Reduction of Groote Eylandt (Australia) and Wessels (South Africa) manganese ores using CH₄-H₂-Ar gas mixture was investigated in a fixed bed laboratory reactor in the temperature range 1000-1200°C. The extent and kinetics of manganese ore reduction as a function of gas composition and temperature were determined by on-line off-gas analysis using mass-spectrometer and dew point sensor. Morphology of ores and its change in the course of reduction was examined by optical and scanning electron microscopy. Phases of raw materials and reduced samples were analysed by XRD and EPMA.
Manganese and iron oxides were reduced to carbide (Mn, Fe)₇C₃. High extent and rate of reduction by methane-containing gas in comparison with carbothermal reduction were attributed to high carbon activity in the reducing gas, which was in the range 15-50 (relative to graphite). The reduction rate of Wessels manganese ore increased with increasing temperature. Reduction rate and extent of Groote Eylandt manganese ore achieved maximum at 1050°C. The decrease in rate and extent of reduction of Groote Eylandt ore at higher temperatures, particularly at 1150-1200°C, was due to sintering and formation of semi-liquid silicate slag. An addition of lime (10-15 mass% CaO) to the Groote Eylandt manganese ore increased melting temperature of slag and significantly increased the rate and extent of reduction at elevated temperatures.