Reduction of MnO and SiO2 from Assmang and Comilog based Slags
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Silicomanganese(SiMn) and ferromanganese (FeMn) represent essential ingredients for the steel producing industries due to enhancing effects on steel quality. While extensive efforts have been made in investigating the kinetics of ferromanganese production, kinetic information on the silicomanganese process is rather scarce. The goal of this work was to investigate how different raw materials/charge compositions affect the reduction rate of MnO and SiO2 in SiMn production. The experimental work was carried out in a thermogravimetric furnace in CO-gas at ambient pressure with coke as reducing agent. Investigated charge compositions contained ore (Comilog or Assmang) and HC FeMn slag in a 1:1 ratio, quartz and coke. Melting behaviour was investigated for the mentioned Comilog charge at temperatures 1200-1400°C and compared to charge based on Comilog and quartz at corresponding temperatures. Both mixing and layering of raw materials in crucible were evaluated. The slag formation temperature was determined to be in the range of 1250-1300°C for all investigated charges. All materials had formed a slag phase at 1250°C when materials were prepared by mixing in the crucible, whereas the quartz particles remained undissolved until 1300°C when prepared by layering. Assmang and Comilog in combination with HC FeMn slag and quartz show highly similar reduction behaviour, however the rapid reduction stage was initiated at a lower temperature for Assmang, i.e 1535°C vs 1545°C for Comilog. Charges based on Comilog ore, HC FeMn slag and quartz start to reduce at approximately 50°C lower temperature compared to charges based on Comilog, quartz and coke (and limestone), in spite of lower sulphur content, lower basicity and lower driving force. There was no observed correlation between the total basicity/viscosity and the reduction rate. However, it was shown that the rate constant increases with the sulphur content. Foaming was observed at 1550°C for Assmang charges, whereas the first occurrence was at approximately 1560°C for Comilog. It was concluded that the foaming phenomena is a result of initiation of the rapid reduction stage.