfer Scale-Up in the Bioleaching of Manganiferous Minerals by Heterotrophic Microorganisms

In the present work, the bioleaching of italian manganiferous minerals (mainly constituted by pyrolusite and psilomelane) was carried out by a mixed culture isolated from naturals environments. The biological reduction occurs in microaerobic conditions that are naturally formed in the shaken flask tests. In fact, this system is a very common and useful apparatus to study small-scale submerged fermentation systems, and, considering its lay-out, the oxygen supply may become limiting if the oxygen requirement is larger than the overall oxygen transfer capacity. Considering its extensive use, an empirical model with dimensionless parameters has been proposed in order to correlate the oxygen mass transfer coefficient in shaken flasks to predict the oxygen mass transfer in several experimental conditions. The comparison between the bioleaching tests in shaken flasks and in microfermenter indicate how the oxygen mass transfer is the main parameter for controlling the scaling-up of the bioreductive process.