THE OPTIMIZATION OF MANGANESE-DIOXIDE BIOLEACHING MEDIA BY FRACTIONALFACTORIAL-EXPERIMENTS

The microbial leaching of manganiferous minerals originating from Gree ce and Italy has been the subject of EU research for about 3 years, in order to develop an economical process of biotreatment. A heterotroph ic mixed culture, selected from natural water was found to be capable of reducing the MnO2 in microaerobic conditions. The first culture med ium, formulated in a preliminary way, was employed in the selection an d cultivation of the microbial strains in the first steps of this stud y. For this reason an optimization study of the culture media was carr ied out by means of fractional and full factorial experiments in order to establish the correct medium composition for the biotreatment. The bioleaching tests were carried out in shake flasks using a low grade Italian mineral. The factors analysed were the concentrations of miner als, molasses, NH4NO3, KH2PO4, MgSO4, yeast extract and NaHCO3. The ma nganese extraction yield was the response of the process. A reduction of the salt concentrations present in the media was found to be possib le with a significant reduction in cost. The experimental results show the potential application of the mixed culture for the bioleaching of manganiferous minerals not treatable by means of conventional process es. Copyright (C) 1996 Elsevier Science Ltd.