Pre-reduction of manganese ores for ferromanganese industry

Abstract

Pre-reduction of manganese ores by solid carbon was investigated to try to increase the efficiency and cost effectiveness of the ferromanganese industry. The pre-reduction reactions of manganese ore containing 57·2%MnO₂ has been conducted by solid carbon in a rotary kiln furnace at 800–1100°C. The reaction was stopped intentionally at the formation of MnO in order to investigate the pre-reduction behaviour of manganese ore and the factors affecting the process. The ore and reduced samples were characterised by X-ray diffraction, X-ray fluorescence, scanning electron microscopy and energy dispersive spectroscopy analysis. The isothermal pre-reduction behaviour was followed using a thermogravimeteric technique and a quadrupole mass spectrometer in order to determine the reduction kinetics and mechanisms of the process. Relatively, the rate of reduction of manganese ore increased with increasing reaction temperature. The highest reduction of MnO₂ to MnO was achieved at 1000°C which was confirmed by bench scale rotary experiments where 45·3%MnO and 1·72%MnO₂ were detected. Application of the optimum reduction condition on a semipilot scale resulted in 44·6%MnO and 2·55%MnO₂. The pre-reduction reactions proceeded in stepwise manner. The calculated values of activation energy (129 kJ mol⁻¹) revealed that a solid state diffusion mechanism plays a significant role in the carbothermic pre-reduction process of manganese ore.