Efficient Extraction of Manganese from Low-Grade Pyrolusite by a Sawdust Pyrolysis Reduction Roasting-Acid Leaching Process

In this work, a novel method for extraction of manganese from low-grade pyrolusite by a sawdust pyrolysis reduction roasting-acid leaching process was explored. The reduction roasting was studied systematically, and the mechanism was also explored by thermodynamic and phase change analysis. Results indicate that sawdust was rapidly pyrolyzed at 250-450 degrees C to generate a large amount of reducing gases such as CO, CH4, and H-2, which gradually reduced MnO2 in low-grade pyrolusite to MnO. The reduction process of MnO2 was identified as MnO2 -> Mn2O3 -> Mn3O4 -> MnO. It was proved that MnO2 of low-grade pyrolusite could be reduced effectively to MnO at lower temperature and shorter duration time by sawdust pyrolysis. Meanwhile, the optimum leaching efficiency of 99.45% for manganese could be attained when sawdust dosage was 11% of the mass of low-grade pyrolusite, the roasting temperature was 500 degrees C, and the roasting time was 25 min.