Consolidification behavior and reduction characteristics of high-silicon ultrafine magnetite concentrate fluxed pellets
The high proportion of pellets in blast furnace smelting technology is an important solution to reduce car-bon emissions and environmental pressures in the ironmaking system.Utilizing high-silicon ultrafine magnetite con-centrate as raw material for pellet production helps expand domestic iron ore resources in China and increase the application of low-grade ores.The influence of basicity on the pelletization and reduction characteristics of high-silicon ultrafine magnetite concentrate pellets was systematically studied.Thermodynamic calculations,mineral phase analysis,scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS),and other methods were used to investigate their pelletization behavior and reduction characteristics.The research results show that with the increase of basicity,the compressive strength of high-silicon ultrafine magnetite concentrate pellets first increases and then decreases,while the porosity first decreases and then increases.Within the basicity range of 0.06 to 0.73,the compressive strength of the pellets exceeds 4 000 N/pellet.The highest compressive strength and low-est porosity of the pellets are achieved at an basicity of 0.24.Increasing basicity reduces the content of silica dioxide phase in the high-silicon ultrafine magnetite concentrate pellets and promotes the formation of calcium iron phase and silicate phase.Under the conditions of basicity of 1.20 and temperature of 1 300℃,the liquid phase proportion in the pellets can reach 24.38%.When the basicity is greater than 0.73,the amount of liquid phase in the pellets rap-idly increases after 1 250℃.With increasing basicity,the calcium content in the slag phase and silicate phase of the high-silicon ultrafine magnetite concentrate pellets gradually increases.Additionally,higher basicity leads to a more polygonal structure of hematite grains and more filling of slag phase between grains.With increasing basicity,the reduction degree and reduction swelling rate of the high-silicon ultrafine magnetite concentrate pellets first decrease and then increase,and the anti-reduction pulverization performance of the pellets weakens.After an basicity of 0.24,the increased porosity and calcium iron phase content in the pellets facilitate the diffusion of reducing gases inside the pellets and promote reduction reactions,effectively improving the reduction degree of the pellets.The reduction degree of the pellets at an basicity of 1.20 is 34.9%higher than at an basicity of 0.06.
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