Bioleaching of manganese from a low-grade pyrolusite ore using Aspergillus niger: Process optimization and kinetic studies.

Low-grade metal resources generated during different mineral processing activities are increasing while there are not many economic and environmentally friendly techniques to manage them. There is no viable technique for the manganese extraction from low-grade ores as the conventional procedures are costly and environmentally unfriendly. In this research, the D-optimal response surface methodology has been used to optimize the bioleaching parameters. Varied contact methods (one-step, two-step, and spent medium), nutrition sources (sucrose and glucose), and pulp densities (1 g.L-1 to 10 g.L-1) were used in different experiments having been done in 30 days using Aspergillus niger. A maximum recovery of over 80% of Mn was achieved based on the acidolysis, complexolysis, and redoxolysis leaching of the organic acids produced by the fungi under the optimum condition; a two-step approach, in a glucose medium, and with a pulp density of 1 g.L-1. A kinetic study was also performed and revealed that the leaching mechanism was a mixed one which consisted of two stages (diffusion through the liquid film and a chemical reaction) for the first 12 day period, and a mechanism of diffusion through the product layer for the rest of the experiment.