Novel Technology And Mechanism For Utilizing Low-grade Manganese Oxide Ores By Biomass Charcoal Based Reduction Roasting-acid Leaching

Abstract:Presently, the coal-based pre-reduction roasting-acid leaching of manganese oxide ores is still the most widely used process of pyrometallurgical reduction, but this process is characterized by high temperature, large energy consumption, severe pollution, etc. Biomass charcoal is the dry distillation product of the agriculture and forestry waste in the absence of air. It is a kind of renewable, clean energy, with the excellent reducing capacity, and the very low content of sulfur and nitrogen. This dissertation focused on low-grade manganese ores from Hunan using the biomass black charcoal as the reductant. On the basis of study on the physicochemical properties of raw materials, the thermodynamic behaviours and conditions of manganese oxides and iron oxides in the process of reduction roasting were identified. The phase transformation procedure of MnO2and Fe2O3reduced by biomass charcoal was revealed. Then, a novel technology for utilizing low-grade manganese oxide ores by biomass charcoal reduction roasting-acid leaching was developed.The main manganese and iron phase in the raw manganese ores was Todorokite (Mn6O12·nH2O) and limonite, Srespectively. Thermodynamic analyses of reduction roasting showed, if controlled the roasting temperature between283.54℃and680.54℃,MnO2could be reduced to MnO, and Fe2O3could be reduced to Fe3O4, which created conditions for the separation of Mn and Fe in the following process of acid leaching.The study of phase transformation procedure in the process of roasting reduction showed the CO concentration and roasting temperature had significant effects on the phase transformation, the MnO2and Fe2O3could be completely transformed into MnO and Fe3O4when the roasting temperature was600℃and the CO concentration was10%-30%. However, when CO concentration was further increased to50%, Fe2O3would be reduced to FeO so that many iron ions entered into the leaching solution, which was unfavorable for the next purification process.Experimental studies on low-grade manganese oxide ores reduction roasting-acid leaching using biomass charcoal as reducers showed, for the carbon-containing pellets, the suitable roasting conditions were:roasting temperature was650℃,time was40min, mass ratio of black charcoal in the pellets was10%, particle size of raw ores was less than0.18mm. Compared with using anthracite as reductant, the roasting temperature was decreased by200℃, and the roasting time was shortened over20minutes. The suitable leaching conditions were:leaching temperature was70℃, leaching time was20min, stirring speed was200r/min, sulfuric acid mole concentration was2mol/L, and the ratio of liquid to solid was3:1. Under the above conditions, the leaching efficiency of manganese could reach90.2%, the leaching efficiency of Fe and A1reached32.4%and48.3%, respectively. After purification, the mass percentage of iron ions in the leaching solution was less than0.008%,which could meet the second level of industrial standards.