Batch and semi-continuous tests in the bioleaching of manganiferous minerals by heterotrophic mixed microorganisms

In the present paper a study on bioleaching of manganiferous ores by heterotrophic mixed cultures is reported. The main goal of this work has been to study the bioreduction process of MnO2 in lab-scale reactor and pilot plant tests, in order to investigate the process' performances in a scale larger than in shaken flasks. Lab-scale reactor tests were carried out in a batch and in a semi-continuous regime, monitoring manganese extraction yields and microbial growth. In the bioleaching tests 95-100% of manganese extraction (in 36-48 h of treatment using a content of pulp equal to 20% (w/v) of ore having a Mn grade of 17-20%) was obtained, Final tests in a pilot plant (V = 70L) were performed under non-sterilised conditions, From the experimental results a flowsheet of the process has been proposed. An approximate economical analysis of the bioleaching process has also been reported. The experimental results showed the technical feasibility of the process although several problems have to be resolved to allow for a full-scale application, such as the biomass disposal, the purification of the leach liquor before the final manganese recovery and the too high cost of the process. (C) 1997 Elsevier Science B.V.