Kinetics and mechanism of the reduction of Mamatwan manganese ore fines by solid carbon

A dissertation submitted to the Faculty of Engineering, University of Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 1991The kinetics of reduction of the manganese ore from the Mamatwan mine has been studied by thermogravimetric (TGA) analysis, x-ray diffraction analysis (XRD), optical microscopy, and energy dispersive analysis of x-rays (EDAX) between 1100 and 1350 degree celcius with pure graphite under argon atmosphere. It has been observed that the rate and degree of reduction increased with increasing temperature and decreasing particle size. The effect of the different reaction atmosphere has also been investigated by replacing argon atmosphere with carbonmonoxide (CO) and carbondioxide (C02)' The results clarified importance of some reactions in the reduction mechanism of the ore. In early stages of reduction, up to about 4 minutes of reaction time, carbothermic reduction of higher oxides of manqanase and iron (Mn203 and Fe2o3) to manganeous oxide (MnO) and metallic iron respectively was observed which was controlled by diffusional process across the boundary layer between the solid phases. Apparent activation energy is calculated as 61.03 kJ for this stage which corresponds to about 30 percent reduction. Metallization started as random nucleation of iron rich carbides around Mno grains inside the particle. After 30 percent reduction the formation of a silicate phase was observed. Up to 70 percent reduction at 1350oC, reduction rate was controlled by chemical reaction between oxide phase and gaseous phase with an apparent. activation energy of 153 32 kJ.MT201