The paper presents results of reduction of pure manganese oxides by methane containing gas in nonisothermal and isothermal experiments and reduction mechanisms. The extent and rate of manganese oxide reduction were determined by on-line off-gas analysis using a mass-spectrometer in a fixed bed laboratory reactor in the temperature range 1 000-1 200°C at different gas compositions.Manganese oxides were reduced to carbide Mn 7 C 3 . 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 rate of reduction of manganese oxide increased with increasing temperature. Increasing methane content in the reducing gas to 10-20 vol% CH 4 favoured the reduction process. Increase in hydrogen partial pressure had a positive effect on the reduction rate. Addition of carbon monoxide to the reducing gas retarded the reduction process. The addition of Fe 3 O 4 to manganese oxide increased the rate of reduction.Reduction by methane-containing gas occurs through adsorption and cracking of methane with formation of active adsorbed carbon. Deposition of solid carbon retarded the reduction.

Reduction of chromium oxide, Cr 2 O 3 , was investigated in a fixed bed laboratory reactor in the temperature range 900 °C to 1200 °C using CH 4 -H 2 -Ar gas mixture. The extent and rate of reduction as functions of gas composition and temperature were determined by on-line off-gas analysis using a mass spectrometer. Samples at different stages of reduction were examined by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. The chromium oxide was reduced to chromium carbide Cr 3 C 2 with a degree of reduction close to 100 pct. The rate of reduction increased with temperature and methane content in the reducing gas. Carbon monoxide, added to the reducing gas, strongly retarded the rate of Cr 2 O 3 reduction. The hydrogen content had a slight effect on the reduction rate. 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-15 to 50 (relative to graphite).

Reduction of Groote Eylandt (Australia) and Wessels (South Africa) manganese ores using CH 4 -H 2 -Ar gas mixture was investigated in a fixed bed laboratory reactor in the temperature range 1 000-1 200°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) 7 C 3 . 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 1 050°C. The decrease in rate and extent of reduction of Groote Eylandt ore at higher temperatures, particularly at 1 150-1 200°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.