Hydrometallurgical Recovery of Manganese from Ferruginous Manganese Ore by Reductive-Acid Leaching with Sodium Dithionite

The leaching behavior of manganese from ferruginous manganese ore in sulphuric acid solution using sodium dithionite as a reducing agent was investigated. The optimum sulphuric acid concentration, leaching time, temperature, pulp density and agitation speed for leaching of manganese was determined. Complete manganese leaching was observed under the optimized conditions of 0.6 MH2SO4, 0.49 M sodium dithionite, 200 g/L pulp density, 60 degrees C leaching temperature, 600 rpm stirring rate and 120 min reaction time. The leaching kinetics and dissolution process have also been analyzed by model fitting and microstructural observation. The kinetics of reductive leaching of manganese ores by sodium dithionite in dilute sulphuric acid did not follow a shrinking core kinetic model. The Avrami model was used successfully to explain the kinetic data. The positive values of both Delta H and Delta S indicates that the leaching process is endothermic and random while the negative values of Delta G indicate that manganese dissolution process is spontaneous in nature. After removal of impurities from the leach solution by precipitation, a high purity (99.2%) alpha-Mn2O3 was synthesized from the concentrated Mn solution. The as-synthesized manganese oxide powder was characterized by chemical analysis, SEM-EDS and XRD analysis. The present process would be a key technology for reductive leaching of manganese oxide ores in an economical and efficient way. [GRAPHICS] .